Aren't they using molten salt for this? I think I heard about molten salt being used in a few cases for energy storage. Too bad I can't recall the details. Have you heard about this?
Oh sure, I more meant at the consumer level. At the production level molten salt is used to smooth out energy production rates at concentrated solar arrays. My understanding is that concentrated solar is no longer able to compete with photovoltaic production in most geographies.