Photovoltaic Training Resource Guide Preview Notes

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© 2011 Jim Dunlop Solar

PhotovoltaicSystems

Training Resource Guide

Ver. 1.02January 2011

James Dunlop, PE

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© 2011 Jim Dunlop Solar PV Systems TRG Preview - 2

Overview

The Photovoltaic Systems Training Resource Guide is a comprehensive set of instructional presentation materials.

This resource is intended to assist faculty and instructors in developing and teaching courses on PV systems technology.

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PV System Training Resources

The Guide is intended to be used in conjunction with the Photovoltaic Systems text and the National Electrical Code®.

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Training Needs

The Photovoltaic Systems text and the Photovoltaic Systems Training Resource Guide can be used for training a diversity of target audiences.

Product Manufacturers

Marketing & Distribution

Project Developers

Electric Utilities

Financiers & InvestorsArchitects & Engineers

Contractors & Installers

Building Officials

Consumers & Owners

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Features

Contains Microsoft PowerPoint® presentations for each chapter in the Photovoltaic Systems textbook, plus an additional chapter on PV System Safety.

Includes almost 1000 total slides, and over 200 new illustrations and photographs.

Note pages are provided for every slide with commentary, references and suggested exercises.

Covers new requirements for PV installations in the 2011 National Electrical Code®.

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Note Pages

Note pages are provided on every slide and contain additional commentary and reference to codes, websites and page numbers in the Photovoltaic Systems text.

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Content

Introduction to PV Systems

Solar Radiation

Site Surveys and Preplanning

System Components and Configurations

Cells, Modules and Arrays

Batteries

Charge Controllers

Inverters

System Sizing

Mechanical Integration

Electrical Integration

Utility Interconnection

Permitting and Inspection

Commissioning, Maintenance and Troubleshooting

Economic Analysis

PV System Safety

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Chapter 1

Introduction to Photovoltaic Systems

Solar Technologies ● History and Development ●Markets and Applications ● Industry Sectors

Solar photovoltaic (PV) systems produce electricity from the sun's energy and are becoming a viable power generation option. The applications for PV devices and systems are diverse, ranging from consumer electronic devices to multi-megawatt central power plants.

Reference: Photovoltaic Systems, Chap. 1

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Advance Organizer

Solar photovoltaic (PV) systems convert solar energy into electrical energy using various components.

load

energysource

power conditioning

energyconversion

InverterPV Array

powerdistribution

LoadCenter

Batteryenergy

storage(optional)

electricutility

PV systems are comprised of various components that in combination convert solar energy into usable electrical power.

Reference: Photovoltaic Systems, Chaps. 1 & 4

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PV System Applications

Spacecraft

Consumer electronicsCalculators, radios and watches

Rural developmentHealth care facilities, schools and community centers

Off-grid powerLighting and appliances for remote homes and facilities

Agricultural usesWater pumping and irrigationFence charging

LightingSigns, security and parking areasTransportation, navigation and aviation aids

Specialty applicationsRemote monitoring, railway signals, security systems and water treatment

Telecommunications facilities

Grid-connected systemsResidential, commercial and utility-scale

Numerous applications exist for PV systems ranging from small cells for consumer electronics, to multi-megawatt central power generating stations covering tens of acres.

Reference: Photovoltaic Systems, p. 8-12

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Market Drivers

Increasing costs and dependence on imported energy

Environmental impacts from fossil fuel use

Electric utility restructuring

Net metering and interconnection rules

Legislative mandates for renewable generation

Financial incentives

Increasing public awareness and interest

Many developments have led to the increase use of PV systems.


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Quality Measuresfor PV Systems

Equipment StandardsComponent Testing

Performance RatingsProduct Certification

Documented SystemsDesign Review & Approval

Education & Training Licensing & Certification

System Testing & Inspection

Quality Components Quality System Designs Quality Installations

Warranties & Service ContractsProduct AssuranceSatisfied CustomersSuccessful Industry

A successful PV industry and satisfied consumers depends on quality components, designs and installations.


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Chapter 2

Solar Radiation

Terminology & Definitions ● Geometric & Atmospheric Effects ● Solar Power & Energy ●

Measurements & Data

Solar energy is the fuel that creates and sustains life on earth. The nature and characteristics of the solar radiation resource are of fundamental importance in understanding how solar PV systems are designed and perform.

