One consistent obstacle for solar energy has been the inability to adequately store the energy harnessed from the sun for use at night and on cloudy, overcast days. Inherently, electricity is difficult to store. Batteries are unable to efficiently store energy on a large scale. However, according to a recent New York Times article, a different approach is being tested which could eliminate the problem.

This new idea is to capture the sun’s heat. Heat is much easier to store than electricity and is already a common practice by industry in general. In speaking with The New York Times, John S. O’Donnell, a solar industry executive with the solar thermal company Ausra, noted that storing heat is much more cost effective than electricity.

There are two slightly different approaches to the idea of a solar thermal power plant. Ausra and O’Donnell’s method utilizes Fresnel lenses, which have a short focal length but focus light intensely, to heat miles of black piping with fluid inside. A competitor of Ausra, SolarReserve, has put forth the idea of a “power tower.” This tower is essentially a water tank surrounded by hundreds of mirrors which tilt on two axes to follow the sun on a daily and yearly basis. Instead of water in the tank, however, are thousands of gallons of molten salt that can be heated to high temperatures without approaching high pressure.

Terry Murphy, president and CEO of SolarReserve, says that his tower is designed to supply 540 megawatts of heat which, thanks to the ability of the salt to reach high temperatures, can produce 250 megawatts of electricity. This is enough to power a fair-size city.

With a molten salt design, the power plant would be buffered from the effects of variance in sunshine. Unlike a photovoltaic plant, a solar thermal plant using molten salt would not lose significant output when a cloud drifted over. This fact is likely to make solar thermal much more appealing to utility companies who may otherwise balk at the idea of solar energy.

The molten salt could also work in Ausra’s black-painted pipe design but because piping is not well insulated the danger of freeze and solidification would be a hazard. These “power tower” plants would also make large-scale solar energy more feasible at higher latitudes and areas with less than exorbitant sunshine.

In the late 1990’s, Murphy built just such a plant in Barstow, CA. Sponsored by the US energy department, the plant apparently ran well, but a significant drop in the price of natural gas at the time greatly reduced the state’s need for renewable energy. Now, again, energy prices are skyrocketing and the need for renewable energy is even more present.

View the complete NYTimes article here.

Photo Credit: Phototronics