How to build a simple solar thermal water collector

In august, during the “Do It Yourself 2.0” workshops set up by Cohabitat, I ran a workshop in which I taught how to build a simple and affordable solar thermal collector that is suitable for domestic hot water.

Of course I made a lot of video and photos so that I could edit it all into a short video. Here’s the video. The commentary is in Polish, but below you find a translated transcript.

For the most important parts for this collector (measuring 1,25 m × 0,85 m (roughly 4 ft × 3 ft) cost less than 200 PLN in Poland, which is equivallent to something like 50€ or $60. We got the window pane for free, but we had to buy copper pipes, aluminum sheet, soldering supplies and all the small bits and pieces.

What is really fun is that you don’t need electricity to make this solar thermal collector. We only used it to make cutting pipes and wood faster, but you can easily cut it all using hand tools, like we did for the first couple of times. And all the soldering was done using gas soldering iron — which in fact is much faster than if we used electric one. This means you can easily build this solar collector on a really off-grid site!


This video shows how to build a very cheap and effective solar thermal collector that can be used, for example, for domestic hot water production.

I ran two weeks ago a workshop on which I shown how to build a collector according to a design I described in my book. I wanted to show that the consecutive steps of the construction are so easy, that anyone can make one for himself — even someone, who will only see it once on the web, or read about it in a book.

The most important parts for this collector cost a bit more than 200 PLN, assuming you can use a lot of reused materials. We started the collector with a fixed dimensions of the window pane of roughly 1m2 of area. To that dimensions we built the absorber plate, flow tubes and casing.

Reusing some materials makes this collector cheaper and easier to build. Fixing the glazing to the casing would be difficult if we didn’t use the window pane. Luckily we only needed to bolt the window pane to the frame.

First step is to cut the copper pipes to appropriate lenght. Since the collector was 124 cm long, we cut the 16 mm (5/8″) pipes to 116 cm (45.7″). These small pipes were connected to a parallel grid using 22 mm (7/8″) pipes.

At the same time, we also cut and manufactured the aluminum fins that were used as the absorber plate. These fins are going to collect all the solar energy, heat up and then conduct the heat to the heat exchanger (copper pipes). To do it efficiently, the area of contact between aluminum fins and copper pipes has to be as large as possible.

We made the fins using our own weight or a piece of wood.

In order for the solar collector to work, you need to make sure it’s sealed properly. Because of that the following step is really crucial, all the connections between the pipes need to be tight. In other case, the water will start leaking, causing the insulation to become wet, and the collector will be useless because of that.

Soldering is not difficult. You only have to cover the connected parts with soldering paste, heat them up and then use the solder. If the solder melts, the parts are hot enough. Use a lot of solder and paste, as it’s easy to leave some parts not sealed properly and fixing it may be difficult later on.

Following that, we connected all the absorber plate fins and copper pipes. To make it easier we used a piece of OSB board, on which we placed the copper grid. Using nails we attached the aluminum fins to the board. This helped a lot in creating a good contact between fins and copper pipes.

It’s required to add a bit of silicone to substitute the air between the fins and copper pipes. It’s better for the fins/pipes to be connected with a layer of silicone, than a layer of air. It’s even better to avoid any layers of air or silicone at all.

At the same time we also built a frame for the casing. We used 4×10 cm (1.5×4″) timber.

When the absorber plate and copper grid were fixed to the OSB board, we painted it all black. It’s important to make the paint layer as thin as possible, to make it easier for the heat to be conducted to the aluminum fins.

When the collector is inside the casing, you need to add the hydraulic joints to both ends of the copper pipes. You can solder them or glue them to the copper. I found it easier to make holes in the frame for the joints and glue them after the collector was bolted to the frame.

The last thing to do is to check if the collector is tight (hermetic). You simply connect a water hose to the joints and run water through it. It’s best to do it prior to adding the aluminum fins, as it might make any repairs easier at that point.


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