What kind of water heater is appropriate (to not use Gas) if you have powerwall and solar?
A Hybrid hot water heater is the most efficient. It uses a heat pump and is about double the efficiency of a typical electric water heater. Here is one: https://www.homedepot.com/p/Rheem-ProTerra-50-Gal-10-Year-Hybrid-High-Ef...
I didn't look to see what other ones are available but gives you an idea about what to look for.
The straight electric heating element type is terribly inefficient, as compared to natgas. I'm not familiar with the hybrids, as TT indicated above, but they've gotta be better than the resistive heating ones.
Whatever you choose, feeding it with a solar water heating system is another option, too.
What about electric point source water heaters?
If you want to avoid using natural gas, heat pump hybrids are by far the best option. I just switched out an on-demand electric for a Rheem hybrid and the usage went from ~10 kWh/day To ~3! Plus, it’s generally much more off-peak usage so if you have TOU rates the savings are even more.
It does require a ventilated space but you can duct it if you have that option. If it’s in a space with too much ambient heat, it’s also ‘free’ air conditioning!
Also, I suggest buying the bigger tank, because the smaller one probably will have to switch on the heating element more often which takes away some of the efficiency.
Same experience as zachbroth - great solution.
The other problem we would like to solve is that we waste a lot of water waiting for it to heat. Will an hybrid also solves this problem?
@oscar - No water heater can solve that problem. You need to install a recirculation pump, and it may depend on how your house is plumed if that can work. Ideally, you have a hot-water return from the furthest location in your house to the hot water heater.
I have 3 Powerwalls and solar, we have a hybrid water heater. It only uses about 600 watts when in heat pump mode and uses about 60KWh a month. Has worked perfectly for us so far.
I added a water heater recirculation loop to my hot water system when I did a remodel. I also insulated every hot water line in the house, all the way down the walls, too. While adding the insulation down the walls is probably a non-starter with a simple retrofit, adding the return line and insulating the hot water pipes was a one-day job. My natgas tankless water heater has its own recirc pump, and keeps the hot water return loop hot all of the time. I get hot water to my furthest fixtures in seven seconds, and the entire system is *much* more efficient than a natgas tanked system.
A simpler solution: a recirculation pump can be put at the point of use, with the cold water line used as the return. They can be controlled with a simple toggle switch or a quick on-off-on-off of the hot water valve. "Hot" water is drawn to the location by the pump, and the cool water that was in the hot water pipes is sent back to the water heater via the cold water line. The pump shuts off when the desired temp is reached. It doesn't save much energy, but it does save a bunch of potable water that would have gone down the drain while waiting for hot water to get there. One caveat: You'll need an AC power source at the location of the pump.
Then there's the old-school method of saving the water while hot water is getting to a far fixture like a shower or tub...a five-gallon bucket. Collect the warming water in a bucket until it's hot enough, and dump it in your garden after you bathe. Die-hard environmentalists have been doing this for generations...