No, they produce heat. Solar thermal systems create a greenhouse effect inside the collector by trapping sunlight (shortwave radiation) and converting it to heat (longwave radiation). That heat is then transferred from the collector to a storage tank inside your home. When domestic water enters your home, it comes in at groundwater temperatures of around 55°. Once inside your home, that cold water is sent to your water heater which typically uses electricity to heat an element and warm your water. For every degree that a solar thermal system pre-heats your water, that is less work your water heater has to do and subsequently less energy (gas or electricity) you have to use. See how it all happens on our How It Works video!