Building a low-cost solar heater with recycled material is very simple and useful, especially for those who need to save money on gas from carafes or who use firewood to heat water. It is also of interest to those who support ecology, aware of the importance of the implementation of alternative energy sources, and people who like manual jobs.
It's about taking advantage of free solar energy and using soda bottles that are thrown away. The idea, in simple terms, is to create a small greenhouse in each bottle and run an irrigation hose (polyethylene) inside it. In this way, the heat that is trapped in the bottle and that is then absorbed by the hose (which is black) is transferred to the water and thus it can be heated and save fuel such as gas, electricity or firewood.
It can be said that, in this way, a device is built to heat water, for sanitary use, with totally renewable energy. It is estimated that a typical family of four uses approximately 80 liters of hot water per day in the kitchen and in the bathroom. One can build this heater any size you want, according to the hot water capacity required for daily use, because it is assembled with columns of 6 bottles, with 2 meters of hose each.
As many columns as you want can be coupled in parallel and the roof of the supporting house is used. Because once built, this ecological heater is placed on the metal roof of the house, and if it is loaded with 100 liters of water, the weight must be supported by the roof structure.
How to build a homemade solar heater step by step
The procedure to build the solar heater is as follows:
1.- Collect at least 30 disposable one and a half liter soda bottles, all the same (important) and remove the label.
2.- Buy in a hardware store or business of the branch, 12 meters of hose for irrigation color black (it is important that it is of that color) and ¾ of an inch in diameter, 8 unions "T" and two elbows, a roll of Teflon and two ¾-inch ball wrenches.
3.- Have an electric drill and a ¾-inch cup bit. If you don't have this tool, you can patiently use a small kitchen saw-type knife to pierce the bottles.
4.- A hole is made in the base of each bottle, equal to the diameter of the hole that the bottle has in the sector where the cap goes. Once the holes have been made in the 30 bottles, five lengths of two meters each must be cut of black polyethylene hose. The bottle is then joined to the other, inserting the neck of one into the hole drilled in the base of another, to form a column of six bottles, and then a 2 meter length of hose is inserted into it. By repeating this step five times, the 30 bottles have been used and a "grill" is available, which is finished putting together elbows at the ends and "T" joints in the middle. This is how the heater collector is assembled as indicated in the figure.
5.- This grill is placed in the sun, on a sheet metal roof and oriented towards the North, preferably, then water is introduced through the lower part. After 15 minutes of exposure to the sun's rays, water at about 45 or 50 degrees comes out of the top, ready to use. This happens by a physical principle called "thermosyphon".
6.- You can add an insulated container to store hot water, for which recycled 200-liter containers are used, which have not been used to transport dangerous chemicals. The type used for the wholesale marketing of olives is ideal, with which you can build a homemade thermo-tank, so that the water heated by the sun, during the day, can also be used at night.
Finally, it is necessary to highlight that this simple device, whose cost can be between 50 and 100 pesos, can be built by school children as technology work and in neighborhood clubs or neighborhood centers as a community task, or simply in the home, as a job and a hobby for the whole family.
There is a lot of information on this topic on the Internet. Here is a university document that contains a detailed step by step guide on how to build your own heater. Instructional guide