Lecture 11- Solar Energy

MA9001: Introduction to EnergyTopic 9: Solar Energy (Part 1)Topic 9: Solar Energy (Part 1)

- The Sun

- Solar Thermal

Solar Photovoltaics- Solar Photovoltaics

Dr. Seri LeeSchool of Mechanical and Aerospace Engineering

Email: serilee@ntu edu sg1

Email: [email protected]: 6790 6940

The Sun

Jupiterearth

2

Jupiter

The Sun• Main source of energy• Was born about 4.5 billion years ago…

Di 1 4 106 k M 2 1030 k• Dia. ≈ 1.4 x106 km, Mass = 2 x 1030 kg• 74% Hydrogen + 24% Helium + 2% other elements• A continuous nuclear fusion reactor:• A continuous nuclear fusion reactor:

Hydrogen Helium + Energy (E = mC2)• 400-600 million tons of Hydrogen burnt per sec.y g p• Will be here for another 5 billion years, before Hydrogen

runs out.• It will contract and gets hotter, then it will burn Helium..• It expands and become larger and…explodes, engulfing

the entire solar system (red giant)3

the entire solar system (red giant) You don’t want to be here when that happens..

The sun (con’t.)Core:Core:- 23% of Radius

1 2% of Volume- 1.2% of Volume- 40% of mass

90% fcore

- 90% of energy produced

14 million degree K- 14 million degree K- 100,000 kg/m3

http://www.eoearth.org/article/Solar_radiation- It takes 100,000 yrs

for a photon from core to reach surface4

for a photon from core to reach surface- From surface, it takes 8 mins to reach the earth.

The Sun ρ ~70 kg/m3T ~14 x105 KConvective zoneConvective zone

ρ g

RadiativeRadiative zonezone

40% of Mass1 2% of Volume

90% of energy

1.2% of Volume0.7RCoreCorephotospherephotosphere

90% of energyT~14 x106 Kρ ~105 kg/m3

T ~5800 Kρ~ 2x10-4 kg/m3 ρ gρ g

5

Solar Energy

• Solar luminosity: power emitted by the sun

= 3.86 x 1026 W 3.86 x 10 W

• Surface Area = 6.07 x 1012 km2 = 6.07 x 1022 cm2

• Surface heat flux ~ 6,400 W/cm2

6

Solar Energy

• Solar constant: Solar intensity 1 au from the sun, at surface above the atmospheree su , a su ace abo e e a osp e e= 3.86 x 1026 /(4π(au)2) = 1360 W/m2

-Centauri

SunEarth 1 au ≈ 150 million km

(11 m)

• Due to absorption by gasses above the

(1 mm) (25 cm)(11 m)

Due to absorption by gasses above the atmosphere, solar constant on earth surface at zenith on a clear day is about 1,000 W/m2.y ,

7Note: au=ASTRONOMICAL UNIT

Solar Radiation: Electromagnetic Wave

(0.4μm) (0.7μm)

http://www.revisionworld.com/

• Solar radiation reaching earth is mainly from

8wavelength : 0.3 μm to 2.5 μm

Solar Radiation Spectrum

9% UV (λ ≤ 0.40 μm),38% i ibl ( 0 40 λ 0 70 )

10

38% visible ( 0.40 ≤ λ ≤ 0.70 μm),53% infra-red (λ ≥ 0.70 μm).

Law of Thermal RadiationStefan-Boltzmann’s Law of radiation- Radiation emitted by a surface at temperature T [K]:y p [ ]

where q = emissive power density, heat-flux* [W/m2]q p y, [ ]σ = Stefan-Boltzmann constant = 5.67 x 10-8 [W/m2·K4]ε = surface emissivity, 0-1

For the Sun; T = 5800K , ε = 1 (blackbody) 64 MW/m2

11* Area under the spectral irradiance curve.

Solar Energy con’t• When smeared over the surface of earth sphere it is reduced

by a factor of 4..

