The global solar company Abengoa Solar has just announced that its massive Solana solar power plant has begun commercial operation in Arizona. The plant represents a transformational breakthrough in utility scale solar power, because it includes an energy storage system based on molten salt. The storage feature enables the plant to keep generating electricity long after the sun goes down.

CSPs use mirrors to concentrate solar energy on a focal point, typically a large tower. According to Abengoa, at 280 megawatts the Solana plant is the world’s largest CSP plant to use parabolic trough mirrors to concentrate solar energy (typical CSP mirrors, called heliostats, are flat and quadrilateral).

It is also the first solar plant in the U.S. with thermal energy storage, in the form of a molten salt system. The storage capacity is about six hours. That enables the plant to keep generating electricity from solar energy well into the early evening hours, when demand in the region typically peaks out.

Solana officially went online yesterday after completing a series of tests that included charging the thermal energy storage system and demonstrating that it could produce electricity for six hours using only stored energy.