Electric water heater off grid

[ericfx1984]

For off-grid electric water heaters I was considering converting a standard AC water heater to 48 volts

But I got to thinking to do it right it's probably going to cost me about $100 to $150 worth of parts added on to the cost of the already existing water heater

Additionally I'm having trouble finding a good way to reliably handle the current at what will be close to 58 volts

Which of course brings on the possibility of using a 12 volt thermal switch and using that as a means for keying a large relay that can handle the current of a pair of 1500 w 48 volts water heating elements

But would it make more sense to just buy a four or $500 inverter and dedicated specifically for the hot water heater?

I know that this is going to be my plan for use with the individual mini splits... I feel like I could attach several 5,000 w inverters to the battery bank and use those to power various different mini splits and be able to shut them off when not in use... The same approach would be a really good way to control when we're using the hot water and when we are not

 

[time2roll]

I recommend a heat pump electric water heater driven by the inverter.

 

[Nobodybusiness]

For off-grid electric water heaters I was considering converting a standard AC water heater to 48 volts

But I got to thinking to do it right it's probably going to cost me about $100 to $150 worth of parts added on to the cost of the already existing water heater

Additionally I'm having trouble finding a good way to reliably handle the current at what will be close to 58 volts

Which of course brings on the possibility of using a 12 volt thermal switch and using that as a means for keying a large relay that can handle the current of a pair of 1500 w 48 volts water heating elements

But would it make more sense to just buy a four or $500 inverter and dedicated specifically for the hot water heater?

I know that this is going to be my plan for use with the individual mini splits... I feel like I could attach several 5,000 w inverters to the battery bank and use those to power various different mini splits and be able to shut them off when not in use... The same approach would be a really good way to control when we're using the hot water and when we are not

I’m guess a Rheem Heat pump water heater is out of the question?
They are a bit pricey but IMHO worth it.

 

[Warpspeed]

Heat pump is the best idea if the budget stretches that far.

 

[efficientPV]

Every successful PV system has excess power daily which is just wasted. Resistance heating is a fine way to use this power which is just free. Diverting this power in the relative scope of things is easy and cheap (less than $20) with a technical background. For 99% of the members here it is a monumental endeavor. Until there is an actual demand and understanding of these products make it fairly expensive. Heat pumps are nice, but for camps it is questionable. For me I would have to spend an additional $3,000 to use a HPWH. As most people spend way too much for camp systems they may already have the infrastructure to support this electrical demand. I have so much hot water that only hot water is provided to my clothes washer and all cycles use hot water.

 

[chrisski]

For off-grid electric water heaters I was considering converting a standard AC water heater to 48 volts

But I got to thinking to do it right it's probably going to cost me about $100 to $150 worth of parts added on to the cost of the already existing water heater

Additionally I'm having trouble finding a good way to reliably handle the current at what will be close to 58 volts

Which of course brings on the possibility of using a 12 volt thermal switch and using that as a means for keying a large relay that can handle the current of a pair of 1500 w 48 volts water heating elements

But would it make more sense to just buy a four or $500 inverter and dedicated specifically for the hot water heater?

I know that this is going to be my plan for use with the individual mini splits... I feel like I could attach several 5,000 w inverters to the battery bank and use those to power various different mini splits and be able to shut them off when not in use... The same approach would be a really good way to control when we're using the hot water and when we are not

I have an RV with a 6 gallon water heater. For me, you hit on the big reasons i believe AC water heaters are the way to go.

-First the big amp loads can be difficult to wire for a 48 volt system. Theres a good reasons hot water heaters are 120 volts or even 240 volts, and that is the higher amperage is hard to move.

-Second is the cost. So few DC units around you’d need to cobble something together.

I’ve not found a good way to incorporate a second inverter unless it was to shut a much larger inverter with a large idle draw to save on the load. That could be 2 kWh+ per day saved.

I’m sure the Route suggested by @efficientPV iof designing a DC may not be that expensive, but I’d need to do a deep dive into that before using.

 

[OffGridInTheCity]

I recommend a heat pump electric water heater driven by the inverter.

I use a Rheem 50ga from Home Depot - over 2 years now . In heat pump mode it maxes out at 400w.
**It can require the full 4,500w briefly when you 1st hook it up as an internal test? of it's heating elements - and it has regular elements for 'quick heat' mode.

Mine's in a cold location under the house - 50F in winter, 75F in summer + 200ft of water circulation for instant hot water and it burns low of 140kwh/month in summer (74F ambient) and 200kwh in winter (50F ambient).

Here's a couple of youtubes by an advanced DIY'er installing / using one. My experience has been very similar.

 

[400bird]

I'm confused by your logic. You don't want to spend $100-150 on relays and hardware to control the DC, but you're ok spending more to run the water heater on a dedicated inverter?

Also, the inverter will cost 10-15% efficiency, so you're good to use more energy to heat water due to the efficiency lost in the inverter.

 

[ericfx1984]

I'm confused by your logic. You don't want to spend $100-150 on relays and hardware to control the DC, but you're ok spending more to run the water heater on a dedicated inverter?

Also, the inverter will cost 10-15% efficiency, so you're good to use more energy to heat water due to the efficiency lost in the inverter.

I think you're misunderstanding... I don't have a preference either way... All that I'm suggesting is the relays will be rather expensive but not a big deal by any means

The good thing about the inverter is it's kind of the devil you know... And yes I'm quite familiar with the 10 to 15% drop in efficiency

Overall I'm really not sure which direction makes no sense but we're getting relatively close to that point... Where the house being 100% off-grid I'm building it 100% with zero debt I need to plan this and do it right a

 

[fromport]

For off-grid electric water heaters I was considering converting a standard AC water heater to 48 volts

But I got to thinking to do it right it's probably going to cost me about $100 to $150 worth of parts added on to the cost of the already existing water heater

Additionally I'm having trouble finding a good way to reliably handle the current at what will be close to 58 volts

Which of course brings on the possibility of using a 12 volt thermal switch and using that as a means for keying a large relay that can handle the current of a pair of 1500 w 48 volts water heating elements

But would it make more sense to just buy a four or $500 inverter and dedicated specifically for the hot water heater?

