Hot water heating via Lithium battery bank

[simonpickard]

Hi,

I’ve seen some blog videos where owners with Lithium battery banks and lots of solar can heat their hot water on the hook without running generators or the engine.

I was wondering how this is done? I’m guessing a high rated inverter but then what? How do you attach this to the hot water heater?

Also, how many amp hours are you looking at to heat a normal sized hot water tank? Roughly what would it take out of the bank?

Anyone who’s done this it would be great to hear from you / or see blog posts / videos of what you did?

Regards,
Simon

[nwdiver]

Some people put their excess solar into the electric heater in their hot water tank, pretty common actually, you have the juice use it, a boat I know with firefly batteries and 2 wind gens plus 750 watts of solar always has hot water in the evening.......his system was sized for flooded batteries and the uptake on the fireflies is faster leaving a lot of energy for warming water........with lithiums you may have a full charge by noon and all afternoon to heat your water tank.....

[simonpickard]

Thanks, but how is this heating done? I get the solar/battery part. But I’ve never seen a boat be able to use the battery bank to heat the hot water. The heater is only linked to the shore power / engine.

[FlyingScot]

I use my 2000 watt inverter. It uses 30 amps @ 12v for approximately 3.5 hours to heat to full temp from ambient (6 gallon). If you have a 120v hot water heater you can purchase a 1500 watt @ 240v rated element and swap with your 1500 watt @ 120v element. Presto you now have a 375 watt @ 120v element. I am planning to swap my 2nd hot water heater to the inverter. I have 1440 watts of solar.

[simonpickard]

Thanks FlyingScot.

So you just ran a wire from the Inverter to the water heater? So you can heat via engine / shore / inverter?

30amps to get the water hot seems pretty good! I was expecting the drain to be higher than that.

[FlyingScot]

Originally Posted by simonpickard

Thanks FlyingScot.

So you just ran a wire from the Inverter to the water heater? So you can heat via engine / shore / inverter?

30amps to get the water hot seems pretty good! I was expecting the drain to be higher than that.

I'm not a certified electrician or marine electrician and there are likely too many inverter, AC breaker panel and shore power configurations for to me properly help but I will say that our boat, like many, excludes large loads from the inverter (Aircons and water heaters). I swapped the wiring to the breaker and the nuetral bus bar to place the water heater on the ones that can run from the inverter.

Yes 30 amps is very manageable. But remember it's also about 100ah and you have to harvest that. My inverter is a partial sine wave type and these are very efficient at resistive loads like water heaters. YMMV

[Eirik]

I have my water heater wired after the inverter. The heater has a 750 W 230 V AC element and thus draws around 65 A from the LFP bank when heating. What I have done is to wire the tank via a timer, so that it will run for around 45 minutes, which is sufficient to heat the 20 l tank. I usually do this in the morning. That way it will not drain the bank excessively, and I do not need to worry about forgetting to turn the heater off, etc. The bank has a capacity of 600Ah, and is charged via solar (2*100 W) and the engine’s generator (115 A, reduced to 80 A). I never need to use shore power.

[mbartosch]

Similar setup here: the stock 1000 W water heater is wired to the AC distribution of Entropy. Our 1200W Victron Multiplus inverter powers the AC heater just fine from the 400 Ah LiFePO4 bank.
We usually run the water heater for 10 min (controlled by a timer relay) which is sufficient to get warm water for a nice shower. That takes about 12 Ah (which is about the equivalent of brewing 6 large coffees with the electric kettle).

[Rapanui]

We heat our water from the inverter powered by 3 off 120 Ahr AGM batteries. Have wired in a rotary selector switch on the input to the AC panel to select either shore power or inverter. The heating element is 1200W so draws about 100A for 5 or 10 minutes at a time which is usually enough to get a couple of warm showers early morning. 10 mins heating takes about 5% of the battery capacity. We monitor battery State of Charge using a Smartgauge and virtually all battery charging is from 480W of solar. Normally by midday the batteries are at 100% and if we havn't run the engine to heat water I can give the water a longer heating boost and still be back at 100% by sundown

[LoudMusic]

My hot water heater has a 110v 15a wall plug. The outlet it's normally on goes to a breaker that is only on shore/genny. The past three months I just unplugged it from there, slapped an extension cord on it, and ran it to an outlet that goes to a breaker that goes to my inverter, same as any other 110v outlet on the boat. It draws about 900w I think? We mostly ran it when the solar was bangin' out 600+w as to not over tax the batteries, but there were times we ran it exclusively on battery. We have 2100w of solar, 3x300Ah 12v lithiums (max draw 3600w continuous) and a 2800w inverter.

There were also times we were heating water and still putting power into the batteries. But now I'm just bragging

EDIT: The next time I'm on the back side of the breaker panel I intend to move the hot water heater's breaker to the inverter's bus. When we're on genny or shore the inverter automagically passes AC power through, rather than doing two inversions. I think the boat was originally wired the way it is because the batteries were puny. We have big battery capabilities. No longer need to worry about that.

[john61ct]

Note that a LFP bank just reduces voltage drop at smaller Ah sizings.

A big enough lead bank would also get this done, not the chemistry but your bountiful energy inputs that makes the difference.

[Moontide]

There are also 12 volt water heater elements. Look on Amazon or EBay. Saves the losses from the inverter.

[senormechanico]

That takes huge wiring where you still get losses, but inverters are very efficient at big loads.
Take your pick.

[john61ct]

12V is too low, DC elements in general pretty ineffectual.

[motion30]

I also run my water heater through the inverter, the stock 1250 watt heating element used about 103 amps. I switch to a thousand watt 120 volt element and it draws 87 amps. takes just over an hour for the hot water heater to shut off. Might load is carried by my solar