Awesome! How To Build A Water Heating Solar Panel From A Rubber Mat And An Old Fridge Condenser!

Awesome! How To Build A Water Heating Solar Panel From A Rubber Mat And An Old Fridge Condenser!


The Goal of this project was to harness the sun’s energy to heat water for the home for as cheap as possible.
The upper limit of expenditure being $5. The idea is a brilliant one of course, but what makes this really possible at such a cost is the utilisation of old parts whenever possible; the main one being the condenser from the back of an old refrigerator.

Have you ever wondered what the condenser at the back of your refrigerator is for? Yes, it is for dissipating the heat collected by the high-pressure gas which condenses into liquid after absorbing it from the system. We are going to invert this process in order to turn water from cold state to a warmer and eventually hot state by passing it through the condenser under a controlled environment that harnesses the heat from the sun:

After our first attempt at a home built proof of concept solar thermal panel, we were a bit disappointed with the results. It took about 4 hours before the thing started work, and was a bit costly (at over 50 dollars) to make.

Here’s what you need (mostly scrap material):

  • Water
  • 2 buckets
  • Drill (with both drill bits and screw bits)
  • Some scissors
  • A saw (a simple hand saw will do)
  • Some wood
  • A pane of glass.
  • The back of a small refrigerator.
  • 12 feet of air pump hose used in fish tanks
  • Backing material (we used an old door mat)
  • A box of wood screws
  • Aluminum Foil
  • A Roll of duct tape

Tools: Drill, hak saw and a pair of scissors


rubber door mat - diy solar thermal panel
rubber door mat (thesietch)


the frame - diy solar thermal panel
the frame – diy solar thermal panel (


As you can see I sort of built the frame around the collector, leaving enough backing to hold it all together.

The frame is held on by building a similar frame on the back and driving large wood screws through the front frame, the backing and into the back frame.

I added some foil to the backing. The reason for this is that counter to what you would think, you do not want the backing to warm up. You only want the collector to absorb heat (it was so nice of the fridge company to paint it black for us). The foil will take any sun that was not absorbed by the collector on the first pass and bounce it back over the collector for another try at absorption. The glass cover will keep all the heat inside the panel for further absorption.

Light can pass through glass, but heat can not.


glass pane affixed - diy thermal solar heater (thesietch)
glass pane affixed – diy thermal solar heater (thesietch)


Set your cold water bucket (source) up higher than your warm water bucket (return) and the whole thing will gravity siphon. Due to the design of this collector (both ports return to the same location on the panel) it will not thermo siphon. For that to happen I would need to cut the long return pipe and have it exit at the top of the panel.

A word of warning, this panel works VERY WELL. We tested it on a very sunny day and within seconds the water coming out of the panel was hot enough TO SCALD. I burned my fingers. This very hot water is only formed when the water inside the panel is allowed to sit for about a minute without moving. If the water is moving (do to the gravity siphon) the water exiting the return pipe is about 110 degrees, and while hot, will not burn you.

The water does not flow through the panel very fast (as the pipes are very small) but that is sort of a good thing as it allows the water to heat up a lot on its journey through the collector. It does take a while to heat up a 5 gallon bucket of water, I ended up building an insulated return bucket that was all black and sealed on the top except for the port where the water tube enters. This kept the returned hot water hot long enough to be of use.


diy solar thermal panel
diy solar thermal panel (thesietch)


As stated in the source article (see link below for complete tutorial), the major advantage of such a system over just leaving a bucket of water in the sun is that even in fair weather (say 50 degrees) you can have water warmed at 110 degrees. This would not be possible with the ordinary bucket method. And to repeat the note of caution you should be careful when siphoning the water because it could heat up enough to cause scalding.

What experience do you have with such projects? Share with us below:



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