APS solar power plant can deliver power six hours after dark

The Solana Generating Station combines uses concentrated solar power (CSP) technology with thermal energy storage to deliver renewable power up to six hours after the sun goes down.

The solar power project, which delivers electric power to customers of Arizona Public Service Co. (APS), sits on a three-square-mile area near Gila Bend, Arizona and has a capacity of 280 MW. This capacity is enough to provide energy for 70,000 Arizona homes — a city the size of Yuma

“Solana represents an important technological advance in solar energy production compared to the more-common photovoltaic technology, which needs direct sunlight in order to produce electricity,” according to APS.

The project was constructed and is owned by Abengoa Solar.

The plant’s CSP technology produces electricity by collecting the sun’s heat to create steam that turns conventional turbines. The process begins with 2,700 parabolic trough mirrors, which follow the sun to focus its heat on a pipe containing a heat transfer fluid.

This fluid, a synthetic oil, can reach a temperature of 735 degrees Fahrenheit. The heat transfer fluid then flows to steam boilers, where it heats water to create steam. The steam drives two 140 MW turbines to produce electricity, much like a traditional power plant.

In addition to creating steam, the heat transfer fluid is used to heat molten salt in tanks adjacent to the steam boilers. The thermal energy storage system includes six pairs of hot and cold tanks with a capacity of 125,000 metric tons of salt, and the molten salt is kept at a minimum temperature of 530 degrees Fahrenheit.

When the sun goes down, the heat transfer fluid can be heated by the molten salt to create steam by running it through the tanks instead of the field of parabolic mirrors.

APS serves more than 1.1 million customers in 11 of the state’s 15 counties.

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