Does an Electric and Gas Hybrid water heater exist?

[kampto]

Off grid here, my water heater is propane. My solar has my battery's at 100% by half day so Im not utilizing extra >2000 watts of solar rest of day because the AC load is low. Would be cool to put that to work to with an electric water heater (120/240v). Just enough to keep it warm. But then on cloudy or snowed in days I would use propane to heat water. Does a Hybrid water heater exist? A smaller tank, 30gal or so.

 

[SparkyJJO]

People have done a DIY of their own so to speak by putting an electric in series before their gas, so the solar preheats the water going into the gas heater. Solar preheated water cuts gas usage, but of course if solar isn't there then you don't get the preheating and the gas does all the work.

 

[wpns]

Your best bet is to put them in series as @SparkyJJO said. Use as big a tank as you can, then you'll capture the maximum surplus solar.

 

[Suijkerbuijk]

Off grid here, my water heater is propane. My solar has my battery's at 100% by half day so Im not utilizing extra >2000 watts of solar rest of day because the AC load is low. Would be cool to put that to work to with an electric water heater (120/240v). Just enough to keep it warm. But then on cloudy or snowed in days I would use propane to heat water. Does a Hybrid water heater exist? A smaller tank, 30gal or so.

Yes in my country it call solar boiler.
Thare are different models

 

[Zwy]

I installed a 50 gallon hybrid heat pump water heater ahead of the 50 gallon propane power vent water heater. The propane unit is backup and can be used during winter with limited PV available. The hybrid can use the heat pump or the electric element or both. I like options.

 

[efficientPV]

Heating elements will fit inside a standard pipe. Another tank in series is not a solution unless you want to take the easy way out and get a 2 gallon tank. Just heat water and pump it thru existing tank. Another tank just added heat loss.

 

[kampto]

Yeah, In series will push hot water thru a cold water tank or vs versa. I wont use house water most of the day so want to warm water in single tank for when needed later using electricity during sunny days or propane on cloudy days/nights.

Found some RV units that can do electric or gas only, or both. They kinda small and location would need safety mods I think.

Direct Spark Ignition Porcelain Lined, Steel Tank Water Heaters, 16 Gallon for RVs & Campers - Suburban

16 Gallon Suburban Advantage Tank Water Heater with Direct Spark Ignition

suburbanrv.com

Will keep googling..

 

[Suijkerbuijk]

Wy not use a boiler?
We have eco boilers in my country that you just connect on the power outlet.
Reason its eco its really good isolated inside .
So your warm up in the day and stay hot in the night for shower and more
It have timers so you can set the time to heat up again

 

[SparkyJJO]

Yeah, In series will push hot water thru a cold water tank or vs versa. I wont use house water most of the day so want to warm water in single tank for when needed later using electricity during sunny days or propane on cloudy days/nights.

Found some RV units that can do electric or gas only, or both. They kinda small and location would need safety mods I think.

Direct Spark Ignition Porcelain Lined, Steel Tank Water Heaters, 16 Gallon for RVs & Campers - Suburban

16 Gallon Suburban Advantage Tank Water Heater with Direct Spark Ignition

suburbanrv.com

Will keep googling..

Not exactly. Both tanks are hot. If you push hot water (solar heated) into the gas water heater, it won't use as much gas. If the electric tank is not heated at all due to no solar to run it, then the gas water heater acts just like it normally would by itself. Cold water in, hot water out.

 

[kampto]

Not exactly. Both tanks are hot. If you push hot water (solar heated) into the gas water heater, it won't use as much gas. If the electric tank is not heated at all due to no solar to run it, then the gas water heater acts just like it normally would by itself. Cold water in, hot water out.

You are correct!, if gas is after then no worries, gas will heat up the water. But the other way I would need to push all the cold water out of the gas tank before the electric heated water gets thru without gas on. Plan is in summer gas off all the time, luke warm water is all i need.

 

[Zwy]

Heating elements will fit inside a standard pipe. Another tank in series is not a solution unless you want to take the easy way out and get a 2 gallon tank. Just heat water and pump it thru existing tank. Another tank just added heat loss.

