DISH SUN WITH STORAGE

Solar dish-turbine with CAES to deliver utility-scale CSP
Rikki Stancich, 13 September 2010 (CSP Today)

"…[T]he sheer volume of wind and solar projects currently in the pipeline has triggered renewed interest in…compressed air energy storage (CAES)…[that] makes it possible to store gigawatts of off-peak energy that can be discharged during peak demand…resolving intermittency issues…

"…[O]ff-peak energy from a power plant or renewable energy source is used to run air compressors that pump air into either storage tanks or underground caverns where it is stored under pressure. When electricity is needed, the air is expanded via turbines, to generate energy…a CAES system in Germany and Alabama Electric Cooperative’s CAES plant in the US, have been online for more than 15 years…[but] there has been little investment to date…A significant portion of the US lies on bedded salt or domal salt geology, which lends itself to compressed air energy storage…[so] it seems likely that CAES will gain ground in coming years. In the US during the first half of 2010, four new CAES projects were announced…A handful of renewable technology providers have already been working on projects that combine CAES and renewable energy for several years."

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"Arizona-based Brayton Energy LLC is one such technology provider that is supporting the development of a hybrid dish-Brayton (turbine) compressed air storage system with its partner and owner of the project SolarCAT Inc [SCI]...[SolarCAT buys] cheap off-peak power (around 4c/kw) from the utility during the night, which is used to power a compressor for storing compressed air in a chamber (an underground salt mine cavity, which are abundant in the region)…During the day, the air is delivered…to a network of 320m2 parabolic dishes, where the compressed air in the solar receiver is heated by around 230kW of concentrated solar energy…The expanded air drives a turbo-alternator, generating energy that is then sold back to the utility at a higher price during peak load times.

"The idea is to have each ground-mounted central compressor/storage system serving around 30 dishes…[T]he overall solar-to-electric efficiency is over 30%…[and the company is aiming for] 40% efficiency…The turbo-alternator’s air-cooled design provides variable speed for high part-load efficiency, while its hybrid design means it can be supplemented with fossil fuel in order to be compliant with utilities demand for ‘firm’ power generation…The zero water requirement of the Brayton engine cycle also makes the system a good match for the water scarce region."

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"Brayton Energy is simultaneously developing a standalone Solar Dish-Turbine system for SolarCAT, which uses the same dish and components, but without the CAES (essentially a solar receiver and a purpose-built microturbine). The company is also working in conjunction with SolarCAT to develop a manmade storage vessel…According to the company’s latest peer review report to the DoE, both the standalone and storage system show potential of producing power competitive with today’s fossil-fuel power plants…

"…Earlier this year, Brayton Energy’s partners, SolarCAT and Southwest Solar, procured 300 acres of land adjacent to an existing salt cavern (on top of the Luke salt dome), within the Phoenix metropolitan market. The site is suitable for installing a 100MWe (peak) generating system, while the adjacent salt caverns can provide roughly 1 GWh energy storage capacity…The initial objective of the project, which is partially funded by a US$2.3million US Department of Energy grant approved in 2008, was to deliver energy at a price of 7.5 to 10 c/kWh…While the project completion date was set for December 2010, the timeline has been delayed by testing on the dish, which in turn has delayed testing on the receiver and power conversion unit (PCU)…[They] are now looking at around 2013…"