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DETAILED RESIDENTIALPHOTOVOLTAIC SYSTEM

REFERENCE DESIGNS

FINAL REPORT

E. M. Mehalick, R. Landes, N. TruncellitoGeneral Electric Energy Systems and Technology Division

King of Prussia, PA 19406

ABSTRACT

This document summarizes the detailed residentialphotovoltaic system designs developed by General Electricfor Sandia National Laboratories. The specific designsare presented in SAND79-7056, SAND80-7148, SAND80-7170,SAND80-7171, SAND80-7172, and SAND80-7173.

Prepared for Sandia National Laboratories under Contract 13-8779.

"\I

Section

TABLE OF CONTENTS

Page

1

2

3

INTRODUCTION • •

ObjectiveBackground •

SYSTEM SELECTION •

Classification and Evaluation of PV SystemsClassification of PV Systems • • • • • • • •Evaluation of PV Systems Within a Category ••Relative Effectiveness By Category (Collector)System/Site Selections. • •••••••

SYSTEM DESIGN SUMMARIES

Type

1-1

1-11-2

2-1

2"-22-22-32-52-6

3-1

A PV System for An All-Electric Residence in the Southwest 3-4Side-By-Side PV/Thermal System for the Northeast ••••• 3-14A PV System With Battery Storage for the Southwest. • • • • • 3-27Passive House Design for the Northeast • • • • • • • • • • •• 3-37Integral Mounted PV Array for the Southeast • • 3-46A PV System for a Temperate Climate •• ". • • 3-55

4

5

DESIGN CONCERNS

Array Sizing • • • • • •Roof Constraints • • • • • • • • • •Array Mounting Approach • • • •Power Conversion Subsystem • • • • • • • • •Isolation Transformer and Grounding • • • • • •Exterior Disconnect SwitchesBattery Location Concerns ••••Module Interconnection • •• • • • • • • • •Fire Safety

DESIGN STUDIES •

4-1

4-14-14-24-24-34-34-44-44-4

5-1

Power Conversion Subsystem Correlations • • • • • • •• 5-1Sensitivity of Photovoltaic Module Performance to RoofInsulation for the Integral Mount Configuration • • • • • 5-8

Alternate Battery System Shunt Analysis • • • • • 5-10System Current Characteristics • • • • • • • • • • • •• 5-15Array Open Circuit Voltage. • •• • • • • • • • •• 5-19

6

APPENDIX A

REFERENCES

SUMMARY OF SYSTEM CONFIGURATION EVALUATIONS

6-1

A-I

iii

Figure

LIST OF ILLUSTRATIONS

Page

1-11-21-31-4

2-1

Utility Feedback System ••••On-Site Battery Storage System ••••Side-By-Side PV/Thermal System. • •••Alternate PV/Thermal System Configurations

Alternate Mounting Techniques for PV Modules •

1-2. . . .. 1-3

1-31-4

• • • • 2-7

5-1

5-25-35-45-55-65-75-8

5-9

5-105-115-12

5-13

5-14

5-15

5-165-175-18

5-19

5-20

iv

System Losses for the Southeast Design as a Functionof Limiting Voltage Range. • • • • • • •••

System Losses for Boston"Design 1 •System Losses for Phoenix, Design 1System Losses for Boston, Design 4 . . . . . . .System Losses for Santa Maria, Design 6 •••.System Losses for an El Paso Single Family ResidenceComparison Between Minimum Loss Voltage and Insolation.Correlation Between Minimum Loss Voltage and NormalizedAmbient Temperature • • • • • • • • • • • • • • • • • •

Correlation Between Normalized %Increase in Loss WithNormalized Voltage Operating Range About Minimum Loss Voltage

Module Cross Section for Integral Mount Configuration • • • •Assumed Attic Temperature as a Function of Ambient TemperatureCell Temperature and Module Efficiency as a Function ofAmbient Conditions for the Integral Mount Configuration.

Cell Temperature and Module Efficiency as a Function ofAttic Temperature for the Integral Mount Configuration

Available Power, Hot Water Usage, and Preheat TankTemperature for a PV System in Albuquerque

Current Duration for the Sixth DesignSanta Maria, CA • • • • • • • • • • •

Current Distribution for the Fourth Design, Boston • • • • • •Current Duration for the Fourth Design PV Array, Madison.Current Distribution as a Function of Solar Array Energyfor Boston . . • • . . • . . . . . . . . • . . . . . .

Current Distribution as a Function of Solar Array Energy,Madison .• G • • • • • • • • • • • • • • • • •

Effects of Ambient Temperature and Solar Intensity on OpenCircuit Voltage. • • • • • • • ••••••••

5-25-35-35-45-45-55-5

5-7

5-75-95-11

5-11

5-12

5-13

5-165-165-17

5-17

5-18

5-19

Table

2-12-22-32-42-5

LIST OF TABLES

Page

Summary of System Configurations • • • • • • • • • • • • • •• 2-2Generic System Configurations for Residential Demands. • 2-4Summary of System Options ••••••••••••••• 2-4Selected System Designs •• • • • • • • • • • • • • • • 2-8Summary of Subsystem Options Addressed in the Designs 2-8

Economic Assumptions for Optimization • • • • • • • • •3-1

5-1 Material Combinations for Thermal Path from Solar Cellto Attic . . . . . . . . . . . . . . . . . . . . . .

v

. . . .

3-2

5-9

FOREWORD

The Detailed Residential Photovol taic System Reference Designs Study was per

formed by the Advanced Energy Programs Department (AEPD) of the General Electric

Company, Energy Systems and Technology Division under Sandia National Laborato

ries, Contract 13-8779. Mr. E.M. Mehalick served as the GE Program Manager, and

Dr. G. Jones served as the Sandia Technical Monitor.

The project team led by AEPD included Massdesign Architects and Planners, Inc.,

who provided the details of the house design and analysis support related to the

solar array installation and Johnson and Stover, Inc., who provided the installa

tion drawings and specifications for the electrical equipment associated with the

photovoltaic system.

The following individuals supported the program. From AEPD, Mr. G. 0 I Brien, Mr.

R. Schaeffer and Mr. R. Felice provided electrical PV system design support; Mr.

J. Parker and Mr. N. Truncellito provided system performance analysis; and Mr. R.

Landes reviewed and selected system configurations. Mr. G. Tully, President of

Massdesign supplied his direct support on all of the house designs and system

integration. From Johnson and Stover, Mr. G. Johnson provided all of the

electrical system design details. The program success was a direct result of the

dedicated effort of all the team members.

The quality of the reports written during the program were enhanced by the review

and suggestions of Dr. G. Jones at Sandia.

VI

SECTION 1

INTRODUCTION

Objective

The objective of the Detailed Residential Photovoltaic (PV) System Reference

Designs Program was to develop regionally appropriate detailed photovoltaic

system designs covering the major system options for the 1986 time frame in

habitable residences. The initial selection of the systems was based on previqus

work of all contractors in the PV residential area and consistent with the

National PV Residential Program test plans. The designs were prepared for four

regions of the country: the Southwest, the Northeast, the Southeast, and a

temperate climate (e.g., California or Hawaii). A total of thirteen system

configurations/regions were initially identified and six detailed designs

developed. The systems considered various hardware options for the major

subsystems. The output from the program included a separate report for each

design with a complete system description, including design requirements,

functional characteristics and site characteristics; a block diagram; full scale

electrical lirie drawings; thermal d~awings; pictorial layouts; a summary of

performance characteristics and tradeoffs; and subsystem and component

specifications. The reports have sufficient information to obtain detailed cost

data from independent sources for installation of the proposed photovoltaic

systems. The systems developed can be used as reference designs for typical

equipment requirements, system performance estimates, installation details

and system cost estimates.

The six designs completed are listed below:

1. A PV system for an all-electric Southwest residence employing a direct mountarray

2. A PV/thermal side-by-side system for a Northeast residence

3. A PV system with battery storage for the Southwest employing a standoff array

4. A PV system for a passive house design for the Northeast

5. A PV system for a Southeast residence employing an integral mount array

6. A PV System for a temperate climate with either a standoff or an integralmounted array

The designs provided detailed drawings for installation of direct mounted modules

(both shingle and batten types), standoff mounted modules and integral mounted

modules.

1-1

This report provides a summary description of all the designs, a discussion of

the initial system configuration review and selection, a summary of several

designtradeoffs completed during the program and a discussion of design issues

and COne erns •

Background

A residential PV system consists of three primary subsystems: the array subsys

tem, the power processing and control subsystem and the storage subsystem. In the

simplest configuration, the system is grid connected with feedback of excess

energy to the utility and thus eliminating the storage subsystem (Figure 1-1).

The economic viability of this system is dependent on the sellback credit ratio

(a fraction of the normal utility charge to a customer) that the utility is

willing to offer for the feedback energy. Previous studies have indicated that

thi s system shows economic viability with a sellback credit of 50% or more in

most regions of the country, References 1 and 2. The alternate basic configura

tion incorporates battery storage into the design (Figure 1-2). This option adds

flexibility to. the system and delivers more energy directly to the house loads;

however, it is costly, adds control complexity and increases maintenance

requirements.

In the broader sense, photovoltaic systems can also be combined with thermal

systems; either in a side-by-side system configuration (Figure 1-3) or through

the use of a combined PV/thermal collector. The side-by-side system uses separate

UTILITYBACK UP

PV DC!AC GENERALARRAY INVERTER LOADS

MAX. POWERTRACKER

HEATto---PUMP

"'"'-HOT

WATER

Figure 1-1. Utility Feedback System

1-2

UT'L'TYBACKUP

~~

DCIAC GENERALINVERTER LOADS

SHUNT-:..~

~][J-I PUMP

.1 ~,

- -~

HOT-~.. WATER

Figure 1-2. On-Site Battery Storage System

UTILITYBACK UP

fT;;Bi TES

Figure 1-3. Side-By-Side PV/Thenlal System

PV and thermal arrays, both of which are currently available. Combined PV/T

collectors were ultimately dropped from consideration because of poor observed

and projected performance. All of the configurations include the power processing

and control subsystem which is centered around the dc/ac inverter. This subsystem

provides the interface between the dc photovol taic array and the ac house loads

and the utility.

Several alternate system configurations can also be considered for the side-by

side PV/thermal system (Figure 1-4). The first variation only provides supplemen

tal thermal energy to the domestic hot water heater. This thermal system is less

complex than the combined space heating and domestic hot water heating system and

1-3

FOSSIL FIRED HEATING SY TEM

SOLAR HOT WATER HEATING SYSTEMBACK-UP

Figure 1-4. Alternate PV/Thermal System Configurations

shows better economic viability. The second variation considers the side-by-side

PV/thermal system incorporated into a house utilizing fossil energy for space

conditioning. The actual system design remains the same with economics slightly

less attractive than for the all electric house, based on current costs of fossil

fuel s.

Another system configuration variation for any design includes a waste heat

recovery unit for hot water heating. Several manufacturers are currently

marketing these units which recover heat from the air conditioner or heat pump

refrigerant as it leaves the compressor. The self-enclosed units consist of a

heat exchanger, sealed motor pump, temperature sensor for the domestic hot water

tank and a control valve to shut down the fluid flow when the hot water tank is

at an upper temperature limit. The General Electric Hot Water Bank unit was used

in one of the detailed designs. The annual results indicated a savings of 38% of

the hot water requirements. Relatively low installation costs makes this unit an

attractive option for the system.

The designs described in Section 3 address each of these basic and alternate

system configurations.

1-4

SECTION 2

SYSTEM SELECTION

Residential PV system studies were reviewed to select configurations which appear

most viable in 1986 in three specified geographic regions in the United States.

The three regions were the Northeast, encompassing Madison, WI to Boston, MA; the

Southeast covering Charleston, SC to Miami, FL; and the Southwest which includes

the Albuquerque, NM and Phoenix, AZ climates.

Previous studies reviewed included the following:

• MIT/Lincoln Solar Research Facility Description

Arlington Solar Research Facility Description

Hybrid Systems Study

Optimization Hybrid Systems Study

• GE Space Division

Conceptual Design and Analysis Study

Regional Conceptual Design and Analysis Study

Photovoltaic Residential Prototype Definition Study

• Westinghouse

Conceptual Design and Analysis Study

Regional Conceptual Design and Analysis Study

• Aerospace CorporationPhotovoltaic Total Energy Residential Systems Study

• Spectrolab

Photovoltaic Systems Concept Study

• Martin Marietta

Photovoltaic Residential Prototype Definition Study

• MIT/Energy Laboratory

Grid-connected Photov6ltaic Economic Study

Specific document numbers and dates of issue for each of the above indicated

studies are contained in the list of references.

2-1

Classification and Evaluation of PV Systems

Classification of PV Systems

On the basis of collector configuration, each of the PV system concepts reviewed

were classified into one of the following three categories:

• PV only

• Separate PV/Thermal

• Combined PV/Thermal

A basic schematic was prepared for each system along with a brief description of

its configuration and operation. Table 2-1 lists all of the configurations.

Evaluation of each system included a listing of major advantages and disadvan

tages, as well as a set of conclusions based on the results of regional perform

ance and economic analyses conducted on previous studies. Details of this evalua

tion are presented in Appendix A.

Table 2-1. Summary of System Configurations

Category Identifier System Title

PV Only

Systems

Ia

Ib

Ic

Id

All Electric/Battery

All Electric/Feedback

Fossil Heating/Feedback

All Electric/Maximum Power Tracking/Battery

IIa

IIb

IIc

IId

He

IIf

IIg

Separate

PV/Thermal

Systems

Combined

PV/Thermal

Systems

All Electric/Solar Assisted Heat Pump/Feedback

Direct Solar Heating/Feedback

Solar Rankine Driven Heat Pump/Feedback

Solar Absorption Cooling/Feedback

Air Solar Boosted Heat Pump/Battery

Air Solar Assisted Heat Pump/Battery

Solar Boosted Heat Pump/Feedback

IIIa Solar Assisted Heat Pump/Feedback

IIIb Direct Solar Heating/Feedback

IIIc Solar Boosted Heat Pump/Feedback

IIId Stand Alone/Direct Heating/Battery'--- --"'- 1

2-2

The combination of generic system combinations is represented in the matrix shown

in Table 2-2. The PV only system with feedback is the simplest system. The system

complexity increases with the addition of battery storage or solar thermal

options. Any of the blocks in the table represent a possible system configura

tion. Table 2-3 lists ·the subsystem options which can be included under each of

the system configurations. Further options can exist wi thin a subsystem as the

type of array flat plate mounting technique. There are four possible mounting

options: stand-off mounting, direct mounting, integral roof mounting or rack

mounting. These various options were considered in final design selections.

Evaluation of PV Systems Within a Category

The following set of criteria was used to rate each system within each of the PV

system categories:

• Economic/Performance Results

• Current Technology Status

• Projected Status for 1986

• Development Risk

• System Complexity

• Projected System Cost

• Regional Applicability

• Duplication of System Components

A rating designation of either good, fair or poor was then assigned to each

system for each of the above criteria (see Appendix A). Based on these ratings,

the systems were ranked wi thin their category. The results of this ranking are

presented below.

PV ONLY SYSTEMS

Rank System Title

1 Ib, All Electric/Feedback

2 la, All Elect~ic/Battery

3 Ic, Fossil Heating/Feedback

4 Id, All Electric/Maximum Power Tracking/Battery

2-3

Table 2-2. Generic System Configurations For Residential Demands

BASE ELECTRICAL LOAD}DOMESTIC HOT WATER RESIDENTIALSPACE HEATING DEMANDSSPACE COOLING

SOLAR THERMAL OPTIONS------.,.~

INCREASING

COMPLEXITY

PV ONLY SYSTEMS PV ONLY PLU~ PV ONLY PLUS PV ONLY PLUSWITH UTILITY SOLAR THERMAL SOLAR SPACE HEATING SOLAR HEATING,

FEEDBACK DOMESTIC HOT WATER AND DHW COOLING AND DHW(GRID CONNECTED) SYSTEM

----------- ---------- ---------- ----------APPLICABLE TO ALL SIDE-BY-SIDE ARRAYS SIDE-BY-SIDE ARRAYS SIDE-BY-SIDE ARRAYS

REGIONS OR OR TECHNOLOGY JUMPCOMBINED ARRAYS COMBINED ARRAYS FROM HEATING

APPLICABLE TO APPLICABLE TO SYSTEMSALL REGIONS COLD REGIONS APPLICABLE TO ALL

REGIONS

PV ONLY SYSTEMSWITH BATTERY

STORAGE(GRID CONNECTED)

----------APPLICABLE TO ALL

REGIONS

PV ONLY SYSTEMS II

WITH BATTERIES I'(STAND ALONE)

----------~APPLICABLE TO

ALL REGIONS ,

(j >Z l-ll! X< ww ...Ja: 0U :Ez 8

PHOTOVOLTAIC1OPTIONS

Table 2-3. Summary of Subsystem Options

COLLECTOR SUBSYSTEM STORAGE & POWER CONDITIONING

FLAT PLATE ARRAYS - SHINGLE TYPEPLUS SEVERAL FLAT PANELS

SELECTED CONCENTRATOR ARRAYSROOF MOUNTED SINGLE AXIS TRACK WITH

ADJUSTABLE TILT

SIDE-BY-SIDE PV/THERMAL FLAT PANELS

COMBINED FLAT PLATE PV/THERMAL PANELS

HEATING SYSTEMS COOLING SYSTEMS

UTILITY FEEDBACK

BATTERIES

MAX POWER TRACKING

LINE COMMUTATING INVERTERSELF COMMUTATED INVERTER

DOMESTIC HOT WATER

HEAT PUMP

RESISTANCE HEATING

FOSSIL HEATING

SOLAR SUPPLEMENTED

(SEVERAL VARIATIONS)

HEAT PUMP

ABSORPTION CHILLER

VAPOR COMPRESSION

SOLAR SUPPLEMENTED

SOLAR DRIVEN RANKINE

FOSSIL

RESISTIVE HEAT

SOLAR SUPPLEMENTED

2-4

IIa,

IId,

IIc,

IIb,

IIf,

IIg,

IIe,

Rank

1

2

:3

4

5

6

7

SEPARATE PV/THERMAL SYSTEMS

System Title

All Electric/Solar Assisted Heat Pump/Feedback

Solar Absorption Cooling/Feedback

Solar Rankine Driven Heat Pump/Feedback


Air Solar Assisted Heat Pump/Battery Storage


Air Solar Boosted Heat Pump/Battery

COMBINED PV/THERMAL SYSTEMS

Rank

1

2

:3

4

IIIa,

IIIb,

IIId,

IIIc,

System Title

Solar Assisted Heat Pump/Feedback


Stand Alone/Direct Heating/Battery


Relative Effectiveness by Category (Collector) Type

Having ranked systems within a category, a comparative assessment was then made

of the relative effectiveness of collector types as represented by the three

categories. In this manner, similar systems appearing in more than one category

(i.e., having different collector types) could be compared prior to making

appropriate regional selections.

