Off grid opportunity loads

photonboy

I have got great sun at my off grid cabin and want to take advantage of the relay system on my respective charge controllers.   I was looking for help in suggesting components that would allow the relay after a predefined charging level (bulk) divert to an opportunity load with a contractor.  I could heat some water or a resistive heater to lesson the load on the propane heater.   I am trying to keep the cabin warm enough to minimize draining efforts each time.  I will be installing a closed loop solar thermal system and could dump the excess DC into that, or a simple resistive heater to keep the crawl space warm.  Are there some good threads on this with crude schematics?  I should say that in the 4 panel system I have, 1 panel is on a separate charge controllers which would allow the batteries to continue to bulk charge during diversion.  Thanks for the suggestions 

NANOcontrol

I do this with heating water.  I built a controller that pulls excess power from raw array voltage that supplies a MPPT charge controller.  I have three hot water tanks, one just for laundry which has lowest priority.  The system does not use any charge controller, inverter or battery capacity.  This leaves batteries always in the highest charge condition. Pulling power from batteries makes sense to solar people, it makes no sense to me. There are a lot of diversion schemes out there which are ill conceived and costly.  Good commercial products just don't exist.

photonboy

Thanks Nano…..Agreed on all the above.     I have done some reading on heating elements and there should be no difference between ac/dc.  Can you use the built in thermostat on the water to regulate temperature or are you using an external sensor?  Seems there are some wattage limited thermostats at https://windandsolar.com/shop/dc-water-heating-elements.   In the ideal world you could put the DC right on the element/thermostat connectors as you would for AC.  Seems like a lot of people are/want to play this game.