Solar Heater for My Shop





Introduction: Solar Heater for My Shop

About: I have always been a frustrated astronaut, but a hearing loss kept me grounded. Now after over 30 years in a highly technical public service position, I have more time to devote to my passions; electronics, ...

After changing TV providers, I found myself with this extra wide Satellite dish. I thought "Boy that would make a great reflector for a solar oven." So I sprayed some adhesive on it and grabbed a Mylar "Space Blanket" out of my "Go bag" and covered the face of the dish wit it. Then pointed it at the sun, and put my hand just about where the LNB would have been. Ouch! I will not try that again!

Step 1: Adding the "Black Box"

After some experimenting, I added a small black "key lock box". Then I was getting readings of well over 500 degrees F.(260C) So I figured anything I was cooking would be burnt on the outside before it was done on the inside.

My next thought was "If I add a coil of copper tubing, It should heat water pretty fast"

Step 2: Coiled to Strike! Err, I Mean Heat.

Using some 1/4 inch copper tubing, I made two small coils inside the box, drilled a couple holes for the ends to pass through at the bottom. And stuffed fiberglass insulation behind them so they would stay in contact with the dish side of the box.

Step 3: Adding Pump and Storage

I had a 20 pound propane tank (the kind used for grills) that had the valve broken off. I twisted the remainder out of the tank with a pipe wrench. Then filled it with water so I could drill and tap a second hole without fear of any lingering propane igniting. I found a nipple at my local hardware that fit the original hole. Inside this I epoxied a 3/8th inch "drop tube" to send the hot water to the bottom. The second hole that I had drilled near the top, I tapped for a 3/8th inch pipe fitting. This would become the "output fitting"

I then purchased a 12 volt DC 50 psi "beverage" pump and some 3/8th inch ID plastic tubing that I routed up to the coils on the dish and down to my pump and storage tank.

Step 4: The Heat Exchanger

Being someone who keeps everything, (Much to my wife's dismay) I had a dead window air conditioner. After removing the cover, I decided the fan and outside heat exchanger would be about the right size. So I removed both and mounted them in an old PC case. (See I told you I never get rid of anything) I was able to leave the fan connected to the original control box after disconnecting the compressor wires. I the used my tubing cutter to cut the top and bottom copper tubes leading from the compressor.

My pump drawls from the top of this coil/heat exchanger and pumps to the up side of the dish coil. The down side or hot side attaches to the "drop tube" on the storage tank. The out put tube on the storage tank goes to the bottom of the fan/heat exchanger.

I point the dish at the sun, and turn the pump on for a bit before starting the fan. This heats the water in the storage tank quite quickly. Then when I turn on the fan, I get nice warm air out of my solar heater.

The photos above show first the room temperature, then the air temperature at my heater.

I have an old DisEqC rotor on the dish, I am working on a way to control it to automatically follow the sun, perhaps in my next instructable.

Have fun and stay warm!

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    is it feasible to take another heat exchacher, paint it black, & put it at the focal point of the parabola?

    2 replies

    Absolutely, if I had a small one on hand I would have done this. Thanks for the question!

    You could probably increase the heat transfer of the box to the coils by pouring molten lead into the box, just enough to cover the coils, then fill the remainder of the box with insulation. When I do something like this I use a strong acid (the Works toilet bowl cleaner) in place of flux to prep the surfaces for good adhesion to both surfaces.

    Next step is to connect this to Arduino Sun Tracker Turret:

    2 replies

    Check out my version at:

    Update! Check out my Arduino controlled solar tracking system!

    I would do some research, but antifreeze for RVs might work. It is made different than standard automobile antifreeze. People use it to cool their laser cutter tubes when the machines are not in a heated space.

    This is great. Just want to add this:

    I'd suggest using propylene glycol. One way to get this is from AMSOIL (American Synthetic Oil (?) ) from independent dealers for automobiles. I believe this will be better against corrosion and I believe a similar chemical is used in building hot water heating systems. I would estimate a 50% solution will give a -25 degree F freezing point and will have a 15% reduction in heat transfer. (~$40/gal.)