References:Photovoltaic Systems, Chap. 2National Renewable Energy Laboratory - Renewable Resource Data Center: www.nrel.gov/rredc

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Electromagnetic Spectrum

Wavelength (µm)

nearinfra-red

nearultra-violet

Visible light

0.3 0.5 0.7

Wavelength

Gam

ma

rays

1 Å

10 Å

100

Å

0.1 µm

1 m

m

1 µm

10 µ

m

100 µm

10 m

m

100

mm

1 m

10 m

100

m

103

m

104

m

105

m

X ra

ys

Ultr

avio

let R

adia

tion

Visi

ble

Ligh

t

Infr

ared

Rad

iatio

n

Mic

row

aves

Shor

t Rad

io

Wav

es (F

M/T

V)

AM

Rad

io

Long

Rad

io W

aves

Solar spectrum

0.25 µm 4.5 µm

The electromagnetic spectrum ranges from short wavelength gamma rays and x-rays, to long wavelength radio waves. The solar spectrum includes visible light and near infrared radiation.

Reference: Photovoltaic Systems, p. 30

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Atmospheric Effects

Parallel rays from sun

Earth’s Surface

Outer Limits of Atmosphere

Direct Radiation

Diffuse Radiation

Atmospheric Absorption, Scattering and Reflections Cloud

Reflections

Solar Constant = 1366 W/m2

Diffuse Radiation

Sun

Reflection

TOTAL GLOBAL SOLAR RADIATION - DIRECT + DIFFUSE

Reflected (Albedo) Radiation

Approximately 30% of extraterrestrial solar power is absorbed or reflected by the earth’s atmosphere before reaching the surface. Effects vary significantly with altitude, latitude, time of day and year, atmospheric constituents, weather patters and wavelength of solar radiation.


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Earth’s Orbit Around the Sun

Autumnal Equinox:September 22 / 23

Declination = 0°

Ecliptic Plane

Sun

Perihelion: January 2-5Aphelion: July 3-7 96 million miles

(1.017 AU)90 million miles

(0.983 AU)

Summer Solstice:June 20 / 21

Declination = +23.5°

Vernal Equinox: March 20 / 21Declination = 0°

Winter Solstice:December 21 / 22Declination = ( -23.5°)

The earth’s closest approach to the sun occurs in the winter in the northern hemisphere, and contributes to more extreme summers and winters in the southern hemisphere at similar latitudes and elevations.


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Solar Declination

Equator

Tropic of Cancer (23.5° N)

Tropic of Capricorn (23.5° S)

Arctic Circle (66.5° N)

Antarctic Circle (66.5° S)

Sun’s Rays

North Pole

23.5 °

Ecliptic Plane

Solar Declination


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Chapter 3

Site Surveys and Preplanning

Customer Development ● Site Assessment ●Locating PV Arrays ● Shading Analysis ● Project

Planning and Preparation

Site surveys are used to collect information and analyze details about the conditions and issues affecting the design, planning and installation of PV systems.

References: Photovoltaic Systems, Chap. 3Solar Photovoltaic Installation Guideline, California Dept. of Forestry and Fire Protection, Office of the State Fire Marshal: http://osfm.fire.ca.gov/pdf/reports/solarphotovoltaicguideline.pdf

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Site Survey Equipment

Suggested Exercise: Identify the site survey equipment on the slide and discuss.


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Array Orientation

West

North

East

South

Zenith

South-facing array

Southwest-facing array

Tilt Angle

Azimuth Angle

Surface Normal

Surface Direction

Maximum annual solar energy is received on a surface that faces due south, and is tilted from the horizontal at an angle slightly less than local latitude. The installation of PV arrays on buildings may be constrained by the direction and slope of a roof, or by nearby obstructions.

Reference: Photovoltaic Systems, p. 45-47, 66-67

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Array Tilt Angle

West

North

East

South

Winter Solstice

Equinoxes

Summer Solstice

ZenithLatitude+15° tilt maximizes fall and winter performance

Close to Latitude tilt maximizes annual performance

Latitude-15° tilt maximizes spring and summer performance

Arrays with lower tilt angles (e.g., local latitude - 15°) will produce proportionately more energy in the summer than winter. Conversely, arrays with tilt angles higher than the local latitude (e.g., latitude + 15°) will produce more energy in the winter than at lower tilt angles. For most U.S locations, varying the tilt angle for south-facing arrays by as much as ±15° from the local latitude still results in receiving at least 90 to 95 percent of the maximum available solar energy on an annual basis.


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Solar Shading Calculators

Solar shading calculations are devices used to determine the extent of shading in the solar window.

Solar Pathfinder

Solmetric SunEye

A solar shading calculator is a special device used to view obstructions in the solar window, and to estimate the reduction in solar energy received at different times of the day and year. They provide a graphical representation of shading patterns for all times of the year at any location, from all obstructions in any direction, superimposed on sun path charts.

Suggested Exercise: Demonstrate the features, setup and use of solar shading calculators.

Reference: Photovoltaic Systems, p. 69-77 & CD-ROM

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Chapter 4

System Components andConfigurations

Major Components ● Balance-of-System● System Classifications and Designs

Photovoltaic systems are an assembly of electrical components that are intended to produce power suitable for operating electrical loads and appliances, or to interface with other electrical systems, like the utility grid. PV systems are versatile power generators, and the configurations and components required vary depending on the type of system and its intended application.