Who cares about any heat loss when the electricity is free? Without a dump load or consumption, the potential energy wouldn't get used. The "lost" energy can be absorbed back into the hot water heater when using the heat pump mode.

The advantage of 2 tanks is I have 100 gallons of hot water available. This allows us to get thru a few days during winter cloudy/foggy conditions which will help extend remaining battery bank capacity during low PV production.

Any heat loss also helps maintain my basement temp in winter, I see everything as a positive with very few negatives.

 

[Zwy]

You are correct!, if gas is after then no worries, gas will heat up the water. But the other way I would need to push all the cold water out of the gas tank before the electric heated water gets thru without gas on. Plan is in summer gas off all the time, luke warm water is all i need.

I've had this working since March and can tell you the only time I notice anything is if I was to take a shower in the evening after work and no one had run any hot water in the house since early morning. The shower temp is still hot but gets hotter the longer you take a shower so even with a thermostatic valve you might have to turn the water temp down slightly. It is not cold water, it is hot.

I haven't plugged the propane back in since I unplugged it before leaving on vacation the first week of September. I turned off the heat pump water heater and turned it back on the day before we returned using the app on my phone. I ran the water for about 10 to 15 minutes while unpacking the camper and had hot water at the sink.

Don't worry about one tank being colder than the other. Heat pump or electric water heater ahead of the gas water heater with the water temp set higher than the gas. You will never notice it.

I think the heat pump water heater in series ahead of the gas water heater was one of the best additions to my system. The others were mini split heat pumps allowing zoning in different parts of the house and using excess PV for heating purposes.

 

[efficientPV]

Heat pump in front of a gas water heater, now I've heard everything.

 

[SparkyJJO]

Heat pump in front of a gas water heater, now I've heard everything.

Hey, but it works. No one makes a heat pump gas fired water heater all in one, that I know of.

 

[EnergizerNate]

How do you all control the electric/heat pump water heater so it only runs if batteries are charged and you have extra solar? I like this idea...

 

[SparkyJJO]

There's a few different ways. Some inverters have dry contacts that you can program to do whatever you want so at full charge the relay closes, and you can use that to control the dump load. Or you can use a voltage controlled relay so when batteries hit full charge voltage, it triggers the dump load. There's other ways too I'm sure.

 

[wpns]

How do you all control the electric/heat pump water heater so it only runs if batteries are charged and you have extra solar? I like this idea...

Well, I'd use something like a Shelly Pro 1 PM, but you could use a contactor hooked up to "your device that watches SOC", or a Smart Load output from your inverter, or <lots of options>. Depends on what you have for process tools.

 

[Offgrid Jungle]

I am using the Shelly Plus Add On module to connect to my thermistor sender. That gives me the temperature reading of the water, allowing endless possibilities to turn on and off at any SOC or PV output.

Shelly add on

 

[Zwy]

Heat pump in front of a gas water heater, now I've heard everything.

It goes like this, gas water heater has been in place long before the PV system was installed and worked with no problems. After PV system was up and running, there was excess PV not being used in the off grid system.

Looking for something that would work for capitalizing on the excess PV, it was decided to add an electric hot water heater ahead of the gas water heater. More research reveals the hybrid heat pump water heaters which can be used in heat pump mode, electric 4500W element mode or a combination of both. A water heater that works very well for an off grid PV system that has excess photons collected. Heat pump mode can be used most of the year, the electric element allows for using large amounts of generation in a short period of time and the gas water heater can heat water in times of very low PV production.

`As for cost, this post explains it. Payback will be 2.5 to 3.5 years. Plus, we have 100 gallons of hot water instead of 50 gallons. The heat pump water heater qualifies for the federal energy efficiency tax credit of 30% of the cost. Local utilities might even kick in a rebate reducing payback sooner. If the heat pump water heater lasts 10 years and payback was 2.5 years, at $1.45/gallon propane and 300 gallons per year, I net $3,262.50 over the lifetime of the heat pump water heater. If it lasts longer than 10 years, I net an extra $435 per year. If propane is higher than $1.45/gallon, I net even more. The cost to run the heat pump water heater is $0.00 if excess PV is used to operate it.