Disk: A=πR2 Sphere: A= 4 x πR2

• It is further reduced by a factor of approx. 2 after the atm. absorptionabsorption

• Hence, the time & area averaged solar intensity on the ground level ~ 1360/4/2 = 170 W/m2

• Or, in terms of energy, 170 W/m2 x 24 hrs/day ~ 4 kWh/m2/day

• For one year, we get 5.4GJ/m2 (~ one barrel of oil/m2)

12

For one year, we get 5.4GJ/m ( one barrel of oil/m )

*BOE: barrel of oil equivalent = 42 USG ≈ 159 litres ≈ 6.12 GJ

Solar Irradiance Map

13

Averaged solar irradiance ~ 4 kWh/m2/day

Total Available Power

OilOil

Annual Global Consumption by Humans (at 15TW)

CoalCoal

GasGas

OilOil

UraniumUranium

CoalCoal

Wind

Annual Solar (at 120,000TW)Annual Solar (at 120,000TW)

Hydro


Photosynthesis

less than 0.02% meets the global need every hour ~ global consumption/year

14

Source: National Petroleum Council, 2008

Solar Energy: Heat or Electricity

Solar Thermal:• Using direct sun rays for living space and water heating• Using direct sun rays for living space and water heating• Use heat energy collected for refrigeration and cooling:

e.g. absorption cycle.g p y• Use heat in producing electricity, i.e. thermoelectricity

15http://www.makeitsolar.com/solar-energy-information/05-solar-panels.htm

Solar Energy: Heat or Electricity

Solar Photovoltaic:• Convert sun rays to electrical energy for various• Convert sun rays to electrical energy for various

applications using photovoltaic or solar cells

• Batteries may be used for storage of the energy

to be used when there is no sunlight

16

Solar Thermal Energy (classifications)Can be classified into:1.Low temperature: for heating swimming pool1.Low temperature: for heating swimming pool2.Medium Temperature: Water heating for home

and commercial buildingsand commercial buildings3.High temperature: concentrated for thermal

electric productionelectric production

17

Solar Thermal Energy (classifications)Can also be classified into:Can also be classified into:• Passive Solar Heating

Direct exposure to sun rays Building design– Direct exposure to sun rays. Building design incorporating direct harvesting of sun’s heat without external assisting devices. Use airwithout external assisting devices. Use air circulation for space heating

• Active Solar Heatingg– Use thermal collector e.g. for hot water or

swimming poolsg• Solar Thermal Engines (concentrator solar)

– Extension of active solar heating using complex g g pcollectors to get high temperature fluids to run steam turbines or refrigeration systems 18

Passive Solar Thermal• Buildings

incorporating p gpassive solar heating design ideas capture heat from sun for heatingfor heating.

19

SUSTAINABLE ENERGY SYSTEMS ENGINEERING THE COMPLETE GREEN BUILDING DESIGN RESOURCE

PETER GEVORKIAN

Active Solar Water Heating1. Fluid-filled pipes (painted black and are laid

on a silver-coloured reflective base) exposing ) p gto sun’s rays.

2. Combination of magnifying glasses with fluid-g y g gfilled pipes

3. Pipes may carry special heat-absorbing fluid y y gsuch as bromide that heats up rapidly.

4. A small pump may be used to circulate the fluid.

20

Active Solar Thermal: Pool Heatinge.g. For hot water shower or for warming the

water of swimming pool.g p

4 types of solar collectors:4 types of solar collectors:1.Rigid Black Plastic Panel2 Rubber Mat2.Rubber Mat3.Tube and Fin metal panel4 Plastic pipe systems4.Plastic-pipe systems

21

Pool Heating (con’t)1. Rigid Black Plastic Panel1. Rigid Black Plastic Panel• Modular panel (4ft wide and 8, 10, or 12 ft length).• Avd: Light chemically inert durable and high• Avd: Light, chemically inert, durable and high

efficiency• Disavd: it hasDisavd: it has

numerous system surface attachmentsurface attachment that limits mounting locationslocations.