PV only solar arrays used in conjunction with an all electric load proved the

most suitable system for residential use. Their potential economic viability was

as good as, or better than, other solar energy options such as separate or

combined PV/Thermal systems in all regions studied. Feedback generally proved the

more cost effective approach when compared to battery storage for most systems

investigated. Battery storage achieved cost effectiveness in high insolation

areas, such as Phoenix.

It appeared that except at very low array costs, the higher thermal and

electrical efficiencies of the separate PV/Thermal panel systems more than com

... dnsate for the potential savings in structural and installation costs provided

by the combined PV/Thermal collectors. As a result, lower annual costs would be

2-5

possible with the separate PV/Thermal panel systems than with the combined

collector systems. Separate PV/Thermal systems also exhibited some advantages in

the Sunbelt areas, with the solar thermal systems capable of providing air condi

tioning, if appropriate solar cooling equipment is cost effective, or just

domestic hot water.

Combined PV/Thermal systems, while they may have roof space savings and may have

potential for lower cost in comparison to equivalent separate electrical and

thermal collectors, have exhibi ted poor performance in recent tests. Therefore

they currently do not offer significant promise.

The solar assisted heat pump (also referred to in the literature as a parallel HP

system) proved more cost effective and less complicated than a solar boosted heat

pump system (also referred to as a series HP system), with either the separate or

combined PV/Thermal collector.

System/Site Selections

The goal of the program was to have a set of site/system selections which covered

the major system options. Therefore, in addition to the results of the system

rankings and relative evaluations, a qualitative analysis was also used to narrow

the selected system configurations.

The array subsystem options were restricted to roof mounting due to the lack of

ground area for the arrays in a residential development. Only flat plate modules

were addressed. A roof-mounted concentrator was considered but eventually dropped

wi th Sandia concurrence. The type of flat plate roof mounting was considered a

key option since the different approaches required different installation details

and, therefore, varying installation costs. Thus, direct-mounted, stand-off and

integral array options received high consideration (See Figure 2-1) Rack-mounted

arrays were not included due to limited applications. Rack-mounted residential

arrays, however, were installed at the Southwest Residential Experiment Station

The reader is directed to that program for details of this mounting approach.

Similarly, the differences between feedback and battery systems received high

consideration and a separate design was developed for each. However, the dif

ferences in installation details between a stand-alone system and a grid

connected battery system were considered insignificant and separate designs were

nQt developed. PV-only systems with feedback were used in most of the remaining

2-6

designs since the systems have shown the highest potential in most previous

studies.

For PV/Thermal systems, side-by-side collectors were considered. A hot water only

system was addressed as an option of the solar assisted heat pump system

configuration. Solar cooling was eventually ruled out since solar thermal cooling

systems are not currently economically viable. Similarly, combined PV/Therma1

collectors were eliminated due to their current low performance and limited

region applicability.

For the power conditioning subsystem, installation details do not vary sig

nificantly for the different types of units available. Two primary options were

considered in the designs based on currently available hardware.

Finally, in addition to the three geographic regions initially considered, a

temperate climate with low space conditioning loads rounded out the weather

environment. House design variations appropriate for each of the environments

also were developed.

Summarizing all the considerations described, the six systems and regions identi

fied in Table 2-4 were selected. Subsystem options for several of the designs

were added to further expand the total coverage of hardware variations. Table

2-5 lists these options.

Figure 2-1. Alternate Mounting Techniques for PV Modules

2-7

Table 2-4. Selected System Designs

MountingSystem Configuration Configuration Location

PV-only with feedback Direct Southwest ,

Side-by-side PV/T Solar Assisted Heat Pump. Direct Northeast

PV-only with battery storage Standoff Southwest

PV-only for a passive house design Direct Northeast

PV-only with feedback Integral Southeast

PV-only with feedback Integral and Temperate ClimateStandoff

Table 2-5. Summary of Subsystem Options Addressed in the Designs

2-8

ARRAY SUBSYSTEM

GE PV Shingle Direct Mount Module(Two Design Generations)

ARCO Solar Batten Direct Mount Module

Solarex Stand-Off Mounted Frame Module

Side-by-Side Flat Plate Thermal Collectors

Integral Glass Laminated Modules

STORAGE SUBSYSTEM

Feedback Energy to Utility

Lead Acid Battery Storage

HVAC SUBSYSTEM

Heat Pump (HP)

Fossil Heating/Vapor Compression Cooling

Solar Assisted HP

Solar Domestic Hot Water (DHW)

Space Conditioning Heat Recovery for DHW

POWER PROCESSING AND CONTROL SUBSYSTEM

Windworks Gemini Inverter

Abacus Sunverter

DESIGN NUMBER

1 and 4

2

3

2

5 and 6

1, 2, 4, 5 and 6

3

1, 2, 3, 4, 5

2

2

2

3

1, 3 and 4

2, 5 and 6

SECTION 3

SYSTEM DESIGN SUMMARIES

A new house design was developed for each application. The designs were all

single familiy detached houses but they included one-story, two-story and zero

lot-line type configurations. The floor areas ranged from 142 m2 to 161 m2

wi th south facing roof areas ranging from 44 m2 to 104 m2 • All the houses

were assumed newly constructed in 1986. The designs included basic energy

conservation features and additional passive design features projected for 1986

but consistent with the aesthetic design of the house.

The electrical energy derived from the PV system serves the normal household

electrical requirements including general appliances, lighting, cooking and hot

water heating. In general, the homeowner was considered the system user; there

fore, operation and maintenance requirements typical of conventional HVAC systems

were assumed. The systems excluded instrumentation, since a mature system in

stallation was assumed. Specifications for equipment were based on currently

available components or similar currently available equipment if the component

was not available.

To evaluate the performance of the system designs, typical hourly electrical load

profiles and space condi Honing demands for the house were used. These load

profiles were developed in the GE Regional Residential Study, Reference 5, and

updated in the Residential Load Center Program, Reference 14. All the system per

formance analyses were completed based on these hourly loads and using Typical

Meteorological Year (TMY) weather data as developed by Sandia National Laborato

ries. Life cycle cost analyses, based on system performance results and system

cost estimates, were used for system sizing and tradeoffs.

The six designs developed included:

1. A PV system for an all-electric Southwest residence employing a direct mountarray

2. A PV/thermal side-by-side system for a Northeast residence

3. A PV system with battery storage for the Southwest employing a standoff array

4. A PV system for a passive house design for the Northeast

5. A PV system for a Southeast residence employing an integral mount array

6. A PV System for a temperate climate with either a standoff or an integralmounted array

3-1

• System Life: 20 years

• Maintenance: $lOO/Year

• 1980$

• Battery Life: 10 Years

A separate report was written for each design, References 3 through 8. A complete

set of full sized drawings were also delivered to Sandia for each of the designs.

The system sizes ranged from 4 kW to 8 kW systems. The system sizing for all the

designs was completed on a marginal cost basis. A consistent set of economic

assumptions was used and they are summarized in Table 3-1.

All of the economic calculations were completed for a 1986 start in constant

"1980$. The overall average inflation rate of 5 percent was assumed through the

time frame of the analysis. This value is low according to cur.rent. rates but

since the marginal cost analysis becomes independent of the inflation rate and to

maintain similarity to previous work, this value was used. In addition, a

resul tant homeowner mortgage rate of 10 percent for a 20-year loan was assumed

with a marginal income tax rate of 35 percent for the homeowner. This is

equivalent to a taxable income of approximately $25,000 at present tax rates.

Since several states and local communities have already exempted solar systems

from property tax, no additional property tax were assumed. These figures imply

an annual cost or "fixed charge" of about 9.1% of the initial photovoltaic system

cost. Annual operating costs were assumed to be $lOO/year for operation and

maintenance and 0.5% of system cost for insurance. All components of the solar

system were assumed to have the same lifetime as the system (20 years) except for

batteries (10 years).

An electricity price escalation of 4% over inflation was also used in the

analysis, although the marginal benefit/cost analysis allows the extension to

other escalation rates and system lifetime assumptions by a constant adjustment

factor as done in Reference 16.

Table 3-1. Economic Assumptions for Optimization

• 1986

• General Inflation Rate: 5%

• Insurance: 0.5% of Capital Cost

• Electricity Price Escalation: 4% Over Inflation

• Mortgage Rate: 10%

• Tax Bracket: 35%

• No Property Tax

3-2

.'

Cost estimates were made for each. of the systems to calculate the levelized

annual costs. The array cost assumed was the National PV Program goal of 70i/peak

Watt or $700/kWp factory price. Including the markups, the cost is $925/kWp on

site. The balance of system costs were made up of array installation estimates,

power conditioning subsystem costs, storage subsystem costs and remaining

equipment costs. Power conditioning costs were based on 1986 price projections.

The 1986 battery costs were varied from $O/kWh to $150/kWh to assess the effect

of these values on system sizing. All the costs are in 1980$ and include in

general, two 15% markups for distribution and contractors. These markups are

probably low, but were used in the analysis until more detailed numbers are

available for distribution networks.

Regional energy price estimates were assumed for each design to determine the

system-levelized annual benefits.

The following subsections provide a brief summary description of each of the

designs.

3-3

A PV SYSTEM FOR AN ALL-ELECTRIC RESIDENCE IN THE SOUTHWEST

A simple, utility feedback, photovoltaic system was designed for a single story

all electric house in the Southwest. The two major system elements are the photo

voltaic array and the power conversion subsystem. The photovoltaic array uses the

GE Block IV shingle module in a direct mount configuration. The system was sized

nominally at 8 kWp based on minimum life cycle costs but key parameters were

evaluated parametrically and changes in some of the assumptions were also

evalua=ted. For example, sellback rates were varied parametrically indicating at

higher sellback rates (greater than 50%) all of the available roof area should be

utilized for the array, resulting in the 8 kW sized system. As the sellback rates

decreased to 30% or less, a 5 kW system size becomes more appropriate. Assump

tions of fixed and variable system capital costs also affect system sizing,

implying smaller system sizes as fixed costs are lowered.

The system design is applicable to all regions. The effects of varying electrical

load level on the system economics resulted in cost-to-benefit ratio insensitivi

ty to load level at sellback rates above 50%. Therefore, system size would not be

affected by slight variatione in load levels. Profile changes and dramatic

changes in the load would affect system sizing.

3-4

HOUSE DESCRIPTION

• The house design is for a SINGLE-STORY residence of NEW CONSTRUCTION forthe Southwest region of the country.

• The design includes PASSIVE SOLAR FEATURES and ENERGY CONSERVATIONFEATURES projected for 1986.

• There is 149 m2 (1600 ft2 ) living area with 104 m2 (1120 ft2 )south facing roof area.

• The house is ALL ELECTRIC with a 3-ton heat pump and electric hot waterheater.

• The site layout has a detached garage with a lot area between 1/6 and1/4 acre.

3-5

SYSTEM DESCRIPTION

• The system is grid connected with an 8 kW NOCT array rating using a GEBLOCK IV SHINGLE MODULE ARRAY. The array consists of a total of 475MODULES COVERING 93 m2 in a redundant parallel-series network.

• The power conversion subsystem uses a 10 kVA LINE COMMUTATED MAX POWERTRACKING INVERTER to convert dc genera ted power to ac. A 15 kVA SINGLEPHASE ISOLATION TRANSFORMER is used to match ac supply voltage to theload.

• The system operation is PARALLEL AND SYNCHRONIZED WITH THE UTILITY.

• Excess generated power is FEEDBACK to the utility.

• The system represents the SIMPLIEST PHOTOVOLTAIC DESIGN with a minimumof components and controls.

PVARRAY

UTILITY BACKUP

3-6

- ROOF MOUNTED SHINGLE93m2

Dc/ACINVERTER

MAX POWERTRACK

GENERALLOAD$

HEATPUMP

HOTWATER

SYSTEM OPERATION

• The system has automatic startup and shutdown control.

• The system automatically shuts down with loss of the utility.

• System operation is summarized by the sequence below.

1. At sunrise in the automatic "on" mode, the ac and dc contactorswill close when the array bus voltage reaches a threshold of 180Vdc.

2. During the daylight period the inverter will continue to operate aslong as there is a net power output.

3. The inverter will track the maximum power operating point within +1percent over the range of 180 to 220 Vdc.

4. The interruption of utility-supplied power will eause the dccontactor to open and remain open until line voltage is restored.

5. At sunset, the inverter ae and de contactors will open when the netpower output falls to zero. These contactors will remain openthroughout the night to eliminate the majority of the inverterparasitic losses.

ununRIlYICII-3 WIRE, SlNGLI _ .._VA(;

AOOFAR.RAY2!5S a 19PSHINGLE

POWER COOIVERIION SYSTEM St~VIC£ PI\lI£l

3-7

PHOTOVOLTAIC ARRAY

The array consists of shingle PV modules connected in a 25 series by 19parallel network covering 93 m2 of roof area.

• The array is oriented due south with a roof. pi tch of 260. The overallcell packing efficiency is 76.3% over the 93 m2 •

• The modules are direct mounted on top of the roofing felt and plywoodroof sheathing. They form a weather tight roof.

• The modules are installed by an overlapping procedure similar to conventional shingles. Four electrical interconnections are made with flathead machine screws per module and two roofing nails are used per modulefor attachment to the roof.

STARTER COURSE

3-8

ROOF EDGE

FINISHING ROW OFDUMr1Y EDGESHINGLES

POSITIVE TERMINATION SHINGLES

PHOTOVOLTAIC MODULES

• The module was developed by General Electric Company as part of the JPLBlock IV procurement.

• The module uses 19 ARCO-SOLAR 100 mm cells with an unencapsulated efficiency of 12.3% connected in a series circuit.

• For a NOCT of 640C, the maximum power output is 17.14 Watts and 7.3Volts at SOC conditions (1 kW/m2 , 200C ambient, 1 m/s wind speed).

• A summary of module characteristics include:

Module weight: 3.85 kg

Total cell area: 0.1492 m2

Exposed module area: 0.1955 m2

Module packing factor: 0.763

3-9

POWER CONVERSION SUBSYSTEM

• The PCS provides the interface between the PV array and the normalresidential utility service and loads.

• The subsystem consists of three main components: the inverter, the dcfilter and transformer along with the associated control circuitry.

• The subsystem is sized for 10 kW of power output with a 15 kVA transformer sized to accommodate the out of phase ac voltage (VARS) andcurrent.

• The subsystem can be ottained from the Gemini Corporation, marketed byWindworks, Inc.

KEY INVERTER DESIGN CHARACTERSTICS

OUTPUT POWER RATING

OUTPUT VOLTAGE:

INPUT VOLTAGE:

FULL LOAD POWER FACTOR:

FULL LOAD EFFICIENCY:

FULL- LOAD HARMONIC DISTORTION

OPERATING TEMPERATURE

10 kW CONTINUOUS

240 VAC Utility Residential Service

200 + 20 Vdc

60% Minimum,

92% Minimum

30% Maximum

00 to 400 C

POWER CONVERSION SYSTEM

Voc--~

'oc---.l"---_.......

3-10

PV INTERFACE WITH UTILITY AND HOUSE SERVICE

• Interface arrangements employ CONVENTIONAL WIRING RUNS AND EQUIPMENT asmuch as possible to facilitate acceptance by local regulatoryauthorities.

The PV array source is treated as a CONVENTIONAL UTILITY SERVICEentrance to the residence with the raceway parallel to utility line.

• An external disconnect switch provides an external break. By strict codeinterpretation, this ~witch may be eliminated, especially as PV installations increase.

• An equipment room of 6.1 m2 floor area is located on the west end ofthe house. The equipment room will also house the heat pUmp and electrichot water heater and can be used for extra storage.

• All PV related equipment is wall mounted, except for the transformer.

POSITIVE BUS BARPENETRATION

~-----STANDARO WEATHERHEAD~-----~IN LOOP

l"&' .('IIII STANDARD ENTRANCEr--1 FOR UTI LI TY: SERVICEIIII1II

[~[/I DISCOIINECT .,roJlSWITCH~~i~==~~

SOLAR COLLECTING ARRAYdCONDUIT RUN

I

I--------------------------~

3-11

ARRAY SIZING

• Energy sellback price the utility is willing to pay the homeowneraffects system sizing.

• Sellback rates greater than 50% imply full roof arrays (93 m2 ).

• Lower sellback rates (-30%) imply roof arrays of 50 m2 •

• At higher sellback rates, the economics are insensitive to load level.

ALBUQUERQUE PHOENIX

oo 20 40 60 SO 1 0

COLLECTOR AREA, M2

1.6

1. II0 SELLa- BACK< 1.2 lli!.Q PS/PE~

t: 1.0u. Iw2 I 0.3wen 0.50I- 0.1l- IIII0 ..... OESIGNU

I POINT

I

r-0ESIGNPOINT

IIII

O.SI

0.7

SELLBACK~ PS/PE1.6

oI<ex: 1.2I-

ffizwenol-IIIIoU

PHOENIX

SELLBACK

_____ RATIO PSI?E

=====-;-;;;;;;~::0.30.5

0.7

1.0

1.8

1.6

2I- 1.11<Ill:

!: 1.2Il.

'" 1.0z'"(ll0 0.8l-I-III 0.60U

O. II

0.2

0

0

3-12

2Array Area = 92.9 m

'0.5 1.0ACTUAL LOAD/NOMINAl. l.OAD

1.5

DESIGN PERFORMANCE

• Net system output for both Albuquerque and Phoenix is greater than thetotal electrical load.

• Phoenix shows better load matching characteristics.

• Overall· system efficiency based on incident insolation for gross arrayarea is within the 8% to 8.4% range for the Southwest.

PHOENIX ALBUQUERQUE

UTILITY MAKEUP ·9 MWHUTILITY FEEDBACK -12.6 MWH%OF LOAD SUPPLIED

DIRECTLY -39%

PV LOADSYSTEM 14.8 MWHOUTPUT18.3 MWH

J FMAMJJASOND

1.5

0.5

2.0

::r:::~

>'oa:~ 1.0w

NET FROMUTILITY,......------------.

UTILITY MAKEUP· 8.7 MWHUTILITY FEEDBACK -10.3 MWH%OF LOAD SUPPLIED

DIRECTLY -45%

JFMAMJJASOND

2.0

1.5

o

0.5

1.0

::r:::~

>'oa:wzw

3-13

SIDE-BY-SIDE PV/THERMAL SYSTEM FOR THE NORTHEAST

A side-by-side photovoltaic/thermal system with utility feedback was designed for

a two-story all-electric house in the Northeast. The three major system elements

are the photovol taic array, the electric power conversion subsystem, and the

thermal subsystem. A key to the sizing of the PV and thermal array is the

relative cost of each system. Therefore, the ratio of the costs associated with

each system was varied parametrically to define ultimate sizing of the PV and

thermal array. In general, the results indicate larger PV array area and minimal

thermal array area for the set of cost assumptions. A thermal system of adequate

size, however, was selected to assure sufficient design details for determining

system installation costs. The PV system was sized nominally at 6.7 kWp based on

roof area limitations, side-by-side with a 19.5 m2 flat plate thermal collector

array. The 73.6 m2 photovoltaic solar array uses a batten type solar cell

module, being developed by AReO-Solar as part of: the JPL block IV procurement,

and the 19.5 m2 thermal array uses a Sunworks SOlector@ collector which is

representative of available thermal collectors.

