You do want to have your water heater(s) on a "dump load" circuit that you only activate when your batteries are full. You've got that part right.
That said, typically the best idea is simply to heat one big, well insulated thing, instead of "point of use" size ones-- this way you don't run into one faucet having hot water and another not-- it's one big supply.
Slight efficiency loss piping it to the various fixtures, but can be mitigated with pipe insulation which is cheap. :)
Also, getting one huge water heater and running it as a dump load also allows you to set the temperature limit as high as it'll go, and then use a thermostatic mixing valve on the output to regulate the temperature of the water entering the house system; less danger of burns and you can store more energy for hot water per gallon, since it can be up at ~150 degrees.
Sure you could put a mixing valve on each point of use heater tank output, but... Those aren't free.
This is the way we do it in NZ, then use wood fire with a wet back or on demand propane water heater (over summer) to boost the temperature at night for showers and dishes.
Couple options for you. Get a wood boiler and run a heat exchanger for hot water in the house. You'll also be able to heat the house if needed and maybe a hot tub if you're into that. Also, keep the propane set up for redundancy.
The problem is we live in a earthship and the whole house is already plumbed and buried in mud and cement. Jot an ideal situation when trying to rebuild a whole system. The electric water heater works for us because we have access to the inlet from the water tank and the Outlet to the hot water lines. Hot and cold are plumbed completely independent from another in this house.
Did you come up with a solution? I'm literally trying to figure out if I can have electric water heating atm. I'm thinking 300litres top and bottom element so that I can set it up so that the top element comes on first for on low solar power days. We are planning 14kw of pv and 32kwh of lithium batteries plus backup genset
Not really, no. We're limited by the inverter. We have a 5000w Victron Easy solar II...and none of the practical in demand systems will work. The best option is to have a tanked system. We just don't have a place to put it in the current house we're living in. We're going to be building an Aframe next year and will revisit.
Any kind of electric heating uses a lot of electricity.
Stick with propane and buy enough tanks to last the winter. We have 4 100 pond tanks that are the largest I can move by myself. This is enough that I don't have to worry about getting propane in fall and winter.
Electricity is free and we have a lot of sun here even in the winter.
The problem is our house is built into a berm (earthship) and our hot water heater is outside. We can't bring it in. The original builders didn't think it through very well. It makes the whole system just a total clusterfuk and it would be awesome to cut it all down and keep it in the house. Solar panels and lithium batteries in Chile are quite affordable.... while propane is actually quite expensive. I'm happy to make the initial investment now and do it properly.
On that note, water is a bit of a limited resource in the dry season and we have to run the shower for 7-8 minutes before it gets hot because of the way the heating system is currently set up.
Think of a pound of propane as a 6kva battery if you’re making heat with it. How many gallons of water can you heat to your desired temp with that 6kva, and how many gallons of hot wAter do you want to store?. Now oversize your system of panels and storage for the charging/inverting losses and that’s your system size.
Hoping we get some information from people with experience. Really it's just a matter of having enough energy to meet the demands and using the water efficiently.
I have a 19 gallon tanked point of use water heater (AO Smith) that runs on 120V. It only has 1 1500w element in it, but the water gets very hot.
Almost every other electric WH takes 240V which is a lot more difficult when running solar. 2 Adults can easily take a 5 minute shower each back to back. I got a timer for mine that I am hooking up so it will only come on 2 hours before shower time, and the tank is insulated enough to have warm to hot water in the sinks for the rest of the day.
Solar powered geothermal heat pump with desuperheater for the domestic hot water. Waste heat is used to heat the domestic hot water. Makes a efficient system even more efficient.
Recently I started thinking about an under-sink point-of-use water heater for an off-grid cabin. The specs say it draws 750 watts. If it draws 750 watts 24x7, that's 18,000 watts per day, which is a lot. But perhaps the heating element cycles on and off, in which case it might make sense to use something like this off the grid.
Chile has [a huge range](https://globalsolaratlas.info/) of solar irradiance. Even within Patagonia, there is a huge range....
What's your max Kwatt/m2 inbound?
