Measuring and acting on solar export


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Haxby

Guru

Joined: 07/07/2008
Location: Australia
Posts: 384
Posted: 12:12am 14 Jan 2022      

I'd be reluctant to do any sort of switching with DC. Whether with relays or igbts, either way it gets a bit complicated and needs a lot of thought put into all the ways it can go wrong.

I'm also not really keen on changing elements in the heater, nor keen on adding more elements.

So I think I'll add the transformer to drop the voltage and call it a day. The existing timer will be set from 10am to 4pm. That's 6 hours at 1.4kw. should be plenty. I could have a manual switch to revert back to 3.6kw on the occasional day we have very heavy hot water demand.

If I had off-peak electricity, I'd consider having 2 thermostats on the tank, set to 2 different cutoff temperatures. The higher cutoff temp thermostat would be connected to daytime solar production, and the lower temp thermostat connected to the off-peak electricity.

So the sun does as much as it can during the day, and the off-peak only turns on when the water has dropped to close to an unusable temperature.


Interestingly here in Victoria, we have a government scheme that will install a free heat pump in exchange for your old resistive tank. I hear that the free one is small and not good quality, but you can pay a nominal fee to upgrade to a bigger and better quality unit.

I absolutely love heat pumps, but if I went with this approach, I'd have 3 heat pumps on the side of my house. The noise might become an issue for the neighbours. With the pool heat pump, pool water pump, air conditioning and now a Hot water heat pump, there would always be an industrial hum coming from our house