The heat pump water heater uses such a small amount of electricity that I am still looking for another use for excess PV generation.

 

[ULR]

I have a pilot-light propane water heater at my (not yet solarified) retirement house. It has a "vacation" setting that turns down the main burner start point to "keep the pipes from freezing" levels but leaves the pilot running.

Coming into the house after an absence, I find that the pilot light alone has keep the tank at nearly the normal-operation temperature.

This tells me that if I put an electric water(pre)heater in front of it, once the gas heater fills with hot water it will keep it hot for days with minimal fuel use. So the pre-heater will do essentially all the heating during long-term normal use, if solar power is available to run it, and the main burner in the gas heater will almost never come on - and then only to tweak the last couple degrees into the tank if set that way and the hot water has been unused, say for a day or two - unless solar input is insufficient so you need to heat with gas.

========

Another thing you can do is get a small electric heater and hook it in "parallel" with the gas tank: Mount it low beside the gas tank, plumb the little guy's hot output up to the regular tank's hot output, the little guy's cold input from a low tap (like the flush valve) of the big tank, and arrange the elbows so the regular flow doesn't drive significant water current through the little tank. When the little tank comes on the hot water will circulate to the top of the main tank by convection, bringing the hot/cold boundary down gradually until it reaches the level of the temperature sensor in the little electric tank.

=====

Note that, on some AIOs (e.g. the EG4 xxkPVs) the generator input can be programmed as a "smart load control" OUTPUT to provide AC to a "dump load" when there's surplus solar power. Just the thing for automating the power to an off-the-shelf AC electric water heater for a surplus-solar-power pre-heater.

(I think what's behind those terminals is yet another two-way inverter/synchronous rectifier, maybe with current transformers, another set of bypass relays, and inverter frequency/phase synchronization with the main inverter to let it do generator-assist rather than just rectifying genny into the DC battery bus or inverting battery/solar DC power for smart loads.)

 

[Madcodger]

Hey, but it works. No one makes a heat pump gas fired water heater all in one, that I know of.

Personally, I really like this idea - especially if you can just turn off the heat pump water heater overnight and on cloudy days. We use a heat pump water heater and love it, but on cloudy days in late December when we're looking to extend every available watt, it might be nice to just turn it off and use gas (the backup heat system to the heat pumps, also for those long, cold, cloudy stretches) to supply us with a nice, long shower. I think I could do it by plumbing in a heat exchanger to the primary loop of the hydronic system. Hmmm.....

 

[wpns]

Personally, I really like this idea - especially if you can just turn off the heat pump water heater overnight and on cloudy days. We use a heat pump water heater and love it, but on cloudy days in late December when we're looking to extend every available watt, it might be nice to just turn it off and use gas (the backup heat system to the heat pumps, also for those long, cold, cloudy stretches) to supply us with a nice, long shower. I think I could do it by plumbing in a heat exchanger to the primary loop of the hydronic system. Hmmm.....

Tri- fuel (or quad? Quint?) hot water heater anyone?
Solar thermal
Heat pump
Resistance
Propane
Natural Gas

 

[ULR]

I think I could do it by plumbing in a heat exchanger to the primary loop of the hydronic system. Hmmm.....

I wouldn't want to be one heat exchanger internal leak away from drinking or cooking with hydronic coolant contaminated water.

Maybe use this hack:
- remove the skin and insulation from the water heater temporarily.
- wrap it with a coil of copper water pipe (to be hooked into the hydronic system. Maybe solder it to the tank.
- replace the insulation and skin.
Then if you get a leak of hydronic coolant it drips out of your water heater's insulation into the drip pan rather than going into your drinking water supply.

 

[Madcodger]

I wouldn't want to be one heat exchanger internal leak away from drinking or cooking with hydronic coolant contaminated water.

Well, they are designed for that, and people are often one check valve away from problems (and a failure there is far more likely). Having an exchanger fail in that way is a very low probability. Driving and walking down the street is a much greater risk.

 

[Suijkerbuijk]

You can always go diy lol.