Heating water without shore power?

[a64pilot]

Originally Posted by Gerrycooper56

12 volt heating element in water heater plus 500 watts of solar panels?
Sent from my iPad using Cruisers Sailing Forum

Is not much heat really, especially where he is
at least in this particular case the issue is trying to find a way to heat water less expensively than what shore power costs, and there just isn't any way, from a standpoint of energy, energy off the grid is the most inexpensive energy there is for 99% of people, 1% may have a waterfall in their backyard or something

[lifeofreilly57]

I've had an on demand propane water heater on one boat which is efficient in regards to propane but used a bit more water since it had to sense water flow before firing up, so the hot water isn't instantaneous. You have to run a bit before the hot water comes in, then you go from freezing to scalding.
My current boat has a generator I run to charge batteries, run refrigeration, make water and is also tied to the water heater so I do all at the same time when it's running. But of course this uses more diesel.
The most efficient was one of my first boats, it had a solar shower bag you laid in the sun to heat up but I guess it wouldn't be too good in northern winters.
Depends on what you can get more easily, water or fuel.

[TravellingKiwis]

Has anyone given any thought to:
1. solar water heating (could be as simple as a heat exchanger behind a solar panel and small pump from hot water tank)
2. solar MPPT dump loads into a 12v element or a relay that switches on hot water AC element (110-220v) to pull from invertor when battery bank is XX% full and switches off when reduces to YY%.

I get these get that none of these would work without solar PVs and the last two will only work if you produce more solar than you need, but they do seem like potential options that have not been discussed and if solar is already present, don't require high cost.

[misfits]

Old thread but seeing how it's been resurrected..

I'm one of the crazy people that has an electric boat. The propulsion bank unless you're "motoring", just sits there. So I replaced a 120 volt element in a 6 gallon electric water heater with a 48 volt DC, 1000 watt element. 10 Amps, 30 minutes later I hot water for the day. The solar system tops the bank off no problem.

Just thought I'd share this in case there were other crazy people out there.

[Adelie]

1000w at 48v requires 21amps not 10amps.
For 6gal using a 1000w heater, you’re going to get a 34F temperature rise in 30min.

[Simi 60]

Standard household 180 litre Rheem hot water system running on 240v for us.

Once the batteries are done around 11am, the solar panels do the hot water with no neg drain on the bank.

[misfits]

Originally Posted by Adelie

1000w at 48v requires 21amps not 10amps.
For 6gal using a 1000w heater, you’re going to get a 34F temperature rise in 30min.

I already knew that.
What's your point?