concentrating collector serkan kapucu

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PHYS 471PHYS 471

Solar EnergySolar Energy --20042004--11

Concentrating CollectorsConcentrating Collectors

Instructor : Prof.Dr Ahmet EcevitInstructor : Prof.Dr Ahmet Ecevit

Prepared by:Prepared by:

Serkan KapucuSerkan Kapucu



Table of ContentsTable of Contents1.Introduction.......................................................41.Introduction.......................................................4

2.Concentrating collectors...................................52.Concentrating collectors...................................5

3.Types of concentrating collectors.....................63.Types of concentrating collectors.....................63.1. Parabolic trough system.............................73.1. Parabolic trough system.............................7

3.2. Parabolic dish system....3.2. Parabolic dish system.... ...........................11...........................11

3.3. Power tower system...................................143.3. Power tower system...................................14

3.4. Stationary concentrating solar collectors....163.4. Stationary concentrating solar collectors....16



4.Working principles of concentrating collectors..174.Working principles of concentrating collectors..17

4.1. Trough Systems..........................................184.1. Trough Systems..........................................18

4.2. Dish Systems...............................................214.2. Dish Systems...............................................21

4.3. Central Receiver Systems...........................234.3. Central Receiver Systems...........................23

5. Technology5. Technology ComparisonComparison...................................25...................................25

6. Calculations.......................................................286. Calculations.......................................................28

7. Economic and Environmental Considerations..377. Economic and Environmental Considerations..37

8. Conclusions.......................................................398. Conclusions.......................................................39References........................................................41References........................................................41



1. Introduction1. IntroductionF

or applications such as air conditioning, central power F

or applications such as air conditioning, central power generation, and numerous industrial heat requirements, flatgeneration, and numerous industrial heat requirements, flatplate collectors generally cannot provide carrier fluids atplate collectors generally cannot provide carrier fluids attemperatures sufficiently elevated to be effective. Theytemperatures sufficiently elevated to be effective. Theymay be used as firstmay be used as first--stage heat input devices; thestage heat input devices; thetemperature of the carrier fluid is then boosted by other temperature of the carrier fluid is then boosted by other

conventional heating means. Alternatively, more complexconventional heating means. Alternatively, more complexand expensive concentrating collectors can be used. Theseand expensive concentrating collectors can be used. Theseare devices that optically reflect and focus incident solar are devices that optically reflect and focus incident solar energy onto a small receiving area. As a result of thisenergy onto a small receiving area. As a result of thisconcentration, the intensity of the solar energy isconcentration, the intensity of the solar energy ismagnified, and the temperatures that can be achieved atmagnified, and the temperatures that can be achieved at

the receiver (called the "target") can approach severalthe receiver (called the "target") can approach severalhundred or even several thousand degrees Celsius. Thehundred or even several thousand degrees Celsius. Theconcentrators must move to track the sun if they are toconcentrators must move to track the sun if they are toperform effectively [1].perform effectively [1].



2. Concentrating2. Concentrating

collectorscollectorsConcentrating, or focusing, collectors intercept directConcentrating, or focusing, collectors intercept direct

radiation over a large area and focus it onto a smallradiation over a large area and focus it onto a small

absorber area. These collectors can provide highabsorber area. These collectors can provide hightemperatures more efficiently than flattemperatures more efficiently than flat--plate collectors, sinceplate collectors, since

the absorption surface area is much smaller. However,the absorption surface area is much smaller. However,

diffused sky radiation cannot be focused onto the absorber.diffused sky radiation cannot be focused onto the absorber.

Most concentrating collectors require mechanical equipmentMost concentrating collectors require mechanical equipmentthat constantly orients the collectors toward the sun andthat constantly orients the collectors toward the sun and

keeps the absorber at the point of focus. Thereforekeeps the absorber at the point of focus. Therefore;; therethere

are many types of concentrating collectors [2].are many types of concentrating collectors [2].



3. Types of concentrating3. Types of concentrating

collectorscollectors

ParabolicParabolic troughtrough systemsystem

ParabolicParabolic dishdish

Power Power tower tower

StationaryStationary concentratingconcentrating collectorscollectors

There are four basic types of concentrating collectors:



3.1. Parabolic trough3.1. Parabolic trough

systemsystemParabolic troughs are devices that are shaped like theParabolic troughs are devices that are shaped like theletter ³u´letter ³u´.. The troughs concentrate sunlight onto aThe troughs concentrate sunlight onto areceiver tube that is positioned along the focal line of thereceiver tube that is positioned along the focal line of thetrough. Sometimes a transparent glass tube envelops thetrough. Sometimes a transparent glass tube envelops the

receiver tube to reduce heat loss [3].receiver tube to reduce heat loss [3].

