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Comment by jay_kyburz | Hacker News Reader

Gas is super expensive here in Australia and I plan to try and put 10kw solar on the roof next year. Our hot water is currently gas but I would like to move to electricity. The solar will take 10 years to pay off, I expect adding this to the mix would take another 10 years.

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I have a AO Smith hybrid water heater for the last year and half. Seems to work. Made sense in my case because I wanted to move water heater from the house to the garage. Using a hybrid unit meant I didn't need to plumb gas and figure out how to install a vent.

My suggestion is when you get your solar system installed have the electricians run a 30 amp circuit and disconnect to the water heater location. That way you'll be ready to go. Otherwise you can get stuck if you current water heater dies. You'll be basically forced to replace it with a new gas heater.

Also I saw a youtube video by a off grid nut talking about installing a heat pump water heater. It worked, the only problem it had was the AO Smith unit he was using would test it's heating elements on startup. Which would overload his inverter. I think he fixed that by getting higher resistance heating elements. Otherwise the current draw in heat pump only mode was 300 Watts.

10kW on the roof and a Sanden heat pump hot water set to only run 9-5. I get credit from the Energy Australia for all the summer months which I spend on on the AC heat pump in winter. 25 year warranty on the panels and 20 on the micro inverters. The economics stack up.

Sanden do seem to be the recommended option for this. The problem is if you have a functional gas, the economics rarely stack up to change. If I knew for sure the Sanden would last 10 years yes, but unlike very simple gas water heaters, heat pumps have a disturbingly high failure rate.*

*At least that was the way it seemed from my research, similar situation 6.66kw solar on roof, functional gas hotwater. We do have both Gas and Heat pump house heating/cooling. Heat pump is much cheaper, gas is much faster, even running the largest size possible ducted heat pump split system. I have the gas warm the house from 6am to 8am, then heat pump take over for the rest of the day.

My Daikin is near instant, even when near freezing outside. The compressor is yuge though, so maybe that’s why.

Daikin RXYMQ6AV4A 2 x Daikin FXMQ80PAVE

Also check out https://brighte.com.au/ for an interest free loan for this stuff. backed by Michael Cannon-Brookes.

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