Comment by japanuspus

Just as important here: The higher the temperature of the storage medium, the higher the fundamental limit to how much electric energy you can recover.

Put differently: If you used the same amount of energy to heat one bucket of sand by 200C (A) or two bucket of sands by 100C (B), you would be able to recover more electric energy from case A because of the fundamental Carnot Limit. This is why sand is a good storage medium (as opposed to e.g. water), and why some solar power systems work with molten salts. Also why steam-based power plants need to operate at high pressure to be able to obtain high-temperature steam.