22

Pool Heating (con’t): Rigid Black Plastic PanelPlastic Panel

http://www.heliocol.com/gallery/res.php

23http://www.heliocol.com/gallery/res.php


Pool Heating (con’t)

2. Rubber Mat• Avd: flexibility in


Avd: flexibility in dimensions as the lengthan wide are adjustablean wide are adjustable,hence it can adapt to roof

b t ti R iobstructions. Requires few roof penetration and are highly efficient.Di d M t l d t th f d b• Disavd: Mats are glued to the roof and can be difficult to remove. It cannot be applied in rack type installationsrack-type installations.

24

Pool Heating (con’t): Rubber mathtt // h li l / ll / hhttp://www.heliocol.com/gallery/res.php

25


Pool Heating (con’t)3. Tube and Fin metal panel• It is constructed from copper tubes with aluminumIt is constructed from copper tubes with aluminum

or copper fins to collect solar radiation.• Avd: rigid and durable in construction.Avd: rigid and durable in construction.• Disavd: requires more areas, has low efficiency

and has no http://www.builditsolar.com/Projects/WaterHeating/Woodsy1K/Woodsy1K.htmand has no manufacturer’s warrantywarranty.

26

Pool Heating (con’t)Tube and Fin metal panelTube and Fin metal panel

27http://www.solar.net.cn/image_thum/suneco-solar-glass-tube-collector.JPG

Pool Heating (con’t)4. Plastic-pipe systems• Plastic pipes are connected in parallel or inPlastic pipes are connected in parallel or in

circular pattern.• Avd: cheap installation costAvd: cheap installation cost • Disavd: requires significant larger surface area.

It carries no manufacturer’s warranty.It carries no manufacturer s warranty.

28

Pool Heating (con’t)Some vacuum tube-solar collectors

29

Pool Heating: Panel Selection• In temperate countries, heats to 25 to 30oC.• The panel surface area exposed to sun raysThe panel surface area exposed to sun rays

must be sufficient: express in terms of % multiplier of pool surface area.p p

• Depending on the locations: panel area ranges from 50%-120% of the pool surface area.

30

Pool Heating: Sizing ExampleThere are 10 questions for sizing a system.1. How many months of the year is the pool used?2. Taking into account the geographic location, how long can the2. Taking into account the geographic location, how long can the

season reasonably be?3. Will there be a backup heating system? If so, what kind?4 Does the pool have a screen enclosure?4. Does the pool have a screen enclosure?5. Will a blanket be used?6. Is there a solar window?7. Is wind going to be a problem?8. Is shading going to be a problem? If so, how many hours a

day?9. What direction and at what angle will the collectors be

mounted?10. What is the surface area of the pool?p

31

Specifications of solar panelsCollector Data

Collector Model HC-50 HC-40 HC-30 HC-12.5 HC-10

Size, Nominal 4'x12.5' 4'x10.5' 4'x8' 1'x12.5' 1'x10.5'

Width 47" / 120cm 47" / 120cm 47" / 120cm 11.75" 11.75"

Length 152.1" / 380cm 127" / 323cm 91" / 231cm 151.5" 127" 380cm

Area (sq. ft.) 50.0 / 4.65m^2

41.6 / 3.88m^2

30.0 / 2.77m^2 12.2 10.2

Manifold Diameter 2" / 5.08cm 2" / 5.08cm 2" / 5.08cm 2" 2" Diameter

Weight, Dry 22lbs / 10kg 19lbs / 8.5kg 15lbs / 6.8kg 5.5lbs 4.75lbs

Volume Capacity 3.7gal / 14L 3.1gal / 12L 2.4gal / 9L .93gal .78gal CapacityWorking Pressure 90 PSI 90 PSI 90 PSI 90 PSI 90 PSI

Burst Pressure 270 PSI 270 PSI 270 PSI 270 PSI 270 PSI

32


PressureRecommended Flow 5 GPM 4 GPM 4 GPM 1.25 GPM 1 GPM

Pool Heating: Sizing ExampleSizing of solar panel depends on: wind conditions,

climates, flow rates, orientation and shading of the pool d/ ll tand/or collectors.

