In the following lines we will present some ideas for a solar collector that everyone can make themselves. Many use the power of the sun's rays to heat water when there is no other alternative or want to save electricity. There are various methods and technologies - from simple black painting of outdoor water containers, to high-tech vacuum factory systems. The better the technology, the greater the efficiency, but also the price paid for it. To begin with, we will focus on a very simple but effective idea, and almost all the materials used for its implementation are recycled.
The first thing you need is a copper coil from a junk old refrigerator. We also need a rubber mat (in the case of old mat), glass of the same size (from the old window frames), wooden slats for the frame, aluminum foil, pipe connections (in this case old hoses), adhesive tape, fasteners. These materials are required for the design of the collector itself, and a water tank, valves and pipe connections will be required to build the system.

Method of production:

The old refrigerator coil is cleaned well. A frame is made of the slats in which the rubber substrate is mounted as an insulator at the bottom, the top is covered with an aluminum foil, which is a reflector, and on it is fixed a coil whose edges extend beyond the resulting structure. Everything is insulated very well with adhesive tape so that no gaps are possible, then it is closed with the glass and sealed again with adhesive tape. Through the soft connections, the collector connects to the system.
The system is passive and requires no electrical components but relies solely on the upward movement of heat. The diagram shown illustrates the principle of operation.

A homemade system with a similar principle of operation, but a much larger scale can be made and used to heat an outdoor pool, as shown in the following video.