Figure 3.1.2 Parabolic trough system [3].Figure 3.1.1 Crossection of parabolic trough [4].

The parabolic trough sytem isThe parabolic trough sytem is

shown in the figure 3.1.2 below.shown in the figure 3.1.2 below.

TTheir shapes are like letter heir shapes are like letter ³u´³u´

as shown figure 3.1.1 below.as shown figure 3.1.1 below.



Parabolic troughs often use singleParabolic troughs often use single--axis or dualaxis or dual--axisaxis

trackingtracking..

Figure 3.1.3 One Axis Tracking Parabolic Trough

with Axis Oriented E-W [8].

Figure 3.1.4 Two Axis Tracking Concentrator [8].Axis Tracking Concentrator [8].

The below figure 3.1.3 shows one axisThe below figure 3.1.3 shows one axis

tracking parabolic trough with axistracking parabolic trough with axis

oriented Eoriented E--W.W.

The below figure 3.1.4 shows twoThe below figure 3.1.4 shows two

axis tracking concentrator.axis tracking concentrator.



Temperatures at the receiver can reach 400Temperatures at the receiver can reach 400 °°C andC andproduce steam for generating electricity. In California,produce steam for generating electricity. In California,

multimulti--megawatt power plants were built using parabolicmegawatt power plants were built using parabolictroughs combined with gas turbines [3].troughs combined with gas turbines [3].

Parabolic trough combined with gas turbines is shownParabolic trough combined with gas turbines is shownfigure 3.1.5 below.figure 3.1.5 below.

Figure 3.1.5 Parabolic trough combined with gas turbines [4].



Cost projections for trough technology are higher thanCost projections for trough technology are higher thanthose for power towers and dish/engine systems due inthose for power towers and dish/engine systems due inlarge part to the lower solar concentration and hencelarge part to the lower solar concentration and hencelower temperatures and efficiency.However with longlower temperatures and efficiency.However with longoperating experience, continued technologyoperating experience, continued technologyimprovements, and operating and maintenance costimprovements, and operating and maintenance costreductions, troughs are the least expensive, mostreductions, troughs are the least expensive, mostreliable solar thermal power production technology for reliable solar thermal power production technology for near near--term [4].term [4].



3.2. Parabolic dish3.2. Parabolic dish

systemssystems A parabolic dish collector is similar in appearance to A parabolic dish collector is similar in appearance to

a large satellite dish, but has mirror a large satellite dish, but has mirror--like reflectorslike reflectors

and an absorber at the focal point. It uses a dualand an absorber at the focal point. It uses a dual

axis sun tracker [3].axis sun tracker [3].

Figure 3.2.2 Parabolic dish collector with a mirror-

like reflectors and an absorber at the focal point[Courtesy of SunLabs - Department of Energy] [3].

Figure 3.2.1 Crossection of parabolic dish [4].

The below figure 3.2.1 showsThe below figure 3.2.1 shows

crossection of parabolic dish.crossection of parabolic dish.

The Parabolic dish collector isThe Parabolic dish collector is

shown in the below figure 3.2.2.shown in the below figure 3.2.2.



A parabolic dish system uses a computer to track the sun A parabolic dish system uses a computer to track the sunand concentrate the sun's rays onto a receiver located at theand concentrate the sun's rays onto a receiver located at thefocal point in front of the dish.focal point in front of the dish. In some systems, a heatIn some systems, a heat

engine, such as a Stirling engine, is linked to the receiver toengine, such as a Stirling engine, is linked to the receiver togenerate electricity. Parabolic dish systems can reach 1000generate electricity. Parabolic dish systems can reach 1000°°C at the receiver, and achieve the highest efficiencies for C at the receiver, and achieve the highest efficiencies for converting solar energy to electricity in the smallconverting solar energy to electricity in the small--power power capacity range [3].capacity range [3].

Figure 3.2.3 Solar dish stirling engine [9].

The right figure 3.2.3The right figure 3.2.3

shows the solar dishshows the solar dish

stirling engine.stirling engine.



Engines currently under consideration include StirlingEngines currently under consideration include Stirling

and Brayton cycle engines. Several prototypeand Brayton cycle engines. Several prototype

dish/engine systems, ranging in size from 7 to 25 kWdish/engine systems, ranging in size from 7 to 25 kW

have been deployed in various locations in the USA.have been deployed in various locations in the USA.

