What are the desirable characteristics of hot water storage tank?

The hot water storage tank in domestic solar water heating systems is typically a double walled tank. The space between the inner and the outer tanks is filled with insulation to prevent heat losses. The inner tank is generally made of copper or stainless steel to ensure long life. The outer tank could be made of stainless steel sheet, painted steel sheet or aluminum. Electrical heating elements controlled by thermostats can be provided as an option in the tank itself to take care of those days when sun is not there or demand of water has gone up. The capacity of the tank should be in proportion to the collector area used in the system. A commonly used thumb rule is to provide 50 liters of storage for every sq. m of collector area. Too large or too small tanks are both detrimental to efficiency. ... more