The idea of storing the sun's energy is nothing new. People have been trying to devise a way to pause the process -- hold onto the energy in sunlight for a while before converting it to electricity -- for as long as solar power has been an electricity option. All previous attempts, though, have been prohibitively problematic.
Some have tried to store the sun's energy by using it to pump water uphill, where the energy stays until the water moves back downhill, releasing it. Compressing and then un-compressing air is another option. But both of those methods waste energy -- only about 80 percent of the solar power put in is recovered on the other end [source: Bielo]. Batteries are also extremely inefficient, making them too expensive to be a viable large-scale storage option. You can store as much energy in a coffee thermos as in a laptop battery, which costs 10 times as much [source: Wald].
And there's where the breakthrough comes in: Heat is easy to store.
That's essentially what the thermos is doing, storing the heat of that coffee. And heat generates electricity in a solar-thermal power plant, so storing heat is a way to pause the process: Let the sun heat something up, keep that thing hot until the sun goes down, and then use that heat to generate the steam that turns the turbine.
Of course, as relatively easy as it is to store heat, you've got to find the right substance for a solar-power application. To store the extreme heat that runs a solar-thermal power plant, the substance has to remain stable at high temperatures -- in the area of 750 degrees F (400 degrees C) -- otherwise you'd run into problems with vaporizing and pressure changes [source: Bielo]. It's also helpful is the substance is cheap and readily available.
Enter that white, crystalline stuff in your cupboard that you probably put on your scrambled eggs, your margarita glass and your edamame: salt. Salt melts at only very high temperatures, vaporizes at very, very high temperatures and it's available in virtually unlimited, low-cost supply. Plus, it only loses about 7 percent of the energy put into it [source: Bielo].
Actually, the first salt-storage-equipped solar power plant isn't using table salt. It's using a different salt mixture often applied as fertilizer, a combination of sodium and potassium nitrate. The Andasol 1 power plant in Grenada, Spain, is packed with 30,865 tons (28,000 metric tons) of the stuff [source: Bielo].