UPDATE: Phoenix Area Concentrating Solar Power Plant "On Line" In 2011

Science & Technology (alternative energy)

Solana Generating Station image
Solana Generating Station, Gila Bend Arizona USA. Image credit:Business Wire.

Power Engineering reports progress on the Arizona Public Service (APS) concentrating solar power (CSP) plant to be built and operated by Abengoa, 70 miles southwest of Phoenix Arizona. The 280 MW Solana Generating Station will use a 60/40 alloy of molten Sodium and Potassium Nitrate salts to store the sun's concentrated heat energy, buffering solar input changes to meet 24/7 power demand. Read on for details of how the molten salt storage will affect capacity.

NREL found that when CSP plants store solar thermal energy to use during non-solar periods, dispatching it when it's needed most—in other words, making power when the sun's not shining—they can "achieve higher annual capacity factors—from 25 percent without thermal storage up to 70 percent or more with it."
Compare that with the capacity factors of coal, natural gas combined cycle and nuclear power plants. According to the Operating Performance Rankings industry report in the Nov./Dec. 2008 issue of Electric Light & Power, coal-fired power plant capacity factors range from 72 percent to 93 percent, combined cycle from 41 percent to 86 percent and nuclear from 90 percent to 96 percent.

Abengoa has a nice process flow diagram here.

Below is a hand sketched plot indicating eutectic properties of the salt blend. The literature indicates further work may be done with adjusting the alloy components to lower the melt-point a bit more, reducing the chance of plug formation in valving and piping. There is more progress to be made in other words.

Melting point of potassium and sodium nitrate eutectic salt alloys. Image credit:ChestOfBooks,Scientific American