One nice feature of the Fafco Revolution 500 series Integrated Control Module is the ability to see the water temperature at the top of the water tank, the bottom of the tank, and on the roof at the solar collector.
As long as the water temperature on the roof and the desired temperature is greater than the temperature at the bottom of the water tank, the Integrated Control Module will start the heat exchange pumps, heating the water in the tank. The upper tank sensor tells you the temperature that you can expect to get out of the tank if you open a faucet. This is handy to see how much hot water remains in the tank, and how to set the upper electric element thermostat to meet your typical hot water needs.
It’s amazing to see how hot the heat transfer fluid in the solar collector can get!
This type of solar controller is called a differential controller. As long as the differential between the tank temperature and the roof temperature is great enough, the system will turn on to produce more hot water. This differential controller’s logic works in the same way as a solar pool heating controller. It is the heart of a solar thermal (water heating) system.