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Fri Apr 6, 2012, 10:06 AM

Secret Ingredient To Making Solar Energy Work: Salt

Secret Ingredient To Making Solar Energy Work: Salt
This story appears in the April 23, 2012 issue of Forbes Magazine. Photo by Eric Millette.
By Todd Woody


The solar thermal power plant business is all about big: Square miles of mirrors in the desert that surround 600-foot-tall towers to generate massive megawatts of electricity for multibillion- dollar price tags. Big Solar’s ability to compete against fossil fuels, though, could come down to grains of salt.

In a small lab in the San Francisco Bay Area biotech hub of Emeryville, scientists at a startup called Halotechnics are sifting through thousands of mixtures of molten salt. They’re searching for the right combinations that will allow solar thermal energy to be stored cheaply and efficiently so it can be dispatched to generate electricity after the sun sets. In other words, the 24/7 solar power plant.

Molten salt storage has been around since the 1990s, when United Technologies’ Rocketdyne division developed it for Solar Two, a prototype “power tower” station built by the U.S. Department of Energy in the Mojave Desert. Arrays of mirrors called heliostats focus the sun on a boiler filled with salt that liquefies at high temperatures. The heat released by the molten salt is used to create steam that drives an electricity-generating turbine. Some of that heat can be held in tanks of molten salt and released when needed to produce electricity.

Now salt is back on the table as states such as California green-light big solar thermal power projects to meet ambitious renewable energy mandates. Utilities want those power plants to store solar energy so it can be used to balance a power grid increasingly supplied by intermittent sources of electricity like wind farms. GTM Research estimates solar energy storage will be a $3.7 billion market by 2015.

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