image source: United Technologies
The perennial complaint by renewable energy skeptics about wind and solar power is, that despite the fact that they produce clean power, they are intermittent in nature and require some sort of storage technology to fully exploit the power generated. A recent article at Renewable Energy World spotlights one solution to this very real issue: Molten Salt.
Solar Thermal Power with a Difference
Basically the set-up works like this: Heliostats (large concentrating mirrors) focus the sun onto a central tower, which heats a liquid inside. The liquid in question is molten salt—in this case a combination of sodium and potassium nitrate—which is heated, transferred to a storage tank, and then fed through a steam generator to turn a turbine and generate electricity. The cooled salt is fed back into the tower to repeat the process. The difference between the molten salt and other liquids that are used in this sort of system is that the molten salt retains heat for a long enough time that it can effectively time-shift the stored solar energy from when it is most efficiently generated to when it is most needed.
The original article quotes Terry Murphy, CEO of SolarReserve who helped develop the technology.
Molten salt is a heat storage medium that that retains thermal energy very effectively over time and operates at temperatures greater than 1000Â°F, which matches well with the most efficient steam turbines. Second, it remains in a liquid state throughout the plant's operating regime, which will improve long-term reliability and reduce O&M; costs. And third, it's totally 'green,' molten salt is a non-toxic, readily available material, similar to commercial fertilizers.
Personally, I wouldn't go around touting commercial fertilizers or anything similar to them as being "totally 'green'", but as a way to time-shift renewably generated energy—this really isn't long term storage in the sense of a conventional battery or fuel cell—it certainly is a solution.