Thermal storage tanks are used in solar heating systems and wood boilers where you need to store the produced heat in water for later use.
Diy thermal storage tank.
It s basically a large extremely well insulated storage tank of water that you heat via a back boiler on your wood stove or via solar hot water panels that can feed radiators or underfloor heating any time you like.
If you size your solar hot water also known as thermal storage tank correctly you can easily store the heated water overnight and it will be plenty hot enough to provide comfortable showers or clothes laundering water.
A larger water storage tank keeps its water warm because the property of a considerable time is called thermal inertia.
The answer is a thermal store.
Bigger is not always better but certainly better for tanks.