4841_CH3_Solar Collector_M A Islam

Chapter 3 Solar Collector

DR. M A Islam

EEE, IIUC

Solar Energy – A Bright Idea!

“I’d put my money on the sun and solar energy. What a source of power! I hope we don’t have to wait ‘til oil and coal run out before we tackle that.”

- Thomas Edison

People have been harnessing solar energy for a long time!

Solar collector for heating water

A home in California in 1906

Sun Angles

Two Main Categories:

Solar Thermal Solar Photovoltaic (PV)

Water heating and cooking Electricity production

Solar Thermal Energy

Cooking Water Heating

Solar Water Heating

Solar Water Heating

• Solar water heating is the most efficient and economical use of solar energy

• Residential systems start at $2500 and typically cost $3500-$4500 installed

• Savings of $30-$75 per month, lasting 20 years

• Tax credits and state rebates available

How Does it Work?

How Does it Work?

• Systems can be passive or active

• Passive systems only found in warmer climates, as they are prone to freezing

• Active: Roof-top collectors heat glycol which then passes through a heat exchanger in the storage tank to heat water

• Electric pump can be run on solar PV

Solar Hot Water Classroom Experiments

• Design your own SHW collector

• Variables: – Color of collector – Tubing length, pattern,

material – Light intensity – Insulation – Use of reflective

materials – Rate of water pumping – Etc…

Types

• Back-pass solar collectors – Used to heat air – Glazed surface – May be integrated with thermal mass

• Concentrating solar collectors – Best suited for clear skies – Steam production – Concentrates light at absorber which can increase efficiency at high temperature – Four forms: parabolic trough, parabolic dish, power tower, stationary solar collectors

• Trombe Wall – Thermal mass designed to radiate heat during the night – Glass to allow sunlight through – With added salt fillers stored energy changes from 200 cal/day to 80,000 cal/day

• Batch Solar Collectors – Water heating – Glazed water collectors

• Solar cookers • Liquid Solar Collectors

– Vacuum tubing

SOLAR COLLECTORS

• Types of collectors – Stationary – Sun tracking

• Thermal analysis of collectors • Performance • Applications

– Solar water heating – Solar space heating and cooling – Refrigeration – Industrial process heat – Desalination – Solar thermal power systems

Types of solar collectors

Motion Collector type Absorber

type

Concentration

ratio

Indicative

temperature

range (°C)

Stationary

Flat plate collector (FPC) Flat 1 30-80

Evacuated tube collector (ETC) Flat 1 50-200

Compound parabolic collector (CPC) Tubular 1-5 60-240

Single-axis

tracking

5-15 60-300

Linear Fresnel reflector (LFR) Tubular 10-40 60-250

Parabolic trough collector (PTC) Tubular 15-45 60-300

Cylindrical trough collector (CTC) Tubular 10-50 60-300

Two-axes

tracking

Parabolic dish reflector (PDR) Point 100-1000 100-500

Heliostat field collector (HFC) Point 100-1500 150-2000

Note: Concentration ratio is defined as the aperture area divided by the receiver/absorber area of the collector.

Flat-plate collector Flat-plate collectors are the most common solar collector for

solar water-heating systems in homes and solar space

heating. A typical flat-plate collector is an insulated metal box

with a glass or plastic cover (called the glazing) and a dark-

colored absorber plate. These collectors heat liquid or air at

temperatures less than 80°C.

Flat-plate Collectors

Types of flat-plate collectors Water systems

Glazing

Riser

Absorbing plate

Insulation

A

B Glazing

Riser

Absorbing plate

Insulation

C Glazing

Riser

Absorbing plate

Insulation

D

Glazing

Riser

Absorbing plate

Insulation

Types of flat-plate collectors Air systems

Glazing

Air passage

Insulation

E

F Glazing

Air flow

Metal matrix

Insulation

G

Glazing

Corrugated sheet

Insulation

Figure: shows the schematic of a typical solar system employing a flat plate

solar collector and a storage tank.

useful energy gain (Qu)

collector heat removal factor (FR)

Hottel- Whillier-Bliss equation &

Collector efficiency

However, as the radiation is incident in the collector, a part of this radiation is

reflected back to the sky, another component is absorbed by the glazing and the

rest is transmitted through the glazing and reaches the absorber plate as short

wave radiation.

Therefore the conversion factor indicates the percentage of the solar rays

penetrating the transparent cover of the collector (transmission) and the

percentage being absorbed. In that case,

If I is the intensity of solar radiation, in W/m2, incident on the aperture plane of the

solar collector having a collector surface area of A, m2, then the amount of solar

radiation received by the collector is:

As the collector absorbs heat its temperature is getting higher than that of

the surrounding and heat is lost to the atmosphere by convection and

radiation. The rate of heat loss (Qo) depends on the collector overall heat

transfer coefficient (UL) and the collector temperature.

Thus, the rate of useful energy extracted by the collector (Qu),

expressed as a rate of extraction under steady state conditions, is

proportional to the rate of useful energy absorbed by the collector, less the

amount lost by the collector to its surroundings.

