Étape 1 - Preface
Panel Orientation
The thermal solar panels that we are building will have to be installed facing directly south, ideally forming an angle of 60° with the horizon, (or vertically on the outside wall, if the former is not possible). Rooftop usage of these panels is much less efficient in the winter and causes overheating in the summer (more details in the installation phase).
Inertia
To maximize the effectiveness of the thermic solar energy, it is necessary to minimize the inertia in the light uptake and to maximize it in the storage or the diffusion. The panels work as soon as there is a sunbeam thanks to their low inertia. The heat is retained for a long time with its great volume and its good insulation.
The pipes of the refrigerator grill have a small diameter (4mm), so there is a low volume of heat transfer fluid to heat in the panel. This low inertia quickly increases the temperature as soon as the sun appers from behind the clouds and then heats the hot water balloon. The greater the diameter of the pipes, the more time it needs to heat the larger volume of fluid. and the less efficient the system becomes.
To ensure the temperature of the panels increases quickly, the space between the insulation and the glass need to be as small as possible. So the panel has to be as thin as possible, whilst ensuring that the grid doesn't touch either the insulator nor the glass. Otherwise those elements will conduct heat away from the panels.
Temperature
The temperatures can exceed 150°C (302°F) inside the panel, so it is essential to use materials resistant to heat and to UV radiations. Do not use sticks or paints with solvents which are not resistant to UV radiations. Here, we use PU putty and acrylic paint. For a good longevity, also make sure to use rot-proof local wood.
On winter nights, it can get very cold inside the panel. The different materials, insulation, metal, wood and glass will expand differently between winter night and summer sun. The joints that unite them must be thick to absorb the deformation, if they are not thick enough they will tear off.
Grid
The specific feature and ingenuity of these solar thermic panels is the use of refrigerator grills. But beware, not all grills are good and they must be used in the right direction! The grills must be provided with cooling fins and painted black (see photo). They must not be in galvanized steel, as the paint will not adhere. Similarly, some refrigerators are equipped with pipes connected by wire, but the surface of these grids is insufficient for this use.
The right grilles have a direction of assembly, the fins, comparable to louvers, must capture the sun. In a sense the sun will pass through, it's bad, in the other direction it will capture the rays, it's the good sense! They must be perpendicular to the sun's rays.
Tip: take the grid and lift it between the sun and yourself, in one sense the rays will pass and not in the other.
Refrigerating gas
Refrigerator grills are covered by a refrigerant, harmful to the environment, the greenhouse effect and the ozone layer. In France the refrigerating gases must be recovered. However, there are exemptions for equipment containing less than 3 kg of fluid until 2025. The domestic installations (refrigerator and air conditioner) are degassed before continuing their upgrading process. We can open the circuit without too much conscience.
Safety
Be careful, you will do something that may involve risks.
The information and advice given in this tutorial come from joint workshops and are neither perfect nor exhaustive. If you don't have certain tools or if you don't feel competent, don't hesitate to ask around for help. Remember to wear your safety equipment, to work in ventilated areas and do not put yourself in danger. Be careful, calm, and of course critical of any false good ideas you may have ("that's how it will go...").
Enjoy!
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