A separate thermal system design was also ~eveloped for a side-by-side solar hot

water system for comparison. A solar hot water system, since it was less complex

and has less components, showed better economic viability than the parallel solar

heat pump space heating and hot water system. Both systems probably will be

available in the 1986 time frame.

3-14

HOUSE DESCRIPTION

• The house design is for a TWO-STORY residence of NEW CONSTRUCTION forthe Northeast region of the country.

• The design includes PASSIVE SOLAR FEATURES and ENERGY CONSERVATIONFEATURES projected for 1986. A GREENHOUSE is attached on the southernexposure.

• There is 158 m2 (1700 ft 2 ) of living area with 101 m2 (1090 ft2 )south facing roof area.


• The site layout has a two car attached garage with a lot area of approximately 1/4 acre.

3-15

SYSTEM DESCRIPTION

• The system consists of a separate GRID CONNECTED photovoltaic array witha 6.7 kW NOCT rating and a thermal array which provides a SOLAR ASSISTto the HEAT PUMP and DOMESTIC HOT WATER HEATER.

• The PV array uses the ARCO SOLAR BLOCK IV BATTEN SEAM MODULE in a 28series by a 4 parallel circuit arrangement covering 73.6 m2 of roofarea.

• The thermal array uses19.5 m2 of roof area.

10 Sunworks@

Solector collectors covering

• The power conversion subsystem uses a 8 kW SELF-COMMUTATED MAX POWERTRACK-ABACUS INVERTER to convert dc generated power to ac and to matchac supply voltage to the load.


• Excess generated power is FEDBACK to the utility.

• The thermal subsystem has a 350 GALLON WATER THERMAL STORAGE componentand an 80 GALLON DOMESTIC HOT WATER TANK.

BACK·UP

PV Dc/AC I- GENERALARRAY INVERTER

~

LOADS

MAX. POWERTRACKER f- HEAT

~r4-PUMP

- HOT -~WATERTHERMAL ~ THERMAL

ARRAY. $Tt)~~t;F.

3-16

PV SYSTEM OPERATION

• The system has AUTOMATIC STARTUP and SHUTDOWN control.

• SYSTEM OPERATION is summarized by the sequence below.

At sunriseclosed andenergized.

in the automatic "on"the phase lock loop

mode, the ac line contactor isand maximum power tracker are

2. During the daylight period, the inverter will continue to operateuntil the dc input voltage falls below 160 V.

3. The inverter will track maximum power point wi thin +1 percent overthe range of 160 to 240 Vdc.

4. The interruption of utility-supplied power will cause the accontactor to open and remain open until line voltage is restored.

5. At sunset, the inverter ac contactor will open when the net poweroutput falls to zero. This contactor will remain open throughout thenight to eliminate any parasitic losses.

UTILITYSERVICE

INVERTER

EXTERIORSWITCH

INTERIORSWITCH

SWITCh

MAINCS

VARiSTOR

PVCB

TYPICALSRANCH

SERVICEPANEL

RESIDENTIALLOAD

3-17

THERMAL SUBSYSTEM

.. The system has AUTOMATIC STARTUP AND SHUTDOWN control.

A control centerenergy collection,backup.

regulates operational sequences for solar thermalstorage and utilization loops, as well as auxiliary

o SYSTEM OPERATION is summarized by the sequence below:

1. The collector and storage loop pumps are activated when a temperature differences of S.30 C is registered between the collectorsurface and the bottom of the thermal energy storage (TES) tank.

2. Operation continues until the temperature difference is less than2 .SoC.

3. Flow is diverted through the heat pump when the TES temperature isgreater than S7.SoC

4. Circulation is activated from the TES to the domestic hot water(DHW) tank when a temperature difference of 3.30 C exists betweenthe top of the TES tank and the bottom of the DHW tank and continuesuntil the temperature difference falls to less than 1.loC.

5. Flow is activated to the hydronic coil when the TES temperature is26.7°C or greater. This is an adjustable setting.

6. If the hydronic coil cannot meet the space demand, then the flow tothe hydronic coil is stopped and the heat pump activated andoperated in a conventional mode.

EXPANSION 12RTANK

HYDRONICCOIL

SOLARCOLLECTORS STORAG

HEAT HEAT TANK

DUMP EXCHANGER (TES) (P3) HP gPUMPCOIL

EXPANSION TANK HOT WATER c:><===> FAN

TANKTSUP '0PUMP (P2) /

/......./.......

"- /.... - - TGR

DIFFERENTIALCONTROLLER

3-18

PHOTOVOLTAIC ARRAY

• The array consists of batten PV modules connected in a 28 series by 4parallel network covering 73.6 m2 of roof area.

• The array is oriented due south with a roof pitch of 400 •

• The modules are direct mounted on top of the roofing felt and plywoodroof sheating. They form a weather tight seal.

• The modules are installed by an ovelapping procedure similarconventional batten seam roof. The modules are held in place byscrewed into the roof. Electrical interconnections are madepatented connectors which run along the batten seam.

to aclipswith

...~ ... - C"~"'I'.& ,.pv.::. - __

L:I .. 1..1 l.- i..

)-(.-- - ....-- r--- - - - . r-

++ ++ ++ ++ ++ ++ ++ ++ ++ ++

'-'r ~-TWl'-u--........J..

~,~e..-La- ,.."..."CO •

=~~~+ +~ + +~

.;:.:,toc.=

.-- -++ + +-1-.--++~ ++

-- .. --10.

'='::io'I'=-='JL.::..::1L:..::J- ..- -11..++ + + + +Iol + +

-++

- - ..~J

L::,,::-=-.:-=.nll c-~-~Io. -=-=....-- -++ ++

~ -.-ItI --1'1..::...::,..-- _1 __++Iol ++Iol ++Iol + +•

c..::~'='::Jc..::J~r- ,..-- .-- r-++ ++ ++ ++

~1o..=.=1o...::.::.1ol=-= =-= ~"'=-="c..:.J-...:.:...r___.---- __++~ ++ ++ItJ++al ++ ... ++1oסi ++ ++

~~+ ...U

~ .::..::~ ~ L::..::~'::":J.::..:J..:.:J-- ..:.: -=-=: I ::.:J-=-= ~ -=-= - -J-=-=J -=-=J- - .-- .-- - .-- r-- - .-- __ .-- r- 1.-- ...-- .--f++'" ++ ++~ ++100 ++ ++ ++ ++ ++ ++ ++ ++~ ++IJ ++ ++ ++

3-19


The module was developed by ARCO Solar, Inc. of Chatsworth, California,as part of the JPL Block IV procurement. The development modulecurrently uses circular cells.

The module specified for the design is a high density version which usesARCO-Solar 70 mm square cells with 16 cells connected in series and 7parallel circuits for a total of 112 cells per module.

For a NOCT of 630 C, the maximum power output is 60.0 Watts, and 6.0Volts at SOC conditions (1 kW/m2 , 200 C ambient, 1 m/s wind speed).

A summary of module characteristics include:



Exposed module area: 0.657 m2


Nominal size: 1.2 m long by0.58 m wide

3-20

THERMAL COLLECTORS

• The thermal collector is a flat plate model called the Solector andit is currently available from Sunworks of New Haven, Connecticut.

• The collector uses a SELECTIVELY COATED COPPER absorber, with a SINGLEGLAZING of low iron, 1/4 inch' tempered glass in an extruded ALUMINUMframe.

• The collector has INTEGRAL MANIFOLDING for ease of installation.

• The design installation consists of 10 collectors covering 19.5 m2 •

• A summary of collector characteristics include:

Collector size: 213 m long by 0~91 m wide

Collector weight: 51.4 kg

Effective absorber area per panel: 1.7 m2

.Liquid-Cooled Solector~, Black Chrome Coating

tOO

.10

.80r

~ 10z..~ .eo...... .50

~! 040

~~ .30

! .20

~ f-SINGL GLAZED·- ~

~

~DOUBLE GLAZED - ~

.10

00o .05 .10 ~ ~ n ~ • ~

FLUID PARAMETER (Tj-T.I/ql.OF/BTU/1l2 .,

,45 .50

Single glazed, lo·iron: Double glazed, lo·iron:

Av. flow rate, 278.2Ibs/hr.; Av. mass flow 278.85Ibs/hr.;avo ambo temp. 73.60 of. avo ambo temp. 100.56°F.(x) Field data (0) Field data

Tests conducted by Soiar Energy Analysis Laboratory; Desert Sunshine Exposure Test,lnc.

Data from Sunworks Brochure

3-21


• The Power Conversion Subsystem (PCS) provides the interface between thePV array and the normal residential utility service and loads.

The subsystem consists of three main components: the inverter, the dcfilter and the transformer along with the associated control circuitry,packaged in a single unit.

• The uni t is manufactured by Abacus Controls, Inc., Sommerville, NewJersey.

• The subsystem is sized for a 8 kW POWER OUTPUT with the transformersized to accommodate the adjustment of the ac voltage and current.

Characteristics are summar~zed below.

KEY INVERTER DESIGN CHARACTERISTICS

OUTPUT POWER RATING:

OUTPUT VOLTAGE:

INPUT VOLTAGE:



FULL LOAD HARMONIC DISTORTION:

8 kW CONTINUOUS

240 Vac Utility Residential Service

200 ~ 40 Vdc

Unity

90% Minimum (over 25% to 88% ofoperating range)

5% Maximum

MAXIMUM (+)y~(_) INPOWER 1---_.-1~ ~--t PHASETRACKER SENSE

AMPLITUDECONTROL

,AC LINE

ROOF DC CONTACTORARRAY FILTER I SCR I XFMR nr'll"\ n n :1- AC OUTPUTINPUT I TNV :~TI=~ I vv~

I - SENSE

9 'AN( THERMAL

PLL SWITCH UTILITYV - REFERENCE VOLTAGE

3-22

PV INTERFACE WITH UTILITY AND HOUSE SERVICE

• Interface arrangements employ CONVENTIONAL WIRING RUNS AND EQUIPMENT asmuch as possible to facilitate acceptance by local regulatorYauthori ties.

• The PV array output is treated as a CONVENTIONAL UTILITY SERVICEENTRANCE to the residence with the raceway parallel to utility line.

• An external disconnect switch provides a means to externally disconnectthe array and the power conversion unit. By strict code interpretation,this switch may be eliminated3 especially as PV installations increase.

• An equipment room of 8.2 m2 floor area is located on the west end ofthe house. The equipment room also houses the heat pump, electric hotwater heater and thermal storage tank and can be used for extra storage.

• The Power Conversion Unit is floor-mounted, and all of the remaining PVrelated equipment is wall-mounted •

Array

,.,-----tMa inta in 12 11 Cl earanceBetween Services______~1#4 AWQ. Positive-Conductor

Pl us #4 'AHc;i. Negat i veConductor Run in 111 PVCConduit

~~~+-~~~ Standard Service -Entrance Conductorsfor Ut il ity

.Thermal Collectors

Weatherhead for Utility~~~-----I'Service

~ . Strap Supports in·T.a~ Accordance with Disconnect

L... N.E.C. (Typical) ---'Switch -------- •. --

P,V, SystemConnect ion from ---:~~H+-'!"""""H+THW,

Attic

3-23

ARRAY SIZING

• Energy sellback price the utility is willing to pay the homeowner andrelati ve PV system cost to thermal system cost affects the overallsystem sizing.

• Sellback rates greater than 50% imply full roof arrays.

• Marginal costs were used in the system sizing.

• For thermal system costs greater than PV system costs, system sizingresults in more PV array area and less thermal collector area.

• Thermal collector area was sized primarily to provide a thermal systemof adequate size for cost estimates.

o

MADISON

'1.5

1.4

~1.3

1.2Cll:uu-' 1.1

PV ARRAY AREAI

1.0 73.6~52.6m2~

I PV ARRAY AREAI

73.6nL.,...-s2.6m2-h,.5mZ-,j1

II

I

1.5

1.2

1.1

1.4

10 20 30 40 50 60

THERMAL COLLECTOR AREA, m210 20 30 40 50 60

THERMAL COLLECTOR AREA, m2

PV System Cost "Fpy +CpV x Areapy

py System Cost -2$1603 + $131/m x Area pv

Thermal System Cost"FT + CT x AreaT

Thermal System Cost.C

$4612 x cT x S131/m2ArPV

Base CaseCTc" 1.7P

Cr/Cpv " 2

CT/CpV • 1

CT/Cpy • 1121

1- DESlr,rl POI~TII

20 30 40 50 60GROSS THERl1AL COLLECTOR AREA. m2

10o

1.0

1.8 Ps/PE" •5

1.6

1.4Cll:uu-' 1.2

o 10 20 30 40 50 60

: ROOF AREA (BASED ON 95 m2)

3-24

DESIGN ELECTRICAL PERFORMANCE

• Net PV system output for both Boston and Madison is approximately 67% ofthe load requirements.

• Approximately 39% of the PV output is utilized directly in the house andthe remainder fed back to the utility.

• The net electrical system output in the summer months is greater thanthe load requirements, mainly due to the thermal system providing thehot water requirements.

• Overall PV system efficiency based on incident insolation for grossarray area is approximately 8.8% for this design in the Northeast.

0 0J F MA MJ J A S 0 N D J F MA MJ J A SON D

ANNUAL TOTALS ANNUAL TOTALS

• LOAD J2~7 M\~H • LOAD 14.~ MWH

• PV SYSTEM OUTPUT §'R M\'IH • PV SYSTEM OUTPUTl~:~

MWH

• UTILITY MAKE-UP MWH • UTILITY MAKE-UP MWH

• SELL BACK ~:2 MWH • SELL BACK MWH

3-25

DESIGN THERMAL PERFORMANCE

• Net thermal system output ranges from 35 to 39% of the load requirements.

• Approximately 24% of the space heating requirements and 66% of the DHWrequirements are supplied by the solar thermal system.

• All of the thermal requirements are met in the summer months.

.. Overall thermal system efficiency is approximately 22% for this designin the Northeast.

3.0

::c: BQS.IOli MADISON::c 2.'- 2.5~

• SPACE ::c: SPACE>- HEATING ~ 2.0 HEATING~

Ic::uJ >-z 1.5LI.! U)

0:;.

>- uJ~ ziE w

1.0z >-0 ~

~ ::c:I- 0.50.5 z0~

0 0J F M A M J J A S 0 N D J F M A M J J A S o N D

~ 0.5 ~~::~c HOT:::::0[; "d '.I~

J F M A M J J A SON DANNUAL TOTALS

• SPACE HEATING LOAD 9,76 MWH• SOLAR TO SPACE HEATING 2444 MWH• DOMESTIC HOT WAIER LOAD .75 MWH• SOLAR TO DHW 3, / MWH

. LOADSOLAR SUPPLYo'Sh; DOMESTIC H~O.T~...TER

~ -_ ..~~--::: _- _-~ -.L!--I.'_---! I-..I.' -l

J F MA M J J A SON D

ANNUAL TOTALS

• SPACE HEATING LOAD 13.07 MWH• SOLAR TO SPACE HEATING 2.96 MWH• DOMESTIC HOT WAT~R LOAD 4.89 MWH• SOLAR TO KHW 3.22 MWH

3-26

A PV SYSTEM WITH BATTERY STORAGE FOR THE SOUTHWEST

A photovoltaic system with on-site storage was designed for a single story all

electric house in the Southwest. The three major system elements are the photo

voltaic array, the battery storage subsystem, and the power conversion subsystem.

Marginal life cycle cost analysis was used for system sizing of the array and

battery. The analysis considered various combinations of array and battery sizes

and provided parametric performance results. In general, the results indicate a

relatively small battery capacity for each array size considered, based on

current cost estimates.

The nominal size array output is 6.07 kWp. The modules are standoff mounted. The

baseline design battery capacity for Phoenix is 20 kWh. An Albuquerque applica

tion, where increased electricity cost and improved load match exist, requires a

larger capacity of 25 kWh. Reduced battery capttal costs indicate an increased

optimum capacity for all of the array sizes considered. The array size and

associated array performance ultimately bound the battery capacity, if cost con

straints are neglected. The system economics also indicate a sensitivity to total

electrical load requirements for all battery costs considered. Therefore, changes

in the load requirements and profile affect system sizing and particularly the

optimum battery capacity.

3-27

HOUSE DESCRIPTION

• The house design is for a SINGLE-STORY residence of NEW CONSTRUCTION forthe Southwest region of the country.

• The design includes PASSIVE SOLAR FEATURES and ENERGY CONSERVATIONFEATURES projected for 1986.

• There is 149 m2 (1600 ft2 ) living area with 104 m2 (1120 ft2)south facing roof area.


• The site layout has a detached garage with a lot area between 1/6 and1/4 acre.

3-28

SYSTEM DESCRIPTION

• The system is grid connected with a 6.07 kW array rating using a SOLAREXBLOCK IV INTERMEDIATE LOAD MODULE ARRAY. The array consists of a totalof 100 MODULES with 76.2 m2 of aperture area in a parallel-seriesnetwork.

• The battery storage subsystem includes a 20 kWh LEAD ACID BATTERY tostore PV generated power. A BATTERY CHARGE CONTROLLER controls the busvoltage. A larger capacity of 25 kWh is required for an Albuquerquelocation.

• The power conversion .subsystem (PCS) employs a 6 kVA LINE COMMUTATEDINVERTER to convert PV generated power to ac. A 10 kVA SINGLE PHASEISOLATION TRANSFORMER matches ac supply voltage to the load.

• The system operation is PARALLEL AND SYNCHRONIZED WITH THE UTILITY,without feedback.

• Excess generated power is SHUNTED to ground. Heating domestic hot waterwith the excess energy is a design option.

UTI LITY BACKUP,PV DC/AC GENERAL

ARRAY INVERTER LOADS

--SHUNT - HEAT-

IPUMP

1- - HOT- '----WATER

3-29

SYSTEM OPERATION

• The system has automatic startup and shutdown control.

• The system automatically shuts down with loss of utility power.

• System operation is summarized by the sequence below.

1. At sunrise, in the automatic "on" mode, the ac and dc contactorswill close when the array bus voltage reaches a threshold of 120Vdc.

2. During daylight hours the PV array/battery system will supply theload demand. Excess power is applied to the charge battery.

3. When the battery is fully charged (156 Vdc), the battery chargecontrol sheds PV branch circui t( s) which reduces current flow~

Should the voltage fall below 144 Vdc, the charge control addscireui t( s) •

4. The battery delivers load demands when the voltage level is greaterthan 120 Vdc and the solar array output is not adequate to meetthese demands.

5. The battery supplies power until the bus voltage falls below 120Vdc; at this point the ac and dc contactors will open.

6. If the battery is depleted, a 128-minute time lag is imposed beforeanother discharge attempt is made, thus precluding deep discharges.

7. Twice a month, during off-peak hours, the pes initiates batteryequalization to 173 Vdc.

ISOLATIONDIODES

.....-- FILTER POWER CONVERSION SUB

..!',l.FUSED

OUTDOOR INDOOR I

IAC.... BREAKER DISCONNECT TRANSFORMER I PANELBOARD

SOLAR • r7l r:;-ARRAY • I __ I I

-+ '/)A

~llf• -1>1- I L N

FUSED I,J. ,! I INVERTER'/)B I

'1:7 DISCONNECT

IAND ----l )'--- BATTERY CHARGER,

I••• ANDTIMING AND I

DI CONTROLS

-~~

BATTERY I II~ I LIGHTNING"\-- PROTECTOR

SHUNTS CHARGE

\.CONTROL

BATTERY ~

\INTERLOCK

VENTILATIONSYSTEM

\

3-30

PHOTOVOLTAIC ARRAY

• The array consists of STAND-OFF PV modules connected in a 10 SERIES by10 PARALLEL NETWORK with 76.2 m2 of aperture area.

• The array orientation is due south with a ROOF PITCH OF 260 • Theoverall module packing efficiency is 85.3% over the 76.2 m2 •

• The modules are mounted on WOOD 2 x 4 inch STAND-OFFS. Conventionalasphalt shingles beneath the modules provide a weathertight roof.

• The module frame fits into aluminum clips mounted to the stand-offs andattaches to the clips by four sheet metal screws. Electrical interconnection between modules is made with AMP Inc. connectors and standardcables.

10

UOTE::-:,:

1. ?P~'-IVc:- ~;::>uc..T~ ;;eo....... c.Ao:::.i-leul...l --:'""c:;:o' I~Qt...~TI e>o-i :::::>.or:>E:- e:".::;o"""",'v,~ l--l1e:...b~A."""

GENERAL" ELECTRIC...... DIYlelON

Detaillld RetidInlIII P.Y. system

~~~ooc.#13-8779

'Johnson 8& StoIIer,lnc.8ectrica1 ~ineera127 Tauntonst.MiddlebottJugh,Mase. 02346617-947-8464

. .masS\...~slgn--"-1:II"_""e-.-._o:tI.,..,__

SouthwestAll-Electric HouseWith P. V./Battery

..... Ho~

-....