Example using Helicol Solar CollectorExample using Helicol Solar Collector

• Pool size: 14 ft x 28 ft =392 ft2

• Location: Las Vegas • From Chart, Las Vegas is located in zone 5 which has a

0.52 multiplier.• The collector area is 392 ft2 x 0.52 = 203.8 ft2.• No of panels Helicol HC 40 (40 1ft2) is 5 1 5 panels• No. of panels Helicol HC-40 (40.1ft2) is 5.1 5 panels

33http://www.heliocol.com/

Concentrated Solar Power, CSP • Concentrator Solar Power Tech is to produce high

temperature (500°C - 3000°C, and beyond) heat, which is th t d i t l t i it l ll d l th lthen converted into electricity, also called solar thermal electricity.

• 3 most advanced CSP technologies:• 3 most advanced CSP technologies:

– Parabolic Troughs (PT): most efficient

– Central Receivers (CR) or Solar Tower

– Dish Engines (DE)

• PT & CR suitable for large power plants 30 to 200 MW, or higher.

• DE is more suitable for distributed power, 10kW to 10 MW.34

Benefits of CSP• Zero greenhouse gas (NOx and SOx) emission• ReliableReliable• With the economy of scale, cost can drop

below US$0.04/kWh (US$0.10 now), in thebelow US$0.04/kWh (US$0.10 now), in the next 15 years.

• Use existing technology, “easily” scaled up.Use existing technology, easily scaled up.• Successfully applied in thermal electric power

generation. e.g. A 354-MW solar powergeneration. e.g. A 354 MW solar power generated electric plant using PT in California Mojave Dessert.

35

Example of CSP:• For a 46 MW solar farm using CSP (CT) there

will be 24,000 1-meter-square mirrors per 1 q ptower (all 12 towers). Mirrors are adjusted and calibrated real time using solar sensors with a land-to-power ratio of 4 acres (1 acre≈4047 m2) per 1 megawatt.

• Based on the above example, Singapore (680 km2) with a power capacity/consumption of

12 GW will need 180 km2 (27% of land area)~12 GW will need 180 km2 (27% of land area) if CSP is used.

36http://en.wikipedia.org/wiki/Concentrating_solar_power

Parabolic Trough•It has a long parabolic mirror (usually coated silver or polished aluminum) with a Dewar tubealuminum) with a Dewar tube running its length at the focal point.

• Sunlight is reflected by the mirror and concentrated on the Dewar tube. The trough is usually aligned on a north-south axis, and rotated to track the sun as itand rotated to track the sun as it moves across the sky each day.

37(http://en.wikipedia.org/wiki/Parabolic_trough)

Parabolic Trough (con’t)• A working fluid (eg

molten salt) is heated t 150 350°C itto 150–350°C as it flows through the receiver and is then used as a heat source for a power generation systemgeneration system.

• Trough systems are the most developed CSP technology.

38

Parabolic Trough Solar Farm (con’t)Built in 1984, the parabolic trough technology of thetechnology of the 354MW Solar Energy Generating Systems (SEGS) i C lif i(SEGS) in California USA is still the largest solar power plant in the world.

Concentrated solar power plant using parabolic trough design.

http://en.wikipedia.org/wiki/Solar_Energy_Generating_Systems

39

p p g p g ghttp://en.wikipedia.org/wiki/Solar_thermal_energy#Dish_designs

Solar Tower Technology• It concentrates solar radiation on a tower-mounted heat

exchanger.

• Power towers focus the sun ray with thousands of tracking mirrors (called heliostats) in roughly a 5 square km fieldkm field.

