If it takes X amount of energy to heat a material by Z degrees, then presumably the material radiates exactly X amount of energy back out when it cools down by the same Z degrees, no?
What does it matter that Y kg of rocks stores that energy at a lower temperature than Y kg of water? Or, conversely, that if you insist on having your energy-storage temperature set at some specific Z' degrees, you can store that amount of heat energy in much fewer kg of rocks than of water?
You're mixing up temperature and energy. They're not the same thing.
What does it matter that Y kg of rocks stores that energy at a lower temperature than Y kg of water? Or, conversely, that if you insist on having your energy-storage temperature set at some specific Z' degrees, you can store that amount of heat energy in much fewer kg of rocks than of water?
You're mixing up temperature and energy. They're not the same thing.