Using the sun to support our electrical grid has always had one major issue – the sun only shines about half of the time. Critics of solar energy often point to this fact to justify their position that renewables will never be able to replace fossil fuels. This argument is appealing on its surface: we all know that sunlight and wind are intermittent. But what if the sun didn’t have to be shining for a solar power plant to continue generating power? Can solar match coal and oil’s round-the-clock production capability?
Thanks to innovation in the concentrated solar field, the answer is yes! There are two main types of concentrated solar plants (CSPs). The first is a parabolic trough design which uses curved mirrors to reflect light onto a central fluid-filled tube. The super-heated fluid is used to generate steam which spins a turbine, much like conventional power plants. The other design is a solar power tower which use hundreds of mirrors to direct solar radiation to a small area. The light is converted into heat as it hits the tower, and again this heat is used to turn conventional steam turbines. Since 2006, CSP deployment has exploded, it’s capacity in MW increasing over seven times with exponential growth expected to continue. Expansion of this technology has driven CSP’s price per kWh generated down to levels comparable to fossil fuels – great news for renewable energy advocates.
So how can CSPs solve solar’s intermittent production problem? Salt! New tower CSPs are using molten salt, which is heated above 700°C, to store thermal energy for later use. Molten salt is perfect for this application because it is non-toxic, non-flammable, and low-cost. Using molten salt allows the energy harvested from the sun to be stored for later use, even long after the sun has gone down.
The first large-scale molten salt CSP, Gemasolar, opened October 2011 in Seville, Spain. The 20 megawatt plant supplies power to nearly thirty thousand homes and is designed to run up to 15 hours without any additional solar energy. In fact, last month Gemasolar broke records when it continuously generated power for 36 days. 36 days! That’s over a month of continuous, fossil fuel free energy! Now that this technology has been proven, we expect to see more molten salt CSPs constructed around the world. Let’s just hope we don’t look back towards fossil fuels or we could all become pillars of salt.
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