• The heliostats focus concentrated sunlight on a receiver which sits on top of the tower to heat molten salt to over p500°C. The heated molten salt then flows into a thermal storage tank where it is stored, maintaining 98% thermal efficiency and eventually pumped to a steam generatorefficiency, and eventually pumped to a steam generator.

• The steam drives a standard turbine to generate electricity. y

40

Solar Tower Technologyhttp://en.wikipedia.org/wiki/List_of_solar_thermal_power_stations

41

The PS10 concentrates sunlight from a field of heliostats onto a central tower.(Spain, 11 MW)

Solar Tower Technologyhttp://en.wikipedia.org/wiki/List_of_solar_thermal_power_stationsp p g _ _ _ _p _

42Solar Towers from left:PS10, PS20. (Spain, 11 MW, 20 MW)

Solar Tower Technology• The advantage over Parabolic Trough:1. It is higher temperature hence higher thermal efficiency2. Less need to flatten the ground area (can be built on a

hillside)3 Flat mirrors3. Flat mirrors4. Plumbing is concentrated in the tower.

• The disadvantage:1. Each mirror must have its own dual-axis control, while in

the parabolic trough design one axis can be shared for a large array of mirrors.

http://en.wikipedia.org/wiki/Solar_thermal_energy#Dish_designs43

Solar Dish Engine Di h i t li i t th d t t f h tDish engine systems eliminate the need to transfer heat to a boiler by placing a Stirling engine at the focal point.

http://en.wikipedia.org/wiki/Concentrating_solar_power

44

Solar Dish Engine (con’t)For high temperature solar, heat engine can be used to convert heat to electricity. Up to 600°C, steam turbines, the thermal efficiency is up to 41%.

For higher temperature 700 800°C i lti700-800°C, using multi-stage system, the conversion efficiency of 50% or more is50% or more is achievable.

45

A parabolic solar dish concentrating the sun's rays on the heating element of a Stirling engine. The entire unit acts as a solar tracker.

Solar Air-Conditioning System• Absorption air conditioning system (liquid

absorber))• Adsorption air conditioning system (solid

absorber))

1.They use heat energy from the sun to drive the1.They use heat energy from the sun to drive the system for cooling & heating purposes.

2.As compare to the conventional air-con2.As compare to the conventional air con system, they are general bulky.

3.Suitable for commercial applications where the 3 Su tab e o co e c a app cat o s e e t eheat source can be obtained.

46

Conventional Air-Conditioning System

rejecting heat out of room High PHigh T

High PLow T

condenserrejecting heat out of room High T

VaporLow TLiquid

Compressor(power input)

Expansion Valve (power input)Valve

evaporatorLow PLow TLiquid

Low PHigh TVapor

47absorbing heat from room

Liquid Vapor

Solar Absorption Air-Con SystemExample: Ammonia

Rejecting heat out of room

p& water system

condenser Gas refrigerantLiquid refrigerant

Expansion Valve

desorption

evaporator

LiquidPump

absorptionGas refrigerant

evaporator p


Liquid absorbent(i.e. Lithium Bromide)

Solar Adsorption Air-Con System

rejecting heat out of room

condenser Gas refrigerantLiquidrefrigerant

Expansion Valve

desorption

t

Valve

adsorption

Silica gel

evaporatorGas refrigerant


Photovoltaics: From Sun Light to DC• In a single-junction PV cell, from the whole

spectrum of the sunlight, only those photons p g y pwhose energy is equal to or greater than the band gap of the cell material can free an electron for an electric circuit. The lower-energy photons are not used.

• In Multi-junction PV cell: cell materials with different band gaps are used in cascade or stack mannerstack manner.

• Drawbacks: weather dependent, large surface area neededarea needed.