3-31


• The module is manufactured by SOLAREX CORP., of ROCKVILLE, MARYLAND, andwas developed as part of the 3PL Block IV procurement.

• The module uses Solarex 95 mm SQUARE CELLS with 36 cells connected inseries and 2 paralle~ circuits for a total of 72 cells per module.

• For an estimated stand-off NOCT of 60°C, the MAXIMUM POWER OUTPUT is60.7 Watts, and 13.9 Volts at SOC conditions (1 kW/m2 , 20°Cambient, 1 m/s wind speed).


- Module weight: 15.9 kg- Total-cell area: 0.650 m2- Exposed ;module area: 0.762 m2

- Module packing factor: 0.853- Nominal size: 1.2 m long by 0.64 m

wide1--------------116.8 CM------------..1/

I

~I 'I il ,i Ir--l II :1 \\ I

, !i 1 I, :: il : j 11 ~ I

iLl :, I i! L! ~ lLJ-.JIi II i,l 1\1 il iI' II' lUi1:1' II il ii',

60.4 eM; ,! :, I !I ~, I I 'I". ...--,-t---t-------l- --- ---; I'U,'~ II iIi IUil 'III II I! ill' 1'1'

• I II :I L I 1 , , 1\ I ..

I ~ [-1 ,II,: liill~,ri,nl-, '!L-!U 'L...J! :1 I, :1 Ii ;1 i

'\ \,1 I' l' ':--11 II -:r-1,1",i!I---;I-'ij1I I 'I I '! II ' II I, ;1 ! ,

II II !! II I \I!I II Ii II ILirop VIE:Wr.!------ '120 Q; ---------------------"1

3-32

63.5 eM

I

,'h-../1 l=--~II.

TerminalConnectors

o 9

:1I·j


• The Power Conversion Subsystem (PCS) provides the interface between thePV arr~/batter,y and the normal residential utility service and loads.

• The subsystem consists of three main components: the INVERTER, the DCFILTER and TRANSFORMER along with the associated control circuitr,y.

• The subsystem rating is 6 kVA of power output with a 10 kVA transformersized to accommodate the out-of-phase ac voltage and current.

• The subsystem characteristics are summarized in the table below.

• The GEMINI CORPORATION, of MUKWONAGO, WISCONSIN, manufactures the subsystem components and WINDWORKS, INC. markets them.


OUTPUT POWER RATING

OUTPUT VOLTAGE:

INPUT VOLTAGE:



FULL LOAD HARMONIC DISTORTION

OPERATING TEMPERATURE

10 kVA CONTINUOUS


138 .:!:. 18 Vdc

60% Minimum,

92% Minimum

30% Maximum

00 to 40°C


I TRANSFORMER I

- '-- + C/>A

-II ~- N

I C/>BINVERTER -

II FILTER I

LJ AND t Ii:TTERY CHARGER~

INTERLOCK

I VENTI LATION ISYSTEM 1-----.........-----'

3-33

BATTERY STORAGE SUBSYSTEM

• The battery storage subsystem provides the energy storage capacity forthe solar generated power.

• The subsystem consists of two main components: the BATTERY and theCHARGE CONTROLLER.

• The subsystem includes a 20 kWh LEAD-ACID battery made up of 64 seriesconnected cells producing a nominal 135 Vdc output.

• The charge controller maintains the voltage wi thin a 144 to 156 Vdcrange which is indicative of full battery charge.

• ESB INCORPORATED, EXIDE POWER SYSTEMS DIVISION, of YARDLEY, PENNSYLVANIA, manufactures the battery. GENERAL ELECTRIC COMPANY manufacturesthe charge controller.

102 CM (40 IN)r; II

1 2 3 4

~/1 2 rT 3 4

I~ I

r

FRONT

3-34

lh rD

c::000

fh rll

SIDE

z

::JEuU'lN-

JUNCTIONBOX ONCABINET

WIRING ISOMETRIC

91 CM (36 IN) ,-., ... ....

2 3 4

f-C n M I;;b~I

DOOR

PLAN

ARRAY/BATTERY SIZING

• The array/battery sizing uses MARGINAL COSTS and BENEFITS.

• Battery capital cost affects the relative size of the array and battery.- Battery capital costs greater than $lOO/kWh imply smaller batteries

(-20 kWh).

- Lower battery capital costs imply larger capacities for fixed arraysizes.

• System economics are sensitive to load level for all battery costs. Newoptimum system sizes must be developed for significantly varying loadlevels.

PHOENIX

O'- L..- L..-_L..- L...---'o 20 40 60 80

BATTERY CAPACITY, kWh20 40 60 80CELL AREA, m2

ATTERY COST$/kWh

15010050~o ~~

BATTERY CAP. = 20 kWh

~ 2.0U

w U..J :::. 1. 5U>-0Uj:1.0w<u.a::3 ... 0.5

(/)

oU 0 '-_"'--_"&'-_...1--'---1.._-'

o

BATTERY COST$/kWh

~15010050

- 0III

2CELL AREA = 65.0 m

-a:: 2.0U

w U..J..J1.5U->-0U-... 1.0w<u.a::3 ... 0.5

(/)

oU

ALBUQUERQUE

CELL AREA 6Sm2=

- 2.0a:: 2.0 -U BATTERY COST a::

Uw U $/kWh U 1.5..J:::' 1.5 w..JU 150

..J_>-0 UU- 1.0 ----::;::; 1 00 >-0 1.0...

:::: : ::: 5~U-

w< ...w<u.a::

0.5I u.a:: 0.5..J ... , -

(/) , ..J ...0 I (/)

U 0U

0 20 40 60 80

BATTERY CAPACITY, kWh

BATTERY CAPACITY = 20kWh

BATTERY COST$/kWh

o 20 40 60 80

CELL AREA, m2

3-35

DESIGN PERFORMANCE

• Total net system output for both Phoenix and Albuquerque is approximately 69% of the load requirements.

• Phoenix shows better load matching characteristics.

• Overall system efficiency based on incident insolation for gross arrayarea is within the 5.9 to 6.1% range for the Southwest.

UTILITY MAKE-UP, MWh - 5.0HEATING LOAD, MWh - 1.0COOLING LOAD, MWh - 11,7

2.0

NOTES

1. ARRAY CONFIGURATION1OSxl OP -65. Ii m2 CELL AREA

2. BATTERY CAPACITY 20 kWh

1.8

0.4

0.2

>U

"UJZUJ

~:I:IZo::0.6

UTILITY MAKE-UP, MWhHEATING LOAD, MWhCOOLING LOAO, MWh

4.6- 5.3- 2.8

NOTES

1. ARRAY CONFIGURATION10Sxl0P-65 m2 CELL AREA

2. BATTERY CAPACITY25 kWh

LOAD(14.8 MWh)

NETSYSTEM OUTPUT

(10.6 MWhj

EXCESS(1. 0 MWhj

2.0

1.8

1.6

~ 1.4::::

>- 1.2U

"UJZ 1.0UJ

>-...J

0.8:r:I-Z0:: 0.6

0.4

0.2

3-36

PASSIVE HOUSE DESIGN FOR THE NORTHEAST

A 4.1 kW grid-connected PV system with utility feedback is designed for a

passively heated house having low total electrical load requirements. The major

system elements are the photovol taic array and the power conversion subsystem.

Marginal life cycle cost analysis was used for system sizing. The analysis

considers various array sizes and provides parametric performance results. In

general, with utility sellback rates of 50% or greater, the results indicate a PV

array size as large as the available roof area. This design considers a low

energy consuming house with a minimum of available roof area. The 50 m2 solar

array uses a rectangular shingle solar cell module being developed by General

Electric. The array is wired in a redundant series/parallel matrix.

3-37

HOUSE DESCRIPTION

• The house design is a TWO-STORY residence with a basement of NEWCONSTRUCTION for the Northeast region of the country.

• The design includes PASSIVE SOLAR FEATURES and ENERGY CONSERVATIONFEATURES projected in 1986.

• There is 157 m2 (1690 ft 2 ) of living area with a 9 m2 (96 ft 2 )greenhouse and 57 m2 (614 ft 2) of south facing roof area.

• The house is ALL ELECTRIC with a 2 1/2-ton heat pump and electric hotwater heater.

• The site layout has a detached garage with a lot area of 1/4 acre.

3-38

SYSTEM DESCRIPTION

• The system is grid connected with a 4.1 kW NOCT array rating using a GErectangular SHINGLE MODULE ARRAY. The array consists of a total of 52FULL AND 8 HALF MODULES COVERING 50 m2 in a redundant parallel-seriesnetwork.

• The power conversion subsystem uses a 4 kVA LINE COMMUTATED MAX POWERTRACKING INVERTER to convert dc generated power to ac. A 5 kVA SINGLEPHASE ISOLATION TRANSFORMER is used to match ac supply voltage to theload.


• Excess generated power is FED BACK to the utility.

• The system represents the SIMPLEST PHOTOVOLTAIC DESIGN with a minimumof components and controls.

UTILITY FEEDBACK SYSTEMUTILITYBACK UP

3-39

SYSTEM OPERATION

• The system has AUTOMATIC STARTUP and SHUTDOWN control.

• The system automatically shuts down with loss of the utility power.

• System operation is summarized by the sequence below:

1. At sunrise, in the automatic "on" mode, the ac and dc contactorswill close when the array bus voltage reaches a threshold at lS6 Vdc.

2. During the daylight period, the inverter operates continuously ifthere is a net power output.

3. The inverter will track the maximum power operating point within +1percent over the range of 156 to 180 Vdc.

4. The interruption of utility-supplied power opens the dc contactorand it remains open until the line voltage is restored.

5. At sunset, the inverter ac and dc contactors open when the net poweroutput falls to zero. These contactors· remain open throughout thenight to eliminate the majority of the inverter parasitic losses.

unU1't_~"""S1NGLI-'-YI>C

WALL

~-

;-40

POWE" CONVlfI..ON SYSTEM sr~YIC£ PA'I!l

PHOTOVOLTAIC ARRAY

• The array consists of SHINGLE PV MODULES connected in an 8 series by 7parallel network covering 50 m2 of roof area.

• The array orientation is due south with a roof pitch of 33.70 • Theoverall cell packing efficiency is 97% over the 50 m2 •

• The modules are DIRECT MOUNTED on top of the roofing felt and plywoodroof sheathing. They form a weather tight roof.

• The modules are installed by an overlapping procedure similar to conventional shingles. Each shingle module requires two FCC butt terminationsto electrically interconnect the module to the array. Standard roofingnails are used for attachment to the roof.

3-41

,,


• The module is currently under development by General Electric Company.

• The module uses 94 mm SQUARE SILICON CELLS. with 48 cells connected inseries and 2 parallel circuits per module.

• A half-sized module with one series string of 36 cells is also used inthe installation.

• For a NOCT of 650c, the MAXIMUM POWER OUTPUT is 74 Wand 16.6 V at SOCconditions (1 kW/m2 , 200C ambient, 1 m/s wind speed).

A summary of the module characteristics are:

Full Module Half Module

Module weight: 18 kg 9 kg

Total Cell area: 0.866 m2 0.433 m2

Exposed Module area: 0.916 m2 0.458 m2

Module packing factor 0.945 0.945

ILo.7716..--J1Lo.77481J1~

.049m- I--t- I-- 0.15..

HALF

SHINGLE

H (+)

.-r --~ ~

0.25.;

-i

I

I +I

e

I : + . i J1.37m

o 58m ±.. ~'- -L,_,-,- - ~'L II-I-l--I-+L--I±~~1- ~

I': -f-oo"o.=0==J. • 1.54..··

1.55.. )

0.1111 ..

V""~0

1.73..

O.86m

LFULL SHINGLE

,-H (+)

3-42


• The PCS provides the interface between the PV array and the normalresidential utility service and loads.

• The subsystem consists of three main components: the INVERTER, the DCFILTER and TRANSFORMER along with the associated control circuitry.

• The subsystem is rated at 4.0 kW of power output with a 5 kVA transformer, sized to accommodate the out-of-phase ac voltage and current.

• The subsystem characteristics are summarized in the table below.

• The Gemini Corporation of Mukwonago, Wisconsin, manufactures the subsystem components and Windworks, Inc., markets them.


Output Power Rating

Output Voltage:

Input Voltage:

Full Load Power Factor:

Full Load Efficiency:

Full Load Harmonic Distortion

Operating Temperature

4.0 kW Continuous


168 + 12 Vdc

60% Minimum,

92% Minimum

30% Maximum

00 to 400 C

POWER CONVERSION SVSTEM

Vcc---+l

IOC--"'L~~:...J

3-43

ARRAY SIZING

• The array sizing uses MARGINAL COSTS and BENEFITS.

• Energy sellback price the utility is willing to pay the homeowneraffects the system sizing.

• The assumed energy escalation rate is 4% above inflation.

1.3 1.3 MADISON

1.2 1.2 SELL BACKRATIO

0.8

1.1oSell: 1.0ten8 0.9""-'u>u 08"" ."'---'

0.7

SELL BACKRATIO

~O'30.5

0.7

NOTES1. PRICE OF ELECTRICITY

$0.0832/ KWH

1.1o

§ 1.0tenou"" 0.9-'u>u

"""'-.-'

0.7

~O.30.5. 0.7

. NOTES- 1. PRICE OF ELECTRICITY

$0.0532/KWH

0.6 0.6

8020 40 60

COLLECTOR AREA. H2

OL--I---+--+---t--+---+---t---io8020 40 60

COLLECTOR AREA. ,;.

oo

3-44

DESIGN PERFORMANCE

• Total net system output for both Boston and Madison is approximately 40%of the total load requirements.

• Overall system efficiency based on incident isolation for gross arrayarea is approximately 8.3% for the Northeast.

2.2 2.2BOSTON MADISON

2.0 2.0

1.8 1.8

1.6LOAD

1.6 . 15.6 MWHLOAD

::c: 1.4 14.3 MWH 1.4~. 1.2 1.2~a:l.I.I

1.0z 1.0w

.8 .8

.6 PV SYSTEM .6 PV SYSTEMOUTPUT OUTPUT

.4 5.6 MWH .4 6.3 MWH

.2 SELLBACK .2 SELLBACK2.0 MWH 2.4 MWH

0 AtstoiNtol 0

UTILITY MAKE-UP 10.6 MWH UTILITY MAKE-UP 11.6 MWH%OF LOAD SUPPLIED %OF LOAD SUPPLIED

DIRECTLY 25.3 2 DIRECTLY 25.3INSOLATION ON ARRAY 1338 KWH/m INSOLATION ON ARRAY 1456 KWH1m2

3-45

INTEGRAL MOUNTED PV ARRAY FOR THE SOUTHEAST

A flat plate photovoltaic system with utility feedback is designed for a single

story, all-electric house in the Southeast. The two major system elements are the

photovoltaic array and the power conversion subsystem. Marginal life cycle cost

analysis was used for system sizing. The analysis considers several values of

array area and provides parametric results. The PV system is sized at 5.6 kW at

NOCT conditions. The array covers the complete roof area and is integrally

mounted in the roof. The 86 m2 solar array uses a modified Solarex inter

mediate load module in a 7-parallel by 14-series module array.

3-46

HOUSF. DESCRIPTION

• The house design is for a SINGLE-STORY residence of NEW CONSTRUCTION forthe SOUTHEAST region of the country.

• The design includes PASSIVE SOLAR and ENERGY CONSERVATION FEATURESprojected for 1986.

• There is 161 m2 (1736 ft 2 ) living area with 92.2 m2 (992 ft2 ) ofsouth facing roof area.


3-47

SYSTEM DESCRIPTION

• The system is grid connected with a 5.6 kW NOCT rating using SOLAREXBLOCK IV INTERMEDIATE LOAD MODULES incorporated into an integral mountdesign. The array consists of 98 modules with 74.5 m2 of aperture in a7-parallel by l4-series network.

• The power conversion subsystem (PCS) employs a 6 kVA-SELF COMMUTATEDMAXIMUM POWER TRACKING INVERTER to convert PV generated power to ac andto match ac supply voltage to the load.

