7/29/2019 Solar Power After Sunset-4Jan2012

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7/29/2019 Solar Power After Sunset-4Jan2012

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Sunlight isconcentrated anddirected from a largefield of heliostats(mirrors) to a receiveron a tall tower

' The heated salt $t. from the receiver &|,r is stored in the {.: hot tank $,,*_-xrytY.-q-?glryy1 Wpt|Central !. :i:recetver :, i:,I&EA ;Frt :,rfl

Molten salt is pumped from the hot tankthrough a steam generator that createssteam, which drives a steam turbine,generating electricityConventional steam turbinegenerator (with reheat)

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Electricity(MW)

Cold salt thermalstorage tank

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Cold salt at 288degree C flowsback to the coldsalt tank and isre-usedSource: SolarReserve

wer even after sunsetmedical Engineering at Nanyang Techno-logical University, said thaf although thetechnology was not complicated, Singa-pore did not'have enough land or surficeareas to harness the solar heat at a suffi-cient scale to make the process economic.One crucial role of the US plants willbe to complement solar panels, which pro-_du-ce electricity directly from sunlight.When the panels ramp down at dusl oron cloudy days, the plants will crank up.- As the grid starts depending moreheavily on solar panels or wind turbines,it will need other energy sources that canstep in quickly to balance the system.Most utilities are trying to generate asmany kilowatt-hours of .ene.,i"ble .rrer-gy as they can to meet stiffer state re-quirements on incorporating more alter-native energy, said Mr Kevin Smith, thechief executive of SolarReserve.

and more traction with the fact that wecan provide more capacity," he added.The Energy Department seems toagree: Last September, it gave SolarRe_serve a US$737 million (59957 million)loan guarantee for its project which wiligenerate ll0MW at peak and storeenough heat to run for l0 hours when thesun is not shining. The SolarReserve andBrightSource plants will use computer-operated poster-size mirrors aiming sun-Iight at a tower that absorbs it as h-eat.The SolarReserve plant then absorbsthe heat in molten salt, which can be keptfor later use or used immediatelv to boilwater, generating steam that turns a con-ventional turbine and generator. Bright-Source heats water that can be used atonce as steam or to heat salt for storase.The plants rely on salt because it Janstore more heat than water can. The tech-

nomics are. The simplest, least e*pensivepath for solar thermal is to turn the heatinto electricity immediately. But the com-panies are like a farmer wlo harvests thegrain and stores it in a silo rather thanshipping it straight to market on the ex-pectation that prices will be higher later.

. fhpl expect that in revenue terms,when the energy is delivered will be moreimportant than the amount generated._ Electricity prices usually peak in thelate'afternoon and evening in summer.But the new price peak will be pushedback, to just before and after s.,ns.t.

- The companies would not discuss capi-tal costs but Mr Smith said the storigetechnology came to less than 5 per cent 6fcapital costs and that utility fiim South-ern California Edison would pay extra fora plant that could deliver when the sunwas not shining.