Thanks so much for the great discussion. I'm feeling pretty dense because I'm still pretty confused about things so I'm going to try to sum up:
Water Heater Summary:
on-demand flash heater: 1.41kW output, 30A at 120VAC or 3600w, which for 30 mins/day is 1800wH. With a 90% inverter efficiency would be ~85Ah on a 12v battery (boondox). may be preferred over a tank since water conservation is a goal aligned with energy conservation
to convert a tank WH, replace the plug with a heating element, 400 watts at 110VAC (time2roll). I don't know how much energy that would use over a day but for the sake of a calculation, let's assume 6-gallon tank and it's emptied once at the end of the day.
circus suggests being a guinea pig for a Chinese 12v diesel air heater knock off for water ?
prof farnsworth also suggests on demand can work, but run 24v instead of 12v to keep amperage low
solar heat water if you can (stepandwolf)
Refrigerator:
Go for a compressor fridge with Danfoss compressor. compressors seem to take one of 12v, 24 DC or 110VAC. isotemp water heater is recommended
https://www.indelwebastomarine.com/us/products/isotemp-water-heaters/basic/ - comes with 115 or 230VAC compressor
Inverter:
3000w inverter and avoid Renogy (time2roll, boondox, prof farnsworth).
Large draws:
Use a shed relay to cut power from WH when stove runs (thanks time2roll!)
12v vs 24v:
24v (prof farnsworth, time2roll, boondox) with 24v batteries in parallel - will need DC to DC converter to run to 12v fuse block for lights, etc
propane vs electric
everybody: keep the propane if you can
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My response:
I'm hoping that we can go back to propane but so far there's a hard no coming from my better half so I need to put this together to 1) understand what we are getting into with all-electric and 2) use as evidence to put back the propane or 3) make this all-electric conversion work for us. So, sadly, propane is not really going to work right now :-\
Sounds like the overwhelming suggestion on the base system is to make this work with 24v batteries in parallel. With my current setup (Renogy rover 40A mppt charge controller and 400w solar) the charge controller specs say "24V @ 1040W" but my first battery is 100Ah 12v Renogy battery which explicitly can only be run in parallel. So does that mean this battery is a dead end for me in this scenario? Would it be too much to string multiple batteries in parallel and then boost 12v to 24v for the short run to the inverter?
I will need a new inverter, 3000w, and something more reliable than Renogy. Need to ultimately do the energy budget but this seems likely already.
Refrigerator:
Find a fridge with the 12v compressor. It will probably use half or most of the energy produced by the 400w of solar running at 5-6A most of the day, but maybe less.
Water Heater:
Still most confused about this. What would be the minimum GPM I would need for a shower? I read that 1.5 GPM is standard low flow but the point-of-use water heaters I see that use less than 2kW @110VAC are 0.4 or 0.2 GPM. OTOH, here's a 4-gal tank that uses 1.4kW @110:
https://www.zoro.com/bosch-4-gal-12...k-water-heater-es4/i/G3114273/#specifications
Stove:
Not much feedback here except we should install the shed relay to keep the hot water heater from turning on while running the stove. And cook outside with gas. It would be nice not to have to set up a grill outside every time we want to cook so we'd really like to make the stove work. Looks like the induction cooktop I mentioned at the beginning will use almost the whole capacity of the existing inverter, though I recognize that will. have to get upgraded.
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Finally, TL;DR:
1) Can I use my existing battery to build a bank that will support a 24V system even though they cant be run in series? Should I?
2) Recommendation for a water tank?
3) Suggestions on an inverter?