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PV System Components

1. PV modules and array

2. Combiner box

3. DC disconnect

4. Inverter (charger & controller)

5. AC disconnect

6. Utility service panel

7. Battery (optional)

1

2

3

4

5

7

6

Batteries are used in stand-alone PV systems, but only in grid-connected PV systems using special inverters and designed as a backup power supply for dedicated loads.


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Stand-Alone PV Systems with AC Loads

DC LoadPV Array

Battery

ChargeController

Inverter/Charger

AC Load AC Source(to Charger Only)

An inverter is used in stand-alone PV systems to power AC loads, and is connected to the battery. Many inverters also include a charger, which allows this inverter input to be connected to a generator or other AC source to charge batteries or supplement the AC load. The inverter charger AC input is separate from the AC output of the inverter. The AC output of stand-alone inverters operating from batteries is never connected to the grid, only to the dedicated AC loads served by the system. The inverter must be sized to meet the total connected AC load, for both continuous loads and surge requirements.


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Utility-Interactive PV System

LoadCenter

PV Array Inverter

AC Loads

ElectricUtility

Interactive PV systems operate in parallel with and are interconnected to the electric utility grid. Sometimes called grid-connected or utility-interactive PV systems, these types of systems are perhaps the simplest and least-costly of all PV systems that produce AC power. They require the fewest components, and most do not use energy storage. The primary component in interactive PV systems is the inverter, which directly interfaces between the PV array and electric utility network, and converts DC output from a PV array to AC power and synchronizes with the grid.

Interactive PV systems make a bi-directional interface at the point of utility interconnection, typically at the site distribution panel or electrical service entrance. In a sense, the utility acts as a large storage battery that accepts the power produced by an interactive system. This allows the AC power produced by the PV system to either supply on-site electrical loads or to back-feed the grid when the PV system output is greater than the site load demand. At night and during other periods when the electrical loads are greater than the PV system output, the balance of power required is received from the electric utility.

Reference: Photovoltaic Systems, p. 102-110 & Chap. 12

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Utility-Interactive PV System with Energy Storage

Inverter/Charger

Critical LoadSub Panel

BackupAC Loads

Main Panel

PrimaryAC Loads

ElectricUtility

Bypass circuit

BatteryPV Array

AC Out AC In

DC In/out

ChargeControl

Bimodal systems are utility-interactive systems that use battery storage. They can operate in either interactive or stand-alone mode, but not simultaneously. These types of systems are used by homeowners and small businesses where a backup power supply is required for critical loads such as computers, refrigeration, water pumps and lighting.

Bimodal PV systems operate in a similar manner to uninterruptible power supplies, and have many similar components. Under normal circumstances when the grid is energized, they inverter acts as a diversionary charge controller, limit battery voltage and state-of charge. When the primary power source is lost, a transfer switch internal to the inverter opens the connection with the utility, and the inverter operates dedicated loads that have been disconnected from the grid. An external bypass switch is usually provided to allows the system to be taken off-line for service or maintenance, while not interrupting the operation of electrical loads.


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Chapter 5

Cells, Modules and Arrays

Principles of Operation ● I-V Characteristics ● Response to Irradiance and Temperature ● Series/Parallel

Connections ● Specifications and Ratings

PV systems are comprised of building blocks of cells, modules and arrays to form a DC power generating unit with specified electrical output.


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Solar Cells

Solar cells are semiconductor devices that convert sunlight to DC electricity.

Photovoltaic cell

Phosphorous-doped silicon(N-type) layer ~ 0.3 µm

Electrical Load

(-)

(+)Boron-doped silicon(P-type) wafer < 250 µm

DC current flow

A solar cell converts solar radiation to DC electricity, and is the basic building block of PV modules and arrays. Modern solar cells are created by junctions between different semiconductor materials. A typical crystalline silicon solar cell is a junction between boron-doped silicon (P-type) and phosphorus-doped silicon (N-type) semiconductors. N-type semiconductors are materials having excess electron charge carriers. P-type semiconductors are materials having a deficiency of electron charge carriers, or excess electron voids (holes).


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Key I-V Parameters

PV device performance is specified by the following I-V parameters at a given temperature and solar irradiance condition:

Open-circuit voltage (Voc)Short-circuit current (Isc)Maximum power point (Pmp)Maximum power voltage (Vmp)Maximum power current (Imp)

Voltage (V)

Cur

ren t

( A)

Isc

Voc

Imp

Vmp

Pmp

Area = Pmp

Open-circuit voltage (Voc) is the maximum voltage on an I-V curve, and is the operating point for a PV device with no connected load. Voc corresponds to an infinite resistance or open-circuit condition, and zero current and power output. Open-circuit voltage is independent of cell area, decreases with increasing cell temperature and used to determine maximum circuit voltages for PV modules and arrays. For crystalline silicon solar cells, the open-circuit voltage is typically on the order of 0.6 volts at 25°C.

