Solar Water Heating Systems...One Tank or Two ?

A single tank solar water heating system combines solar preheated water and backup heating into one tank, in contrast to a typical two tank system which separates these functions.  Studies of 37 systems conducted for the Oregon Department of Energy found that single tank solar systems often saved more energy than comparable two tank systems.

The single tank systems performed better mostly due to reductions in standby loads and standby losses. Although there are many contributors to the losses over the course of annual seasons and typical household usage factors, the differences appeared mostly in standby losses in the colder winter seasons. As an example, in a two tank system, when hot water is not being used, the water in the fired backup heater continually cools and asks for heat even if the solar tank is full of 120 degree water. Maintaining this standby load can account for up to 20% of the total energy consumed. In addition, it was found a timer for the electric element in the one tank system can effectively optimize the timing of electric backup heat applied, and minimize the purchased energy needed while matching the variable individuual family requirements.

The bottom line is a single tank system with a timer-controlled electric backup element can be your most cost effective configuration. To learn more, refer to the published article listed below, or contact your Certified Velux Solar Water Heating System provider.