Feedback on 12V water heater element as solar diversion load

enblethen wrote:
My thought you are wasting time and money for the small amount of energy you possibly save.

Exactly. Especially considering that the OP wants to use the excess capacity for resistive heating appliances. The entire output of the OP's system (280W) doesn't even come close to the power required to make either a space heater or electric water heater work with any efficacy. IMO, in order to actually use excess solar capacity, add battery storage capacity so the excess power can be used when needed.