Short-circuit current (Isc) is the maximum current on an I-V curve. Isc corresponds to a zero resistance and short-circuit condition, and zero voltage and power output. Short-circuit current is directly proportional to solar irradiance, and used to determine maximum circuit design currents for PV modules and arrays.

The maximum power point (Pmp) of a PV device is the operating point where the product of current and voltage (power) is at its maximum. The maximum power voltage (Vmp) is the corresponding operating voltage at Pmp, and is typically 70 to 80% of the open-circuit voltage. The maximum power current (Imp) is the operating current at Pmp, and typically 90% of the short-circuit current. The maximum power point is located on the “knee” of the I-V curve, and represents the highest efficiency operating point for a PV device under the given conditions of solar irradiance and cell temperature.

Maximum power point tracking (MPPT) refers to the process or electronic equipment used to operate PV devices at their maximum power point under varying conditions, and is integral to interactive inverters and some battery charge controllers to maximize PV array efficiency and energy production.


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Response to Solar Irradiance

Voltage

Cur

rent

1000 W/m2

750 W/m2

500 W/m2

250 W/m2

Current increases with increasing irradiance

Voc changes little with irradiance

Maximum power increases with increasing irradiance

Maximum power voltage changes little with irradiance

Constant Temperature

Changes in solar radiation have a direct linear and proportional effect on the current and maximum power output of a PV module or array. Therefore, doubling the solar irradiance on the surface of the array doubles the current and maximum power output (assuming constant temperature). Changing irradiance has a smaller effect on voltage, mainly at lower irradiance levels. Because voltage varies little with changing irradiance levels, PV devices are well-suited for battery charging applications.

PV installers may verify performance of PV systems in the field by measuring the solar irradiance incident on arrays with simple handheld meters, and correlating with the actual system power output. For example, if it has been established that the peak output of a PV array is 10 kW under incident radiation levels of 1000 W/m2 at normal operating temperatures, then the output of the array should be expected to be around 7 kW if the solar irradiance is 700 W/m2, assuming constant temperature.


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Response to Temperature

For crystalline silicon PV devices, increasing cell temperature results in a decrease in voltage and power, and a small increase in current.

Voltage

Cur

rent

T = 25°C

T = 50°C

T = 0°C

Increasing temperature reduces voltage

Increasing temperature reduces power output

Increasing temperature increases current

For crystalline silicon PV devices, increasing cell temperature results in a decrease in voltage and power, and a slight increase in current. Higher cell operating temperatures also reduce cell efficiency and lifetime. The temperature effects on current are an order of magnitude less than on voltage, and neglected as far as any installation or safety issues are concerned.


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PV Module Rating Conditions

The electrical performance of PV modules is rated at Standard Test Conditions (STC):

Irradiance: 1,000 W/m2 , AM 1.5Cell temperature: 25°C

Source: SolarWorld USA

Standard Test Conditions (STC) is the universal rating condition for PV modules and arrays, and specifies a solar irradiance level of 1000 W/m2 at air mass 1.5 spectral distribution, operating at 25°C cell temperature.


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Chapter 6

Batteries

Types and Characteristics ● Functions and Features ●Specifications and Ratings

Batteries are used in some PV systems to store energy from the PV array. There are numerous types of storage batteries to choose from, based on the physical and performance characteristics desired.

References: Photovoltaic Systems, Chap. 62008 and 2011 National Electrical Code® (NEC), Articles 110, 480, 690Battery Service Manual, 12th Ed., Battery Council International

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Battery Cell Design

A cell is the basic electrochemical unit in a battery.

Separator

ElectrolyteCase

Electrical load

Negative platePositive plate

-+

A cell is the basic electrochemical unit in a battery. A lead-acid cell consists of sets of positive and negative plates (electrodes) divided by separators, enclosed in a case and immersed in an electrolyte solution.


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Types of Lead-Acid Batteries

Absorbed Glass Mat

Valve-Regulated Lead-Acid Batteries

Flooded Lead-Acid Batteries

Gelled

Suggested Exercises: Download and review battery manufacturer’s literature for common types of batteries used in PV systems. Compare and contrast electrical and physical specifications.


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Chapter 7

Charge Controllers

Types and Characteristics ● Functions and Features ●Specifications and Ratings ● Sizing

Charge controllers are required in most PV systems using a battery to protect against battery overcharging and overdischarging. There are different types of charge controller design, and their specifications dictate their intended operating limits and applications.

