concentrating solar collectors

8/8/2019 Concentrating Solar Collectors

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CONCENTRATINGCONCENTRATING

SOLAR COLLECTORSSOLAR COLLECTORS

Submitted by Submitted by

Kundan kumar Kundan kumar

05012274070501227407

Mechanical engg Mechanical engg



IntroductionIntroduction

Concentrating collector denotes the wholeConcentrating collector denotes the wholesystem where concentrator used for thesystem where concentrator used for theoptical subsystem which directs the solar optical subsystem which directs the solar

radiation onto the absorber while the termradiation onto the absorber while the termcollector or receiver will be used to denote thecollector or receiver will be used to denote thesubsystem consisting of absorber, its cover subsystem consisting of absorber, its cover and accessories.and accessories.

Concentrating of solar radiation is achievedConcentrating of solar radiation is achievedby using reflecting arrangement of mirror by using reflecting arrangement of mirror or refractive management of lenses. Theseor refractive management of lenses. Theseoptical system directs the solar radiationoptical system directs the solar radiationonto an absorber of smaller area which isonto an absorber of smaller area which isusuall surrounded b a transparent cover usuall surrounded b a transparent cover ..



HistoryHistory

I t has been in use for the past 4000I t has been in use for the past 4000years.years.

Egyptians used the solar energy andEgyptians used the solar energy and the solar cookers for their daily purposes. the solar cookers for their daily purposes.

Archimedes has solar reflectors to burn Archimedes has solar reflectors to burn

Romans in a war and the modern solar Romans in a war and the modern solar concentrators are the modification of concentrators are the modification of Archimedes mirrored solar reflectors Archimedes mirrored solar reflectors



NeedsNeeds

These are the areas where this technology can beThese are the areas where this technology can beusedused

Solar furnaceSolar furnace Solar cooker or ovenSolar cooker or oven Solar dryersSolar dryers PhotoPhoto--voltaic cellvoltaic cell For producing electricityFor producing electricity As solar reflectors in warfare As solar reflectors in warfare



Working principleWorking principle

Beyond the earth's atmosphere the intensity of sunlight is about 1,350 Beyond the earth's atmosphere the intensity of sunlight is about 1,350watts per square meter (429 British thermal units [ B tu] per hour per watts per square meter (429 British thermal units [ B tu] per hour per square foot).square foot). Passage through the atmospherePassage through the atmospheredepletes the intensity due to absorption by the various gases and vaporsdepletes the intensity due to absorption by the various gases and vaporsin the air and by scattering from these gases and vaporsin the air and by scattering from these gases and vapors

and from particles of dust and ice also in the air.and from particles of dust and ice also in the air. Thus, sunlightThus, sunlightreaching the earth is a mixture of direct (unscattered) and diffusereaching the earth is a mixture of direct (unscattered) and diffuse(scattered) radiation.(scattered) radiation. At sea level the intensity is At sea level the intensity isreduced to approximately 1,000 watts/square meter (295 reduced to approximately 1,000 watts/square meter (295 B tu/hour/square foot) on a bright clear day. B tu/hour/square foot) on a bright clear day. The intensity is further The intensity is further reducedreducedon overcast days.on overcast days.

Most concentrators utilize direct radiation only.Most concentrators utilize direct radiation only. These concentratorsThese concentratorswork well on bright clear days, poorly on hazy days, andwork well on bright clear days, poorly on hazy days, andnot at all on drab gray days when the sunlight intensity isnot at all on drab gray days when the sunlight intensity isreduced and the light consists principally of diffuse radiation.reduced and the light consists principally of diffuse radiation.

Another limiting factor is that the sun is not a point but has a Another limiting factor is that the sun is not a point but has adiameter equivalent to about onediameter equivalent to about one--half degree of arc.half degree of arc. Concentrator Concentrator

design must consider this arc.design must consider this arc.



classificationclassification There are many ways to characterizeThere are many ways to characterize

concentrators.concentrators. These include:These include:

oo Means of concentrationMeans of concentration----reflection or reflection or refractionrefraction

oo Point, line, or nonPoint, line, or non--focusing focusing

oo Fixed or tracking concentrator Fixed or tracking concentrator oo Fixed or tracking receiver Fixed or tracking receiver



Means of collectionMeans of collection



Point coll

ector

Point coll

ector Fig 8. illustrates the centralFig 8. illustrates the central

receiver concept whereinreceiver concept whereinheliostats (flatheliostats (flator slightly curved mirrorsor slightly curved mirrorsmounted on tracking devices)mounted on tracking devices)redirectredirect

the sun's rays toward a receiverthe sun's rays toward a receiveratop a toweratop a tower

Fig 7. a parabolic dish utilizesFig 7. a parabolic dish utilizesoptical properties of theoptical properties of theparabolic curved surface toparabolic curved surface toconcentrateconcentrate

direct light to the focaldirect light to the focalpoint.point. The dish geometry isThe dish geometry isfamiliar being used forfamiliar being used forautomobile headlights,automobile headlights,searchlights,searchlights,radar, and to receiveradar, and to receivetransmissions from broadcasttransmissions from broadcast

satellites.satellites.



