Run water heater via inverter?

[Bash]

I've just installed a water heater (calorifier) that only draws 750 watts at 115v AC. I have a 2500-watt inverter running off two AGM 210AH 4Ds on a 12v system. I run two 130-watt solar panels (total of 16 amps) backed up by a 200-watt wind generator.

So, during the summer months I have power to spare while on the hook despite running a fridge and a separate, stand-alone freezer. My batteries are usually up to full charge by noon, and the wind/solar charge regulators shut the charging system down periodically between noon and the cocktail hour.

Given the above, is there any reason I shouldn't run the water heater off the inverter between 1200-1300h every day to keep hot water in the fresh-water pressure system?

[djmarchand]

No reason at all not to use excess solar or wind power to heat water. it realize that it will take about an hour to reheat the water heater to peak temps which will consume about 60 amp hours.

David

[Strygaldwir]

So, while your clorifier is on, you're pulling 50 or so amps from your battery. If you're indeed putting out 15 amps you're pulling 35 amps net from your batteries. This exceeds your 20 hour discharge rate so if your ran it more than 5 hours there might be issues. Your battery should be good in that you're not trying to pull more than 20% of their capacity. I just try to make certain you're truly putting out the 15 amps, and that your batteries are truly topped off.

[Bash]

For sake of argument, let's say that I'll only run it one hour a day, between 1200-1300h, and only when I'm seeing output on the solar panels between 14-16 amps unless they are being supplemented by sufficient amperage from the wind generator.

Problem #1 is that I've got to remember to shut the water heater down at 1300h, but I can always set an alarm to remind me.

Any other problems?

[Stu Jackson]

Good advice. If your inverter is > your heater, why not? As suggested, do your energy budget and know what state your bank is before you do so.

Do you have a battery monitor?

[Bash]

Originally Posted by Stu Jackson

Do you have a battery monitor?

Two. Primary monitor is a Link 10. And the solar charge controller also shows the percent of charge.

[onestepcsy37]

bash - what brand and model of water heater is it? i'd like to look at it myself. i don't have as much solar/wind as you do, but if i can run my little honda 1000 for an hour to get hot water it might be worth it on days when i can't get solar hot water....

[AnchorageGuy]

Bash, We have a 2500 watt inverter and we run our water heater all the time off the inverter. It takes about 15 to 20 minutes to heat the water and that's about all we run it. That is enough hot water for two of us to shower and to do dishes after dinner. Been doing it for years. Chuck

[sailorchic34]

750 watts for one hour will heat a 6 gallon tank 50 degrees F. from the start temp. So if the tank is cold ~50-55 degrees F. you might need to run it 75-80 minutes to get it hot enough for dishes and a shower.

[Bash]

Originally Posted by onestepcsy37

bash - what brand and model of water heater is it? i'd like to look at it myself. i don't have as much solar/wind as you do, but if i can run my little honda 1000 for an hour to get hot water it might be worth it on days when i can't get solar hot water....

It's an Isotemp Basic 24 (six gallon). I've just replaced a Force 10 eleven-gallon 1500 watt unit.

In essence, my new unit holds half as much water, requires half as much power, and still cost twice as much as the old unit. But now I've got a stainless tank with better insulation.

[donradcliffe]

You could put the heater on a timer switch so you don't forget to turn it off.

[sailinglegend]

Our immersion heater is 750 watt 230 volts in a 29 litre tank - it has an automatic temperature cut out that can be set just like a domestic heater - and in series an emergency high temp cut out set at 80C. Our tank takes 15 mins and 35 Ah via our inverter to be warm enough for two to shower. No need to get it hot enough for washing up.

[Dockhead]

No reason in the world I can see. I used to do the same thing without any harm until I got my engine coolant loop working, which made it unnecessary for my setup, since whenever I have a surfeit of DC power, I also have calorifier heating via the engine coolant loop.

My only other source of DC power, the Rutland 914i wind generator, produces approximately sweet fanny apple of DC power, so I never have a surplus of DC power unless I'm running the engine

[Stray-Cat]

Originally Posted by Bash

It's an Isotemp Basic 24 (six gallon). I've just replaced a Force 10 eleven-gallon 1500 watt unit.

In essence, my new unit holds half as much water, requires half as much power, and still cost twice as much as the old unit. But now I've got a stainless tank with better insulation.

I considered the Isotemp heater a few years ago when I was replacing the original 12gal raritan
Very nice unit ,it looked like they would outlast the boat
The 750w element is a plus if you you have limited power available
I bought a 11gal force 10 as it was 1/4 the price and I have no shortage of power available (50amp220) shore power

[noelex 77]

There is no reason why you cannot use excess energy to heat your water up via your inverter. However it takes a lot of energy to heat water and with your amount of solar and wind is not enough to make a great deal of impact.

You have not got enough energy to run the hot water for an hour a day. An hour of hot water heating will use about 75AHrs. It would be nice to know what your average daily production is (without regulation) but my guess would be about 100AHrs. This would only leave you with 25AHrs to run everything else which is not viable.
Energy in has to equal (or be a bit greater than) energy out.

My guess is that you will only be able to run the hot water heater for 10mins or so. This may help a little in warming the water up , but it will take a bit of careful monitoring and will have a small detrimental impact on battery life (because of the extra discharge cycle).
On exceptionally good days where it windy and sunny it may be of more practical value, but for an average day your water will only be slightly warmer. This still may be worth the trouble, rather than wasting the power, but don't expect too much.