• The system operation is PARALLEL and SYNCHRONIZED WITH THE UTILITY.


UTILITYSERVICE

INVERTER

INTERIORSWITCH

3-48

SWITCI1

VARISTOR

PV CB

TYPICALBRANCH

SERVICEPANEl.

RESIDENTIALLOAD

----7

PHOTOVOLTAIC ARRAY

• The array consists of INTEGRAL MOUNTED PV modules connected. in a 14series by 7-parallel network covering 80 m2 of roof area.

• The array orientation is due south with a roof pitch of 22.60.

• The modules and mounting extrusions are mounted on the roof rafters andpurlins. No plywood sheating is used. The installation forms a weathertight roof.

• Mounting extensions are attached to the rafters with screws. The modulesare then bolted to the mounting extrusions. This compresses anelastomeric material to form a seal.

• Electrical connections are made with patented connectors and factorysupplied cables.

6d\V I.lo. ~ .1.. 2.. ~ .:i. .r... 1- ~ ~ .:.e. 11. 1k. ~ .M. !2.. .lli. J1. ~ .12.. 20

GBBBBGBBBGG8BBB888B8GDDDDDDDDDODDDDDDDDDBDDDDDDDDDDDDDDDDDDDGDDDDDDDDDDDDDDDDDDOt~~~

o"~~y~BEJ[JEJEJBBEJBBEJ EJEJEJEJEIEIEJG~MYf.--r-11,-'1'" <i: ,Q'~ ~~~E:I';>

3-49


• The module is manufactured by SOLAREX CORP., of ROCKVILLE, MARYLAND andwas developed as part of the JPL Block IV procurement.

• The module uses Solarex 95 mm SQUARE CELLS with 36 cells connected inseries and 2 parallel circuits for a total of 72 cells per module.

• For an estimated NOCT of 71oC, the MXIMUM POWER OUTPUT is 56.9 W, and13.0 V at SOC conditions (1 kW/m2, 200 C ambient, 1 m/s wind speed).

• The design approach uses only the Solarex laminate assembly of themodule. A specially designed frame is used to mate with the integralroof extrusions.

A summary of module characteristics include:



Exposed installed module area:0.815 m2

\CLOSURE STRAP

\ 126.0cm.

2x4 or 2x6PURLIN.

3-50


Nominal size: 1.26 m long by0.655 m wide

65.08cm.

ALUMINUM EXTRUSIONSUPPORTS

2x6 or 2x8 RAFTER

rOWER CONVERSION SUBSYSTEM


• The subsystem consists of three main components: the inverter, the dcfilter and transformer, along with the associated control circuitry,packaged in a single unit.

• The subsystem is manufactured by Abacus Controls, Inc., Sommerville, NewJersey.

• The subsystem is sized for an 6 kW POWER OUTPUT with the transformersized to accommodate the adjustment of the ac voltage and current.

• The subsystem characteristics are summarized below.


OUTPUT POWER RATING

OUTPUT VOLTAGE:

INPUT VOLTAGE:



FULL LOAD HARMONIC DISTORTION

6 kW CONTINUOUS


200 .:!:.. 40 Vdc

Unity


5% Maximum

MAXIMUM (+) ~ (-) INPOWER 1---....-4~ ~--t PHASETRACKER SENSE

~AMPLITUDECONTROL

AC LINEROOF DC CONTACTORARRAY FILTER I SCR I XFMR ~nn :r- AC OUTPUTINPUT I I \1'1_

9 FAN

I - SENSE ( THERMALPI.L. SWITCH UTILITY

V - REFERENCE VOLTAGE

.3-51

ARRAY SIZING

• Energy sellback price the utility is willing to pay the homeowneraffects overall system sizing.

• Sellback rates greater than 50% imply full roof arrays.


1.2

1.1

1.2

:::=1'$/"·.,1.5 1.1

~:.7I

PS/PE • .J

.5

----_.7MIAMI

SJ9.9/m2 INSTALLATION COST (1980$)

3-52

a:'-''-'.J

1.0

.9

.8

IIIIIIIIDESIGN POIHT ~.I

IIIII

.9

·.8

CHARLESTON, SC

SOLAREX IHTElU1EDIATE MODULES

20 30 40 50 60 70 80

COLLECTOR AREA _m2

DESIGN ELECTRICAL PERFORMANCE

• Net PV system output for Miami is 61% of the load requirements and thecorresponding value for Charleston is 68%.

"

• For Miami, approximately 67% of the PV system output is applied directlyto the house load while the utility receives the remaining energy. InCharleston, 53% is applied.

• The monthly net electric'al system output in Miami is always less thanthe total monthly load.

• Overall average annual PV system efficiency, based on incident insolation for the gross array area, is 7% for this design in the Southeast.The corresponding peak module efficiency assumed is 8.8% at 28 degrees C.

14$ X 7p CONFIGURATION

::c:3:1:

2.0

MIAMI

PV SYSTEMOUTPUT

2.0

1.5

1.0

0.5

CHARLESTON

PV SYSTEMOUTPUT

ANNUAL TOTALS ANNUAL TOTALS

LOADPV SYSTEM OUTPUTUTILITY l'lAKE-UPSELL BACK

14.9 MWh9.1 MWh8.8 MWh3.1 MWh

LOADPV SYSTEM OUTPUTUTILITY MAKE-UPSELL BACK

12.7 MWh8.6 MWh8.2 MWh4.1 MWh

3-53

A PV SYSTEM FOR A TEMPERATE CLIMATE

A 4.3 kW grid-connected PV system with utility feedback is designed for a house

having low space conditioning load requirements. The major system elements are

the photovoltaic array and the power conversion subsystem. Marginal life cycle

cost analysis was used for system sizing. The analysis considers various array

sizes and provides parametric performance results. In general, with utility

sellback rates of 50% or greater, the results indicate a PV array size as large

as the available roof area.

This design considers a low energy consuming house with a minimum of available

roof area. The design also provides a comparison of integral and stand-off

mounting techniques for the same array configuration. The array is mounted on the

garage roof which also is a different approach than previous designs.

The 40.3 m2 solar array uses a laminated glass/cell assembly module in an array

with four parallel circuits. Two circuits have 12 series modules and two circuits

have 13 series modules.

3-54

HOUSE DESCRIPTION

• The house design is for a SINGLE-STORY residence of NEW CONSTRUCTION fora TEMPERATE CLIMATE region.

• The house can be sited following a ZERO-LOT-LINE plan.

• The design includes PASSIVE SOLAR and ENERGY CONSERVATION featuresprojected for 1986.

• There is 142 m2 (1530 ft 2) of living space.

• The plan includes a TWO-CAR GARAGE with 44.4 m2 (477 ft2 ) of garageroof area available for mounting the solar array.

3-55

SYSTEM DESCRIPTION

The system is grid-connected with an 4.29 kW NOCT array rating using aglass laminate module assembly in an INTEGRAL and STANDOFF MOUNTINGarrangement. The array consists of 50 modules covering 40.3 m2•

The power conversion subsystem uses a 4 kVAINVERTER to convert dc generated power to acvoltage and load.

MAXIMUM POWER TRACKINGand to match ac supply



• The system has automatic STARTUP AND SHUTDOWN control and shuts downwith loss of the utility.

• System operation is summarized by the sequence below:

1. At sunrise, in the automatic mode, when the input voltage exceeds180 V, the ac line contactor is closed and the phase locked loop andmaximum power tracker are energized.

2. During the daylight period, the inverter operates until the dc inputvoltage falls below 160 V.

3. The inverter tracks the maximum power point within .:1% over therange of 160 to 240 Vdc.

4. The interruption of utility supplied power opens the ac contactorand it remains open until the line voltage is restored.

5. At sunset, the inverter ac contactor opens when the net power outputfalls to zero. This contactor remains open throughout the night tominimize parasitic losses.

UTILlTVSERVICE

INVERTER

3-56

EXTERIORSWITCH

INTERIORSWITCH

SWITCh

MAINCB

VARISTOR

PVCB

TYPICALBRANCH

SERVICEPANEL

RESIDENTIALLOAD

PHOTOVOLTAIC ARRAY

• The array consists of PV modules and mounting accessories which may beused either as an INTEGRAL MOUNT or as a STANDOFF MOUNT. There are 4circuits connected in parallel with two 13 series circuits and two 12series circuits.

• The array orientation is due south with a roof pitch of 18.40 •

• The modules are mounted on a series of channel supports which can beplaced on the roof truss system for an integral mount or on the shingledroof for a standoff mount. Electrical connections are made with patentedconnectors and factory supplied cables.

• The watertight· integrity of the photovoltaic roof is assured by a simplemodule perimeter seal which uses the sloping roof surface to the maximumadvantage. An overlapping seam is used between modules to shed waterwhich runs down the roof surface.

Outlet Box

Positive circuit leads~----------

Conduit:----)~II

=

t. ___c: )(41-201 '" '20'-1011 -------1

3-57


• The module assembly is a laminated glass superstrate/cell unit similarto the Solarex Corporation, Block IV residential module, but withsealant strips attached for mounting.

• The module uses nominal 100 mm square cells with 36 series units of 2parallel cells for a total of 72 cells per module.

• For an estimated NOCT of 710 C the maximum power output is 85.8 W at 13V at SOC conditions (1 kW/m2 , 200C ambient, 1 m/s wind speed).


Module weight = 11.69 kg

Total cell area = 0.72 m2

Exposed module area = 0.8045 m2

Module packing factor = 0.895

3-58

ClOSURE STRIP

RAFTERS OR TRUSSMEMBERS

EDGE SEALI NG STRIP

HORIZONTAL BLOCKING



• The subsystem consists of three main components: the inverter, the dcfilter and transformer, along with the associated control circuitry,packaged in a single unit.

• The subsystem is manufactured by Abacus Controls, Inc., Sommerville, NewJersey.

• The subsystem is sized for a 4 kW POWER OUTPUT with the transformersized to accommodate the adjustment of the ac voltage and current.

• The subsystem characteristics are summarized below.


output Power Rating

Output Voltage:

Input Volt"age:

Full Load Power Factor:

Full Load Efficiency:

Full Load Harmonic Distortion

4 kW Continuous


200 + 40 Vdc

Unity


5% Maximum

MAXIMUM (+)rt""""1(-) INPOWER 1---""" <::... .....--t PHASE

TRACKER SENSE

AMPLITUDECONTROL

AC LINEROOF DC CONTACTORARRAY FILTER SCR XFMR I'Y"'/("\ nn :l- AC OUTPUTINPUT INVERTER uu V..lI.

I - SENSE

9 'AN( THERMAL

PLL SWITCHUTILITY

V - REFERENCE VOLTAGE

3-59

ARRAY SIZING


• The system shows economic viability (LCCR<l) with sellback rates of 30%or greater. These sellback rates imply full roof arrays.

1.2

SANTA MARIA 0.7

ARRAY CONFIGURATION135 x 2P + 125 x 2P

100

GARAGEROOF AREA

40 60 80

COLLECTOR AREA - m2

~PS/PE = 0.3---,--------

20

0.2

oo

0.8

1.0

a:u 0.6~

3-60

DESIGN ELECTRICAL PERFOR'tI.ANCE

• Net PV system output for Santa Maria, CA is 67% of the load.

• Performance results indicate that 56% of the PV syste~ output is applieddirectly to the house load while the utility receives the remainingenergy.

• Overall PV system efficiency based on incident insolation for grossarray area is 9.6% for Santa Maria.

1.4 SANTA MARIA

1.2.t::: LOAD:E

1.0..>tj.c::

0.8wzw>-

0.6..J:cI-z0 0.4:E

ARRAY CONFIGURATION

0.2 13S x 2P + 12S x 2P

0J M J J A S 0 N D

ANNUAL TOTALS

LOAD 11. 3 MWhPV SYSTEM OUTPUT 7.6 MWhUTILITY MAKE-UP 7.1 MWhSELL BACK 3.4 MWh

3-61·

SECTION 4

DESIGN CONCERNS

During the design effort, several concerns were addressed. Some of the design

considerations were only pertinent to a single design, but others were applicable

to all of the designs. All of these are summarized in the following sections.

Array Sizing

The primary area available for residential PV arrays is roof area. In grid

connected applications, the system size should be selected to deliver energy to

the owner's load at the minimum life-cycle cost, including the cost of backup

utility energy. Assuming 1986 array costs of 70~/kWp and 1986 system costs, study

results indicate array areas using all of the available roof area when sellback

rates are 50% or greater. Incorporating cost effective passive house design

features and energy conservation features reduces the overall household energy

requirements and thus reduces the array requirements. This allows more flexi

bility in the architectural house design. Additional background information into

system sizing considerations is provided in Reference 1.

Roof Constraints

The physical size or available dimensions of the roof can impose several con

straints on the array configuration. This is more of a problem for direct

mounting systems where arbitrary row wiring may not be possible; however, cross

row wiring in integral or standoff mountings make the installation details more

difficult and more costly.

Rectangular areas are desirable both from an aesthetic viewpoint and from an

electrical interconnect standpoint. If modules are only connected in series up

the slant height of the roof, the system operating voltage is limited to, at a

minimum, multiples of the slant height. This implies that, for different roof

sizes using the same modules, each system results in a different operating

voltage. A transformer may be required to ultimately match house loads. The

addition of a transformer to match the loads appears more practical and less

costly than changing the specifications for the inverter package for each voltage

input. Thus, a common operating voltage range is difficult to standardize.

Similar concerns result if the modules are connected in series along the roof

length. Reference 9 addresses the problem of roof constraints in more general

terms.

4-1

Array Mounting Approach

Each of the key array mounting approaches, except rack mounting, was addressed.

It is not apparent from the designs which approach is the most cost effective

technique. Indeed, each approach has its advantages and disadvantages. It is

important to note, however, that the array mounting technique has subtle effects

on the system overall costs. Module interconnection layouts, array operating

voltage, replacement or maintenance access, and weather seals all impact the

system. Some of these cost impacts will be evaluated as Sandia obtains detailed

cost estimates for each of the developed designs. In addition, the data being

generated at the Northeast and Southwest Residential Experiment Stations (RES)

will also provide guidance in array mounting approach performance and costs.

Power Conversion SUbsystem

Several design concerns exist in the area of power conversion. Experience at the

RES's have indicated problems in startup and maximUID power tracking. The designer

must be aware of the high open circuit voltage that can exist during startup

conditions when there is a low total power output. The specifications of the unit

must accommodate these initial conditions.

It is easy to specify Power Conversion Subsystem operation with ranges wi thin a

few percent of the maximum power point; however, test data on maximum power

tracking options, has indicated difficulty in achieving these specifications.

Alternate schemes are under development, including the use of a pilot cell. This

approach is an open loop control algorithm and, although relatively simple, may

not represent the true array operating point over the lifetime of the system as

module performance is degraded due to dirt, electrical problems or shadowing.

Thus, additional development is required on these units.

Throughout the study, two primary types of power conversion units were available,

the Gemini and the Abacus Sunverter. During this time period, Abacus was also

developing a lower cost version of the currently available unit. This unit was

specified in several of the designs. After the designs were completed, however,

Abacus changed their development directions and this design version was dropped

from further development. In addition, residential sized development of power

conversion units was underway by several other firms. Optimal inverter conceptual

designs have been developed by United Technologies Corporation, Westinghouse,

General Electric and Airsearch Manufacturing Company (Division of Garrett), under

4-2

DOE contract. DECC, Delta Electronic Control Division of Helionetics, Inc. and

American Power Conversion Corporation also have hardware either presently

available or to be available in the near future. Sandia is also developing a

baseline inverter specification. Thus the state-of-the-art in power conversion

equipment will be changing over the next several years and manufacturers should

be consulted for the latest available information.

Isolation Transformer and Grounding

In many of the designs, the negative bus bar was located along the eave of the

roof. The negative array busbar located near the gutters at the eave of the roof

is subjected to a potential ice buildup from the gutter under a combination of

environmental circumstances in northern installations. Water from this ice backup

could conceivably penetrate the insulation of the busbar or a slender tool being

used to clean debris or the ice blockages could come in contact with the busbar

providing a potential to ground. A wired connection to earth ground for the

negative busbar should be provided as an additional safety precaution. This

connection creates the requirement for an isolation transformer in the power

cpnversion system. While an isolation transformer is not a mandatory system

element except for array bus grounding, its presence can provide a convenient

location for adjustments of system output to the required house service rating.

This feature provides design flexibility in array circuit layout for different

roof designs. The transformer, however, adds economic penalties both in ini tial

cost and in net power loss over the life of the system operation. Elimination of

array bus grounding and the associated isolation transformer, providing the array

output matches the house service rating, can increase the system output at

negligible decrease of safety.

Exterior Disconnect Switches

Almost all of the designs had a fused exterior switch and an interior switch. The

external switch allows to open circuit the array in the event of fires, etc. It

is a redundant switch and, in some measure, tends toward a conservative design

approach. The additional devices and installation, however, are only minor addi

tional initial economic penalties. Non-functional redundancy in this chain may be

eliminated as experience with system installations is gained and NEe codes for

photovoltaic installations are developed.

4-3

Battery Location Concerns

Location of batteries within a residence presents several concerns. Trade-offs

between an interior and exterior location for the batteries resulted in the

interior location based primarily on the requirements for maintaining environment

control and access for maintenance. The batteries were placed in the equipment

room with all the PV and conventional equipment.

The ro.om must be designed to have sufficient ventilation to remove any hydrogen

buildup, to accommodate active battery ingredients spillage and to minimize

access to the equipment from unsuspecting occupants, especially children. To

prevent a hydrogen buildup within the room, a guaranteed amount of ventilation at

all times is required to dissipate the small amounts of hydrogen and chemicals

emitted under normal operating conditions and a positive 30-60 cfm ventilation is

suggested to remove hydrogen during equalization of battery charge. These venti

lation requirements result in a slight increase in infiltration loss in the

house. To accommodate any possible spillage, a 5 em drop in the slab should be

designed around the battery racks. To minimize general access to the batteries,

they can be located in a metal enclosure. The cabinet should be heavily louvered

and have a locked door. All of these design considerations increase system costs.

As storage systems become more widespread, standard designs to resolve these

concerns may be developed.

Module Interconnection

Several of the module interconnection schemes do not currently satisfy the

National Electric Code. For example, the AMP flat conductor cable used for the

direct mount shingle designs is currently in the codes for interior, commercial

under-carpet installations only. The wire runs between battens of the direct

mount batten module also would not be classified as raintight raceways, since the

conductors are not enclosed on all sides. In addition, splice connections would

not be allowed within the batten seams. These apparent code restrictions have to

be resolved for widespread implementation.

Fire Safety

Fire safety is an important issue that could not be specifically addressed in the

design other than for general considerations. It is likely that the module

installations will be considered as a roof covering by local building code

4-4

a fire rating

"Test for Fire

officials. In this case, the module installation must receive

classification in conformance with the requirements of UL-790,

Resistance of Roof Covering Materials".