References: Photovoltaic Systems, Chap. 72008 and 2011 National Electrical Code® (NEC), Articles 110, 690

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PV Systems andBattery Charge Control

A charge controller is required in most PV systems that use battery storage to regulate battery state-of-charge, optimize battery and system performance, and help prevent damage to the batteries or hazardous conditions resulting from the charging process [690.72(A)].

Charge controller protects battery from overcharge by PV array

ChargeController BatteryPV Array

A charge controller is equipment used to regulate the charging of a battery, by limiting the voltage and/or current from the charging source such as a PV array. Charge control is required for most PV systems that use batteries.

Charge control may not be required for very small systems, where the PV array has been carefully matched to the voltage and current charging requirements of the battery, and the maximum charge current multiplied by one hour is less than 3 percent of the manufacturer’s rated ampere-hour capacity. For example, a 200 ampere-hour battery charged by a PV array producing a maximum charging current of 6 amps or higher requires charge control.

References:NEC 690.72(A), 690.2Photovoltaic Systems, p. 175-180

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Typical Charge Controllers

Morningstar TriStar controller

Morningstar ProStar controller

Morningstar lighting controller

Outback MPPT controller

Xantrex C-series controller

Charge controllers used in PV system vary widely in their size, functions and features.

Suggested Exercise: Review charge controller manufacturer’s specifications and installation instructions.


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Chapter 8

Inverters

Definitions and Terminology ● Types and Applications ● Functions and Features ● Selection

and Sizing ● Monitoring and Communications

Inverters are used in PV systems to produce AC power from a DC source, such as a PV array or batteries. Inverter sizes range from module-level inverters rated a few hundred watts to utility-scale inverters 1 MW and larger.


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Stand-Alone & Interactive Inverters

BatteryStand-Alone

InverterAC Load

PV ArrayInteractive

InverterUtility Grid

Interactive Operation with PV Array as DC Power Source

AC load is limited by inverter power rating

PV array size is limited by inverter power rating

Stand-Alone Operation with Battery as DC Power Source

Vs.

Although stand-alone and interactive PV inverters both produce AC power from DCpower, they have different applications and functions.


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String Sizing

Voltage

Cur

rent

Array voltage decreases with increasing temperature

25°C

50°C

0°C

-25°C

STC

DC Input Operating RangeInverter MPPT Range

PV Array IV Curves at Different Temperatures

Properly configuring PV arrays for interactive inverters involves an understanding the array IV characteristics and temperature effects.


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Chapter 9

System Sizing

Sizing Principles ● Interactive vs. Stand-Alone Systems ● Calculations and Software Tools

Sizing is the basis for PV system designs, and determines the ratings for the PV array and other major components needed to produce and deliver a certain amount of energy. Different principles apply to the sizing of interactive and stand-alone PV systems.

References: Photovoltaic Systems, Chap. 9 & Worksheets on CD-ROM

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Sizing Interactive PV Systems

The sizing of interactive PV systems is centered around the inverter requirements.

PV ArrayInteractive

InverterUtility Grid

PV array size is limited by available space and budget

Inverter size is determined by the PV array maximum power

Size of utility service limits maximum system output

The sizing for interactive PV systems is based on the size of the array and inverter requirements.


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Sizing Stand-Alone PV Systems

Sizing stand-alone PV systems begins with determining the electrical load, and then sizing the battery and PV array to meet the average daily load during the critical design month.

Determine Avg. Daily Electrical Load for Each Month

Size PV Array to Meet Loads for Critical Design Month

Determine Load and Insolation for Critical Design Month

Size Battery to Meet Load for Desired Days of Autonomy

Sizing stand-alone PV systems begins with determining the electrical load, and then sizing the battery and PV array to meet the load under the worst case conditions.


determining the

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Chapter 10

Mechanical Integration

Design Considerations ● Array Mounting Configurations ● Structural Loads ● Installation

The mechanical integration of photovoltaic arrays requires an understanding of the site conditions and hazards, the physical and electrical characteristics of PV modules chosen, the desired electrical output for the array, and the mounting system and structural attachments. It also involves considerations for the installation, maintenance and accessibility of equipment, and architectural integration. The objective is to produce the least-cost mechanical installation that is safe, secure and appropriate for the application.

