STORAGE FOR SUN COMING SOON

Thermal storage in the US: Soon to be a given; Unlike their Spanish counterparts, most CSP projects in the US to date have opted against thermal storage. But recent developments suggest the business case for thermal storage in the US may soon be indisputable.
Emma Clarke, 18 December 2009 (CSP Today)

"…The ability to store the sun’s energy means concentrating solar plants can generate power 24 hours a day or when demand for electricity is highest. Conversely, solar PV and wind farms [have to cope with intermittency]…

"The benefits are clear. But the business case is not always as apparent given the high cost of thermal energy storage (TES) technologies. As a result, many of the CSP projects in the United States do not include TES. But this may change as the share of solar power in the grid increases and utilities demand a more stable, predictable power supply…Several existing large-scale storage systems already use molten salt, a mixture of sodium and potassium nitrate, to store solar energy…The first molten salt thermal storage system was installed in the Andasol 1 50MW parabolic trough plant in southern Spain, which came online at the end of 2008…Andasol 2 (in start-up phase) and Andasol 3 (currently in construction) also include thermal storage systems with 7.5 hours’ of thermal storage…"

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"The first commercial plant in the world with a central tower receiver using molten salt technology is the 17MW Gemasolar plant being developed by Torresol Energy. The storage will produce around 63 percent more hours of power than a conventional plant...Given the additional costs of the storage equipment (19 percent of the total project cost) and of building a larger solar field to accumulate the excess energy during the day (the solar field accounts for 43 percent of total costs), the cost-benefit is roughly even…In the US, Abengoa Solar plans to build Solana, a 280MW solar trough plant in Arizona with thermal storage using molten salts.

"Developer, SolarReserve has also filed an application to build a 150MW solar power tower plant with seven hours’ of salt storage in California. The proposed Rice Solar Energy Project will use technology built by Rocketdyne that was tested at the 10MW Solar Two demonstration project near Barstow, California in the 1990s…In this two-tank system, molten salt is used for both thermal transfer and storage…"

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"Most of the projects operating in the United States, however, do not have thermal storage. This is because to date, the economics haven’t added up…[T]he cost of electricity is more expensive if storage is included…[T]he costs can range from an additional US$50 (€35; £31) to US$125 (€87; £77) per kW-hr…Given these costs, storage only becomes viable when there is time-of-day pricing (where a premium is paid for power during peak-demand periods), or where utilities provide capacity credits (additional payment for guaranteeing generation during certain times of the day)…[T]he widespread use of storage in Spain [may be] driven by artificial market factors…

"The business case also depends on the quality of solar radiation and characteristics of electricity demand…[C]ompanies are building plants without storage in California because there is more reliable solar radiation than in Spain, and because utilities don’t need to stabilise power production 24-hours a day…But as the proportion of renewable energy in the grid increases…storage [will] become a critical factor…[and] a number of research projects are underway to reduce the costs…"