Excess PV power to heat water

[EPicTony]

I have a gas water heater. Anyone figure out a way to use an electric heating element or something electric to heat water ?
I don't want to change my gas water tank to electric because of the cost and mine is only 6 years old and works fine. I'm just trying to think of ways to utilize my excess PV power. Thanks for any ideas.

 

[MrM1]

I have a gas water heater. Anyone figure out a way to use an electric heating element or something electric to heat water ?
I don't want to change my gas water tank to electric because of the cost and mine is only 6 years old and works fine. I'm just trying to think of ways to utilize my excess PV power. Thanks for any ideas.

Are u wanting to add a 2nd tank as an electric pre-heater?

It can be done, either as a DC stand alone and some panels or as an AC dump from your array. If you have a tier 1 charge controller you can even control when it's on based on battery SOC.

 

[MisterSandals]

Anyone figure out a way to use an electric heating element or something electric to heat water ?

Are you wanting to just heat some water or are you particularly interested in heating the water in your hot water heater tank?

How much extra power do you have for this?

 

[EPicTony]

Are you wanting to just heat some water or are you particularly interested in heating the water in your hot water heater tank?

How much extra power do you have for this?

Tons in the summer. In winter some on sunny days - I need to figure out how much. How can I do this ? Thanks

 

[MisterSandals]

Tons in the summer. In winter some on sunny days - I need to figure out how much. How can I do this ? Thanks

What is your system? (Point me to a post if you have described it elsewhere)

 

[timselectric]

I'm doing preheating from solar. And keeping the gas water heater for backup. You can use a small electric water heater (15 gallon) ahead of the gas unit. You can also add a circulation pump to circulate the water between the two tanks, if you want.

 

[EPicTony]

What is your system? (Point me to a post if you have described it elsewhere)

In my signature!

 

[efficientPV]

I found BOSCH ES4 water heaters on ebay for $48 shipped. This was brand new, but open box. For ease of thigs that isn't much to pay rather than trying to stick an element in a pipe and doing lots of plumbing. Just add a pump to circulate the water. Preheat tanks sound good though they are mostly a big loss of energy if over 85F.

 

[yodamota]

We do this with a programmable timer in the summer. Ours is already an electric tank however(120VAC). Works really well when the sun is out. Even the element being on for 1 hours makes a big difference ...

 

[wattmatters]

How can I do this ?

You still haven't actually described what it is you are trying to achieve?

As to heating water with solar PV, you can either:
i. add a second electric water heater tank powered by solar PV which then feeds that heated water to the gas HW tank, or
ii. replace the gas tank with an electric HW tank powered by solar PV.

As to how solar PV heats the water, well there are multiple options for that.

e.g. our hot water is powered by our excess solar PV using a smart PV diverter. It send excess available PV power to the hot water heating element but varies the power delivered to ensure there is no grid import.

Here's an example of five days of hot water power diversion.

 

[EPicTony]

You still haven't actually described what it is you are trying to achieve?

As to heating water with solar PV, you can either:
i. add a second electric water heater tank powered by solar PV which then feeds that heated water to the gas HW tank, or
ii. replace the gas tank with an electric HW tank powered by solar PV.

As to how solar PV heats the water, well there are multiple options for that.

e.g. our hot water is powered by our excess solar PV using a smart PV diverter. It send excess available PV power to the hot water heating element but varies the power delivered to ensure there is no grid import.

Here's an example of five days of hot water power diversion.

View attachment 133252

Looks great ! Solar assistant ? What I'm trying to achieve is simply use excess PV to heat water in my 50gal propane water heater (and save on my propane).

 

[Vigo]

Well, here's what i would do. Use one of these car engine coolant heaters. Just find one with an all-metal housing that could survive your water pressure (what is your water pressure?). Cars go up to 20psi so you know none of them will blow up at 20 but most people have something higher than that for water pressure in their house. I have 80psi. Some of those things have adjustable thermostats but if not adjustable you would hopefully shoot for one that is not likely to push your water into the danger zone, i believe many are 135-140f and that's IF it's even allowed to run long enough to accomplish that on 40-80gallons of water!! It would have to run for several hours a day to hit its temp setpoint, there are calculators out there for that. If your gas water heater has an electrical circuit controlled by its thermostat (is that a thing on a gas tank?) you could use that as an 'allow/disallow' in the control circuit to prevent the water ever going past your thermostat set point on the water heater if it happens to be lower than what is on your electric heater doodad.

I believe you would need to mount it below your water heater tank's drain valve, which should be easy since i think most gas heaters have the actual water tank starting about a foot up from the bottom. This would encourage convection flow. Then you would Tee the inlet of this thing off the the drain valve of your water heater. Then hook the outlet of this heater thing into some point higher on the tank than the drain valve, such as behind some other fitting sticking out the side of the tank (thermostat?) or potentially even the hot outlet way at the top, etc. This should allow you to circulate water through the tank using convection only, although i think some of these things are available with pumps on them as well.

As for how to trigger it, maybe your EG4's have some programmable outputs, i've never looked at those. But if you wanted to do a standalone thing i would buy a 'voltage monitoring relay' such as this to trigger an AC contactor/relay such as this to feed the 120v 'coolant' heater. You would set it to turn on at some battery voltage that your system only hits when it is actively getting charged and already 'mostly' charged. For me anything from ~54v up might be ok, my lead acid system tops out at 58.3v before going into float.. You would set it to turn off at any voltage your battery falls to when it loses solar charging but is still 'charged', maybe 52v in my case. This should be able to be set in such a way to only be active when you have 'excess' power, although if you only wanted it to run when your batteries were actually full (vs 'mostly full and still charging') you may need a more complicated control scheme.

That's my first thought for how to add electric heat to a gas water heater tank without modifying the tank itself (other than fittings) and having it only turn on when your system has 'excess' power. Using the cheapest available versions of the 3 things i listed plus a bit of fittings and hoses, it could be done for $100-150.

 

[efficientPV]

There are short RV water heating elements that are about 3/8 inch diameter and 600W which come with a NPT swage fitting. This will fit unto the drain port with some reducers. A $50 ES4 heating tank in series with the cold inlet is probably your best option. Diversion heating is my specialty. Unfortunately, everyone here has so much money and so many panels that they don't care about diverting energy efficiently. And those with small systems don't think they could ever have hot water from PV.

 

[Vigo]

So i can't say i ever looked before this thread, but where is this Bosch ES4 available for $50? A quick google suggests that is not a readily available thing. I have seen a fair number of really cheap 120v 'undersink' or 'showerhead' or 'tankless' heaters that cheap, but never noticed anything that cheap with Bosch written on it..

 

[wattmatters]

What I'm trying to achieve is simply use excess PV to heat water in my 50gal propane water heater (and save on my propane).

Then you can't. There's no option to safely install an electric heating element inside an existing gas burner tank.

You can however feed it pre-heated water from a second (electric) hot water heater/system which can be powered by your solar PV, or just replace it with an electric hot water heater.

Looks great ! Solar assistant ?

Thanks. The charts are via Grafana/InfluxDB installed inside my Home Assistant system, which is monitoring energy from my Fronius Grid tied PV system and its accompanying consumption meter.

Today it is cloudy, so this is where the diverter is really good and using as much production as it can without importing energy from the grid:



I do also have Solar Assistant as well (which also connects with Home Assistant) but that is for monitoring and control of my off-grid PV/battery system.