Local fire companies would have to be alerted and instructed in regards to the

potential danger of the energy-producing roof. The location of the de power line

adjacent to the normal utility line and the exterior disconnect switch should

alert fire personnel that the house has an additional power supply. However, fire

personnel must be informed that disconnect at the switch still leaves the roof as

an active generator in the daylight and only interrupts power supply to the house.

4-5

SECTION 5

DESIGN STUDIES

This section discusses some design studies which were applicable to the designs

in general or were completed after the respective report was written. For

example, power conversion subsystem requirements were evaluated relative to

operating voltage ranges and losses associated with restricted voltage operation

ranges through system simulations. A correlation for estimating power losses for

limited system operation within specific voltage ranges was developed. In

addition, annual distributions of array current characteristics were developed.

Power Conversion Subsystem Correlations

During system analyses of the detailed designs, narrowing the maximum power

tracking operational voltage range over which the power conditioner operates was

found to have only small effects on the total annual energy collected. In fact,

single voltage operation in some cases might be implied. However, the amount of

lost energy and voltage point of minimum energy loss vary with several

parameters. Thus, attempts to correlate the data were made.

Initially, a series of curves showing the difference in energy loss (EV) (for a

restricted voltage range) from the maximum available (maximum power tracking

wi thout limitations, EMP) versus operating voltages were generated. Figure 5-1

shows a typical curve for Miami. The percent energy loss was determined from the

expression EMP - EV which is the ordinate in the figure.EMF

One curve represents losses incurred when the array voltage is limited on the

lower end of the voltage range from 180V to 220V. This means that the system was

constrained to operate at maximum power up to a specific voltage and then limited

to that voltage if the maximum power point was above it. Therefore, as the range

of maximum power voltage operation is increased, the loss of collected energy

over that collected for unconstrained maximum power tracking decreases. The

second curve demonstrates the effect of limiting the voltage on the high end from

220V to l80V. A minimum of three simulation runs were required to establish each

curve, and the point of intersection denotes the minimum loss voltage. Plots of

this type were generated for several locations, and provided an adequate data

base to attempt correlations. It was intended that such correlations would

5-1

LIMIT ON HIGH ENDOF VOLTAGE RANGE

LIMIT ON LOW ENDOF VOLT AGE RANGE

t::N = VOLTAGE VARIATIONABOUT MINIMUM LOSSVOLTAGE

MINIMUMLOSS

VOLTAGE195.5V

NOTES:

1. SOLAREX INTERMEDIATEPV MODULES 14S X 7P

(jZ 1··l.:U<e:l-e:w~

~:;;::::l~X<:;;..J..J::::l 10·u.:;;oe:u.VlVlo..J -3..J 10 <::::lZZ<

180 190 200 210 220

VOLTAGE LIMIT - VOLTS

Figure 5-1. System Losses for the Southeast Designas a Function of Limiting Voltage Range

establish the minimum loss voltage and corresponding losses and thereby eliminate

the need to generate six . computer runs. Note that a voltage range, V, can be

defined around the minimum loss point.

Figures 5-2 through 5-6 show similar curves for different locations and different

array configurations. Several types of panels were simulated utilizing vendor IV

characteristics, including the GE Block IV and rectangular shingle designs, the

ARCO-SOLAR Block IV batten module and the Solarex Block IV module. The locations

for the analyses were Boston, Phoenix, Santa Maria, Miami and El Paso.

Available simulation data of the residential PV systems was screened to establish

correlating parameters. The NOCT temperature and voltage at NOCT conditions were

obtained by modelling, or from vendor data. With this information, attempts were

first made to correlate minimum loss voltage, normalized by the NOCT voltage with

insolation. Figure 5-7 shows relatively good correlation between the minimum loss

voltage (VML ) normalized to the NOCT voltage (VNOCT ) with the total insola

tion (I) incident on the module, normalized to a reference insolation (IREF ).

The worst deviation is 5% from the average curve fit.

5-2

LIMIT ON LOW ENDOF VOLTAGE RANGE

NOTES:

1. ARRAY CONFIGURATION 25S X 19P,BLK IV SHINGLE

2. ALL-ELECTRIC FEEDBACK

LIMIT ON HIGHEND OF

VOLTAGERANGE

IIIIIII

MINIMUM LOSSVOLTAGE

214V

IO. OJ L-_--L__...L.__..l-..I-.......JL..-_-l.__...1.._---I

oz~

u<a::I-a:: 10.0w;;:

a:X

~oJoJ:::lu..::Eoa::u..VIVI

9 0.1oJ<:::lZZ<

190 200 210 220 230 240

VOLTAGE LIMIT, VOLTS DC

250

Figure 5-2. System Losses for Boston, Design 1.lOt

X<::EoJoJ:::lu..::Eoe: 1. 0VIVI

9oJ<:::lZZ<


NOTES: _

1. ARRAY CONFIGURATION255 X 19P, BLK IV SH INGLE

2. ALL ELECTRIC, FEEDBACK

0.11.----L--...L.--..l-_..lJL..-_-l._---J180 190 200 210 220 230


Figure 5-3. System Losses for Phoenix, Design 1.

5-3

100

~ 10::.:U<e::l-e::w3~ 1.0

X<::;;-l-l::>u.::;; 0.1oe::u.IIIIII

9-l

~ 0.01zz<

=

MINIMUM LOSSVOLTAGE

156V

LIMIT ON LOW END OFVOLTAGE RANGE

LIMIT ON HIGH END OFVOLTAGE RANGE

NOTES:

1. ARRAY CONFIGURATION ONRECTANGULAR SHINGLEMODULE 8S X 7P

5-4

o. 001 r__-l-__..J-__L....._~__..J

150 .160 170 180 190


Figure 5-4. System Losses for Boston, Design 4.10

2

\LIMIT ON LOW ENDOF VOLTAGE RANGE

LIMIT ON HIGH ENDOF VOLTAGE RANGE

NOTES

1. 12S x 4P LAMINATED MODULEARRAY

MINIMUM LOSSVOLTAGE = 172V

10- 1 '--_~__.......-'-_.......__l--_-'

160 170 180 190 200


Figure 5-5. System Losses for Santa Maria, Design 6.

100

""(:)z:.::u«

,f 0<:I-

0<:w:c~ 10.0

X«::;;oJoJ:Ju.::;;00<:u.Vl 1.0Vl0oJ

oJ«:JZZ«

LIMIT ONHIGH ENDOF VOLTAGE RANGE

MINIMUMLOSS

VOLTAGE197V


NOTES:

1. ALL ELECTRICALFEEDBACK SYSTEMBLOCK IV SHINGLE25S X 15P

0.1 L-._.L.._-'-_.L-J'--_....._ ........_ ......._--'

180 190 200 210 220 230 240

VOLTAGE LIMIT. VOLTS DC

Figure 5-6. System Losses for El Paso Single Family

1.3

BOSTON RECTANGULAR SHINGLE 85 x 7p

125 X lip

6

----0--IREF = 6000 W-hr/m2-DAY

EL PASO BLK IV 255 x 111p

PHOENIX BLK IV 255 x 19p

MIAMI SOLAREX MODULE 145 x 7p

SANTA MARIA LAMINATED ARRAY

o BOSTON BLK IV 255 X 15p

o6

o~

•

1.2

1.1

1.0

0.9

O. 8 OL.~6---0-.1-7----0.....-8---0.....-9----1·.0----1.·1----1..J.2

I "REF

Figure 5-7. Comparison Between Minimum Loss Voltage and Insolation.

5-5

Figure 5-8 shows the correlation of the same voltage ratio (VML/VNOCT) with

average ambient temperature normalized to the NOCT temperature (TNOCT

). Again.,

a relatively good correlation is achieved with a 3% deviation of the average fit.

Once the minimum loss voltage was determined, the energy loss effects of con

straining the maximum power tracking range were correlated. The correlating

parameter was the ratio of the energy loss from full maximum power tracking for

a I:1V operating range (~p - EI:1V) to the maximum energy loss at the minimum

loss voltage (EMP - EML ). This ratio ranges from 0 to 1 and is plotted versus

the normalized contained voltage operating range (AV/VNOCT ). Figure 5-9 shows

the correlation.

An example illustrates the use of these correlations to determine the fixed

vol tage minimum energy loss point, VML , and the constrained operating voltage

energy loss, EAV • Assume the following:

Location: Phoenix, I = 6560 wh/m2-day

Array Area: 93 m2

183 V

10 V

For these assumptions, the parameter I/IREF is 1.09. Using Figure 5-7, the

ratio (VML/VNOCT) is 1.04. Thus, the operational voltage point for minimum

energy loss from full maximum power tracking for a Phoenix location is 190V.

Computer simulations can be made to establish the annual collected energy at full

maximum power tracking,

lected at the fixed

example).

EMP ' (17.5 MWh for this example) and the energy col

voltage minimum loss point, EML (17.15 MWh for this

Thus, for a constrained operating voltage range of + V

AVloss 'voltage point = 0.055 and Figure 5-9 givesVNOCT

10 V around the minimum

(EMP - EI:1V)

(EMF - EML )= 0.78

Solving for EAV provides the estimate of the energy loss from full maximum

power tracking of 17.23 MWh or a 1.5% energy loss.

5-6

1.3

1.2

1.1

1.0

0.9

o BOSTON BlK IV 25S X 15P

o BOSTON RECTANGULAR SHINGLE

6. El PASO BlK IV 25S X 14P

o PHOENIX BlK IV 25S X 19P

~ MIAMI SOlAREX MODULE 14S X 7P

8S X 7P

0.80.8 0.84 0.86

TAMSTNOCT(OK) I(OK)

0.90

Figure 5-8. Correlation Between Minimum Logs Voltage andNormalized Ambient Temperature

I I

.15.le

o BOSTON BlK IV 255 X 15P

9 BOSTON RECTANGULAR SHINGLE 85 X 7P

6. El PASO BlK IV 255 X 14P

o PHOENIX BlK IV 255 X 19P

b. MIAMI SOlAREX MODULE 145 X 7P

• SANTA MARIA lAMINATED ARRAY 125 X 4P

.05

0.2

0.6

0.4

0.8

I(V~:cT)1Figure 5-9. Correlation Between Normalized %Increase in Loss with

Normalized Voltage Operating Range about Minimum Loss Voltage.

5-7

Sensitivity of Photovoltaic Module Performance to Roof Insulation for theIntegral Mount Configuration

A parametric study was conducted to determine the performance sensitivity of an

integrally mounted photovoltaic module to roof insulation and ambient conditions.

In the analysis, an attic temperature profile was assumed as two piecewise

continuous linear functions of ambient temperature. Results generated using a

one-dimensional Fourier conduction approach indicate that the backface insulation

has little ~5%) effect on module performance, and the highest module efficiency

is achieved for the case of no insulation.

The cell temperature has a significant impact on PV module performance, and this

necessitates the use of an accurate technique for predicting collector heat loss.

Reference 10 provided equations for radiative heat loss while the convective heat

loss relations were furnished by Reference 11. A simple one-dimensional Fourier

approach provided a means of establishing the effective conductance from the

solar cell to the attic. A cross section of the PV module is illustrated in

Figure 5-10 which shows this thermal path, and Table 5-1 presents the correspond

ing material and geometric properties. An energy balance was written for the

module in terms of the front face and back face heat losses, and a Newton-Raphson

method proVided a solution for cell temperature.

The backface heat loss is expressed as:

Qb = Ceff (TCELL - Tattic) (1)

where Ceff is the effective conductance from the cell to the attic and Tattic

is the attic temperature. Two piecewise continuous linear profiles, as shown in

Figure 5-11, were assumed for Tattic as a function" of outdoor ambient tem

perature.

The net front face heat transfer expression is:

+ 3·81 • VWIND

where QABS is the amount of solar energy absorbed by the collector and er isthe collector tilt angle with respect to the horizontal.

5-8

OUTDOOR AIR

ALUMINUM BACK PLATE

GLASS

EVA "-

CELLEVA,

"-

/ TEDLAR .;

1 AIR GAP

/ / /'! - I / /, /' , , /

-(

/ I rI I I- POL YURET1fANE / -

, INSULATION/ i (

(/' / ( -

-,

/( / /" ./, ---

I AIR GAP

~

.'

ATTIC AIR

Figure 5-10. Module Cross Section for Integral Mount Configuration

Table 5-1. Material Combinations for Thermal Path from Solar Cell to Attic

Thickness h k RMaterial (mm) (W/m2_oC) (W/m2_oC) (m2_oC)/W

. -_ .• ------ _.• -.•.•.c::::::::::.....

EVA 0.508 1.64 0.001

TEDLAR 0.051 5.68 0.475 0.00035

AIR GAP 2.54 0.063

POLYURETHANE 25.4 1.08 0.77INSULATION

AIR GAP 2.54 5.68 0.063

I ALUMINUM 1.016 750 5.2 x 10-6

!BACK PLATE

AIR-NATURALI 9·1 O.ll

I CONVECTION

5-9

The energy balance is:

Qb - Qf = 0 (3)

which provides a steady state solution for TCELL '

Figure 5-12 shows the effects of wind velocity and ambient temperature upon cell

temperature and module efficiency for 1 kW/m2 incident and R-4 insulation. Both

ambient temperature and wind speed are observed to have a significant effect.

The sensitivi ty of cell temperature and efficiency to roof insulation is pre

sented in Figure 5-13. The amount of insulation varies from 0 to R-26 (approxi

mately 6" thick), and the greatest influence occurs as the wind velocity de

creases to 0 m/s. The effect on efficiency is less than a 5% reduction as R is

increased, and very little effect is observed at the higher wind speeds. This

indicates that the front face heat loss is more dominant than that of the back

face for the integral mount configuration.

The results of the analysis established the following conclusions:

1. Roof insulation affected module performance by less than 5%.2. Front face heat loss was more significant than backface losses.

3. Wind and ambient temperature may affect performance by as much as 20%.

This analysis can also apply to a direct mounted array with insulation in the

attic ceiling.

Alternate Battery System Shunt Analysis

The design of the battery system in the Southwest was developed so that when the

battery was fully charged and the load was supplied, waste energy would be

shunted to ground. A possible option of utilizing this energy was to direct it to

a resistive heating element in the domestic hot water tank, thus, using the hot

water tank as an additional storage element. In effect, however, as energy is

directed and stored in the hot water tank, the total house load is reduced and.

thus, additional waste energy is generated. A quantitative evaluation of usable

energy was performed based on the system analysis results presented in Reference

5. The design analysis predicted an excess energy of 1.0 MWh in Albuquerque for

an array configuration of 65 m2 of active cell area and a battery capacity of

25 kWh. Almost all of this occurs in the spring and fall seasons. In order to

establish how much of this energy could be utilized, typical hourly hot water

demand profiles used in the analysis were examined. The hourly profiles of

5-10

TATTIC = 2.667 T AMB - 28.33°C

T ATTIC = TAMB + SoC

20

60

40

80

100

UlI-

...<

.....U

°~

00 10 20 30 40 50

TAMB - (DC)

Figure 5-11- Assumed Attic Temperature as a Function of Ambient Temperature

120 0.058

0.066

0.098

0.074>-UZW

U u0 ii:-...I 0.082 LL

...I WW WU ...I

f- :::>c0::E

40 0.090

l.-__--L ....L... .L.-__--J 0.106

10 20 30

Figure 5-12. Cell Temperature and Module Efficiency as a Function ofAmbient Conditions for the Integral Mount Configuration

5-11

120

lKW/M2

INCIDENT INSOLATIONTATTIC= TAMB + 5°C (TAMB~ 200 cl

TATTIC= 2.667 TAMB - 28.33°C (T AMB ;;'20 0 C)

0.058

100

80

;.'60

-'-'wU...

40

20

PANEL BACKFACEPOLYURETHANCE INSUL.

- R-26

___ R-4

NO INSULATION

0.066

0.074,.UZwU

0.082 u:u.ww-'::JC0:;;

0.090

0.098

L-__--'----__-I- L-__I 0.106

20 40 60 80

T ATTIC (OCl

Figure 5-13. Cell Temperature and Module Efficiency as a Function ofAttic Temperature for the Integral Mount Configuration

available excess energy were also constructed and superimpos,ed on the demand

profiles. Figure 5-14(a) illustrates the amount of PV array excess energy

available for a typical spring day. Note that the battery is not fully charged

until noontime. Between noon and 5 0' clock, there are 16.5 kWh of excess energy

present and approximately 16.0 kWh are effectively transferred to a pre-heat

water tank. A two-tank system was considered for simplicity in this analysis. The

corresponding hot water usage is shown in Figure 5-14( b). The hourly pre-heat

tank temperature is shown in Figure 5-14(c). As the excess energy is input, the

temperature steadily rises until the maximum tank temperature of 76.7°C is

reached. This stored thermal energy is sufficient to supply a substantial portion

of the hot water load during the evening peak hours and beyond. On a daily basis

in springtime, 47% of the hot water load can be provided by usage of available

excess energy.

Similar results exist for the fall season. If all of the energy transferred to

the hot water system is used prior to the start of excess energy availability,

5-12

6 ... NOTES: r--

1. ARRAY CONFIGURATION5 ~ lOS X lOP EXCESS ENERGY

~

0::: 4 65 m2 CELL AREA 16.5 kWhW I-3 2. BATTERY CAPACITY0-- 20 KWH ....-Q,J: 3 l-(/)3(/):ll::w ....

2U l-XW

1 I-

0 • • I • • 11. t t •(A)

12

W 100<

8(/)U::J--- 0:::1-0:::J:(/)w-' 6wl-.J:E«0 3 0 4o ....

I-0

2J:

·0

... ....-

l- I--

r--I- - ..... - I--

~

- ~ -~.....I- - ~

-n -t • r

(B)

,. r--I--~-

I-~

--I<- r-- ~ --...~l-

I<- ....-

~

~ • • • • •

75

~ZW 65<0:::I-::J

1---I-<U 55< 0::: 0ww ....J:Q, 45I:EWw0:::1- 35Q,

25

15M 2 4 6 8 10 N

(e)

2 4 6 8 10 M

Figure 5-14. Available Power, Hot Water Usage, and Preheat Tank Temperaturefor a PV System in Albuquerque

5-13

the next day no additional waste energy is generated. If, however, the hot water

storage displaces loads during PV system output, additional waste energy may be

generated.

Overall, this option does provide a means of utilizing waste energy.

System Current Characteristics

In all of the designs, annual distribution of the array voltage and power charac

teristics were generated to predict power conversion subsystem requirements. The

current characteristics were not, however, usually reviewed. It is feasible that

under certain weather conditions, array current output could be above power

conversion equipment limits. Thus the annual distribution of current was

calculated and plotted for several designs. Figure 5-15 shows the hours of

operation for current level for the sixth system design in Santa Maria. A peak

current output of 26 Amps is noted. Figures 5-16 and 5-17 shows similar curves

for the fourth design in Boston and Madison. Typical annual current distributions

at or below system power levels were also determined for the fourth design as

evidenced in Figures 5-18 and 5-19 for Boston and Madison. These curves defined

maximum current requirements of power conditioning equipment and estimate the

amount of energy output occuring at the current levels.

