Today, it is quite possible to make selective coating for glass solar panels on their own. To do this, you can use a variety of materials that are created both with your own hands and bought in a special store.
Type of coating
Currently, there are three types of selective coating. This can be either ordinary paint or chemically treated metal. The third option is ready-to-use films that can be glued to glass. These three types of raw materials differ among themselves in the following indicators:
- ability to absorb;
- emissivity;
- overall level of effectiveness.
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 very carefully choose a substance according to its emissivity. It characterizes the amount of heat that will be released into the environment in the form of radiation. In other words, the higher this parameter, the greater the heat loss, and therefore, the efficiency of the device will decrease.
As regards overall efficiency, it is usually presented as a common coefficient, which is considered the ratio of the first two indicators. Actual thermal performance will not be accurately reflected, but the effectiveness of selective coating is determined quite accurately.
Paint application
Today, some people believe that black paint can be used as a good coating for the glass of a solar collector, since it warms up well and absorbs sunlight well. However, this is not so, 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 capable of radiating heat in the infrared spectrum to the atmosphere. Thirdly, such a coating will fade over time due to exposure to ultraviolet rays of the sun, due to which the ability to absorb will decrease. Another disadvantage is the strong decrease in the efficiency of the absorber at high temperatures. The last thing worth mentioning is that the paint coating will also serve as thermal insulation, because of which heat will not pass inside.
These disadvantages completely exclude the possibility of using conventional paint as a selective coating of glass. For this purpose, it is necessary to use only special means.
What to apply paint on?
After acquiring a suitable paint, the question arises of how to properly apply it to glass. To begin with, it is worth saying that it is applied to the substrate, and not to the panel itself. The substrate is aluminum or copper. This type of metal is excellent because it is able to effectively remove heat from the absorber, that is, paint, and transmit it to the panel.
How to paint glass panels?
Before applying selective coating to solar panels, you need to polish a sheet of copper or aluminum. To do this, use the mechanical grinding method, as well as further coating with GOI paste. It is important to note here that it is necessary to carry out the work as qualitatively as possible, 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 a spray gun. 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 presented in two types: single-layer and multi-layer on a metallized substrate.
As for the effectiveness of the films, the coefficient is quite high and comparable with the same indicator for paints, but if we talk about the cost, it is very different. A high-quality film is characterized by the fact that its emissivity is 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. It is not necessary to carry out any complex manipulations, the film is glued very easily. However, before applying it, it is worth processing the metal sheet in the same way as was done in the case of paint, that is, you need to process it with a grinding machine with an abrasive wheel.
Selective glass for home
In addition to the use as a coating of solar panels, selective coating of a double-glazed window is in no less demand. Selective glasses, or multi-functional, 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.
Selective absorbent coating applied to ordinary glass creates a good protective film. The main task of such elements is to create the most favorable indoor conditions both in the summer season and in the winter. The essence of their work is quite simple: in the summer, the glass eliminates a certain amount of sunlight, which prevents the room from heating up very much, in the winter they will serve as an excellent obstacle to thermal energy, preventing it from leaving the room.
The Importance of Selective Glasses in Cold Weather
Today, everyone knows that windows protect a certain part of the wall, preventing heat from leaving the room. However, if you really look at things, then through poor-quality glass more heat will leave than through ventilation or even an ajar door. The whole problem is that choosing a quality material for the window will not be enough. About 90% of the window is occupied by glass, which means that it should also be as useful as possible in terms of heat conservation. It is with this task that selective glasses work best. The peculiarity of spraying is also that there is a very thin layer of silver atoms on the surface. They perfectly transmit the short waves that the sun radiates, thereby transmitting heat inside. But at the same time, silver strongly blocks the passage of long waves, which are usually emitted by heating devices. Thus, it turns out that heat is stored as well as possible indoors.
Soft and hard coatings
There are currently two different types of glass coatings. It may be a soft selective coating, or it may be hard. They differ in application technology. Because of this, naturally, the level of their thermal insulation will also differ. For comparison, you can give a simple example. Suppose the temperature inside the room is +20 degrees Celsius, and the temperature outside the window is –26 degrees Celsius. An ordinary double-glazed window in this case will maintain a temperature inside of about +5 degrees, a solid selective coating will provide a temperature of +11 degrees Celsius, a soft coating will maintain +14 degrees.
It is worth adding here that for such a surface there is a special marking. Hard or pyrolytic surfaces will be marked with the letter K. A soft surface, or, as it is also called, magnetron, is marked with the letter I.
If to summarize all of the above, then we can draw two small conclusions. Firstly, selective coating can be applied independently if solar panels are available. This can increase their effectiveness. Secondly, selective glasses are perfect for home insulation.