WATER AND BIG SUN

Cooler, smarter options for hot CSP technologies; Increasing water scarcity is forcing CSP developers into a corner, given the sheer volume of water required by certain technologies for cooling and mirror washing, and communities’ growing concern over water use. Smart solutions are in demand.
Bob Moser, 10 June 2011 (CSP Today)

"…[W]et and dry cooling methods [for solar power plants are] the only feasible options today - both of which have drawbacks. But developers and researchers are exploring different configurations for hybrid cooling systems…[Wet cooling uses too much water]…Dry cooling has been around for the last 15 years, but…CSP plants [in] dry, sunny [U.S.] areas…during the summer months when CSP must perform…[suffer] with dry cooling because of intense solar radiation…

"…A recent study by NREL found that…[the] minimal use of water, primarily in an air-cooled condenser, may prove to be the best way to lower the amount of water used while still harnessing its benefits as a cooling agent, says Jordan Macknick, energy and environmental analyst with NREL…NREL's study found that dry cooling would generally achieve a 90-92% decline in water consumption, with an increase in cost for generating electricity of 3-8%, depending on the climate…"

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"Non-traditional water sources are the other option with the best potential for applicability at low cost…Shallow brackish water and recycled wash water collected from mirror washing are the two options furthest along…

"NREL has been working with researchers at the University of Colorado-Boulder on ways to reduce the amount of water used to wash CSP mirrors. Current practice usually involves spraying the mirrors with a hose, but a high-pressure spraying system with a squeegee involved could reduce washwater by 90% if it's automated…[but that’s] a drop in the bucket compared to the daily water demand for wet cooling. About 20 to 30 gallons of washwater are used for every Mwh generated, compared to 700 to 900 gallons per Mwh used now for wet cooling…"

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"Non-water liquids could become feasible as a cooling source but would add considerably to capital costs, requiring another stage to cool down that liquid, which couldn't simply be evaporated like water. Some researchers are reportedly testing high-pressured carbon dioxide gas or ionized air… CSP developers [may try] to choose sites more carefully…The ideal CSP locale would have clear, sunny skies but cold ambient temperature…

"When compared to water usage at coal-fired energy plants in the American southwest that includes water used during the coal mining, transport and cooling at the plant, CSP's wet-cooling system uses less water. And compared to biofuels based on corn or soybean, CSP wet cooling waters less per acre…[But] CSP uses more water per MW than a combined-cycle gas-fired plant…"