5-14

28

26 AMPS

5000

4010 HOURS

ARRAY CONFIGURATION13S x 2P + 12S x 2PINTEGRATEDARRAY MODULES

2000 3000 4000

HOURS AT CURRENT> I

1000

OL.-__...l-__--J. .L.-__-1..__---J

o

Ul0.

~ 16

....Zw0::0::B 12

20

Figure 5-15. Current Duration for the Sixth Design, Santa Maria, CA.

50

3500300025002000

NOTES:

1. ARRAY CONFIGURATION 56RECTANGULAR SHINGLES 8S X 7P

15001000500o ......--~--....J-----L.----L----.JL...---..I...,;;=-----Io

40

~ -_. 33. 6 AMPS

~30

l

f- 20zLU0:::

~ 10U

HOURS AT CURRENT> I

Figure 5-16. Current Distribution for the Fourth Design, Boston

5-15

50

40

l/)wffi 30c..:E0«I-

ffi 200::0::::::>U

10

NOTES:

1. ARRAY CONFIGURATION56 RECTANGULAR SHINGLES8S X 7P

3580 HOURS

o 500 1000 1500 2000 2500 3000 3500 4000

HOURS AT CURRENT> I

Figure 5-17. Current Duration for the Fourth Design PV Array, Madison

NOTES:

1. ARRAY CONFIGURATION 56RECTANGULAR SHINGLES8S X 7P

so40

33.6 AMP

1_- 6• 4 MWH

20 30

CURRENT, AMPERES

10

7)-

(,J::x:

ffi:: 6z~w ....lo-

S<.V::::>...lZwz> 4 -<'w)-...l<'0:::O:::w 3 -0:::::<'0

I0:::0- I

<'1- 2 f-...l<.0l/l

1 I

00

Figure 5-18. Current Distribution as a Function of Solar Array Energy for Boston

5-16

594010

0..--.---.........----.&..- --'- ...1..- -1

o

8 33.4 AMP

I 7.1 MWH7

>-(J:t

ffi:: 6NOTES:z:E

w , 1- ARRAY CONFIGURATION 56...JQ. 5 RECTANGULAR SHINGLES<V:J...J 8S X 7PZwZ> 4<w>-...J<0::C:::W 30::::<0c:::Q.

2<I-...J<0V)

Figure 5-19. Current Distribution as a Function of Solar Array Energy, Madison

Array Open Circuit Voltage

Many of the designs developed used the array open circuit voltage as the

condition for start-up. Some early test data from the Northeast and Southwest

Residential Experiment Stations indicated that actual open circuit voltages could

exceed power conversion equipment limits under certain weather conditions. Thus

for the temperate climate design in Santa Maria, Reference 8, the open circuit

voltage was plotted for several weather conditions. Figure 5-20 shows these

results. The array NOCT voltage is 185V. A curve similar to this figure helps to

identify maximum array open circuit voltage that may exist for a given array

configuration and should be investigated to assure system operation within the

power conversion subsystem limitations.

5-17

300ARRAY CONFIGURATION: 12S X 4P LAMINATED ARRAY MODULE IN SANTA MARIA

0-50100

TOTAL NORMAL

INTENSITY (W 1M 2)

50

V = 0 MIS

WIND SPEED

V = 1 MIS

403020

T AMB - °C

10o

........................

......................

..........................

......................

.................. , ......

..........................

............ 1500

240

260

200 II...- --' --L ~____.,;;::t.__L. ...DI> ___J

-10

U>0 220

wl.J«I-1o>I;:)

U~

U

ZWCO

VlI-1o 280>

Figure 5-20. Effects of Ambient Temperature and SolarIntensity on Open Circuit Voltage

5-18

SECTION 6

REFERENCES

1. "Photovoltaic System Sizing Analysis," G. Jones & E. Mehalick, Paper Presented at the Fourteenth IEEE Photovoltaic Specialists Conference, SanDiego, CA, January 7-10, 1980

2. "Final Report - Regional Conceptual Design and Analysis of ResidentialPhotovoltaic Systems," SAND78-7039 , General Ele~tric Company, January, 1979

3. The Design of a Photovoltaic System for a Southwest All-Electric Residence,"SAND70-7056, General Electric Company, February, 1980

4. The Design of a Side-by-Side, Photovoltaic Thermal System for a NortheastAll-Electric Residence," SANDSO-7148, General Electric Company, November,1980

5. The Design of a Photovoltaic System with On-Site Storage for a SouthwestAll-Electric Residence, SANDSO-7170, General Electric Company, March, 1981

6. "The Design of a Photovoltaic System for a Passive Design Northeast AllElectric Residence," SANDSO-7171, General Electric Company, October, 1981

7. "The Design on a Photovoltaic System for a Southeast All-ElectricResidence", SANDSO-7172, General Electric Company, October, 1981

8. "The Design of a Photovoltaic System for a Temperate Climate All-ElectricResidence," SANDSO-7l73, General Electric Company, December, 1981

9. "Integrated Residential Photovoltaic Array Development," DOE/JPL 955894-3,General Electric Company, August, 1981

10. "Solar Energy Thermal Processes," J.A. Duffie and W.A. Beckman, Wiley 1974

11. "Thermal Performance Testing and Analysis of Photovoltaic Modules in NaturalSunlight," LSSA Project Task Report 5101-31, Jet Propulsion Laboratory,California Institute of Technology, 29 July, 1977

12. G. Darkazalli, "A Description of the University of Texas at Arlington SolarEnergy Research Facility Photovol taic/Thermal Residential System,"MIT-Lincoln Laboratory, COO-4577-5, March 16, 1979

13. E.C. Kern and M.C. Russell, "Hybrid Photovoltaic/Thermal Solar EnergySystems," MIT-Lincoln Laboratory, COO-4577-l, March 27, 1978

14. E.C. Kern and M.C. Russell, "Optimization of Photovoltaic/Thermal CollectorHeat Pump Systems," MIT-Lincoln Laboratory, COO-4577-7, June 1979

15. "Conceptual Design and Analysis of Photovoltaic Systems," Final Report,General Electric Co., ALO-3686-14, March 19, 1979

6-1

16. E.J. Buerger, et aI, "Regional Conceptual Design and Analysis Studies forResidential Photovoltaic Systems," General Electric Co., SAND 78-7039,January, 1979

17. N.F. Shepard, R. Landes and W. Kornrumpf, "Definition Study for Photovoltaic Residential Prototype System," General Electric Co., ERDA/NASA 1979/76-1, September, 1976

18. P.F. Pittman, "Conceptual Design and Systems Analysis of Photovoltaic PowerSystems," Final Report, Westinghouse Corp., ALO/2744-13, May, 1977

19. P.F. Pittman, et aI, "Regional Conceptual Design and Analysis Studies forResidential Photovoltaic Systems," Westinghouse Corp., SAND 78-7040, July1979

20. "Photovoltaic Systems Concept Study," Spectrolab, Inc., ALO/2748-12, April,1977

aI, "Definition Study for Photovoltaic ResidentialFinal Report, Martin Marietta Corp., ERDA/NASA-19768,

M.S. Imamura, etPrototype System,"September, 1976

22. V. Chobotov and B. Siegel, "Analysis of Photovoltaic Total Energy Systemsfor Single Family Residential Applications," Aerospace Corp. , ATR-78(7694-02)-1, August, 1978

21.

23. P.R. Carpenter and G.A. Taylor, "An Economic Analysis of Grid-ConnectedResidential Solar Photovoltaic Power Systems," MIT Energy Laboratory, MTI-EL78-007, December, 1978

24. Kern, E.C., "Phase-One Experiment Test Plan Solar Photovoltaic/Thermal Residential Experiment," COO-4577-6, March 15, 1979

25. Final Report - Analysis and Design of Residential Load Centers," SAND80-7017, General Electric Company, October, 1981

6-2

APPENDIX ASUMMARY OF SYSTEM

CONFIGURATION EVALUATIONS

APPENDIX A

SUMMARY OF SYSTEM CONFIGURATION EVALUATIONS

PV ONLY SYSTEMS

System I(a) All Electric System/Battery Storage

Block Diagram

BACK-UP


~_....SHUNT - HEAT- PUMP

TIHOT

"""'-WATER

Description

This system involves all-electric loads with space heating and cooling providedby a heat pump. The PV system includes batteries connected directly across thesolar array bus, with the solar array operating point established by the voltageof the battery. Battery charge control is accomplished by limiting the batterycharge voltage to a prescribed level. Control is exerted by partial shunting ofdiscrete sections of the solar array current to limit battery charge voltage.Excess battery temperature is also limited by shunting out array sections. Batterydischarge control is only exerted when the battery has been almost depleted, asindicated by a lower discharge voltage limit. When this occurs, the transfer ofpower through the inverter is interrupted completely and is not restored untilthe battery is fully charged. This would occur when the upper charqe voltaqelimit is reached. The inverter supplies power up to its rated limit. Any demandin excess of this limit is supplied by direct tie-in to the utility.

Variations of this basic system involves, (1) utilization of excess PV energy foruseful auxi1iarv heatina (e.g., domestic hot water) in place of wasteful dissipationthrough the shunt and (2) nightime utility charging of the batteries where advantage can be taken of lower nightime rates.

A-l

Studied By

• General Electric (References #15, #16, and #17)

• Martin Marietta (Reference #21)

, Westinghouse (Reference #18)

• MIT-Lincoln Lab. (Reference #14)

Advantages and Disadvantages

Advantages

• No max power tracker

• Does not require feedback to utility

Conclusions

Disadvantages

• Initial cost and maintenance of batteries

• Energy dissipated throughshunt when PV system output exceeds what load andbattery will accept

• Energy losses through batteryheat dissipation

• Digital shunt and batterycharge control devicesrequired

• Somewhat lower annual energydisplacement than no batterysystem

• Battery generated hydrogen gasexplosive harard. Cost ofsafety features to meet localcodes

This PV only system is less economical and displaces less energy than a systemwithout battery storage utilizing a maximum power tracker and utility feedback.Major factors contributing to disadvantage of this system include cost of batterystorage and the losses associated with the charge/discharge cycles.

Though applicable to all regions, this system proved most cost effective in highinsolation areas, providing a significantly larger percentage of electrical load,for-example, in Phoenix than in Boston. A considerable battery development effortis of course necessary to meet battery projected 1986 cost and technical goals.

A-2

System I(b) All Electric/Feedback

Block Diagram

UTILITY


MAX. POWERTRACK

HEAT~

PUMP

- HOTWATER

Description

This system involves all-electric loads, wlth space heating and cooling provided by a heat pump. The PV system includes a maximum power tracking inverterand permits feedback of excess PV energy to the utility grid connected in parallel with the photovoltaic system. The utility distribution system essentiallybecomes the storage medium for the residential PV system. When PV maximum poweroutput is less than load demand or during nightime periods, power is supplied bythe utility.

Since the inverter AC power output is synchronized with the utility back-up source,any loss of utility power results in interruption of the inverter operation. Thisinterruption is necessary to prevent excess array output from damaging residentialloads through over-voltage.

Studied By

o General Electric (References #15, #16, and #17)

o Martin Marietta (Reference #21)

• Aerospace (Reference #22)

A-3

Conclusions

Advantages

• Simplest system

• Utility essentiallyacts as electricalstorage medium forall excess energygenerated by PV array

Conclusions

Disasvantages

• Acceptance of feedbackby util ity

• Low buy-back rate makessystem less attractive

This system is the least complex to implement, assuming of course, utilityacceptance of excess PV array output. Large scale sell-back of power tothe utility from many residences can pose a serious problem to the utility.

Of the PV only systems investigated, the feedback system provided the highestenergy displacement for an all-electric residence. Besides being approproatefor all regions, it provided higher performance and cost effectiveness than PVonly systems with batteries.

System I(c) Fossil Heating/Feedback

Block Diagram

BACK-UP


MAX. POWERTRACKER VAPOR

""'- COMPR.COOLING

FOSSILFUEL FURN.

HEATING

HOTWATER

A-4

Description

This system involves the general household electrical loads and an electricallydriven vapor compression space cooling unit. Domestic hot water and spaceheating are provided by a fossil fuel fired furnace. This PV system is identical to system Ib, having a maximum power tracking inverter and feedback ofexcess energy to the utility grid.

Studied By

• General Electric (Reference #16)



Advantages

• Utility essentiallyacts as electricalstorage medium

• Simpl~ system

Conclusions

Disadvantages

• Acceptance of feedback by utility

• Economic viabilitydependent on buy-backrate

• PV cannot be useddirectly for heating

This system proved only slightly less economical than the PV only feedbacksystem lb. Thus, either back-up energy form, electrical or fossil, can effectively be accommodated by the PV only systems.

Fossil fuel fired burners providing space heating and hot water are primarilyapplicable in the cold and moderate (hot/cold) climate regions where they arepredominantly in use today.

A-5

System led) All Electric/Battery Storage/Max. Power Tracking

Block Diagram

BACK·UP

PV POWER DC/AC GENERAL...ARRAY TRACKER INVERTER LOADS

~~-- -- HEAT, PUMP

I..- HOTWATER

Description

This system involves an all-electric load, with space heating and cooling provided by a heat pump. The PV system includes a pulse width modulated (PWM) downconverter/maximum power tracker in series with the inverter, and battery storageunder control of a battery charge controller. The PV system operates at maximum power, unless the output exceeds the load and battery requirements. At thispoint, the duty cycle of the PWM automatically decreases to move the systemoperating voltage toward the open circuit voltage of the array until the available source power is equal to the total power demand of the load and batteries.The utility tie-in permits grid power to supplement PV maximum power output whenload demands exceed the photovoltaic system output.

A variation of this system is the placement of the pulse width modulatedconverter/maximum power tracker in the charge leg of the batteries (i.e., inparallel with the inverter). Therefore, PV power can pass directly to the inverter and on to the load without passing through the PWM/maxim4m tracker. OnlyPV power to the batteries passes through the PWM/maximum power tracker. Withthis system, maximum power tracking takes place only during periods of batterycharging. During the sunrise and sunset periods of the day, when some loadsharing battery discharge is required, the solar array bus voltage is clampedto the battery discharge voltage and the maximum power tracking battery chargeregulator is disabled. Maximum power tracking takes place when array output

A-6

capability exceeds the load demand. However, as with the series system, ifthe total available power at the array maximum power point is greater thanwhat the inverter and batteries will accept, the duty cycle of the PWM regulator automatically decreases to move the system operating voltage toward theopen circuit voltage of the array until the available sourqe power is equalto the total power demand of the load and batteries. When the load demandexceeds the power available from the solar array, the batteries discharge, andas previously indicated clamps the DC bus voltage to the battery dischargevoltage, forcing operation at a voltage considerably less than the solararray maximum power voltage.

Studies By


• Martin Marietta (Reference #21)


Advantages

o Potentially highersystem output withpower tracker forbattery storagesystems

• Does not requirefeedback to utility

Conclusions

Disadvantages

; Increased controlcomplexity

~ Cost of additionalequipment

~ Higher losses

These systems with battery storage and maximum power tracking, are higher costconfigurations and displace less energy than either the battery/shunt system(la) or maximum power tracking/feedback system (lb). Therefore, they provide nosignificant improvement or advantage over these other PV only systems.

Comparison Evaluation of PV Only Systems

A comparitive evaluation of each of the PV only systems against a set of criteriapreviously described in Section 2.0,is presented in Table A-I. The evaluationresulted in the following rankings of PV only systems.

Rank

1

23

4

System Title

Ib, All Electric/FeedbackIa, All Electric/BatteryIc, Fossil Heating/FeedbackId, All Electric/Max. PowerTracking/Battery

A-7

> I m

TABL

EA

-I.

COM

PARI

SON

EVAL

UATI

ONOF

PV-O

NLY

SYST

EMS

SY

ST

EM

I(a)

SY

ST

EM

I(b

)S

YS

TE

MI(

c)

SY

ST

EM

I(d

)S

ELE

CT

ION

AL

LELECT~IC

CR

ITE

RIO

NA

LL

-EL

EC

TR

ICA

LL

-EL

EC

TR

ICF

OS

SiL

HE

AT

ING

BA

TT

ER

YF

EE

DB

AC

KF

EE

DB

AC

KP

OW

ER

TR

AC

KIN

GB

AT

TE

RY

EC

ON

OM

iC/P

ER

FO

RM

AN

CE

FA

IRG

OO

DF

AIR

FA

IR-

PO

OR

RE

SU

LTS

CU

RR

EN

TT

eCH

NO

LOG

YF

AIR

FA

IRF

AIR

FA

IRS

TA

TU

S

PR

OJE

CT

ED

ST

AT

US

FA

IR-

GO

OD

GO

OD

GO

OD

FA

IRFO

R19

86

DE

VE

LOP

ME

NT

RIS

KF

AIR

-G

OO

DG

OO

DG

OO

DF

AIR

SY

ST

EM

CO

MP

LE

XIT

YF

AIR

GO

OD

GO

OD

PO

OR

PR

OJE

CT

ED

SY

ST

EM

CO

ST

FA

IRG

OO

DG

OO

DF

AIR

RE

GIO

NA

PP

LIC

AB

ILIT

YG

OO

DG

OO

DF

AIR

-G

OO

DG

OO

D

DU

PL

ICA

TIO

NG

OO

DF

AIR

...G

OO

DF

AIR

FA

IRO

FS

YS

TE

MC

OM

PO

NE

NT

S

RANK

ING

21

34

-,_.-

_-'

0•_

_•.

.._

__

_•••~

•.•

,.

SEPARATE PV/THERMAL SYSTEMS

System II(a) All Electric/Solar Assisted HP/Feedback

Block Diagram

BACK·UP

PV DC/AC100- ..... GENERAL

ARRAY INVERTER LOADS

MAX. POWERTRACKER ~

HEAT~I'-

PUMP

- HOT~ r-

WATER

THERMAL I- THERMALARRAY STORAGE

Description

This system involves all electrically driven loads with solar thermal energyused to supplement space and hot water heating. A heat pump provides thespace heating and cooling requirements. The PV system includes a maximumpower tracking inverter and permits feedback of excess PV energy to the utilitygrid which is connected in parallel with the photovoltaic system. Separatethermal collectors, either liquid or air, provide relatively low temperatureenergy to either a liquid or rock bed storage unit, which in turn provides solarspace heating to supplement the heat pump and preheates domestic hot water. Avariation of this system is one in which the solar collectors provide onlysupplemental energy for domestic hot water heating.