References:Photovoltaic Systems, Chap. 8Minimum Design Loads for Buildings and Other Structures, ASCE 7Wind Load Calculations for PV Arrays; Stephen Barkaszi, FSEC & Colleen O’Brien, BEW Engineering: www.solarabcs.org/wind/

Mounting hardware manufacturers websites:Unirac: www.unirac.comProfessional Solar Products: www.prosolar.comIron Ridge: www.ironridge.comDirect Power & Water: www.dpwsolar.com

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Types of Mounting Systems

Orientation typeFixed-tilt, adjustable and sun-tracking arrays

Ground-mounted arraysRacks, poles and sun-tracking mounts

Roof-mounted arraysRacks for flat roofsStandoff mounts for sloped roofsDirect mounts

Building-integrated PV arraysReplace conventional building material or an architectural feature

PV arrays can be mounted on the ground or attached to buildings or other structures using a variety of methods. PV array mounting orientations can also be classified as fixed-tilt, adjustable or sun-tracking mounts. Ground-mounted designs include racks, poles mounts and sun-tracking arrays. Common building mounts include standoff mounts and rack mounts that can be retrofitted to existing rooftops. Building-integrated PV arrays, including direct mounts and integral mounts are integrated with building components and cladding materials such as windows, awnings and roofing tiles.


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Structural Evaluation

Trusses or beams

Point attachments to structure

Roof surface

PV Modules

Module support rails

Module attachments

For common standoff-mounted PV arrays installed just above and parallel to sloped roofs, the mounting methods are quite similar among different PV modules and mounting system suppliers.

Key points of the structural evaluation include:•PV module allowable loads and required position of deflection support and attachments.•PV module attachments to underlying beams or rails (machine screws or clamps).•Allowable deflections in beams or rails•Point attachments to structure


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Chapter 11

Electrical Integration

Terminology and Definitions ● Circuit Design Requirements ● Specifying Electrical Components

● Code-Compliant Installation Practices

The electrical integration of PV systems involves the design and assembly of the various components into a complete power generation unit. The requirements for PV system installations are governed by the National Electrical Code, NFPA 70.

References:Photovoltaic Systems, Chap. 11National Electrical Code, NFPA 70

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Interactive PV SystemComponents and Circuits

Interactive System

PV Array

Source Circuit Combiner Box

DC Fused Disconnect

Ground FaultProtection

AC Fused Disconnect

Electric Utility

Utility Disconnect

Integral components in many small string inverters < 12 kW

PV Source CircuitsPV Output

Circuit Inverter Input Circuit Inverter Output Circuit

Inverter Main Service Panel

For simple interactive PV systems, the PV array is connected to the DC input of inverters, and there is no energy storage. The inverter input circuit includes the conductors between the DC photovoltaic output circuits and the inverter DC input terminals. For simple interactive PV systems without energy storage, the PV output circuit is connected to the line terminals of a DC disconnect, and inverter input circuit then runs from the load terminals of the disconnect means to the inverter DC input. The inverter produces AC power based on the array output, only when the array is exposed to sunlight. For interactive-only inverters, the inverter rating and efficiency limits the size of PV array that that can be connected to its DC input. In an interactive system, the PV output circuits and inverter input circuit are essentially the same circuit, separated by a disconnect means.

References: Photovoltaic Systems, Chap. 4NEC 690.2, 690.60, 705

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Chapter 12

Utility Interconnection

Codes and Standards ● Utility Considerations ●Supply and Load Side Connections ●

Interconnection Agreements

Nearly all electric utilities allow the interconnection of customer-owned and operated PV systems to their distribution systems. The technical and safety requirements for interconnected power sources are addressed in national codes and standards, while the specific procedures and policies vary among local utilities.

References: Photovoltaic Systems, Chap. 12Connecting to the Grid – A Guide to PV Interconnection Issues, Interstate Renewable Energy Council: www.irecusa.orgDatabase of State Incentives for Renewable Energy: www.dsireusa.org

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Point of Interconnection

Interactive inverters may be connected to either the load side or the supply side of the service disconnecting means.

Distribution Equipment

To Utility

To Branch Circuits

Service Disconnect

Supply Side

Load Side

The output of interactive PV inverters may be connected to either the supply side or load side of the service disconnecting means. For many smaller systems, the point of connection is usually made on the load side of the service disconnect at any distribution equipment on the premises, usually at a panelboard. When the requirements for load side connection become impractical, interactive PV systems and other interconnected power sources may be connected to the supply side of the service disconnecting means. In cases of very large PV installations, existing service conductor ampacity or distribution transformers may not be sufficient and separate services may be installed. Power flow can occur in both directions at the point of connection, and the interface equipment and any metering must be sized and rated for the operating conditions.

Systems larger than 100 kW at other points on a premises, provided qualified persons operate and maintain the systems, and that appropriate safeguards, procedures and documentation are in place.

References:Photovoltaic Systems, p. 336-340

NEC 690.64, 705.12, 230.82(6)

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Utility Interconnection Agreements

Interactive PV systems require approval from the local electric utility before beginning parallel operations.

