Home Thermal Energy storage is under appreciated. A building doesn't actually have to be high capacity since every mass inside has some capacity Even the air. It's possible to marginally over heat or over cool and ride a slightly fluctuating temperature rather than going for true thermostasis. Technology Connections on youtube talked about this 'untapped energy storage' . In some countries, a hot water storage tank is already common. It's pretty obvious you can make a cold one too if needed.