# How to solar power an electric water heater



## Guest

Hi folks,

I just bought a 50 gallon electric water heater to be used in my small hotel under construction in Panama. Originally I wanted my water to be solar heated but lack of quality materials forced me to look for an alternative. I can get solar panels though and I was wondering what it would cost to power my water heater (and possibly other appliances during the day) that way. I am not thinking of a full solar system with batteries and so on, just some panels on the roof to safe a buck (water heats during the day, insulated tank stays warm during the night) . 

WeÂ´re located in Panama (the country) and the sun is as powerful as it can get, especially during the tourist season. Water is already 80F when it goes into the tank, so it wonÂ´t need to be heated that much. Now the essential statistics: the tank has two 4500 watt heating elements and runs on 240 volts. I never paid much attention during science classes, so question is, how much power do I really need?


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## artificer

Take a look at another current thread. they only wanted 1500 watts of power, and it was going to be REALLY expensive.

Your best bet is to just use solar water heating panes, and maybe a small PV panel to power a circulation pump.

Michael


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## Esteban29304

Or, look up plans to make a " solar batch " hot water heater .


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## TnAndy

Benfatto said:


> Now the essential statistics: the tank has two 4500 watt heating elements and runs on 240 volts. I never paid much attention during science classes, so question is, how much power do I really need?


You need 4500 watts every second the heater is on. ( only one of the two elements runs at a time on the typical electric water heater ).

That means you need about 5,000 to 6,000 watts of solar panels ( about $7500 to $10,000 ), plus you'd need to find a DC heating element if you plan to use the PV panels directly, and one that will fit your water heater ( good luck, probably isn't one made ), OR you'd need to invert the DC from the panels into AC ( about dollar a watt ) to use the existing AC heating elements + grid tie or some type of battery system to make it work well....more bucks..... 

Time you're done, you'll have 10-20 thousand in heating water.....compared to a local electric rate of what.....20 cents/kwhr ?

Or you can heat the water directly with the sun using water panels/small pump, or make a batch heater as suggested above, for a couple thousand bucks, tops.
Living in the tropics, a solar water heating system ( NOT a solar electricity making system ) is much more simple, as you don't have freezing temps to contend with ( and thus antifreeze or drainback design ), so your cost is much lower. You see them all over the place down there, join them instead of trying to re-invent the wheel.

I'm surprised a hotel, even a small one, can get by with a 50gal water heater. You sure that's right ?


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## farminghandyman

TnAndy said:


> You need 4500 watts every second the heater is on. ( only one of the two elements runs at a time on the typical electric water heater ).
> 
> That means you need about 5,000 to 6,000 watts of solar panels ( about $7500 to $10,000 ), plus you'd need to find a DC heating element if you plan to use the PV panels directly, and one that will fit your water heater ( good luck, probably isn't one made ), OR you'd need to invert the DC from the panels into AC ( about dollar a watt ) to use the existing AC heating elements + grid tie or some type of battery system to make it work well....more bucks.....
> 
> Time you're done, you'll have 10-20 thousand in heating water.....compared to a local electric rate of what.....20 cents/kwhr ?
> 
> Or you can heat the water directly with the sun using water panels/small pump, or make a batch heater as suggested above, for a couple thousand bucks, tops.
> Living in the tropics, a solar water heating system ( NOT a solar electricity making system ) is much more simple, as you don't have freezing temps to contend with ( and thus antifreeze or drainback design ), so your cost is much lower. You see them all over the place down there, join them instead of trying to re-invent the wheel.
> 
> I'm surprised a hotel, even a small one, can get by with a 50gal water heater. You sure that's right ?


I really doubt that there is a difference in the elements, and I would think you would be able to run the elements on DC if wanted, 

some dump loads are either HW elements or resistance heaters,

but I would think you would do better with a direct Hot water heating panel or a batch type pre heater at least,


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## nadja

My risitance element for my wind gennie is actually 3 ph. ac as that is the power coming in from the gennie. It is converted with a rectifier to dc before anything else, which means my dump load is dc


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## Guest

Thanks for the many responses. 

As stated in my first post, I was going to build a solar heated (thermosyphon) system, but some of the materials are hard to get (not to mention expensive). Since you have convinced me that powering the electric heater with solar panels is a bad idea, I will (in time) build the thermosyphon system. And yes, 50 gallons is enough. As said the water is already 80F when it goes into the tank (and we only have 4 rooms). For that reason many of the cheaper hotels & hostels in this country do not even have hot water.

If I understand it correctly, if I want to solar power a large fridge in the event of a daytime power cut, I will need an amount in watts coming from solar panels equal to or higher than rated power of the fridge? And can I use solar panels in combination with electricity use from the grid, or does it have to run separately?


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## TnAndy

Benfatto said:


> If I understand it correctly, if I want to solar power a large fridge in the event of a daytime power cut, I will need an amount in watts coming from solar panels equal to or higher than rated power of the fridge? And can I use solar panels in combination with electricity use from the grid, or does it have to run separately?


Now you're getting in to a whole more more complicated question. Using PV panels to run into a resistance heating load only when the sun is shining is a one thing.....running a motor on a fridge is another.