High optical efficiency and low start up losses makeHigh optical efficiency and low start up losses makedish/engine systems the most efficient of all solar dish/engine systems the most efficient of all solar

technologies. A Stirling engine/parabolic dish systemtechnologies. A Stirling engine/parabolic dish system

holds the world¶s record for converting sunlight intoholds the world¶s record for converting sunlight into

electricity.In 1984, a 29% net efficiency waselectricity.In 1984, a 29% net efficiency wasmeasured at Rancho Mirage, California [4].measured at Rancho Mirage, California [4].



3.3. Power tower system3.3. Power tower system A heliostat uses a field of dual axis sun trackers that A heliostat uses a field of dual axis sun trackers thatdirect solar energy to a large absorber located on adirect solar energy to a large absorber located on a

tower. To date the only application for the heliostattower. To date the only application for the heliostat

collector is power generation in a system called thecollector is power generation in a system called the

power tower power tower [3].[3].

Figure 3.3.2 Heliostats [4].Figure 3.3.2 Heliostats [4].Figure 3.3.1 Power tower system [4].

Heliostats are shown inHeliostats are shown in

the figure 3.3.2 below.the figure 3.3.2 below.

The Power tower system isThe Power tower system is

shown in the figure 3.3.1 below.shown in the figure 3.3.1 below.



A power tower has a field of large mirrors that follow A power tower has a field of large mirrors that followthe sun's path across the sky. The mirrors concentratethe sun's path across the sky. The mirrors concentratesunlight onto a receiver on top of a high tower. Asunlight onto a receiver on top of a high tower. A

computer keeps the mirrors aligned so the reflectedcomputer keeps the mirrors aligned so the reflectedrays of the sun are always aimed at the receiver, whererays of the sun are always aimed at the receiver, wheretemperatures well above 1000temperatures well above 1000°°C can beC can be reached.reached. HighHigh--pressure steam is generated to produce electricity [3].pressure steam is generated to produce electricity [3].

The power tower system with heliostats is shown in theThe power tower system with heliostats is shown in the

figure 3.3.3 below.figure 3.3.3 below.

Figure 3.3.3 Power tower system with heliostats [4].



3.4. Stationar y concentrating3.4. Stationar y concentrating

solar collectorssolar collectors

Stationary concentrating collectors use compoundStationary concentrating collectors use compoundparabolic reflectors and flat reflectors for directing solar parabolic reflectors and flat reflectors for directing solar energy to an accompanying absorber or aperture throughenergy to an accompanying absorber or aperture througha wide acceptance angle. The wide acceptance angle for a wide acceptance angle. The wide acceptance angle for these reflectors eliminates the need for a sunthese reflectors eliminates the need for a sun tracker.tracker.This class of collector includes parabolic trough flat plateThis class of collector includes parabolic trough flat platecollectors, flat plate collectors with parabolic boostingcollectors, flat plate collectors with parabolic boosting

reflectors, andreflectors, and solar cooker. Development of the first twosolar cooker. Development of the first twocollectors has been done in Sweden.collectors has been done in Sweden. Solar cookers areSolar cookers areused throughout the world, especially in the developingused throughout the world, especially in the developingcountries [3].countries [3].



4. Working principles of 4. Working principles of

concentrating collectorsconcentrating collectorsUnlike solar (photovoltaic) cells, which use light to produceUnlike solar (photovoltaic) cells, which use light to produceelectricity, concentrating solar power systems generateelectricity, concentrating solar power systems generateelectricity with heat. Concentrating solar collectors useelectricity with heat. Concentrating solar collectors usemirrors and lenses to concentrate and focus sunlight ontomirrors and lenses to concentrate and focus sunlight ontoa thermal receiver, similar to a boiler tube. The receiver a thermal receiver, similar to a boiler tube. The receiver absorbs and converts sunlight into heat. The heat is thenabsorbs and converts sunlight into heat. The heat is thentransported to a steam generator or engine where it istransported to a steam generator or engine where it isconverted into electricity. There are three main types of converted into electricity. There are three main types of concentrating solar power systems: parabolic troughs,concentrating solar power systems: parabolic troughs,dish/engine systems, and central receiver systems.dish/engine systems, and central receiver systems.

These technologies can be used to generate electricity for These technologies can be used to generate electricity for a variety of applications, ranging from remote power a variety of applications, ranging from remote power systems as small as a few kilowatts (kW) up to gridsystems as small as a few kilowatts (kW) up to gridconnected applications of 200connected applications of 200--350 megawatts (MW) or 350 megawatts (MW) or more. A concentrating solar power system that producesmore. A concentrating solar power system that produces350 MW of electricity displaces the energy equivalent of 350 MW of electricity displaces the energy equivalent of

2.3 million barrels of oil [5].2.3 million barrels of oil [5].