It is also known that the rate of extraction of heat from the collector may be

measured by means of the amount of heat carried away in the fluid passed

through it, that is:

However, above Equation 4 proves to be somewhat inconvenient because

of the difficulty in defining the collector average temperature. It is

convenient to define a quantity that relates the actual useful energy

gain of a collector to the useful gain if the whole collector surface

were at the fluid inlet temperature. This quantity is known as “the

collector heat removal factor (FR)” and is expressed as:

The maximum possible useful energy gain in a solar collector occurs when

the whole collector is at the inlet fluid temperature. The actual useful

energy gain (Qu), is found by multiplying the collector heat removal factor

(FR) by the maximum possible useful energy gain. This allows the

rewriting of equation (4):

Equation (7) is a widely used relationship for measuring collector energy

gain and is generally known as the “Hottel- Whillier-Bliss equation”.

A measure of a flat plate collector performance is the collector efficiency (η)

defined as the ratio of the useful energy gain (Qu) to the incident solar

energy over a particular time period:

Collector efficiency

Solar Cooking

Benefits of Solar Cooking

• Consumes no fuels/wood

– No loss of trees & habitat

– Trees sequester carbon

• Generates no air pollution

• Generates no greenhouse gases

• Produces no smoke

– Cooking smoke kills over 1.6 million people each year, mostly women & children, according to a recent report

• Eliminates fire dangers

More Benefits of Solar Cooking

• Eliminates work

– No daily search for firewood

• 2 Billion people rely on wood for cooking fuel!

– No risks to women and children

– Frees time for other activities

– No need to stir food

– Helps to liberate women

More Benefits of Solar Cooking

• Cooks foods slowly and thoroughly

• Preserves nutrients • Foods will not burn • Pots are easy to clean;

less clean water is needed

• Use for canning vegetables

• Use for dried fruit • Kill insects in dry grains

Solar Cooking How Long Does it Take?

• Vegetables: 1.5 hrs

• Rice/wheat: 1.5-2 hrs

• Beans: 2-3 hrs

• Meats: 1-3 hrs

• Bread: 1-1.5 hrs

TEI Patra: 3-18 July 2006 Intensive program: ICT tools in

PV-systems Engineering

Parabolic Trough System



Parabolic trough collectors



Parabola detail



Receiver detail



Central receiver system



Tower detail



Heliostat detail



Central receiver-1



Central receiver-2



Central receiver-3



Central receiver-4



Central receiver-5



Central receiver-6



Central receiver-7



Central receiver-8

Fun Student Projects!

Solar Electric (Photovoltaic)

• Photovoltaic (PV) systems convert light energy directly into electricity.

• Commonly known as “solar cells.”

• The simplest systems power the small calculators we use every day. More complicated systems will provide a large portion of the electricity in the near future.

• PV represents one of the most promising means of maintaining our energy intensive standard of living while not contributing to global warming and pollution.

Solar Electric Systems

How Does it Work? • Sunlight is composed of photons, or bundles of radiant

energy. When photons strike a PV cell, they may be reflected or absorbed (transmitted through the cell). Only the absorbed photons generate electricity. When the photons are absorbed, the energy of the photons is transferred to electrons in the atoms of the solar cell.

How Does it Work?

• Solar cells are usually made of two thin pieces of silicon, the substance that makes up sand and the second most common substance on earth.

• One piece of silicon has a small amount of boron added to it, which gives it a tendency to attract electrons. It is called the p-layer because of its positive tendency.

• The other piece of silicon has a small amount of phosphorous added to it, giving it an excess of free electrons. This is called the n-layer because it has a tendency to give up negatively charged electrons.

How Does it Work?

Helpful PV Animations

http://www1.eere.energy.gov/solar/animations.html

http://www.managenergy.net/kidscorner/animations/solar_an.html

http://www1.eere.energy.gov/solar/animations.html

http://www.managenergy.net/kidscorner/animations/solar_an.html

Best Place For Solar Panels?

• South Facing roof, adequate space

• No shading (time of year, future tree growth)

• Roof structure, condition

Large Scale PV Power Plants

Prescott Airport Location: AZ

Operator: Arizona Public Service Configuration: 1,450 kWp

SGS Solar

Location: AZ Operator: Tucson Electric Power Co

Configuration: 3,200 kWp

Centralized Wind-Solar Hybrid System

• In hybrid energy systems more than a single source of energy supplies the electricity.

• Wind and Solar compliment one another

Solar Concentrators • These 20-kW Solar

Systems dishes dwarf visitors in Alice Springs, Australia.

• The concentrators use an array of mirrors to focus sunlight onto high-efficiency solar cells.

• Four supports hold the cells in front of the mirrors

• The supports also supply cooling water and electrical connections

How Does the Color/Wavelength of Light Affect PV Efficiency?

• Test 5-8 colors using different backgrounds on PowerPoint Slides – Purple

– Blue

– Green

– Yellow

– Orange

– Red

– White

Approximate Wavelength: 390-455 nanometers






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4841_CH3_Solar Collector_M A Islam