Retrofit cover plate and assembly to adapt alternative energy supplies to electric water heaters

A multi-functional retrofit cover plate assembly and method for an electric water heater to provide interconnection with an alternative energy system to heat water in a water holding tank of the electric water heater. The cover plate is adapted for replacement connection over a bottom access opening formed in an outer casing of the electric water heater which permits access to a bottom resistive heating element and electrical connections. The retrofit cover plate is shaped to define an internal dedicated compartment. A dual resistive heating element is provided for replacement of the bottom resistive heating element. An electronic switch unit is further provided and it has a power cut-off switch for connection to an alternative supply voltage. A temperature sensor is provided for mounting against an outer surface of the tank of the water heater to feed actual temperature signals of water temperature within the tank, in a lower region thereof, to the electronic switch unit which operates the power cut-off switch upon a predetermined temperature having been attained in the tank of the water heater. The retrofit cover plate and the assembly also make it possible to covert the water heater to a high temperature water heater or to adapt the electric water heater to a thermal fluid heat source.