4.1. Trough Systems4.1. Trough SystemsThese solar collectors use mirrored parabolic troughs toThese solar collectors use mirrored parabolic troughs tofocus the sun's energy to a fluidfocus the sun's energy to a fluid--carrying receiver tubecarrying receiver tubelocated at the focal point of a parabolically curved troughlocated at the focal point of a parabolically curved troughreflector reflector [5].It is shown in the figure 4.1.1 below.[5].It is shown in the figure 4.1.1 below.

Figure 4.1.1 Parabolic trough with mirrored parabolic troughs [10].



The energy from the sun sent to the tube heats oilThe energy from the sun sent to the tube heats oilflowing through the tube, and the heat energy is thenflowing through the tube, and the heat energy is thenused to generate electricity in a conventional steamused to generate electricity in a conventional steamgenerator. Many troughs placed in parallel rows aregenerator. Many troughs placed in parallel rows arecalled a "collector field." The troughs in the field arecalled a "collector field." The troughs in the field areall aligned along a northsouth axis so they can trackall aligned along a northsouth axis so they can trackthe sun from east to west during the day, ensuringthe sun from east to west during the day, ensuringthat the sun is continuously focused on the receiver that the sun is continuously focused on the receiver pipes. Individual trough systems currently canpipes. Individual trough systems currently can

generate about 80 MW of electricity.generate about 80 MW of electricity.



Trough designs can incorporate thermal storageTrough designs can incorporate thermal storage--

setting aside the heat transfer fluid in its hot phasesetting aside the heat transfer fluid in its hot phase

allowing for electricity generation several hours intoallowing for electricity generation several hours into

the evening. Currently, all parabolic trough plants arethe evening. Currently, all parabolic trough plants are"hybrids," meaning they use fossil fuels to"hybrids," meaning they use fossil fuels to

supplement the solar output during periods of lowsupplement the solar output during periods of low

solar radiation. Typically, a natural gassolar radiation. Typically, a natural gas--fired heat or afired heat or a

gas steam boiler/gas steam boiler/reheater reheater is used. Troughs also canis used. Troughs also can

be integrated with existing coalbe integrated with existing coal--fired plants [5].fired plants [5].



4.2. Dish Systems4.2. Dish SystemsDish systems use dishDish systems use dish--shaped parabolic mirrors asshaped parabolic mirrors as

reflectors to concentrate and focus the sun's rays onto areflectors to concentrate and focus the sun's rays onto areceiver, which is mounted above the dish at the dishreceiver, which is mounted above the dish at the dish

centcenter er. A dish/engine system is a stand alone unit. A dish/engine system is a stand alone unit

composed primarily of a collector, a receiver, and ancomposed primarily of a collector, a receiver, and an

engine.I

t works by collecting and concentrating the sun'sengine.I

t works by collecting and concentrating the sun'senergy with a dishshaped surface onto a receiver thatenergy with a dishshaped surface onto a receiver that

absorbs the energy and transfers it to the engine. Theabsorbs the energy and transfers it to the engine. The

engine then converts that energy to heat. The heat isengine then converts that energy to heat. The heat is

then converted to mechanical power, in a manner similar then converted to mechanical power, in a manner similar

to conventional engines, by compressing the workingto conventional engines, by compressing the workingfluid when it is cold, heating the compressed workingfluid when it is cold, heating the compressed working

fluid, and then expanding it through a turbine or with afluid, and then expanding it through a turbine or with a

piston to produce mechanical power. An electricpiston to produce mechanical power. An electric

generator or alternator converts the mechanical power generator or alternator converts the mechanical power

into electrical power.into electrical power.



Each dish produces 5 to 50 kW of electricity and canEach dish produces 5 to 50 kW of electricity and canbe used independently or linked together to increasebe used independently or linked together to increasegenerating capacity. A 250generating capacity. A 250--kW plant composed of kW plant composed of

ten 25ten 25--kW dish/engine systems requires less than ankW dish/engine systems requires less than anacre of land. Dish/engine systems are notacre of land. Dish/engine systems are notcommercially available yet, although ongoingcommercially available yet, although ongoingdemonstrations indicate good potential. Individualdemonstrations indicate good potential. Individualdish/engine systems currently can generate about 25dish/engine systems currently can generate about 25

kW of electricity. More capacity is possible bykW of electricity. More capacity is possible byconnecting dishes together connecting dishes together.. These systems can beThese systems can becombined with natural gas, and the resulting hybridcombined with natural gas, and the resulting hybridprovides continuous power generation [5].provides continuous power generation [5].

