The residential solar thermal systems are designed according to the needs of the total number of occupants in the home. For design purposes, every person is assumed to use 20 gallons of water each and every day and each systems is designed to store hot water for every person for each day. For example, a family of four will need two solar collectors with hot water storage tank of storing up to 80 gallons per day.
A flat plate solar thermal system installed with two collectors and an 80 gallon hot water storage tank would cost around $8,000 while a system with three solar collectors and storage of 120 gallons would cost around $10,000. However, it is important to remember that the ease or difficulty of installation may also affect the total cost of installation.