But its not free, solar geyser can run up to R40k, probably less for me because my usage is lower.why waste power when the sun does it for free? I'd rather run my pool pump then.
But lets say 250w panel is R2000, you buy 10 (R20000) then even in a bad day in winter those 10 are making 5kwh (2 hours of full sun), and thats all the hot water heated and done. Any additional power can be used elsewhere. Summer you making way too much power, run the AC's all day because why not.
Obviously this could be done far more efficiently if you looking at the house as a whole and not just a single element (water heating)