Figure 4.2.1 Combination of parabolic dish system [4].

The right figure 4.2.1The right figure 4.2.1

shows the combination of shows the combination of

parabolic dish system.parabolic dish system.



4.3. Central Receiver Systems4.3. Central Receiver SystemsCentral receivers (or power towers) use thousands of Central receivers (or power towers) use thousands of individual sunindividual sun--tracking mirrors called "heliostats" totracking mirrors called "heliostats" toreflect solar energy onto a receiver located on top of tallreflect solar energy onto a receiver located on top of talltower. The receiver collects the sun's heat in a heattower. The receiver collects the sun's heat in a heat--transfer fluid (molten salt) that flows through thetransfer fluid (molten salt) that flows through thereceiver. The salt's heat energy is then used to makereceiver. The salt's heat energy is then used to makesteam to generate electricity in a conventional steamsteam to generate electricity in a conventional steamgenerator, located at the foot of the tower. The moltengenerator, located at the foot of the tower. The moltensalt storage system retains heat efficiently, so it can besalt storage system retains heat efficiently, so it can bestored for hours or even days before being used tostored for hours or even days before being used to

generate electricity [5]. In this system, moltengenerate electricity [5]. In this system, molten--salt issalt ispumped from a ³cold´ tank at 288 deg.C and cycledpumped from a ³cold´ tank at 288 deg.C and cycledthrough the receiver where it is heated to 565 deg.Cthrough the receiver where it is heated to 565 deg.Cand returned to a ³hot´ tank. The hot salt can then beand returned to a ³hot´ tank. The hot salt can then beused to generate electricity when needed. Currentused to generate electricity when needed. Currentdesigns allow storage ranging from 3 to 13 hours [4].designs allow storage ranging from 3 to 13 hours [4].



Figure 4.3.1 The process of molten salt storage [11].

Figure 4.3.1 shows the process of molten salt storage.Figure 4.3.1 shows the process of molten salt storage.



5. Technology Comparison5. Technology ComparisonTowers and troughs are best suited for large, gridTowers and troughs are best suited for large, grid--

connected power projects in the 30connected power projects in the 30--200 MW size,200 MW size,

whereas, dish/engine systems are modular and can bewhereas, dish/engine systems are modular and can be

used in single dish applications or grouped in dish farmsused in single dish applications or grouped in dish farms

to create larger multito create larger multi--megawatt projects. Parabolicmegawatt projects. Parabolictrough plants are the most mature solar power trough plants are the most mature solar power

technology available today and the technology mosttechnology available today and the technology most

likely to be used for near likely to be used for near--term deployments. Power term deployments. Power

towers, with low cost and efficient thermal storage,towers, with low cost and efficient thermal storage,

promise to offer dispatchable, high capacity factor, solar promise to offer dispatchable, high capacity factor, solar--

only power plants in the near future.only power plants in the near future.



The modular nature of dishes will allow them to be used inThe modular nature of dishes will allow them to be used in

smaller, highsmaller, high--value applications. Towers and dishes offer value applications. Towers and dishes offer the opportunity to achieve higher solar the opportunity to achieve higher solar--toto--electricelectricefficiencies and lower cost than parabolic trough plants,efficiencies and lower cost than parabolic trough plants,but uncertainty remains as to whether these technologiesbut uncertainty remains as to whether these technologiescan achieve the necessary capital cost reductions andcan achieve the necessary capital cost reductions and

availability improvements. Parabolic troughs are currentlyavailability improvements. Parabolic troughs are currentlya proven technology primarily waiting for an opportunity toa proven technology primarily waiting for an opportunity tobe developed. Power towers require the operability andbe developed. Power towers require the operability andmaintainability of the moltenmaintainability of the molten--salt technology to besalt technology to bedemonstrated and the development of low cost heliostats.demonstrated and the development of low cost heliostats.Dish/engine systems require the development of at leastDish/engine systems require the development of at leastone commercial engine and the development of a low costone commercial engine and the development of a low costconcentrator concentrator [4].[4].



