Picture of Batch Solar Water Heater
Aim: To build a solar batch water heater using some old materials and some new. The idea behind this heater is to use as many old materials as possible, keeping them out of landfills and to use new materials as efficiently as possible. For this reason the box has been designed to use exactly two sheets of plywood without any waste. This also gives the box a trapezoid shape, making it stronger and angling the sides to reflect light onto the bottom of the tank. This was a lucky accidental feature;-)
I think this is a very simple design most people are capable of making with fairly basic tools, cheaply and without advanced carpentry skills. it is a effective heater - I have seen the water on top reach 150F on a hot spring day.
I have built a few of these and am still working on improving the design. I will log in and update this as I have more pictures and info. If these are not completely clear directions, well, this is my first instructable, so it will only get better.

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Step 1: Materials Needed

Picture of Materials Needed
Double glazed patio sliding glass door, 3' wide ideal. Should measure about 36” x 79”
Old water heater tank. I have only used 40 gal gas heaters so far, but I see no reason why larger tanks and electric tanks should not work, fine.

½ inch sheet of plywood
5/8 inch sheet of plywood
2 sheets of 1 inch foam insulation with reflective foil surface
Rustoleum or equivalent flat black metal paint, 1 pint
Stain or exterior primer and paint, 1 quart of each
¾ inch steel plugs for extra tank holes, maybe.
2 cut off pieces of 2 x 8, 16” long
One tube of latex or other caulking
Box of 1 5/8” drywall screws
10 3" wood screws for tank supports
16" long 1/2" copper pipe with cap and
2" long 3/4" threaded steel pipe
JBWeld for above
Teflon pipe tape

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rleard16 days ago

I had a solar heater on my roof. Worked great at 7 am it was 65 df and about 8 am all hell broke loose. I installed a water heater relief valve on the top of the system. Well it hit what ever the relief valve was set for and did its jobs. One thing you may want to due is to add it in with a temp control shower controler. This way you can add cold water mix. That way you do not scald anybody.

Mr Ganeshruskin

Can you pls mail me more pictures on Batch Solar Water Heater on my Mail ID

I intend to build one myself.


Satish Khabiya

pddonovan20119 months ago

Well, I love this Instructable, any time someone re-purposes something that is really hard to get rid of I am impressed. As far a Black is concerned, I once heated an entire pool to 76 degrees with a 100 foot roll of 3/4 I.D. black plastic Air Brake Hose for Truck Air Brakes. I just spread the loops across the roof of my house and plumbed the filter outlet to the tube and then to the pool. The pool was 58 degrees when I filled it and warm and comfy three days later. The pool is 45 feet by 26 feet and 10 feet deep on the deep end.

wndwalker2 years ago
just a thought, I keep seeing people say, "use flat black paint to increase the surface heat". I once saw a demo that compared flat black colored cardboard side by side w/ a very dark colored green cardboard both with thermometers placed under them, all inclosed in a Styrofoam box. The heat source came from 2 60wat bulbs placed above each piece of board. There seemed to be a significant difference in the temp, with the green being the higher temp. Made sense to me as nature itself uses green not black to improve the suns reaction in making the plants food. anyone interested can easily perform this same experiment to see for them selves..Just hoping this may help improve your heat exchanger.
ganeshruskin (author)  wndwalker1 year ago
Yes, but plants aren't trying to make heat, but carbohydrates out of water and CO2. in fact plants want to limit the amount of heat they produce. I've not done the experiment you talk of but my understanding of physics is that if there is color coming off something, then light is being reflected, meaning heat is being lost. Could be wrong of course, but i havn't taken the time to experiment with it yet, so....
(removed by author or community request)
antioch antioch2 years ago
Mainstream science would disagree regarding the dark green theory:

Plants are green because that part of the light spectrum is reflected. So, to most plants, green seems to be kinda useless.
Black means the abscence of light, hence black objects (black holes) are considered to be the most absorbant there.

Maybe the dark green paint was matte and had a certain chemical setup while the black paint was glossy or less absorbant due to ingredients.

My main question would be where exactly the thermometers were placed. If "under" means inside the box while the painted cardboard was tightly against the wall then, of course, the temperature in the dark green box would have to be higher since the black one absorbs heat better, channeling it to the outside.
ganeshruskin (author)  wndwalker2 years ago
sweet, i will try this...
wndwalker2 years ago
@ (author) ganeshruskin, Your right, I wasn't as clear as I could have been,sorry. My idea was, if you could heat up a used water heater by putting it into a trough and heating it with the sun, what if you used a radiator from a used air cond or car or truck or? place it in such a way in a trough type design using Mylar to reflect the sun onto the radiator and heating the water. Radiators are used to get rid of heat, could we just reverse the idea and collect heat the same way? One other "idea," when heating a pipe becomes possibly dangerous, how about a one way valve? water expands when heated, therefore "pushes" the water through the pipe from hot to cooler "collector" where the water would be used or not. if not than circulated back to the "heater." Again, use a one way valve, the type used on lawn sprinkler systems to avoid reverse osmosis from lawn chemicals etc polluting your water supply . I've never done this, but the idea seems doable...

