A glycol-Water solution circulates from the panels to the
heat exchanger in the storage tank. Circulating potable water
is not recommended because it can cause corrosion and
deposition in the collection system. The storage tank is 300 L,
larger than a standard hot Water heater tank. V/ater can be
heated up to 80 OC, so a mixing valve is required at the tank
outlet to cool the water to less than 50 °C for household use.
Temperature is measured in the tank and at the panels. A
controller turns on the pump when the panel temperature is
higher than the tank temperature and turns the pump off
when the panel temperature drops below the tank temperature.
There is also a check valve in the line to prevent natural
circulation from the hot tank to the cold roof panels at night.
As a backup for the solar system, we installed a tankless,
gas-fired water heater. The solar system provides all our hot
Water during the summer, but We do need the backup heater
during the winter.