50http://science.nasa.gov/science-news/science-at-nasa/2002/solarcells/

Photovoltaics: Solar Cell Physics

MA9001: Introduction to EnergyT i 9 S l E (P t 2)Topic 9: Solar Energy (Part 2)

NP e

eP e

- by Prof. Christian KlocS h l f M t i l S i d E i i

51

School of Materials Sciences and Engineering

Photovoltaics • Using solar collector to convert sun rays to

electricity, directly.y y

• Silicon cells or multi-junction solar cells (100 times more expensive)times more expensive)

• Concentrated PV:

1. Low Concentrated PV (LCPV)

2 Medium Concentrated PV (MCPV)2. Medium Concentrated PV (MCPV)

3. High Concentrated PV (HCPV)

52

Low Concentrated PV (LCPV)• A solar concentration of 2-100 suns.• The heat flux is low, do not need to be activelyThe heat flux is low, do not need to be actively

cooled.• Since a low concentration ratio can have a highSince a low concentration ratio can have a high

acceptance angle, may not require active solar tracking.g

http://en.wikipedia.org/wiki/Concentrating_solar_power

53

Medium Concentrated PV (MCPV) • A solar concentration of 100 - 300 suns.• The CPV systems require two-axes solarThe CPV systems require two axes solar

tracking and cooling (whether passive or active), which makes them more complex.p

54http://en.wikipedia.org/wiki/Concentrating_solar_power

High Concentrated PV (HCPV) • A solar concentration of > 300 suns.• It employs concentrating optics consisting of dish p y g p g

reflectors or fresnel lenses. • The solar cells require high-capacity heat sinks.• Multijunction solar cells are currently favored over

silicon as they are more efficient.• Typically 8 A/cm2 at 500 suns. Though the cost of

multijunction solar cells is roughly 100 times that f bl ili ll h ll iof comparable silicon cells, the cell cost remains a

small fraction of the cost of the overall concentrating PV system so the systemconcentrating PV system, so the system economics might still favor the multijunction cells.55

Concentrated Photovoltaics and Concentrated Photovoltaics and Thermal (CPVT)

Th CPVT t h l d b th l t i it• The CPVT technology produces both electricity and thermal heat in the same module. Thermal heat that can be employed for hot tap waterheat that can be employed for hot tap water, heating and heat-powered air conditioning (solar cooling), desalination or solar process(solar cooling), desalination or solar process heat.

56

Thermal Challenges and OpportunitiesThermal Challenges and Opportunitiesin Concentrated Photovoltaics

Seri Lee, Ph.D.Nanyang Technological Universityy g g y

+65 6316-8976 [email protected]

Agenda

• Introduction to ERI@N• CPV Overview• Power Matrix and Thermal SolutionsPower Matrix and Thermal Solutions• CPV Dependencies

P f Effi i R li bilit- Performance - Efficiency - Reliability

• Cost and Economics• Summary and Conclusions

58Seri Lee, EPTC 2010

ERI@N ERI@N -- Energy Research Institute @ NTU

Official opening: 15 June 2010 65 participating professors 17 commercial partnerships 3 dedicated laboratories

totaling 2500 m2totaling 2500 m 5 joint, international

university partnerships 17 joint research projects

112 d t t d t


112 graduate students 65 research fellows/associates

ERI@N: ERI@N: Centres of Excellence

Centre for Sustainable Energy

Research (CSER)

Centre for Maritime Centre for Maritime Energy Research

(CMER)

Solar Energy & Solar Fuels Centre

(SEFC)

Centre for Electro-mobility (CEM)

with TUM

Green Ships Green Ports

Energy Storage Systems E-Car Technology,

Wind / Marine RenewablesEnergy StorageG & S

PhotovoltaicsSolar ThermalPhotocatalysis,

Infrastructure and Systems

Green & Smart BuildingsFuel Cells

yPhotoelectrochemconversions


Concentrated Photo-Voltaics (CPV)• Concentration at 500 - 600 suns typical; done up to 1,000 - 2,000 suns• Multi-junction cells, as compared to silicon cells, are ~100X morej , p ,

expensive per size but >2X more efficient favored choice for CPV• Conversion efficiency: ~40% at cell; 30% at module; 25% at system level