ParabolicTroughParabolicTrough Dish/EngineDish/Engine Power Tower Power Tower

SizeSize 3030--320 MW320 MW 55--25 kW25 kW 1010--200 MW200 MW

Operating TemperatureOperating Temperature

(ºC/ºF)(ºC/ºF)390/734390/734 750/1382750/1382 565/1049565/1049

Annual Capacity Factor Annual Capacity Factor 2323--50 %50 % 25 %25 % 2020--77 %77 %

Peak EfficiencyPeak Efficiency 20%(d)20%(d) 29.4%(d)29.4%(d) 23%(p)23%(p)

Net Annual EfficiencyNet Annual Efficiency 11(d)11(d)--16%16% 1212--25%(p)25%(p) 7(d)7(d)--20%20%

Commercial StatusCommercial StatusCommercially ScaleCommercially Scale--upup

PrototypePrototypeDemonstrationDemonstration AvailableDemonstration AvailableDemonstration

TechnologyTechnology

Development RiskDevelopment RiskLowLow HighHigh MediumMedium

Storage AvailableStorage Available LimitedLimited BatteryBattery YesYes

Hybrid DesignsHybrid Designs YesYes YesYes YesYes

Cost USD/WCost USD/W 2,72,7--4,04,0 1,31,3--12,612,6 2,52,5--4,44,4

(p) = predicted; (d) = demonstrated;

Table 5.1 Key features of the three solar technologies [4].

Table 5.1 highlights the key features of the three solar technologies.Table 5.1 highlights the key features of the three solar technologies.



6. Calculations6. Calculations

Heat from a solar collector may be used to drive a heatHeat from a solar collector may be used to drive a heat

engine operating in a cycle to produce work. A heatengine operating in a cycle to produce work. A heat

engine may be used for such applications as water engine may be used for such applications as water pumping and generating electricity.pumping and generating electricity.

The thermal output QThe thermal output Qoutout of a concentrating collector of a concentrating collector

operating at temperature T is given byoperating at temperature T is given by

QQoutout = F'[= F'[gammagamma.A.Aininqqinin -- U.AU.Arecrec(T(T -- TTaa)],)],

A Ainin :: the area of the incident solar radiation (the area of the incident solar radiation (mm22).).



A Arecrec :: the area of the receiver (the area of the receiver (mm22))

gamma:optical efficiencygamma:optical efficiency

qqinin : the incident solar irradiation (: the incident solar irradiation (W/mW/m22))

TTaa :the ambient temperature (:the ambient temperature (°°CC))

U :the heat loss coefficient (U :the heat loss coefficient (W/mW/m22KK))

F¶ :collector efficiency factor F¶ :collector efficiency factor

The quantity AThe quantity Ainin/A/Arecrec is called theis called the concentration ratioconcentration ratio..



High concentration ratios are obtained by making AHigh concentration ratios are obtained by making Ainin thethearea of a system of mirrors designed to concentrate thearea of a system of mirrors designed to concentrate the

solar radiation received onto a small receiver of area Asolar radiation received onto a small receiver of area Arecrec..

Heat losses from the receiver are reduced by the smaller Heat losses from the receiver are reduced by the smaller

size of the receiver. Consequently, high concentrationsize of the receiver. Consequently, high concentration

ratios give high collector temperatures. The stagnationratios give high collector temperatures. The stagnation

temperature Ttemperature Tmaxmax is given by:is given by:

gammagamma.A.Aininqqinin = U.A= U.Arecrec(T(Tmaxmax -- TTaa).).



For example, if the optical efficiency isFor example, if the optical efficiency is gammagamma = 0.8,= 0.8,

the incident solar irradiation is qthe incident solar irradiation is qinin = 800W/m= 800W/m22, the, the

ambient temperature is Tambient temperature is Taa = 30= 30°°C, and the heat lossC, and the heat loss

coefficient is U = 10W/mcoefficient is U = 10W/m22K, then a concentration ratioK, then a concentration ratio

A Ainin/A/Arecrec = 1 (no concentration) gives T= 1 (no concentration) gives Tmaxmax = 94= 94°°C, and aC, and a

concentration ratio Aconcentration ratio Ainin/A/Arecrec = 10 gives T= 10 gives Tmaxmax = 670= 670°°C.C.



The collector efficiencyThe collector efficiency et aet acc at operating temperature T isat operating temperature T is

et aet acc=Q=Qoutout/A/Aininqqinin = F'[= F'[gammagamma--U.AU.Arecrec(T(T --TTaa)/A)/Aininqqinin]]

= F'= F'gammagamma(T(Tmaxmax -- T)/(TT)/(Tmaxmax -- TTaa).).

