All Solahart systems, in which the tank is roof-mounted, uses the Thermosiphon principle to gather heat from the sun and transmit it to your hot water.
The Thermosiphon principle is based on two naturally occurring phenomena: -
a). Dark objects absorb heat
b). Hot water rises
All Solahart collector panels are coated with a dark, heat-permeable surface. This coating suck up the suns rays and heats the cold liquid in the collector board. As the fluid heat up it raise to the top of the collector board and into the tank where it relocate cooler fluid which stream in to the foundation of the collector panel where the progression is recurring.