Studied By


A-9


Advantages

• Utility essentiallyacts as electricalstorage medium

s No fossil back-upsystem required

Conclusions

Disadvantages

• Acceptance offeedback byutil ity

• Thermal dumprequired

This system is economically viable in all regions, approaching the performanceand cost results of the PV only all-electric/feedback system. Since solarthermal energy is used only for domestic hot water during the summer, smallthermal collector areas are required for an optimized economic system. Theseconclusions are based on a solar thermal to PV collector cost ratio of 2 to 1(Reference #16). However, as this ratio is reduced to one or lower, optimizedsolar thermal collector areas increase to 30% or more of the roof area.

System II(b) Direct Solar Heating/Feedback

Block Diagram

BACK-UP

Description

This system involves the general household electrical loads and an electricallydriven vapor compression space cooling unit. The PV system includes a maximumpower tracking inverter and utility feedback capability. Solar thermal collectors,backed-up by a conventional fossil fuel burner, provide space heating and domestichot water requirements.

A-IO

Studied By




Similar considerations as listed for the System IIa, Solar Assisted Heat Pump/Feedback. Additional disadvantages are due to need for fossil back-up system.

Conclusions

This system is less economical than seoarate PV/T systems providing an allelectrical load (IIa), where solar thermal only supplements the heat pump andelectrical hot water units. Separate solar systems used for space cooling andheating (i.e., PV for vapor compression cooling, solar thermal for heating)creates seasonal mismatch of collector areas required. As in the case ofsystem IIa, comparitively small thermal collector area required for optimizedeconomic system. However, increased thermal collector areas become moreeconomic as their cost is reduced and fissil fuels escalate in price.

This system is primarily appllcable in cold and moderate climate areas, wherefossil burners and presently in use and a low to moderate cooling load exists.

System II{c) Solar Rankine Driven HP/Feedback

Block Diagram

BACK·UP

Description

This system ~s.similar to System la, Solar Assisted Heat Pump/Feedbackw~th the add:tlon of a ~eat pump that can be driven electrically or 'wlth appro~rlate clutchlng by a solar driven Rankine engine during thespace coollng season. Highe~ tempe~ature collectors (e.g., vacuum tube)are.used to operate the Ranklne englne at higher efficiency levelsDurlng the heati~g season, solar thermal supplements the conventio~alheat pump operatlon.

A-ll

Studied By'



Advantages

• Permits use ofhigher temperature,high efficiency,vacuum tube collectorsrequired fo~ Rankinedriven heat pump

• Allows us~ of thermalenergy in summer

Conclusions

Disadvantages

• Complexity of Rankinesystem

• Potentially increasedmaintenance requirements

• Thermal dump systemrequired

Significant cooling requirements must exist in order to achieve economicviability. The regions designated in this program, have moderate to highsummer cooling loads and therefore this system would be applicable. However,maximum return would dictate its application in the warmer regions where bothhigher insolation and higher cooling requirements exist.

From both the performance and cost standpoint, this system compares favorably withSystem IIa, Solar Assisted Heat Pump/Feedback.

System II(d) Solar Absorption Cooling/Feedback

Block Diagram

BACK UP

GENERALLOADS

ABSORPTIONCHILLER

HEATING

HOTWATER

A-12

Description

In this system, the general household electrical loads are provided by thePV array associated with a maximum power tracking inverter. The system also hasfeedback capability. Solar thermal collectors, backed-up by a conventionalfossil fuel burner, provide space heating, hot water, and space cooling usingan absorption chiller.

Studied By

~ General Electric (Reference #16)


Advantages

o Permits use of highertemperature, higherefficiency, vacuum tubecollectors requires forabsorption chiller

$ Allows use of thermalenergy in summer

Conclusions

Disadvantages

I Higher level of technology over solarheating

• Solar cooling technologycurrently not as advancedas heating technology

Comments regarding regional applicability of the Solar Rankine Driven Heat Pump/Feedback System, IIc, apply equally well to this system.

The cooling system employing an absorption chiller yields better system performance than one using a Rankine driven heat pump. This is due to the factthat the absorption chiller requires a lower solar temperature than the Rankinesystem, and thus the collector can operate at hiqher efficiency. However, fromboth the performance and economic standpoint, the Rankine driven heat pumpsystem provides somewhat better overall results.

System II(e) Air Solar Boosted Heat Pump/Battery Storage

A-13

Block Diagram

UTILITY

HEATING

HEATPUMP

COOLING

.... _---,REJECT EXCESS IHEAT INSUMMER IAT NIGHT (FLUSH) I

Description

This system involves all electrically driven loads, with solar thermal energyused to supplement space and hot water heating. A heat pump provides thespace heating and cooling requirements. The PV system is the same as thatdescribed in connection with System la, All Electric System/Battery Storage.Air thermal collectors provide energy to the rock bed storage which in turnserves as a heated air source (i.e., solar boost) for the heat pump duringthe heating season. The solar thermal system can also provide space heatingdirectly when higher temperatures are available. During the cooling season,the rock bed storage serves as a sink for the heat pump during the daytimehours. The nightime hours are used to flush out the heat accumulated in storageduring the day.

Studies By

o Spectro1ab (Reference #20)


Advantages

• Rock bed heat sourcefor heat pump improvesCOP

Disadvantages

o Rejects excess collectedto atmosphere during cooling season

~ Large rock bedt Adequate stratification

difficult to achieveA-14

Conclusions

If the rock bed storage is large and sufficiently stratified, this systemcombines the best features of both the solar boost (also called the series)and solar assisted (also called the parallel or solar supplemented) heatpump systems. However, detailed study (Reference #20) indicated that rockbed size and stratification proved inadequate to achieve the theoreticalpromise of this system.

System II(f) Solar Assisted Heat Pump/Battery Storage

Block Diagram

UTILITY

THEATPUMP

COOLINGHEATING

Description

Similar to System IIa, All Electric/Solar Assisted Heat Pump, with the use ofair thermal collectors and rock .bed storage in place of hydronic collectors andwater storage system. Battery storage, as in System IIc, is also used in thisPV system instead of utility feedback.

Studied By

• Spectrolab (Reference #20)


Advantages

• Lower thermaloperating temperature

; Possible lower equipment costs

Disadvantages

• Large rock bed storage

o DHW only summer demand

A-15

Conclusions

~his s~stem is econom~cally attractive in ~ll regions, with increased viability~n reglons where heatlng loads exceed coollng loads. Use of utility feedbackl~ p1a~e of battery storage would further enhance performance and economicvlablllty of this system.

Since solar thermal used only for domestic hot water during the summer, smallthermal collector areas required for optimized economic system, particularlyin warmer climate regions.

System II(g) Solar Boosted Heat Pump/Feedback

Block Diagram

UTILITY

I PV I I DC/AC I I GENERALARRAY llNVERTER I I LOADSMAX POWER --lHOT WATERI-TRACKER

HEAT

ICOOLING'-- PUMP

TOWER f COOLINGr--- HEATING

I: COLOSTORACE

(WATER SOURCEITHERMAL I I THERMAL I HEAT PUMP)ARRAY I STORAGE

HYDRONIC

Description

This system involves all electric loads, with space heating and cooling providedby a heat pump. The PV system includes a maximum power tracking inverter andutility feedback capability. The hydronic solar thermal system can operate ineither of two modes (i.e., dual modes), (1) as a water source for the heat pumpor (2) provide direct solar space heating. In addition, the solar thermal systemsupplements the electrical resistance heated domestic hot water supply. In thecooling mode, a wet cooling tower and cold thermal energy storage are used toincrease the overall efficiency of the heat pump. Heat is rejected from theheat pump condenser to the ambient air through the coolin9 tower. Cold waterstorage permits shifting operation of the compressor to periods when either solarphotovoltaic power is available or inexpensive off-peak utility power can bepurchased at lower rates.

A-16

Winter operation involves the use of electric resistance heating when thermalenergy storage tank temperature is below 45°F; thermal storage acts as asource for the heat pump between 45°F and 80°F, and direct solar is fed to theair handling duct when thermal storage temperature is above 80°F. For summercooling, the cold water storage tank temperature is maintained between 40°Fand 60°F. If photovo1taic power is available to run the compressor and tank temperature is above 40°F, the heat pump will be operated to remove heat from thetank. If tank temperature goes above 60°F, the compressor is operated independently of the availability of photovo1taic power. When tank temperature goesbelow 40°F, any photovo1taic power available is fed to the utility.

A variation of this system uses a dual mode heat pump, capable of uti1itzingeither ambient air or solar heated water as a source. When thermal storage dropsbelow a minimum temperature level, the heat pump switches to ambient'air source ifoutside temperature level is high enough to provide COP greater than 1, rather thanswitching to auxiliary resistance heating at a COP of 1.

Studied By

• MIT-Lincoln Laboratory and University of Texas at Arlington(Reference #12 and #24)


Advantages

• Higher COP forheat pump

• Cold thermal storagepermits operation ofheat pump to store PVpower

Conclusions

Disadvantages

• Cooling tower to rejectheat from heat pumpcondenser in cooling mode

• Cold water storage tank

s In solar direct heating mode,needs larger than normal heattransfer surface area

t In heating mode,when collectoror storage inadequate, heat pumpmust shut-off, requiring auxiliary electric resistance heating (COP=l)

This system is under test at the University of Texas at Arlington Solar EnergyResearch Fac il ity as part of MIT -L inco 1n Laboratories "Solar Hybrid EnergyProject."

A-17

This system is primarily applicable in areas where both substantial heatingand cooling loads exist. To take maximum advantage of the solar boost mode,the area should experience a significant amount of days in which the temperaturedrops below the 20°F mark.

Comparison Evaluation of PV Only Systems

A comparitive evaluation of each of the separate PV/Thermal systems against aset of criteria previously described in Section 2.0 is presented in Table A-2.The evaluation resulted in the following ranking of separate PV/Thermal systems.

Rank System Title

1 IIa, All Electric/Solar Assisted HeatPump/Feedback

2 lId, Solar Absorption Cooling/Feedback

3 IIc, Solar Rankine Driven Heat Pump/Feedback

4 lIb, Direct Solar Heating/Feedback

5 IIf, Air Solar Assisted Heat Pump/BatteryStorage

6 IIg, Solar Boosted Heat Pump/Feedback

7 lIe, Air Solar B-osted Heat Pump/Battery

A-18

~p

TABL

EA

-2.

COM

PARI

SON

EVAL

UATI

ONS

OFSI

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COMBINED PV/THERMAL SYSTEMS

System III(a) Solar Assisted Heat Pump/Feedback

Block Diagram

UTILITY

HYD

PV I DC/AC I I GENERALARRAY !INVERTER I I LOADS

THERMAL MI\~.90IAI"ARRAY

RONICitt"'C.~l!~

- HEAT-PUMP

COOLINGHEATING f--r---

~ HOT ~ I--WATER

I THERMAL II srORAGE I

Description

This is the same system as IIa, with combined PV/Thermal collectors replacingseparate collectors. A variation of this system involves elimination of themaximum power tracker and utility feedback capability; instead, using batterystorage, a shunt regulator and battery charge controller.

Studied By

• General Electric (Reference 16)

~ Westinghouse (References 18 and 19)

• Spectro1ab (Reference 20)

; MIT-Lincoln Laboratory (Reference 13)

A-20


Advantages

• Potentially lowercost collectors thanequivalent separatecollectors

• Lower installationcosts

• Lower roof spacerequirements

Conclusions

Disadvantages

• Combined collectordegrades performanceof both PV and thermal

• Limits flexibility betweenPV and thermal collectorarea required for the variousregions being considered

• DHW only thermal load insummer

• No acceptable combined collector desi gn presentlyavailable

This system is most applicable in regions with high heating; however, theseregions usually have relatively lower annual insolation. The lower insolationlevels coupled with degraded performance associated with combined PV/Thermalcollectors necessitates large collector areas to satisfy a reasonable solarthermal contribution. During the summer months, collector thermal output isused only to provide domestic hot water with resultant waste of excess solarthermal energy.

Though less viable than PV only or separate collector systems, this system,serving the all-electric load with a solar assisted heat pump, is more costeffective than the combined collector, direct solar heatino/battery storaqesystem (IIIb) whieh uses a fossil fuel b~ner for thermal back-up, or thesolar boosted heat pump system (rrre).

System III (b) Direct Solar Heating/Beedback

Block Diagram

PV DclAC GENERALARRAY INVERTER LOADS

THERMAL MAX. POWERARRAY TRACKER COOLING"---

YAP. COMP

...- HEATING

THERMAL-- - FURNACE f--STORAGE

t - HOTWATER A-21

FOSSIL FUEL

Description

This is the same system as lIb, with combined PV/Thermal collectors replacingseparate collectors. A variation of this system involves elimination of themaximum power tracker and utility feedback capability; instead, using batterystorage, a shunt regulator and battery charge controller.

Studied By

I General Electric (Reference 16)

• Westinghouse (Reference )8)

• MIT-Lincoln Laboratory (Reference 13)


Same as System IlIa, Solar Assisted Heat Pump/Feedback. Additional disadvantagedue to need for fossil back-up system.

Conclusions

This system is considerably less effective than System IlIa, Solar Assisted HeatPump in most locations - except for cold areas,where thermal demands are high.As pointed out in the conclusions associated with System IlIa, combined collectorsare not as effective as the other collector options reviewed in this report.Therefore, this system would seem to offer less promise in the future thanSystem II Ia.

System III (c) Solar Boosted HP/Feedback

Block Diagram

UTILITY

HYO

PV I OC/AC I I GENERALARRAY IINVERTERI LOADSTHERMAL

MAXPQWERARRAYRONIC TRACKER

HEAT

ICOOLING IPUMP

TOWER COOLINGr-- HEATING

I HOT IWATER I

(WATER SOURCEI THERMAL I HEAT PUMP)I STORAGE

A-22

Description

Again this system is the same as System IIg, with combined PV/Thermal collectorsreplacing separate collectors and without a cold water storage tank. A variationof this system involves elimination of maximum power tracker and utility feedbackcapability; instead, using battery storage, a shunt regulator and battery chargecontroller.

An additional variation of this system uses a dual mode heat pump, capable ofutilizing either ambient air or solar heated water as a source. When thermalstorage drops below a minimum temperature level, heat pump switches to ambientair source if outside temperature is high enough to provide COP greater than 1,rather than switching to auxiliary resistance heating at a COP of 1.

Studied By

~ Spectrolab (Reference 20)

~ Westinghouse (Reference 18)

~ MIT-Lincoln Laboratory (Reference 13)


Advantages

~ Water source improvesCOP of heat pump

Conclusions

Disadvantages

• In heating mode whencollector or storageinadequate, heat pumpmust shut-off, requiringauxiliary electric resistance heating (COP=l)

• Cooling tower to reject heatfrom heat pump condenserin cooling mode

• In solar direct heating mode,needs larger than normalheat transfer surface

This system is not as effective as the combined collector solar assistea heatpump, system IlIa, from both the performance and economic s~andpoin~. Thissystem is primarily applicable in areas where both substant1al heat1ng andcooling loads exist, and optimum array sizes are comparatively larg~. Whensmall collector areas are used, insufficient stored thermal energy 1Savailable to the heat pump evaporator to allow full-time solar boost operation.Under this condition, the space heating load is met by electric resi~tanceheating at a COP of 1. The large size thermal energy storage.establ1shed asoptional to reduce auxiliary resistance heating adds substant1allv to the costof the solar boost system.

A~3

This system is also considerably more complex and has a higher initial costthan either combined PV/Thermal Systems IlIa or IIIb.

System III(d) Direct Heating/Battery Storage/Stand Alone

Block Diagram

PVARRAY

THERMALARRAY

HYDRONIC

SMALL 1':'1.5 KW)AUXiLIARY

ENGINEGENERATOR

FOSSILFUEL

Description

This is a completely autonomous system with no connection to the utility grid.Combined PV/Thermal collectors are used in conjunction with electrical andthermal storage. Back-up is handled by a small auxiliary diesel electricgenerator (on the order of 1.5 KW) and a fossil fuel burner. Loads are allelectric with the exception of space heating. The PV array (or battery storage)provides electrical energy to the general household loads, a vapor compressioncooling unit, and the domestic hot water heater. Thermal energy generated inthe combined array (or by the fossil burner) provides direct space heating andsupplemental hot water heating.

Both the electrical and thermal storaqe are essential to a stand-alone system.During the day, energy derived from the solar system is stored to get throughthe night. If storage energy is inadequate, the auxiliary supply either pro-vides energy directly or increases the energy store. This allows the auxiliarysystems to be of low capacity. Thus, the storage systems not only provide storage,but handle peak loads.

A-24

The solar system should be capable of providing on the order of 80% to90% of the household electrical and thermal loads. The auxiliary electricalgenerator should run no more than 1000 hours per year and fossil fuel usesapproximately 10% for electrical back-up and 20% for thermal back-up.

In addition to the combined PV/Thermal collectors depicted in the aboveschematic, variations of the system involve the use of PV only collectors,and PV only side by side with combined collectors sized appropriately forthe specific locations.

Another variation of the stand-alone system involves the all-electric residence,pv only array, and heat pump for providing space heating and cooling. Energyfor hot water is partially supplied by excess PV electrical energy in spring andfall and by reject heat from the air conditioning in the summer.

Waste heat from the diesel generator represents another potential source ofthermal energy that could be applied in satisfying residential demand.

Studied By

, Westinghouse (References 18 and 19)


Advantages

• No utility interface

• Potential for lowerenergy cost

Disadvantages

I Potential noise andenvironmental problems

• Must assure continuousinternal energy availability

; Residence designed to minimize exceptional loads

• Load management unit may benecessary to minimize extremesdue to the system1s limitedpeak power

; Extensive amount of equipment and maintenance

A-25

Conclusions

Stand~alone systems are viable virtually everywhere that ut'ility back-upsystems are viable. Stand-alone systems favor combined PV/Thermal collectorsin cold regions. Large collector array areas are required to meet 90% oftotal annual load requirements in colder/lower insolation areas, such asCleveland. In regions with moderate heating requirements, the collector arearequired for optimum electrical input can readily exceed the optimum combinedcollector area needed for direct thermal conversion. Since combined collectorsare more costly, a combination of PV only and combined collectors are moreappropriate for these regions. In very warm areas, where air conditioning loadspredominate, PV only collectors meet requirements.

Comparison Evaluation of Combined PV/Thermal Systems

A comparitive evaluation of each of the combined PV/Thermal systems againsta set of criteria previously described in Section 2.0 is presented in Table A-3.This evaluation resulted in the following ranking of combined PV/Thermal systems.

Rank System Title

1 II la, Solar Assisted Heat Pump/Feedback

2 IIIb, Direct Solar Heating/Feedback

3 II Id, Stand-Alone/Direct Heating/Battery

4 II Ic, Solar Boosted Heat Pump/Feedback

A-26

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