Measuring and acting on solar export


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Technophiliac

Regular Member

Joined: 18/12/2020
Location: New Zealand
Posts: 87
Posted: 08:46am 14 Jan 2022      

  Haxby said  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.

Exactly, I've been pondering how to do this too. One can buy 3 phase elements that also have a central temperature probe provision. I understand a temperature controlled probe / relay could be used this way for the 2nd thermostat.

  Haxby said  
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.


Some SSR's may be best avoided, however I find it difficult to believe they are all untrustworthy. I am "currently" testing a heat sink mounted one, with no problems to date although "currently" its only switching / breaking <=25A @ 13 volts DC.

  Haxby said  
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  


From a green energy perspective I expect Heat Pumps require bigger inverters compared to simple resistive Hot Water elements. Even with slow start motors I anticipate higher peak power requirements than pure resistive elements will minimally have. Plainly there will be variance in peak power load with different models and manufacturers. Slow start motors may well have lower peak power demand, I doubt it will match a hot water element. This may or may not be a consideration depending on each case. Plainly efficiency is in their favor. Are there any that run at lower voltages?