Modern photovoltaic panels are a complex multi-layer structure. Its central part is occupied by semiconductor cells stacked in rows, which are extremely sensitive to mechanical damage. To completely exclude the contact of the converters with the external environment, special protection of solar panels is used. It is based on durable transparent coatings, the properties of which determine the performance of solar modules and their service life.
Solar glass – types and characteristics
There are five main types of glass coating, which differ in manufacturing technology, the content of chemical elements – “additives” and physical and technical parameters.
1. Sheet “float” glass.
It is used in the cheapest modules made mainly by little-known Chinese firms. