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| Català: Planta de concentració fotovoltaica a Torregrossa (Lleida) (Photo credit: Wikipedia) |
Solar power is abundant and relatively easy to harvest, but it isn’t constant. A team at the Massachusetts Institute of Technology thinks they can solve that problem and make solar power cheaper in the process.
In a concentrated solar power (CSP) plant, an array of mirrors is used to focus sunlight on a tower, which heats up a working fluid that heats water to power turbines. (The fluid is usually molten salts, which absorb and hold heat better than water does and work at higher temperatures). The big problem is that such plants can be expensive and don’t work well on cloudy days.
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Alexander Slocum and a team at MIT decided to use some already-tested technologies in a different way. Instead of pumping molten salt into a tower, they decided to design a plant with the mirrors on a hillside. The tank of salts would be on the ground. The tank is divided into two with a moveable barrier, with the hot salts on top and the cold ones on the bottom. This removes the need for pumping systems that would supply two tanks. Simplifying the design this way reduces costs, and could help make solar power competitive with fossil fuels such as coal or natural gas.
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The whole system is much more thermally efficient. The hot salt increases in volume, pushing the barrier down, and the cold salt that passes the edge of the barrier gets heated up. Once the salt is pumped to the heat exchanger, it is put back in the bottom of the tank where it gets heated again. The thermal efficiency is greater because the heated salt is always at the same level in the tank. This forms convection cells in the salt, mixing it and preventing hot spots and reducing stresses on the tank. Such a system, Slocum says, can operate for a whole day with no sunlight for every ten days of full sun.
Slocum outlines his idea in the journal Solar Energy
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The PS10 solar tower plant outside Seville, Spain is the first commercial solar tower in the world. Photo by Denis Doyle/Getty Images
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