The available mechanical power from the thermal power The available mechanical power from the thermal power

output of the collector that would be obtained using a Carnotoutput of the collector that would be obtained using a Carnot

cycle is Qcycle is Qoutout(1(1 -- TTaa/T), where the temperatures are absolute/T), where the temperatures are absolute

temperatures.temperatures.



TheThe second law efficiencysecond law efficiency et aet a22 of a heat engine isof a heat engine is

defined bydefined by

et aet a22=(mechanical power delivered)=(mechanical power delivered)

/(available mechanical power)./(available mechanical power).

Suppose a heat engine with second law efficiencySuppose a heat engine with second law efficiency et aet a22

uses as input the thermal power Quses as input the thermal power Qoutout from the solar from the solar

collector. The first law efficiency of the engine iscollector. The first law efficiency of the engine is

et aet a11 = (mechanical power delivered)/Q= (mechanical power delivered)/Qoutout == et aet a22(1(1 -- TTaa/T),/T),



where Twhere Tmaxmax depends on the design of the collector anddepends on the design of the collector andon the solar radiation input qon the solar radiation input qinin. Now, given F',. Now, given F', gammagamma,,et aet a22, T, Taa, and T, and Tmaxmax, we can find the maximum efficiency, we can find the maximum efficiencyobtainable, and the optimum operating temperature Tobtainable, and the optimum operating temperature Toptopt

from the condition d(from the condition d(et aet a)/dT = 0. This occurs at the)/dT = 0. This occurs at the

optimum temperatureoptimum temperatureTToptopt = [T= [TmaxmaxTTaa],],

and the maximum efficiency is obtained by puttingand the maximum efficiency is obtained by putting

T = TT = Toptopt in the equationin the equation

et a

et a ==

et a

et acc..

et a

et a11..

½½



For example, putting F' = 0.9,For example, putting F' = 0.9, gammagamma = 0.8,= 0.8, et aet a22 = 0.6,= 0.6,

TTaa = 30= 30°°C = 303K, we get the efficienciesC = 303K, we get the efficiencies et aet amaxmax for for

different degrees of concentration shown in Table 6.1.different degrees of concentration shown in Table 6.1.

Very low overall efficiencies are obtained unlessVery low overall efficiencies are obtained unlessoperating temperatures greater than 500operating temperatures greater than 500°°C are used.C are used.

Expensive concentrating systems are needed to reachExpensive concentrating systems are needed to reach

these high temperatures, so commercial viability isthese high temperatures, so commercial viability is

difficult [12].difficult [12].



Efficiencies for Converting Solar Radiation to WorkEfficiencies for Converting Solar Radiation to Work

TTmaxmax TToptopt etaetamaxmax

100100°°CC 6363°°CC 2.2%2.2%

200200°°CC 106106°°CC 4.8%4.8%

400400°°CC 179179°°CC 8.5%8.5%

800800°°CC 297297°°CC 13.2%13.2%

16001600°°CC 480480°°CC 18.4%18.4%

Table 6.1. Different degrees of concentration [12].



7. Economic and Environmental7. Economic and Environmental

ConsiderationsConsiderationsThe most important factor driving the solar energyThe most important factor driving the solar energysystem design process is whether the energy itsystem design process is whether the energy itproduces is economical. Although there are factors other produces is economical. Although there are factors other

than economics that enter into a decision of when to usethan economics that enter into a decision of when to usesolar energy; i.e. no pollution, no greenhouse gassolar energy; i.e. no pollution, no greenhouse gasgeneration, security of the energy resource etc., designgeneration, security of the energy resource etc., designdecisions are almost exclusively dominated by thedecisions are almost exclusively dominated by theµlevelized energy cost¶. This or some similar economicµlevelized energy cost¶. This or some similar economic

parameter, gives the expected cost of the energyparameter, gives the expected cost of the energyproduced by the solar energy system, averaged over theproduced by the solar energy system, averaged over thelifetime of the systemlifetime of the system..



Commercial applications from a few kilowatts toCommercial applications from a few kilowatts tohundreds of megawatts are now feasible, and plantshundreds of megawatts are now feasible, and plants

totaling 354 MW have been in operation in Californiatotaling 354 MW have been in operation in Californiasince the 1980s. Plants can function in dispatchable,since the 1980s. Plants can function in dispatchable,gridgrid--connected markets or in distributed, standconnected markets or in distributed, stand--alonealoneapplications. They are suitable for fossilapplications. They are suitable for fossil--hybrid operationhybrid operationor can include costor can include cost--effective storage to meeteffective storage to meet

dispatchability requirements. They can operatedispatchability requirements. They can operateworldwide in regions having high beamworldwide in regions having high beam--normalnormalinsolation, including large areas of the southwesterninsolation, including large areas of the southwesternUnited States, and Central and South America, Africa,United States, and Central and South America, Africa,

