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Photo: Torresol EnergyCross-posted from Climate Progress.

While Americans celebrated U.S. history on the Fourth of July yesterday, a company in Spain celebrated an historic moment for the solar industry: Torresol’s 19.9 megawatt (MW) concentrating solar power plant became the first ever to generate uninterrupted electricity for 24 hours straight.

The plant uses a Power Tower design which features a field of 2,650 mirrors that concentrate sunlight onto a boiler in a central receiver tower. The plant also utilizes molten salt as a heat transfer fluid that allows it to generate electricity when there’s no sunlight. Recharge News reported on the milestone:

After commissioning in May, the plant was finally ready to operate at full-blast in late June and benefited from a particularly sunny stretch of weather, according to Diego Ramirez, director of production at Torresol. “The high performance of the installations coincided with several days of excellent solar radiation, which made it possible for the hot-salt storage tank to reach full capacity,” Ramirez explains.

Torresol says that the plant will provide electricity for about 20 hours each day on average, with numerous days in the summer seeing 24 hours of supply. How does that compare with a similar-sized photovoltaic plant? The 21.2 MW Solarpark Calaveron in Spain generates about 40 gigawatt hours (GWh) a year. This smaller 19.9 MW power tower plant will generate about 110 GWh per year.

Yesterday’s news is a big milestone for Power Tower technology, which is still very nascent compared to the more mature parabolic troughs. There are only a few operating commercial-scale plants around the world, and Torresol’s is the only one with molten salt storage.