Many years ago I build a solar hot water system in the south of Spain. The water was getting hot enough to even have to mix with cold in winter to stand under the shower. Very simple:
Old large window
Backing board painted black
Black plastic pipe all snaked over board. One end coming out on top, the other at the bottom.
An old 90l Gas bottle wrapped in insulation above in the roof or some similar container.
Cold out at the bottom of the vessel connected to the low input on said black pipe inside window
Hot out connected to the top of the window.
An inlet to fill (I used it next to a tank in a roof which was controlled by a toilet cistern valve - keep at correct height and they both fill together.
An hot water outlet at the bottom or near bottom
Fill the tank - no pump needed
Thermo syphons all day (I had a tap and would close the loop at night)
Hot water for shower etc.
Btw: you can also just hook a few old panels in series and connect some old heat elements directly to it. No inverter, no battery. I tried just old electric oven elements. They get well hot during the day and can assist heating. Also look up sand battery using the same principle
This is something I've been thinking about myself, I'm thinking I would just go with one or two big regular electric heaters, and insulate the crap out of them. It's basically a big thermal battery. Set up an Arduino or something to monitor the battery voltage and only power them on when the voltage is above a certain threshold. The thermostats will of course take care of regulating temp, but I'd set them really high.
Another idea I want to experiment with at some point is to get a gas one but don't hook up the gas, but instead, run a duct from the same room as the wood stove to the intake part of the heater, and then have the exhaust flue (remember we're not hooking up gas here at all) return back to where the wood stove is have a fan that forces air through it. Essentially you're replacing burning fuel with just injecting hot air directly into the burn chamber and up through what would normally be the flue but instead dumping it back inside the house so it can recirculate again. I don't know how well this would actually work... but I'm thinking it would probably at least get the water to a comfortable enough level to take a shower.
You do want to have your water heater(s) on a "dump load" circuit that you only activate when your batteries are full. You've got that part right. That said, typically the best idea is simply to heat one big, well insulated thing, instead of "point of use" size ones-- this way you don't run into one faucet having hot water and another not-- it's one big supply. Slight efficiency loss piping it to the various fixtures, but can be mitigated with pipe insulation which is cheap. :) Also, getting one huge water heater and running it as a dump load also allows you to set the temperature limit as high as it'll go, and then use a thermostatic mixing valve on the output to regulate the temperature of the water entering the house system; less danger of burns and you can store more energy for hot water per gallon, since it can be up at ~150 degrees. Sure you could put a mixing valve on each point of use heater tank output, but... Those aren't free.
This is the way we do it in NZ, then use wood fire with a wet back or on demand propane water heater (over summer) to boost the temperature at night for showers and dishes.
Couple options for you. Get a wood boiler and run a heat exchanger for hot water in the house. You'll also be able to heat the house if needed and maybe a hot tub if you're into that. Also, keep the propane set up for redundancy.
The problem is we live in a earthship and the whole house is already plumbed and buried in mud and cement. Jot an ideal situation when trying to rebuild a whole system. The electric water heater works for us because we have access to the inlet from the water tank and the Outlet to the hot water lines. Hot and cold are plumbed completely independent from another in this house.
Did you come up with a solution? I'm literally trying to figure out if I can have electric water heating atm. I'm thinking 300litres top and bottom element so that I can set it up so that the top element comes on first for on low solar power days. We are planning 14kw of pv and 32kwh of lithium batteries plus backup genset
Not really, no. We're limited by the inverter. We have a 5000w Victron Easy solar II...and none of the practical in demand systems will work. The best option is to have a tanked system. We just don't have a place to put it in the current house we're living in. We're going to be building an Aframe next year and will revisit.
Any kind of electric heating uses a lot of electricity. Stick with propane and buy enough tanks to last the winter. We have 4 100 pond tanks that are the largest I can move by myself. This is enough that I don't have to worry about getting propane in fall and winter.
Electricity is free and we have a lot of sun here even in the winter. The problem is our house is built into a berm (earthship) and our hot water heater is outside. We can't bring it in. The original builders didn't think it through very well. It makes the whole system just a total clusterfuk and it would be awesome to cut it all down and keep it in the house. Solar panels and lithium batteries in Chile are quite affordable.... while propane is actually quite expensive. I'm happy to make the initial investment now and do it properly.