Total Available Power

OilOil

Annual Global Consumption by Humans (at 15TW)

CoalCoal

GasGas

OilOil

UraniumUranium

CoalCoal

Wind


Hydro


Photosynthesis

less than 0.02% meets the global need every hour ~ global consumption/year

62

Source: National Petroleum Council, 2008

Solar IrradiationCPV’s sweet spot is >5

kWh/m2/day

Excellent for CPV

Source: Pharabod and Philibert, 1991Good for CPV


CPV Installations - ProjectedThe CPV Challenge Report, July 2009


CPV Modules and Systems

Fresnel lens

Primary mirror

Secondary mirror

Optical rod

Solar cell

Reflection and Transmission Typesyp


CPV Power Matrix at 1000 suns

Heat LoadHeat LoadPower

Produced

Cell Size Cell Area Voltage Current Concent. Power In Mod eff Elec out Heat out(mm) (mm^2) (V) (A) (Suns) (W) (%) (W) (W)1 1 2 68 0 1 1000 1 28 0 3 0 7

(WT)1 1 2.68 0.1 1000 1 28 0.3 0.72 4 2.68 0.4 1000 4 28 1.1 2.93 9 2.68 1 1000 9 28 2.5 6.54 16 2.68 1.7 1000 16 28 4.5 11.55 25 2 68 2 7 1000 25 28 7 0 18 05 25 2.68 2.7 1000 25 28 7.0 18.06 36 2.68 3.9 1000 36 28 10.1 25.97 49 2.68 5.3 1000 49 28 13.7 35.38 64 2.68 6.9 1000 64 28 17.9 46.19 81 2.68 8.8 1000 81 28 22.7 58.3


9 81 2.68 8.8 1000 81 28 22.7 58.310 100 2.68 10.9 1000 100 28 28.0 72.0

Thermal Management - Perspectives104

)10

103

Surfaceof Sun

Rocket Nozzle

ux (W

/cm

2 102

101Earth Orbit Entry

1000X CPVsCPUs (90s)

Logic Chips

ThermalManagement Nuclear Blast

(1 Mt, 1 mile)

CPUs (00s)

Hea

t Fl

100

10-1

100W Light Bulb

Solar Heating

g p(80s)

100 1000 10000

10-2 Body Heat

Solar Heating

Temperature (K)100 1000 10000

• at 1000X, CPV heat density is ~70W/cm2

• exceeding that of an earth orbit entry• need low cost, light weight and high performance thermal solutions

Power Matrix and Thermal Solutions

200 400 600 800 1000 1200 1400die size (mm)

suns

SolutionsCPV heat dissipation in watts, WT , at 28% efficiency

cell size

2 0.6 1.2 1.7 2.3 2.9 3.5 4.0

4 2.3 4.6 6.9 9.2 12 14 16

Today’s sweet spot

6 5.2 10 16 21 26 31 36

8 9.2 18 28 37 46 55 65

10 14 29 43 58 72 86 101

12 21 41 62 83 104 124 145

14 28 56 85 113 141 169 19814 28 56 85 113 141 169 198

Need low cost, light weight, high performance and uniform temperature

Simulated Temperature Distribution (4 x 4 module)


solutions

CPV Performance Dependency- Concentration Temperature Irradiation- Concentration, Temperature, Irradiation

• Output voltage decreases with increase in temperature - weakOutput current decreases with decrease in irradiation linear


• Output current decreases with decrease in irradiation - linear

CPV Reliability Dependency• Tj = 100oC, lifetime expectancy is ~20 kHr

• 10oC cooling extends lifetime by ~40%

(kH

r)

• Tj ~ 70oC required for 50 - 60 kHr of lifetime

Life

time

• Cooling improves long-term reliability


• Cooling improves long-term reliability• Longer lifetime increases net $ gain

CPV Optical EfficiencyPrimary/Fresnel

Lens

Irradiance distribution over rod entry aperture (11 mm sq.)