Most utilities have standard procedures and agreements for customers to interconnect PV systems, and generally include the following provisions:

Use of listed equipment approved for interactive operationPermitting, inspection and approval by the AHJSize limits and tiersLocation of disconnecting means and labelingInsurance and liabilitiesMetering and billingTesting and monitoringMaintenanceApplication and processing fees

Interconnection agreements are a contract between a distributed generation owner (utility customer) and an electric utility, and establish the terms and conditions for the interconnection. Most utilities have simple interconnection agreements for the installation of small PV systems at residential and commercial facilities. Larger commercial installations generally have additional requirements, while solar farms larger than 5 to 10 MW are often owned and operated by utilities themselves. Independently-owned solar generation may be subject to qualifying facility requirements.

While the administrative details for interconnection agreements vary between utilities, most have common technical requirements based on national codes and standards. For investor-owned utilities, interconnection rules and policies are often dictated by state public utilities commissions. Although municipal and cooperative utilities may be exempted from state utility commission rules, most follow similar technical guidelines and administrative practices for interconnection as investor-owned utilities.

Suggested Exercise: Obtain and review the utility interconnection agreement from your local utility.

References:Photovoltaic Systems, p. 342-347Database of State Incentives for Renewable Energy (DSIRE): www.dsireusa.org

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Chapter 13

Permitting and Inspection

Permit Submittal Guidelines ● Plan Review ●System Labels ● Inspection Checklists

The requirements for PV system installations and equipment are governed by national codes and standards that are adopted into local building codes. Approvals for PV installations are granted by local jurisdictions through the permitting, plan review and inspection process, and helps ensure the safety of PV systems.


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Codes, Standards and Enforcement

The electrical safety system is based on codes, standards and enforcement to help ensure the safety of electrical installations.

Almost every aspect of PV equipment, system designs and installations are governed by the electrical safety system.

Worker Safety, Installation & Building Codes

(NEC, ICC & OSHA)

Inspection, Code Compliance& Approval

(AHJ & Utilities)

Product Standards, Testing& Certification

(ANSI, ISO/IEC & NRTLs)

Safer Equipment & Systems


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Common Code Violations

Common code compliance problems with PV system designs and installations include the following:

Unsafe wiring methods, insufficient conductor ampacity or insulation type.Lack of or improper placement or ratings of overcurrent protection devices and disconnect means.Use of unlisted equipment or improper application of listed equipment.Improper system grounding.Lack of or improper labeling on systems and components. Insecure attachment or weathersealing of PV arrays to rooftops and other structures.

A thorough understanding of the National Electrical Code is critical for qualified PV installers, especially the first four chapters dealing with all electrical installations.

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Chapter 14

Commissioning, Maintenance and Troubleshooting

System Commissioning ● Maintenance Plans ●Diagnostics

Once PV systems are installed, they are commissioned to verify the installation matches the plans and code requirements, and that performance expectation are met. Although PV systems usually require little maintenance, a maintenance plan ensures that essential service is performed on a regular schedule. Maintenance helps identify and avoid potential problems that affect system functions, performance, or safety. When problems do occur, a systematic troubleshooting process is used to diagnose and indentify the problems, and take corrective actions.

References:Photovoltaic Systems, Chap. 14Battery Service Manual, 12th Ed., Battery Council International

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Maintenance Plan

A maintenance plan includes a list and schedule for all requiredsystem maintenance and service.

Inspections of components and wiring systemsEvaluation of structural attachments and weathersealingCleaning and removing debris around arraysPerforming battery maintenanceConducting electrical tests and verifying performance

A maintenance plan includes a list and schedule for all required system maintenance and service. Component manufacturer’s instructions often include recommended maintenance needs and intervals. A maintenance inspections involve identifying degradation or problems with the system or components that affect performance, safety or functionality.


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Performance Measurements

Operating parameters in PV systems are measured to verify expected performance.

Most inverters include integral monitoring and displays as standard features.

Measurement on any energized equipment should be performed by qualified persons using appropriate test instruments and PPE.

Measurements of current, voltage and power can be made at the PV source and output circuits, inverter input and output circuits, and load and battery circuits, as applicable for a given system design. Measurements are compared with expectations for performance verification purposes.


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Measuring Power

A standard watt-hour meter can be used to measure average power over brief intervals.

The watt-hour constant (Kh) indicates the watt-hours accumulated per revolution of the meter disk.

Multiply Kh by the disk revolution rate to calculate average power through the meter.

3600

average power (W)Wh meter constant ( )rev

revdisk revolution rate ( )sec

avg h rev

avg

h

rev

P K N

whereP

K

N

= × ×

=

=

=

Standard utility watt-hour meters are often used to record the energy produced by PV systems over time, but can also be used to measure average power over brief intervals. The watt-hour constant (Kh) indicates the watt-hours accumulated per revolution of the meter disk. Most residential meters have Kh = 7.2. The smaller the constant, the faster the meter spins for a given amount of power passing through it.

