Jerry Peck
First a couple of questions.
Was this a single element 80 gallon solar assisted water heating system? Only one element on an 80 gallon tank would not be practical by itself.
What is the size of the existing element?
If there are two heater element hub openings in the tank, then you can use two elements. If we assume the electrical circuit is the correct size for the existing element, then two elements of that size will be okay. This will not overload the electrical circuit as only one element will be on at any one time (if wired properly).
You will need to feed the top thermostat’s ‘line’ terminals with the supply circuit conductors, then feed the top element from from the ‘normally on’ terminals of the top thermostat, now feed the bottom thermostat from the ‘normally off’ terminals of the top thermostat. The bottom thermostat terminals for the bottom element are ‘normally on’.
This way the top element comes on and heats the top portion of the water. When the top portion of the water is hot enough and satisfies the top thermostat, the circuit power is routed through the top thermostat, bypassing the top element terminals, to the terminals
connected to the bottom thermostat. The bottom element now comes on and heats up. When the bottom water is hot enough, the bottom thermostat shuts off. When the water begins to cool or hot water is used, the top thermostat kicks the top element back in, taking the power away from the bottom element. Only one element is on at any given time.
If you do not understand what is stated above, call a licensed and qualified electrical contractor. Even if you do understand the above, I recommend that you call the electrical contractor because of the nature of electrical work and the chance of electric shock and electrocution.