I know that this is going to be my plan for use with the individual mini splits... I feel like I could attach several 5,000 w inverters to the battery bank and use those to power various different mini splits and be able to shut them off when not in use... The same approach would be a really good way to control when we're using the hot water and when we are not

If you have the ability, go with a hybrid water heater.
This is what I used with a 2 person +pets household in 2022 with my 40 gallon Rheem unit:


Should be half to a third of the energy used with resistive heating.

 

[dougbert]

FWIW, here are links to my FULL BATTERY DIVERSION water heater solution, using PV through Inverter into normal electric water heaters. Just put in different coils

Solar house generator I started DIY back in 2000 - My path from Trace to Xantrex (on FLA battery) to XW Pro inverters on Tesla Model S batteries

Well I have been working on project plans on upgrading my system, as I have referenced in prior posts. This will all be DIY, just getting the parts will be difficult thing I have come up with 5 phases for the project to be implemented over time as funds become available. Later phases can...

diysolarforum.com

Something I built DIY back in 2000 - my path from Trace to Xantrex to XW Pro inverters

Looking back on power generation today, we hit a 121.5 amps @ 48v, incoming from the 4 arrays That converts to 243 amps @ 24v, yet the highest current flow before the voltage change, was 221 amps @ 24v, which is a gain of 530 watts of more power Definitely a great gain by switching to the...

diysolarforum.com

Solar house generator I started DIY back in 2000 - My path from Trace to Xantrex (on FLA battery) to XW Pro inverters on Tesla Model S batteries

Looking back on power generation today, we hit a 121.5 amps @ 48v, incoming from the 4 arrays That converts to 243 amps @ 24v, yet the highest current flow before the voltage change, was 221 amps @ 24v, which is a gain of 530 watts of more power Definitely a great gain by switching to the...

diysolarforum.com

 

[AntronX]

Use $16 100A DC solid state relay engaged by existing thermostat in the water heater. At 58Vdc 4500w 240vac heating element will pull 4.64A or 270 watts. Over 12 hours it will dump 3.24 kWh which is about right for hot water usage for 2 people. To heat water faster connect upper element in parallel via another SSR controlled by upper thermostat.

 

[sunsurfer]

I'm looking at doing something similar. My batts/charge controllers are moving 160ft away from my water heater to get better sun light. I picked up a cheap Ream marathon with dead elements. I got factory elements (different size thread for the plastic tanks) that are rated 4800w @240v. They will pull 1200w each @ 120v. I have a cheap 3500w modified sine wave inverter I'm gong to run extra solar to heat water.

heat pump water heaters are pricy and they are slower to heat. I do like the idea though. I'm going to build a DIY heat pump for the water heater this summer. Sometimes my 5000BTU window unit is to cold at night so I was looking at about 2000BTUs pulling heat from the room and sending it to the water heater. I have an insulated sleeping area so it doesn't take much to keep it cool. Works good for when off the batteries over night.

 

[12VoltInstalls]

Since the OP post suggested using excess PV to heat hot water and mentioned a 58V input to a 48V element that seems to be the simplest. Although they mentioned a 12V SSR which confused me.

I’m surprised nobody developed on using a straight DC element.

The bottom element could be a DC element, and run the top element on 120VAC (or 240AC if system has that provision?).
In a sunshiney day even a 600W DC element would put the aforementioned ~3kWh into the storage tank; the AC element could be leaned on via inverter or generator if more hot water quicklier is required.

Alternatively, if more kWh excess is available and quicker recovery hot water is not critical, a second 600W or even 300W element in the upper hole could be incorporated.

IIRC those 12VDC elements are around $25-$30 and a 120A+ DC relay is fairly inexpensive (cuz the AC water heater relay won’t be safe for DC)

 

[ericfx1984]

Since the OP post suggested using excess PV to heat hot water and mentioned a 58V input to a 48V element that seems to be the simplest. Although they mentioned a 12V SSR which confused me.

I’m surprised nobody developed on using a straight DC element.

The bottom element could be a DC element, and run the top element on 120VAC (or 240AC if system has that provision?).
In a sunshiney day even a 600W DC element would put the aforementioned ~3kWh into the storage tank; the AC element could be leaned on via inverter or generator if more hot water quicklier is required.

Alternatively, if more kWh excess is available and quicker recovery hot water is not critical, a second 600W or even 300W element in the upper hole could be incorporated.

IIRC those 12VDC elements are around $25-$30 and a 120A+ DC relay is fairly inexpensive (cuz the AC water heater relay won’t be safe for DC)

sorry i meant a DC, not sure WHY i typed 12v... planning out lots of stuff at thee moment.

 

[yodamota]

We currently use the existing heater element in our hot water tank. These are the tanks used in most homes in canada. I used the existing wire in the tank and ran the wire down to the breaker box. I have a plug so it can be unplugged when not in use. It is otherwise set up on a programmable timer. This is something which we set up with things we had lying around.
When there is enough sunshine we set the timer to come on at 11am and shut off around 3pm. Water is piping hot by that time for showers/dishes.

I really would like to make this system automated as sometimes its cloudy and we are not at home. The timer will keep trying to power the water heater even though the solar is not coming in. That is the improvement. I am hoping to hook it up to our Aux float setting (outback CC). Which will turn the hot water heater on. Just one more project....

Heater is running on 120v. It uses about 1000+ watts. I believe we have it set to 140*F