Optical RodIrradiance distribution over cell (5.5 mm sq.)

Power generation is limited by die hot-spot temperatures and the minimum density of

Model MeasuredPrimary Lens Efficiency 89% 84%Optical Rod Efficiency 96% 95%


irradiationp y

System Efficiency 85% 80%

Secondary Entry Irradiation DistributionDistributionProjected area into the secondary aperture is much smaller for

(L) with no deviation (R) with 1o deviation 10% loss

smaller for tolerance to whole system

Acceptance

Poor system thermal management increases

ti l i li t phalf-angle

(±1o)

optical misalignment, causing further losses in efficiency


CPV Economics

“Bring installed cost down below $2/W, d h ld i !”Cost

($/kWh)and the world is yours!”

Price: grid electricity

Cost: CPV electricity

Grid Parity

Time (years)


Strategy driver Lowest $/W

CPV Cost Break-Down (Example)

S t C t B k D ($/W)System Cost Break‐Down ($/W)2010 2011 2012 2015 Notes

System Installed

6.25 5.25 3.00 2.00 all inclusive

Power Module ~40% of System

2.50 2.10 1.20 0.80 optics, die, heat sink

Rest of System ~60% of System 3.75 3.15 1.80 1.20

tracker, inverter, deployment


60% of System deployment

Typical thermal budget : 10 - 15% of module cost

CPV EconomicsSi l l l i ( l )

60

- Simple constant value analysis (case example)

40

50

$)

510

XLT (kHrs)LT (kHrs)55

60

65

20

30

Net Gain ($ 15

20

Default conditions: • 10mm die size

65

70

0

10

10mm die size• 1,000 suns• $0.28/kWh elec. price

20 25 30 35 40Efficiency (%)

Net gain increases with increase in:


Net gain increases with increase in:• long-term reliability • conversion efficiency

Heat-Sink Temperature Distributionp

Need low cost, light weight, high performance, uniform temperature solutions

Tj Management

Tj_typ = 100oC for long term reliability Performance gain ~3% over 20oC coolingg g InGaP/GaAs cells have excellent reliability up to 125oC Lowering Tj below 100oC for efficiency gain alone is

usually not compelling comes at a higher cost

Proper thermal management can improve optical Proper thermal management can improve opticalcharacteristics and efficiency by minimizing thermallyinduced distortions

Light weight thermal solutions reduce Light weight thermal solutions reduce the weight and cost of tracking systemand improves overall system reliability

Thermal Solutions

Passive aluminum heat-sink Active liquid cooling solutionPassive aluminum heat sink solution

Active liquid cooling solution

Design

10•10mm die•1000suns72 W•72 WT

Thermal Max HS temp = 90°C Max HS temp < 90°C

Weight 3.45 kg (attached to tracker) 0.15 kg (95% reduction)

78Seri Lee, EPTC 2010Light weight solution reduces the tracker loading,

reducing system cost and increasing reliability

Summary and Conclusions Ensure Tj_typ ≤ 100oC for meeting minimum reliability requirement

Lowering Tj improves efficiency, but usually not compelling enough

Enhance cooling for longer-term reliability to increase net gain in ROI

Proper system thermal management can prevent steep-loss of efficiency d t th ll i d d di t ti d d t i ti f tidue to thermally induced distortions and deterioration of optics

Light weight thermal solutions (attached to the local frame) reduce themechanical load on the tracker and improve system cost & reliability

Need low cost, high-performance, light weight thermal solutions

CPV thermal management should focus on: CPV thermal management should focus on: 1) improving long-term reliability2) maintaining and improving the power conversion efficiency


Thank You!Thank You!Thank You!Thank You!

That’s all folks!That s all, folks!

Bye for nowBye for now.

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Lecture 11- Solar Energy

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Transcript of Lecture 11- Solar Energy