Linear lensLinear lens



Hemispherical bowl collector Hemispherical bowl collector



NonNon--focusing collectorsfocusing collectors



Improvements in collectorsImprovements in collectors



GraphGraph



Annual collection efficiencyAnnual collection efficiency

Collectors that maintain their surfaces facing theCollectors that maintain their surfaces facing thesun (right angle for most collectors) have thesun (right angle for most collectors) have thehighest annual collection efficiency.highest annual collection efficiency. The parabolicThe parabolicdish and other twodish and other two--axis tracking collectors areaxis tracking collectors areexamples.examples.

The central receiver has low collection efficiencyThe central receiver has low collection efficiency than disc than disc

The parabolic trough is a single-axis trackingsystem; thus, the surface is only occasionally at aright angle to the sun and has a lower annualcollection efficiency than the central receiver.



Fixed collectors with tracking receivers such as the bowl andFixed collectors with tracking receivers such as the bowl andRussell collector have even lower collection efficiency.Russell collector have even lower collection efficiency. TheTheleast efficiency is exhibited by Winston and other fixedleast efficiency is exhibited by Winston and other fixedcollectors and receivers.collectors and receivers.

The theoretical annual efficiency of the three principalThe theoretical annual efficiency of the three principalconcentrating collectors utilized in the United S tates is 80concentrating collectors utilized in the United S tates is 80

percent for the dish, 60 percent for the central receiver, and percent for the dish, 60 percent for the central receiver, and43 percent for the parabolic trough on an annual basis43 percent for the parabolic trough on an annual basis

Collector efficiency is determined for the period extendingCollector efficiency is determined for the period extending from the beginning of tracking when the sun climbs to 15 from the beginning of tracking when the sun climbs to 15 degrees above the horizon until tracking stops when the sundegrees above the horizon until tracking stops when the sundeclines below 15 degrees atdeclines below 15 degrees at

the end of the day. the end of the day.



Factors r elating efficiencyFactors r elating efficiency

The efficiency depends on direct solar radiationThe efficiency depends on direct solar radiationand system optics.and system optics.

Actual efficiency depends on mirror or lens surface Actual efficiency depends on mirror or lens surfaceaccuracy, surface dust and film, energy absorptionaccuracy, surface dust and film, energy absorptionby lens or mirror,by lens or mirror, the properties of the reflecting, the properties of the reflecting,material, pointing accuracy, effects of temperaturematerial, pointing accuracy, effects of temperaturevariations on these factors, weather variations on these factors, weather³³includingincludingclouds, dust and haze, and so on.clouds, dust and haze, and so on.

The efficiency is further reduced by receiver The efficiency is further reduced by receiver performance and receiver subsystem design, performance and receiver subsystem design,including care given to reduction of heat loss byincluding care given to reduction of heat loss byconduction, convection, and radiation.conduction, convection, and radiation.



Advantag esAdvantag es

Wide range of application in various fieldsWide range of application in various fields

Applicable in mostly thermal use where Applicable in mostly thermal use where

temperature above 400C i.e. mostly between temperature above 400C i.e. mostly between100100--400C.400C.

Thermal loss is very low and the collectionThermal loss is very low and the collectionefficiency is higher.efficiency is higher.



Disadvantag esDisadvantag es

Complex in design and maintenance is highComplex in design and maintenance is highsince the presence of an optical.since the presence of an optical.

I

t is costlyI

t is costly Most of the diffused radiation is lost becauseMost of the diffused radiation is lost because

it does not get focused.it does not get focused.

Can be used only when there is ample sunCan be used only when there is ample sunrays, i.e. cant be used in misty or sunnyrays, i.e. cant be used in misty or sunnydays.days.



ConclusionConclusion

Although solar energy research, development, and Although solar energy research, development, andsystems experiments were conducted in the latesystems experiments were conducted in the late1800s and early 1900s, it was the sharp increase in1800s and early 1900s, it was the sharp increase in

the price of oil in 1974 precipitated by the Middle the price of oil in 1974 precipitated by the Middle--Eastern oil embargo the previous year that escalatedEastern oil embargo the previous year that escalatednational and international investment in solar national and international investment in solar energy.energy.

I

t may be beneficial in a large taking into accountI

t may be beneficial in a large taking into account the solar energy however if we consider the cost the solar energy however if we consider the cost factor it is only good for mass activities rather than factor it is only good for mass activities rather thansingle product.single product.



T hank you T hank you

concentrating solar collectors

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