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Good job! Did you get a multi-year lock on the price paid for energy you put into the grid? Or were you effected by the rate structure change? My next step is to install solar thermal to eliminate the power needed to heat our water.
I’m in California, on NEM 2.0 for 8 more years unless NEM 3 gets rescinded. I also want to switch out my water heater to eliminate most of my fossil fuel burning, but instead of solar thermal I’ve been looking at heat pump water heaters. Much easier and cheaper to install, even with having to run a 240V line across the garage. If you currently have an electric resistance water heater, going with heat pump is a drop-in replacement and uses much, much less energy.
There are 120V HPWHs now too. Depending on your water use and incoming water temps, it could be an even cheaper solution since you might avoid the wiring run.
Yeah, but they tend to be lower efficiency (UEF 3.0) and CA rebate program requires UEF 3.3 or higher, which apparently you can only get by switching to the higher voltage.
Edit: to clarify, I was referring to the California state rebate of $700 or $900 (depending on capacity) taken off the purchase price at checkout. The federal tax credit of 30% applies to the 120V drop-in replacement as well as the 240V models.
There are a few over 3.3 on the ESTAR product finder, and I think this is just a reflection that these products are new and there aren’t that many out there. It’s all a bit dumb since a 240V can be run in hybrid/high output/electric resistance mode and kill your efficiency, but the 120V are usually HP only and they have the exact same compressor since they only need like 800watts in HP mode, so there’s no reason for their efficiency to be lower whatsoever. Do what you need to do to get that incentive money though.
I checked Home Depot today and, oddly, all the Rheem 240V models are selling for less than the 120V models of the same capacity, even before rebates.
If I do get a 240V model, I certainly would just disable the resistance heating mode, which all the Rheem models (and probably all models, period) have the option to do.
Why not just run a heat pump with the electricity you made? Probably more efficient overall.
Solar module efficiency is what, about 20% at best? Thermal is more like 60%. This means less roof area needed on a house that doesn’t have a lot of solar exposure.
Then there’s cost. With the thermal system I’m planning there will be 40gal of potentially very hot water mixed down to the (lower) maximum temperature of my 40gal electric water heater, which will again be mixed down to the maximum temperature allowed for domestic use. In effect the design will be one battery feeding into another. 'Seems cheaper than lithium batteries, and since this will be a passive system, no controller will be needed.
You also have to deal with a ton of extra plumbing and envelope penetrations, and the space the thermal solar collector takes up doesn’t fit nicely with a solar PV array either. A HPWH might use 800 kWh/year, so thats like less than two 400+ W panels to cover all your water heating. I think thermal solar is fine tech and there are certainly situations where it makes sense (perhaps yours) but overwhelmingly HPWH is more cost effective and simpler.
Solar module efficiency is what, about 20% at best? Thermal is more like 60%. This means less roof area needed on a house that doesn’t have a lot of solar exposure.
So anything above a CoP of 3 and you need less area. That’s pretty doable these days. Maybe read up on how heat pumps work first before making assertions.
Also you can totally store hot water from a heat pump.
The main disadvantage is cost and complexity.