Solar hot water, me too

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Murphy's friend


Joined: 04/10/2019
Location: Australia
Posts: 612
Posted: 09:00am 08 May 2023      

An update; This hot water controller has been working very well for 4 weeks now.

On sunny (Winter) days the thermostat switches off around noon, on a recent rainy day, when heavy overcast, it still managed to get the water very hot but not quite hot enough for the thermostat to open.

I'm happy with that system. Matching the panel string max power voltage to the control trip point *is* important as is the element wattage.

Having that analog Ampmeter was a much better indicator of the power being fed to the element as the original neon light is.

My 160 liter hot water storage unit normally comes with a 3.6KW element but, having only about 2KW of solar panels, I got it with the optional 2.4KW element.

Improvements could be using 7 panel strings which would raise the MPPV to around 250V instead of the 210V I have now.

For those wishing to build this without the solar power diversion feature (once the thermostat opens) just delete the relay and the extra IGBT in the schematic above.