Australia, China, India, the Mediterranean region, and Australia, China, India, the Mediterranean region, and

the Middle East, . Commercial solar plants havethe Middle East, . Commercial solar plants haveachieved levelized energy costs of about 12achieved levelized energy costs of about 12--15¢/kWh,15¢/kWh,and the potential for cost reduction are expected toand the potential for cost reduction are expected toultimately lead to costs as low as 5¢/kWh [6].ultimately lead to costs as low as 5¢/kWh [6].



8. Conclusions8. Conclusions

Concentrating solar power technology for electricityConcentrating solar power technology for electricitygeneration is ready for the market. Various types of generation is ready for the market. Various types of single and dualsingle and dual--purpose plants have been analysedpurpose plants have been analysedand tested in the field. In addition, experience has beenand tested in the field. In addition, experience has beengained from the first commercial installations in usegained from the first commercial installations in use

worldwide since the beginning of the 1980s. Solar worldwide since the beginning of the 1980s. Solar thermal power plants will, within the next decade,thermal power plants will, within the next decade,provide a significant contribution to an efficient,provide a significant contribution to an efficient,economical and environmentally benign energy supplyeconomical and environmentally benign energy supplyboth in largeboth in large--scale gridconnected dispatchable marketsscale gridconnected dispatchable markets

and remote or modular distributed markets. Parabolicand remote or modular distributed markets. Parabolicand Fresnel troughs, central receivers and parabolicand Fresnel troughs, central receivers and parabolicdishes will be installed for solar/fossil hybrid and solar dishes will be installed for solar/fossil hybrid and solar--only power plant operation. In parallel, decentralisedonly power plant operation. In parallel, decentralisedprocess heat for industrial applications will be providedprocess heat for industrial applications will be providedby lowby low--cost concentrated collectors.cost concentrated collectors.



Following a subsidised introduction phase in greenFollowing a subsidised introduction phase in greenmarkets, electricity costs will decrease from 14 to 18markets, electricity costs will decrease from 14 to 18

Euro cents per kilowatt hour presently in SouthernEuro cents per kilowatt hour presently in SouthernEurope towards 5 to 6 Euro cents per kilowatt hour inEurope towards 5 to 6 Euro cents per kilowatt hour inthe near future at good sites in the countries of thethe near future at good sites in the countries of theEarth¶s sunbelt. After that, there will be no further Earth¶s sunbelt. After that, there will be no further additional cost in the emission reduction by CSP.additional cost in the emission reduction by CSP.

This, and the vast potential for bulk electricityThis, and the vast potential for bulk electricitygeneration, moves the goal of longterm stabilisationgeneration, moves the goal of longterm stabilisationof the global climate into a realistic range. Moreover,of the global climate into a realistic range. Moreover,the problem of sustainable water resources andthe problem of sustainable water resources anddevelopment in arid regions is addressed in andevelopment in arid regions is addressed in an

excellent way, making use of highly efficient, solar excellent way, making use of highly efficient, solar powered copowered co--generation systems. However, during thegeneration systems. However, during theintroduction phase, strong political and financialintroduction phase, strong political and financialsupport from the responsible authorities is stillsupport from the responsible authorities is stillrequired, and many barriers must be overcome [7].required, and many barriers must be overcome [7].



ReferencesReferences

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bereiche/comenius/charles/solar.htmlbereiche/comenius/charles/solar.html

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r1/Chapter1.htmlr1/Chapter1.html

[7]http://www.eere.energy.gov/[7]http://www.eere.energy.gov/[8]http://rredc.nrel.gov/solar/pubs/redbook/[8]http://rredc.nrel.gov/solar/pubs/redbook/

interp.htmlinterp.html



[9]http://www.sunwindsolar.com/a solar/[9]http://www.sunwindsolar.com/a solar/optics htmloptics html

[10]http://www.eere.energy/gov/solar/solar.[10]http://www.eere.energy/gov/solar/solar.

heating htmlheating html

[11]http://www.energylan.sandia.gov/sunlab/[11]http://www.energylan.sandia.gov/sunlab/

stfuture.htmlstfuture.html

[12]http://www.jgsee.kmutt.ac.th/exell/Solar/[12]http://www.jgsee.kmutt.ac.th/exell/Solar/

Conversion.htmlConversion.html

concentrating collector serkan kapucu

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