You have to have reliable power WHEN the fridge thermostat says "run". That means you have to do one of two things:

Use grid power, and let your PV backfeed the grid ( in compliance with all of your power company's requirements ) to reduce your electric bill....this is "using the grid as your battery"......

OR

You have to set up a battery bank and the associated equipment ( PV panels, charge controller, inverter, etc ) to supply power to the fridge when it needs it.

It's not a matter of "I have a fridge that uses 1500watts, so can I put up 1500watts of PV panels and be done with it ? "

You have to know the TIME factor, for one thing....yes, when running, the fridge uses X number of watts.....but how LONG per day does it run ? That gives you the watt/hours.

Once you know that, you can go about designing a system to supply it. It might take as little as 500 watts of PV panels, depending on the solar conditions where you live, and how much the fridge consumes ( in watt/hrs ). It might take 3,000 watts of PV. There is no way to know without a whole lot more info.

BUT the more you learn, the more you will LOVE your local electrical supplier....ahahahahaaaa......because, as a rule, they are a bargain.


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## nadja

Hello Andy. Here in Az. I think I heard this morning that the local power co. are asking for an 18% raise. I cannot imagine how much it will cost down in the phoenix area if that happens. My elec. bill down there was as much as $700.00 in the summers.


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## TnAndy

No doubt, Nadja......but if my bill were 700/mo, I'd be figuring out a way to cut that first. Either you've got WAY too much house, or it needs a lot of work.

I know it gets WAY hot in Phoenix ( been there in the summer ), but enough insulation can fix a lot of load problems.


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## Esteban29304

Here is a link for some solar projects & a lot of information . 
A good home built " batch heater " will raise the temperature of your water from the 80 degrees to probably high enough that when the water goes into your electric water heater, it will not turn on . Storing in your electric water heater will lose some heat, so wrap a " water heater insulation blanket " around it. CHEAP to build & would be great in your area.

http://www.builditsolar.com/Projects/WaterHeating/water_heating.htm


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## SolarGary

Esteban29304 said:


> Here is a link for some solar projects & a lot of information .
> A good home built " batch heater " will raise the temperature of your water from the 80 degrees to probably high enough that when the water goes into your electric water heater, it will not turn on . Storing in your electric water heater will lose some heat, so wrap a " water heater insulation blanket " around it. CHEAP to build & would be great in your area.
> 
> http://www.builditsolar.com/Projects/WaterHeating/water_heating.htm


Hi, 
There are also several simple thermosyphon systems at the same link. Thermosypphon would be good for Panama since you don't have to worry about freeze protection.

Gary


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## Guest

TnAndy said:


> BUT the more you learn, the more you will LOVE your local electrical supplier....ahahahahaaaa......because, as a rule, they are a bargain.


They certainly are for $20 a month. And I am not as naive to think the whole world will use solar power or any other alternative energy by tomorrow. My reasons are purely practical.

At times we donÂ´t have electricity for several hours, the record was more than a day. Food spoils and I have to close my restaurant. That is unacceptable. 

I was hoping that solar panels could offer a solution. However, since I can buy a small generator for only $99 it is probably way more cost effective (and better for the environment too, all things considering). I do have a problem with noise, but I can build a generator house for that.

I will build a thermosyphon system in time though.


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## TnAndy

Benfatto said:


> At times we donÂ´t have electricity for several hours, the record was more than a day. Food spoils and I have to close my restaurant. That is unacceptable.


A 99 buck generator is probably worth what you pay for it....not much, in terms of longevity.

Since the electrical service is spotty, what you might look into is setting up a battery bank, charging it with grid power when it's available, then using that power back thru an inverter when the grid is down. If you set it up correctly, you can add the solar charging part down the road if service becomes more unreliable for longer periods.

Solar definitely has good purposes, that being to run things like refrigeration and lights that simply can't be done easily without electricity, but heating water, which was your primary question, is done best by direct heat....especially in your climate area.


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## Jim-mi

Please take that $99 toy generator idea outside and bury it under six feet of rock.........

That would be nothing but grief.......;.....

A very good friend of mine runs a very nice restaurant. Between the walk in freezer-coolers-etc.-etc. even a good 10,000 watt gen might not keep up with the "power demand".

You might want to consider first a high quality standby generator.

Yes the cost could be in the thousands . . . . .BUT . .do a list of what your spoiled food items could be . . . . . . .take this 'total' times how often the power goes out in a year . . . . .. .makes the price of a QUALITY generator come way down.


Plus your still "open" for business..............


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## jwal10

How about a small energy efficient solar powered refrigerator for the most parishable items....James

http://www.sunshineworks.com/sundanzer-refrigerators-freezers.htm

http://www.sunshineworks.com/solar-refrigerators-freezers.htm


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## Guest

jwal10 said:


> How about a small energy efficient solar powered refrigerator for the most parishable items....James
> 
> http://www.sunshineworks.com/sundanzer-refrigerators-freezers.htm
> 
> http://www.sunshineworks.com/solar-refrigerators-freezers.htm


Interesting, but not for my restaurant. I might consider it for a cabin I own.


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