A solar-powered photovoltaic thermal fluid heating system having an array of photovoltaic modules, an energy conversion control unit, sensors for tank temperature, with resistance heating element / tank flush water heater adaptor installed in a fluid-filled gas or electrically heated thermal storage tank. The advantages of the present invention include, without limitation, include an simple, safe, and efficient method for utilizing solar energy for the heating of water that is protected from the dangers of freezing and / or overheating, and easily retrofittable to new and existing gas and electric hot water storage tanks.