ganeshruskin (author)  wndwalker2 years ago
Yes, there is no reason you couldn't use an old radiator, but the point of this design is to store the water as it is heated, you know, 40 gal of it, and a radiator only holds maybe a gallon, so you need a separate storage tank, which changes the design. If you build one, please let me know how it works.
And valves are only needed if you have a situation where the water in the pipes could freeze while the water in the tank is brought to boiling, pretty unlikely ;-)
The tanks also come with a built in safety pressure and temperature valve.
ganeshruskin (author) 2 years ago
Has anyone else actually built one of these and installed it?
I am about to try manufacturing these again down in Flagstaff and just curious if anyone has developed any improvements on this?
wndwalker2 years ago
one last comment, I was thinking that if a radiator from whatever can be used to "get rid" of heat, why couldn't the reverse be true? couldn't it collect heat as fast as it gets rid of it? If so, than why not put a "collector", (your used water heater) close to your use source, insulate the heck out of it and the pipes coming to it, use a "one way valve" in certain places so that when the water heats up it pushes the water through the pipe into the collector, Also have a return line so that it keeps circulating around until it begins to cool, neutralizing the pressure, and leaving nothing but useable hot water. Just an idea I have.
ganeshruskin (author)  wndwalker2 years ago
I dont know if i entirely understand you here walker, sounds unnecessarily complicated to me, but i could be wrong....
pcline23 years ago
Nice 'ible. I am assuming that you can just add this to your existing plumbing system between the cold water supply and "inside" water heater. Do you think there would be any issues with the pressure of the system, either normal operating pressure, or additional pressure created from superheating during the summer?
ganeshruskin (author)  pcline22 years ago
Yes, you could, and i am quite confident there would be no problems with pressure or over heating.
In the summer however i would just turn the other heater off and if you only used it in the summer you could plum this into the hot system anywhere. I have yet to try this however, so i will let you know when i have tried this out.
These are usually painted matt black - to absorb the heat - not reflect it away... I made a similar thing using a central heating radiator.
Rainh2o3 years ago
Just a thought but if you where line the inside with a recycled mirror it would be way more could glue the mirrors onto the insulation...this would reflect way better then the foil covered insulation...also if you mount it so you could properly tilt it directly into the sun, that would increase the efficiency
good idea, but the glass on a mirror will absorb about 16% of light's energy, mylar sheeting would be the ideal reflective surface. cheap, easy to get, as reflective as a mirror, without the energy absorbtion
OH YES...forgot about can get that from certain chip bags on the inside...good response...
or it's like $12 for that much at the hydroponics store.......
profpat3 years ago
great recycling method, you may also use large steel drainage pipes just plugs the ends with end plates. the thinner walled piped works great!! some people also use old refrigerator condensing coils as the heat collector..
triumphman3 years ago
Where do you connect this into your heating system. Do you run a line to your furnace (all- in- one) cold water inlet? My furnace has no separate holding tank. Or where exactly, this is critical! I want to minimize the use of oil. My furnace keeps the water hot 24/7. So its very wasteful. I just got hit with an over $1,000.00 bill for only 300 gallons of oil!!! Any help will be deeply appreciated!
JeremyA4 years ago
How about some focused fresnel lenses to add a turbo charge to it. Just get the little cheap ones that they sell as book magnifiers and mount them on sticks that you can move over the tank. focus them a few times a day and it should significantly increase the heat. Just a quick though I haven't thought of all of the implications yet.
Bosun Rick4 years ago
Why no mention of what you did with the flue pipe that runs up through most gas water heaters? (I  don't think electric heaters have a flue pipe) I would suggest that the flue pipe be blocked off at each end; or have some method of heating it's interior surfaces to aid in the solar heating cycle. Just a thought.
Jaymee4 years ago
Will this work in Canadian winters?
no you will have to fill the tank with 60-40 anti freeze and add a solar activated 12v circulation pump down to a coil in your water storage tank
codydean4 years ago
i believe it would work even better if the tank was painted black.
yes flat black enamel paint Tremclad
This sounds like a great idea. Have you any figures as to total cost?
fjpalacios14 years ago
Just got a free 40 gallon water heater yesterday. I have a design that's a bit different however very similar. I'll post my results and design when completed.
However, thanks for the idea and motivation to save energy.
jomac_uk4 years ago
Curious question, you have covered the foil covered insulation with foil, would it not have been easier to have used a solvent to remove the manufacturers print on the insulation panel?
newbeatle4 years ago
i have read that someone tolds you what i like to tell you , paint the tank enterely black and check if this raises the temperature of the water. nice work how much cost to you make this ?

salutes frem mexico

el ing. aLex
roliop4 years ago
Perhaps line the inside of the lid with aluminium foil and prop it up to shine even more light onto the tank.

profpat4 years ago
nice one, i have been thinking of building a solar water heater, but most of the design i see use lots of copper tubing for the heat collector, which to is a tedious work to layout....

this one give a better and simpler design idea..
Legeir0074 years ago
Great job!
martyjr94 years ago
the tank should be flat black to absorb the light otherwise looks good
bigdan874 years ago
I like the nice and simple design. If you are up to a more involved project, check out designs with curved panels behind the tank so that every bit of light entering the box is reflected directly onto the tank. More efficient, but also way more complicated to build than this design. Another way to boost efficiency is to cover the tank with a selective coating, rather than just black paint.
nieks4 years ago
This is a good idea, but I think you might be able to make it more efficient? Maybe, as a start, paint the tank completely black. This will ensure light absorbtion.
piperjon nieks4 years ago
Hmm, in reading the instructions, step 3, the author does say to "Paint tank with flat black metal paint. Rusty metal primer is recommended but optional." But it sure doesn't look in the later to last pictures that it has been done so. I'm very seriously contemplating doing this, as I've put off replacing my useless water heater for quite some time. So, if you have any ideas for increasing the efficiency, I'd love to hear them! I'm no master of design, but I'm good with my hands and have no fear of tools of any kind. :-) And then I'll do an instructable! - Pj
ganeshruskin (author)  piperjon4 years ago
Yes, yes, yes!
Sorry people, this picture is from a workshop I lead on building one of these, and we didn't have time to paint it. Yes it needs to be painted flat black for sure.
I will change that picture for a correct one soon. My camera is almost ready for action!
thanks for the comments, any more?
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