Water heating from photovoltaic, or yes now I'm the idiot...

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Photowhit
Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
in Off Grid Solar & Battery Systems #1
In the past of course I've been one of those wanting people to use solar hot water heaters, the most effiecent and quickest payback of all the 'solar' projects... ...I don't have the time. I want to disconnect this fall and I have my hands full just getting trees down and cleaned up and my array up and running.

So, options, my array will be oversized for my battery, so the simplest might be to;

1; swap out my 220 elements for 110 elements in my water heater, (actually I think I could only run 1 at 1500watts) I've heard it done, but not first hand, I understand it takes forever to heat up. I guess the thermostat/controller might have to be swapped out as well? I'll insultate well....

2; install an on demand propane hot water heater, I suspect I will want this as a back up, but actually plan on a double waterheater storage for solar (2 - 30 gallon tanks) and hope not to need any other heating (I'll do vacuum tube hot water heater next year.) I've done an outside version and have a window in the bath I could take out, to direct vent...

3; survive the winter, showering at work and using a 2gallon sun shower filled from warmed water from microwave or induction stove top... yuck...Did sponge baths for 9 months while cycling, so suspect I'd get use to it, and it would only be 1 or 2x a week....

Anyone done the 110 conversion? I recall it taking 4 hours, just to take the chill off...

Thoughts, ideas, ...Thanks in advance.
Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
- Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #2
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    Re: Water heating from photovoltaic, or yes now I'm the idiot...

    Re 110 volt conversion. You will not have to swap out the thermostats etc, they are identical on both 110 and 220 volt water heaters. You can also leave the original 220 volt element in place, as long as 1/4th the stated element wattage is acceptable. That means that a 3000 watt 220 volt element, will act as a 750 watt element if run on 110 volts. Been there, done that in the past. On the other hand, using a 110 volt element on 220 volts will heat water amazingly fast, a 1500 watt 110 volt element becomes a 6000 watt element when pushed with 220 volts - - until it burns out. People I've known have done that.
    But seriously (the above was serious enough) I do not believe you will be happy at all with trying to electrically heat water from PV. And don't forget that with Fall, comes short days and greatly reduced hours of sun on you're PV panels. I built my own solar hot water heater close to 10 years ago and it works wonderfully well. Then come Winter, the water tank is instead heated by a "coil" on the wood stove. I take free hot water for granted and wouldn't want it any other way.
    Oh, and an additional note on electric hot water tanks with two elements: Whenever the hot water has been used up, or when starting with a tank of cold water, only the top element is supplied with power, to more quickly heat the top roughly 10 gallons, then when the upper thermostat is satisfied, it switches over the power, taking it away from the upper element and instead, supplying it to the bottom element, to slowly heat the rest of the tank. A lot of folks don't know that. So make VERY sure the tank is full of water and ALL air is out, before applying power, otherwise the upper element will be burned out. Literally. And since the upper 10 gallons will then never get heated, power will never be switched to the lower element, which won't be burned out, and you will never get any hot water until that burned out top element is replaced..
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  • Ken Marsh
    Ken Marsh Solar Expert Posts: 114 ✭✭✭✭
    #3
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    Re: Water heating from photovoltaic, or yes now I'm the idiot...

    Wayne has it right on. You can hook both elements to run at the same time using the bottom thermostat.
    Each KwHr will heat 6 gal of water 70 deg F.
    This means that if you have a water heater with both upper and lower element being 4 Kw (most of them are that now)
    and you hook them up to run together on 120 V, you will draw 2Kw and heat 12 gal/hr.
    By your bottom stamp it looks like you may have considerable extra PV.
    This would be the way to go.
    But in the winter months you probably will still have to supplement.
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #4
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    Re: Water heating from photovoltaic, or yes now I'm the idiot...

    Buy a propane demand, use it until you can build a solar collector,a nd then use it for supplement of a solar preheat tank.

    Heating water with PV is extremely inefficient in a number of dimensions, and doing it with a battery based sytem is crazy IMHO.

    Tony
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #5
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    Re: Water heating from photovoltaic, or yes now I'm the idiot...
    icarus wrote: »
    Heating water with PV is extremely inefficient in a number of dimensions, and doing it with a battery based sytem is crazy IMHO.

    I agree, Just that have a 6+Kw array and a 800Ah 24V battery, and likely a 2Kwh use other than summer. I'm at 11Kwh daily use in the heat wave running a Central air and waterheater, though I turn both off or down(AC) when I move to the cabin on weekends. So I think, I could run during the 4 hour peak with out reducing my charging, and storing heated water isn't too bad. (I hadn't planning on the extra array, just allowed to salvage 2.6KW of a shipping damaged pallet at less than 30 cents a watt)
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • silvertop
    silvertop Solar Expert Posts: 155 ✭✭✭✭✭
    #6
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    Re: Water heating from photovoltaic, or yes now I'm the idiot...

    If propane stays low in price an on demand might be good for you, where I live It's more expensive and I don't want to trade one fuel for another so I plan on going with a 110v tanked electric heat pump. I can run this ( 660W ) off my PV and set this on a noon day timer8)
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #7
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    Re: Water heating from photovoltaic, or yes now I'm the idiot...

    I had a 6.5 gallon electric point-of-use water heater given to me, reportedly provides @10 minute shower during the summer and heats the water in @30 minutes. came out of a summer use cabin, so the new question is how much longer will it take during the winter when the incoming water is 30-40 degrees cooler?

    I'll heat only when full sun and likely full or near full battery bank. it's a 1500 watt element. I'll also replace the shower head with a low flow, to help compensate for the cold water mixing in, It'll be interesting...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #8
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    Re: Water heating from photovoltaic, or yes now I'm the idiot...
    Photowhit wrote: »
    so the new question is how much longer will it take during the winter when the incoming water is 30-40 degrees cooler?

    Use a tempering tank. --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #9
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    Re: Water heating from photovoltaic, or yes now I'm the idiot...
    vtmaps wrote: »
    Use a tempering tank. --vtMaps

    I had to do a Google search:blush:, that's a great idea! Thanks!
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #10
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    Re: Water heating from photovoltaic, or yes now I'm the idiot...

    Electrically heated tank inline with a modulated propane on demand heater. If there's spare PV you can heat the tank and the modulated heater will reduce the amount of propane based on how hot the incoming water is- if it's hot enough then it won't come on at all. With a 6kW array you'd be crazy not to use it to heat water!
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