A larger water storage tank keeps its water warm because the property of a considerable time is called thermal inertia.
Diy thermal storage tank.
The answer is a thermal store.
Bigger is not always better but certainly better for tanks.
The biggest advantage of diy water storage tank over commercial equipment is that you can expand the storage tank size without spending much money.
Build a solar hot water tank for that heated water and enjoy it the next morning too.
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.