We were surprised at first to read that the giant Abengoa Solana solar energy project had to import 120,000 metric tons of molten salt from Chile. After all, Arizona has numerous massive salt deposits some of which are being actively mined. But then we learned that the molten salt mixes for thermal storage are typically 60% sodium nitrate and 40% potassium nitrate. The mixtures vary and and also include calcium nitrates.
The 280-megawatt, 3 square mile, $2 billion project will use the molten salt as a heat storage sink that will allow electricity to be generated for as long as 6 hours after the sun sets, according to a report in the Arizona [Phoenix] Republic. [Right, diagram of plant design. Credit, US Dept. Energy]