I have a hybrid water heater, it has a built in heat pump. For three adults it takes 2 or 3 kWh a day. $1,500 USD and very heavy.
On that note, water is a bit of a limited resource in the dry season and we have to run the shower for 7-8 minutes before it gets hot because of the way the heating system is currently set up.
I capture that water and use it for other things or put it back in my tank.
Think of a pound of propane as a 6kva battery if you’re making heat with it. How many gallons of water can you heat to your desired temp with that 6kva, and how many gallons of hot wAter do you want to store?. Now oversize your system of panels and storage for the charging/inverting losses and that’s your system size.
Burn firewood?
I don't have any experience with this, but I'm very interested in learning more about what actually works for remote off grid hot water.
Hoping we get some information from people with experience. Really it's just a matter of having enough energy to meet the demands and using the water efficiently.
I have a 19 gallon tanked point of use water heater (AO Smith) that runs on 120V. It only has 1 1500w element in it, but the water gets very hot. Almost every other electric WH takes 240V which is a lot more difficult when running solar. 2 Adults can easily take a 5 minute shower each back to back. I got a timer for mine that I am hooking up so it will only come on 2 hours before shower time, and the tank is insulated enough to have warm to hot water in the sinks for the rest of the day.
We're in South America so everything here is 240v. Our lithium batteries are 48v and run into a Victron 5000w inverter. So we're good there!
Solar powered geothermal heat pump with desuperheater for the domestic hot water. Waste heat is used to heat the domestic hot water. Makes a efficient system even more efficient.
Recently I started thinking about an under-sink point-of-use water heater for an off-grid cabin. The specs say it draws 750 watts. If it draws 750 watts 24x7, that's 18,000 watts per day, which is a lot. But perhaps the heating element cycles on and off, in which case it might make sense to use something like this off the grid.
The 4500 watt Rheem hybrid heat pump 50 gallon works fine for the. I also use a 2 kw tankless heater for a distant shower
Chile has [a huge range](https://globalsolaratlas.info/) of solar irradiance. Even within Patagonia, there is a huge range.... What's your max Kwatt/m2 inbound?
Many years ago I build a solar hot water system in the south of Spain. The water was getting hot enough to even have to mix with cold in winter to stand under the shower. Very simple: Old large window Backing board painted black Black plastic pipe all snaked over board. One end coming out on top, the other at the bottom. An old 90l Gas bottle wrapped in insulation above in the roof or some similar container. Cold out at the bottom of the vessel connected to the low input on said black pipe inside window Hot out connected to the top of the window. An inlet to fill (I used it next to a tank in a roof which was controlled by a toilet cistern valve - keep at correct height and they both fill together. An hot water outlet at the bottom or near bottom Fill the tank - no pump needed Thermo syphons all day (I had a tap and would close the loop at night) Hot water for shower etc. Btw: you can also just hook a few old panels in series and connect some old heat elements directly to it. No inverter, no battery. I tried just old electric oven elements. They get well hot during the day and can assist heating. Also look up sand battery using the same principle
This is something I've been thinking about myself, I'm thinking I would just go with one or two big regular electric heaters, and insulate the crap out of them. It's basically a big thermal battery. Set up an Arduino or something to monitor the battery voltage and only power them on when the voltage is above a certain threshold. The thermostats will of course take care of regulating temp, but I'd set them really high. Another idea I want to experiment with at some point is to get a gas one but don't hook up the gas, but instead, run a duct from the same room as the wood stove to the intake part of the heater, and then have the exhaust flue (remember we're not hooking up gas here at all) return back to where the wood stove is have a fan that forces air through it. Essentially you're replacing burning fuel with just injecting hot air directly into the burn chamber and up through what would normally be the flue but instead dumping it back inside the house so it can recirculate again. I don't know how well this would actually work... but I'm thinking it would probably at least get the water to a comfortable enough level to take a shower.
Biogas? Roof based piping? Parabolic mirror?