Multiply Kh by the disk revolution rate to calculate average power through the meter. The disk has markings on the top and sides with a scale of 0 to 100. Electronic meters use progressing LCD hash marks to simulate disk revolutions are rate of energy flow.

For example, the average power through a meter with Kh=7.2 that makes 10 complete revolutions in 40 seconds is:Pavg = 7.2 Wh/rev x 10 rev/40 sec x 3600 sec/hr = 6480 W.

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Chapter 15

Economic Analysis

Incentives ● Value Assessment ● Life Cycle Costs Analysis ● Financial Tools


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Financial Incentives

Federal tax credits and deductions

Rebate programs

Production incentives

Grants and loans

Sales and property tax exemptions

Financial incentives are intended to stimulate industry development, expand markets and reduce costs to the consumer. Many PV installations and consumer sectors are eligible for federal, state and local levels incentives.

Incentive programs for PV systems often have specific requirements for eligible systems that impact the work planned, the project finances, and the corresponding value of the system to the customer. Incentives may be capacity-based, in the form of rebates and one-time payments to the owner based on the size of the system. Alternatively, performance-based incentives pay the owner for energy produced by the system over time, promoting higher-quality system designs, installation and maintenance.


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Life-Cycle Cost Analysis

Life-cycle costs represent the total costs of owning and maintaining an asset over its lifetime, and can be used to compare the costs of PV systems and alternate energy sources.

CC

PV

PV

PV

whereL = life-cycle cost ($)I = initial cost ($)M = present value of maintenance costs ($)E = present value of energy costs ($)R = present value of repair and replacements

PV PV PV PVLCC I M E R S= + + + −

PV

($)S = present value of salvage value ($)

A life-cycle cost analysis is used to compare the value of competing energy supply options, such as PV systems, generators or the utility grid. The analysis involves estimating all initial and recurring costs over the anticipated system life, including the cost of the equipment and installation, and the costs for maintenance and equipment replacements. Financial incentives and salvage value subtract from the life-cycle costs. Economic factors are then used to estimate the total life cost of installing and operating the system in present day dollars. Dividing the life-cycle cost by the amount of energy produced over the system life provides a comparison of various energy supply options.

References:Photovoltaic Systems, p. 401-412CD-ROM worksheets and example in text

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Chapter 16

PV System Safety

Hazards and Avoidance ● Personal Protective Equipment ● Fall Protection ● Electrical Safety

This section covers some of the basic safety requirements for PV systems and for workers who install them. The materials presented in this section are intended only as an overview, and do not present the complete requirements for compliance with installation safety codes or standards, nor does it replace recognized OSHA safety training.

References: Photovoltaic Systems, Chap. 3National Electrical Code® (NEC), NFPA 70Standard for Electrical Safety in the Workplace, NFPA 70ECFR 29 Part 1910 -- Occupational Safety and Health StandardsCFR 29 Part 1926 -- Safety and Health Regulations for Construction

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Fall Protection

Falls are the leading cause of deaths in the construction industry.

Most fatalities occur when employees fall from open-sided floors and through floor openings.Many PV arrays are installed on rooftops or elevated structures.

Each employee on a walking/working surface with an unprotected side or edge 6 feet (1.8 m) or more above a lower level shall be protected from falling by the use of guardrail systems, safety net systems, or personal fall arrest systems.

There are many different types of work environments that contribute to fall hazards. The requirements for fall protection are quite complex and vary depending on the situation. Working on roofs, ladders, scaffolding and lifts all require fall protection considerations.

References:29 CFR 1926 Subpart E: Personal Protective Equipment (safety belts, lifelines, lanyards and safety nets)29 CFR 1926 Subpart M, Fall Protection

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Electrical Hazards

Four main types of electrical injuries:Electrocution or death due to electrical shockElectrical shockBurnsFalls (caused by shock)

Electrical accidents are caused by a combination of three factors:Unsafe equipment and/or installation, Workplaces made unsafe by the environment, and Unsafe work practices.

There are four main electrical hazard categories. Electrocution or death due to electrical shock, electrical shock, burns and falls (caused by shock).

The severity of the electrical shock depends on the path, amount and duration of current through the body. Currents above 10 mA can contract muscles, and currents above 75 mA can cause a rapid, ineffective heartbeat. Shock-related injuries include burns, which can cause tissue damage, or ignite clothing. Arc flash burns are associated with electrical arcs and explosions. Electric shock can also cause indirect injuries by workers falling from elevated locations. About 5 workers are electrocuted every week, causing 12% of young worker workplace deaths (OSHA).

Reference: 29 CFR 1926 Subpart K

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Summary

The Photovoltaic Systems Training Resource Guide is a comprehensive set of instructional presentation materials not found collectively from any other source.

Documents

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