Water tanks

Water tanks are used for sensible thermal storage in many variations, such as thermosiphon systems, integrated storage collectors, residential hot water tanks, ferroconcrete seasonal storage, gravel/water storage, and aquifers.

Water tank storage is most common in active solar systems for domestic hot water heating (DHW), often in combination with space heating (combi-systems).

The storage tank is often made of steel and has a typical volume between 150 litres for domestic hot water up to 5000 litres for space heating and DHW.


insulated water tank

typical volume

150-5000 litres

typical heat density

0.2 GJ/m3

temperature range

up to 110°C

storage timescale


development status

proven technology


cheap, reliable

simple thermal coupling


heat loss over time