    Also, for reference, the sun, on a clear day and maximum impingement, estimate 430 Btu/s.f./hr. solar gain. (Keep in mind a typical house furnace is 48,000 Btu/hr output (80% eff., 60 MBH input (60,000 btu/hr.) (1400 s.f. house, above average insulation, 80 degree design delta T)). Natural gas is doing THAT much for you!

    Don't expect any usable capacity from hot water storage from 20 gallons. (lol) You might need a bladder type expansion tank too (Watts domestic hot water (2 gal (?) - Home Depot, set for 20 psi (?)).

    Great project. I'd be interested in your results and comments. (I bet I know what they'll be like (lol)) -Ohio

    3 replies

    well, he already took measurements and it shows about 17 Deg Celsius in crease in Temp. does that not show that his 20 Gal tank is working? After all he is only heating his shop. On the other hand what did you mean when u said " will have 15% reduction in heat transfer"? I thought the idea is to get maximum heat transfer from the dish to his shop. I agree Glycol is better than water and will keep the tubes from freezing and will also prevent oxidation of the tank. True 50% solution is good for -25C as it says on the Glycol jog.

    The water volume in this tank in this scenario is a thermo-mass storage (buffer); it will also take longer to heat up. In heating hot water systems, it with be a bladder-type expansion tank. In contrast, in domestic hot water, it is your hot water ready for use. These are slightly different functions although both yield a hot water supply.
    The use of glycol is primarilty because of the need of using an anti-freeze solution. Glycol has a different specific heat, and therefore different heat transfer rate. This medium at this concentration is this much less than water's heat transfer. Yes, it would be higher if only water could be used. Corrosion inhibition is the next desire.
    Polyethylene glycol will get acidic. This is why there are/were problems with automotive engine cooling systems when trying to get 100,000 miles between changes. I mentioned it for this reason.

    Okay, I am using the equivalent of a 4' parable, so radius is 2'
    2' squared x 3.14 x .2 for the average depth = 25.12 square feet
    25.12 x 430 BTU/Hr = 10801 BTU/Hr
    say there is 8 hours usable sunshine = 86412.8 BTU/DAY
    Guessing its 60% efficient thats 51847.68 BTU/day free added heat to my shop.
    My pump and fan are run off of photo voltaic cells charging a deep cycle battery
    Granted that's just over an hours worth of heat from my household furnace, but as there is no heat in my shop, I'll take it!
    Thanks for all the info I didn't have to look up to make these calculations!

    sorry for my ignorance, but what is a LNB and what is the black box ? Is it the unit that captures and transfers heat to the water - have you thought of using an oil as it has a greater calorific capacity than water.

    Think you idea is great.


    1 reply

    Hi Murry,

    An LNB is a low-noise block down converter, or essentially the part that captures the signal reflected from the dish for satellite TV. The black box in my design is simply a metal box with a black powder-coat paint that I wound copper tubing inside to collect the heat. And yest I have considered a great many different fluids, and will probably use a mixture of auto antifreeze and water (auto antifreeze is mostly propylene glycol)

    Thanks for your interest!

    I am thinking a truck/tractor eaton transmission heat exchanger tank, or even an EGR cooler would work very well for mounting to the dish in place of your coil/key box. You could also use any automotive Radiator/heater core/ac condenser/ac evaporator as the interior heat exchanger, specially if your looking to upscale in size. I am a Diesel Mechanic, and I know I can go to work tomorrow and find all the components I need in the scrap bin, solder/braze up some holes and good to go. I may even go with a large air tank off of a truck for the storage tank, as well as a large aluminum Charged Intake Air Cooler as the heat exchanger, equipped with dual 12inch 12vdc radiator fans. Also a front wheel drive car ac condenser that already has a large dc powered fan and shroud attached to it would be ideal, I would think

    I was wondering if water recirculation could be done drip-coffee-maker style where check valves and water temperature differences would control the recirculation

    Oh wow ! Just the thing I was looking for. I was gonna try that too, but am too lazy. But now that you have done it. I'll surely do it.

    Thanks for the inspiration and will be waiting for your solar tracking upgrade. If possible try to make it analog, I mean add a comparator instead of arduino to drive the motos.

    It is a 52 inch ellipsoid, designed for multi-sat HD TV on the Ku band.