I find it always fascinating that water is often in the center of energy production and storage, like turning it to steam or in a dam, using gravity storage or in this instance a large thermos. I wonder if this same concept cold be used with something like molten salt if the heat source is hot enough, to store it in a large thermos to heat water, would it be more efficient or could it even work, the heat source would have to be really hot but it could potentially store more energy than water without increasing pressure. Energy storage is one of the trickiest things that we have to solve to have a good energy mixture in the future.
