Friday, October 11, 2013

Arizona Residents Can Now Get Solar Power After Dark

Solar power is going to power the future; even Big Oil admits that. But before that happens, the rather important problem of energy storage needs to be solved. A large new solar plant in Arizona has found a solution: The Solana Generating Station, which has a 280 MW capacity, is the first in the nation to keep power flowing after dark. Thanks to a molten salt storage system, the plant can keep full power flowing to Arizona residents for up to six hours after the sun goes down.According to Abengoa, the plant has passed its commercial operations tests, which means it's now ready to start servicing the 70,000 or so households it's projected to power. And for Arizona, it's another milestone for a state that's made a heavy push into the solar world.“Solana is a monumental step forward in solar energy production,” Arizona Public Services President Don Brandt said in a release earlier this week. “Solana delivers important value to APS customers by generating power when the sun isn’t shining. It also increases our solar energy portfolio by nearly 50 percent. This provides a huge boost toward our goal to make Arizona the solar capital of America.”Solana is a concentrating solar power (CSP) plant, which makes it fairly novel; rather than rely on solar panels, 2,700 parabolic mirrors reflect the sun's heat onto pipes in the mirrors' trough which contain a synthetic oil. The oil, which can reach temperatures of 735 degrees Fairenheit, carries the sun's heat to steam boilers, which produce enough steam to power a pair of 140 MW turbines.

Steam turbines are common enough in power production, but the real trick is in the system's ability to store that heat and release it after dark. The heat transferring oil doesn't just go to boil water. It's also diverted to a molten salt storage facility featuring six pairs of hot and cold salt tanks, containing a max total of 125,000 metric tons of salt that is kept at a minimum of 530 degrees.After dark, heat from that system is bled back into the heat transfer fluid, which brings the stored heat to boilers. In tests earlier this week, the system successfully kept the plant's production at full capacity for six hours after dark. As great as it is for Arizona and Abengoa, it's a win for the Department of Energy as well, which guaranteed $1.45 billion worth of loans for the project.

Storage has been one of solar power's biggest problems, and until batteries stop sucking, photovoltaics will remain beholden to the sun. It's not just after dark, either; with both photovoltaics and wind power, fluctuations in solar or wind intensity are difficult to smooth out. But with a molten salt storage system, the occasional cloud can be compensated for.That's one reason concentrated solar power has begun to take off, especially in the form of large solar projects. Abu Dhabi has a 100 MW CSP plant up and running, and India is planning a positively gargatuan 4,000 MW plant. California will soon be home to a plant larger that Solana; the Ivanpah plant is slowly being connected to the grid, and will eventually total 392 MW of capacity. While solar in the US still has a long way to go to compete with fossil fuels, the success of large capacity projects is the latest sign that renewables are indeed winning.

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