To date, it is quite possible to issue a selective coating for solar panel glasses on your own. To do this, you can use a variety of materials that are created both by hand and bought in a special store.
Cover type
Currently, there are three types of selective coverage. It can be either ordinary paint or chemically treated metal. The third option is ready-to-use films that can be glued onto glass. These three types of raw materials differ from each other in the following indicators:
- absorption capacity;
- emissivity;
- general performance level.
If we talk about the first parameter, then in this case the amount of heat that the selective coating can convert from solar energy is determined. This indicator plays a very important role, but is not the main one when choosing.
When choosing a coating, that is, an absorber, you need to carefully choose a substance according to its emissivity. It characterizes the amount of heat that will be given to the environment, inform of radiation. In other words, the higher this parameter, the greater the heat loss will be, and consequently, the efficiency of the device will decrease.
As for the overall efficiency, it is usually presented as an overall coefficient, which is considered the ratio of the first two indicators. The actual thermal performance will not be reflected accurately, but the efficiency of the selective coating is determined quite accurately.
Apply paint
Today, some people believe that black paint can be used as a good coating for solar collector glass, as it warms up well and absorbs sunlight well. However, this is not the case, and there are several reasons why such paint is not effective.
Firstly, the paint is able to absorb only that part of the radiation that is visible, the rest of the radiation is not used. Secondly, it is able to radiate heat in the infrared spectrum into the atmosphere. Thirdly, such a coating will fade over time due to exposure to the ultraviolet rays of the sun, due to which the absorption capacity will decrease. Another disadvantage is a strong decrease in the efficiency of the absorber at high temperatures. The last thing to say is that the paint coating will also serve as thermal insulation, due to which heat will not pass inside.
These shortcomings completely exclude the possibility of using conventional paint as a selective glass coating. For this purpose, it is necessary to use only special means.
What to paint on?
After acquiring the right paint, the question arises of how to properly apply it to the glass. To begin with, it is worth saying that it is applied to the substrate, and not to the panel itself. Aluminum or copper is used as a substrate. This type of metal is great because it is able to effectively remove heat from the absorber, i.e. paint, and transfer it to the panel.
How to paint the panel glass?
Before applying the selective coating on solar panels, you need to polish a sheet of copper or aluminum. For this, a mechanical grinding method is used, as well as further coating with GOI paste. It is important to note here that it is necessary to carry out the work with the highest quality, since any roughness is an increase in heat loss, as the emissivity will increase.
The easiest way to cover the desired sheets is to use an airbrush. The paint is applied as usual, but there is a minus, which is that it is difficult to control the thickness of the layer. If it is too large, the quality of heat absorption will decrease, if the layer is too thin, then heat loss will increase.
Film for panels
There is another option for applying a selective absorbent coating. For this, a special film was developed, which is currently available in two types: single-layer and multi-layer on a metallized substrate.
As for the effectiveness of films, the coefficient is quite high and comparable to the same indicator for paints, but iftalk about the cost, it is very different. Quality film is characterized by its emissivity of 5% or less.
As for the application process, the procedure is very simple. A single-layer self-adhesive film is attached to a sheet of metal, which can be made of zinc, copper, aluminum. No complicated manipulations are necessary, the film is glued very easily. However, before applying it, it is worth treating the metal sheet in the same way as it was done in the case of paint, that is, you need to process it with a grinder with an abrasive wheel.
Selective home glass
In addition to being used as solar panel coating, selective coating of insulating glass is in no less demand. Selective glass, or multifunctional glass, as they are also called, are used for ordinary houses, for glazing commercial buildings, sports complexes, municipal institutions, etc. Such glasses can provide good protection from sunlight and create a favorable indoor microclimate.
The selective absorbent coating applied to ordinary glasses creates a good protective film. The main task of such elements is to create the most favorable conditions indoors both in the summer season and in the winter. The essence of their work is quite simple: in summer, glasses filter out a certain amount of sunlight, which does not givethe room gets very hot, in winter they will serve as an excellent barrier to thermal energy, preventing it from leaving the room.
Importance of selective glasses in cold weather
Today, everyone knows that windows are the protection of a certain part of the wall, preventing heat from escaping from the room. However, if you really look at things, then more heat will escape through low-quality glass than through ventilation or even an ajar door. The whole problem lies in the fact that it will not be enough to choose high-quality material for the window. Approximately 90% of the window is occupied by glass, which means that it should also be as useful as possible in terms of heat retention. Selective glasses are the best solution for this task. The sputtering feature also lies in the fact that there is a very thin layer of silver atoms on the surface. They perfectly pass the short waves that the Sun emits, thereby passing the heat inside. But at the same time, silver blocks the passage of long waves, which are usually emitted by heating devices, quite strongly. Thus, it turns out that the heat is kept inside the room as well as possible.
Soft and hard surfaces
Currently, there are two different types of glass coating. It may be a soft selective coating, or it may be hard. They differ from each other in application technology. Because of this, of course, the level of their thermal insulation will also differ. For comparison, a simple example can be given. Let's say the air temperature inside the room is +20 degrees Celsius, and the temperature outside the window is -26 degrees Celsius. In this case, an ordinary double-glazed window will maintain an internal temperature of about +5 degrees, a hard selective coating will provide a temperature of +11 degrees Celsius, a soft coating will maintain +14 degrees.
Here it is worth adding that there is a special marking for such a surface. Hard or pyrolytic surfaces will be marked with the letter K. Soft surface, or, as it is also called, magnetron, is marked with the letter I.
Summing up all of the above, we can draw two small conclusions. First, the selective coating can be applied independently if solar panels are available. This can improve their efficiency. Secondly, selective glass is perfect for home insulation.
