Solar Southwest Initiative

Almost everyone wants clean renewable energy to power our future economy. Solar and wind energy are, for most people concerned about the planet's future, our next energy system. But these devices, solar and wind generators,are not the solutions by themselves. To phase out the use of fossil fuels and actually mothball or shut down coal and gas fired power plants, we will need new clean energy storage in addition to renewable generators.

The Critical Role of Energy Storage

The way the electric system works is that electrical energy gets generated and released to the grid just fractions of a second before it is used. Energy consumers like ourselves have structured our lives and work to use electrical energy on demand and in order to receive that energy when we need it, some portion will need to have been stored and ready for use. Fossil fuels, like coal, gas and oil, and fissionable fuels like uranium, it turns out, function as very extensive energy stores, allowing energy to be released when it is needed. A grid run largely on renewable energy represents a new technical and organizational challenge for grid operators, increasing the value of energy storage that can be released rapidly to serve the energy demand of grid customers.

Solar and wind energy alone are intermittent and do not come naturally with energy storage. Solar thermal electric has the potential for storing the sun's energy as heat. One of the least expensive energy storage mechanisms is to store thermal energy in a high heat capacity fluid, such as molten salt. Molten salt is a combination of chemical salts, usually a combination of sodium nitrate and nitrite, that can cycle between two fairly high temperatures, releasing its heat at the higher temperature but remaining liquid at the lower temperature. Currently molten salt storage costs $50/kilowatt-hour, substantially less expensive than lead-acid batteries. Some thermal energy storage solutions suggest using pressurized water, though this solution has not yet been fully implemented.

Integrated with thermal storage, solar thermal power plants can tap into the essentially limitless power of the desert sun and release that power when it it needed by the grid. In the 1990's, using a molten salt storage system, Solar Two, a demonstration plant funded by the US Department of Energy, generated power for 7 days continuously on solar power alone. Commercializing this technology will allow solar power plants to replace the output of coal and natural gas power plants, which in combination of energy efficiency and a leveling of power demand, effectively reduce our greenhouse gas emissions.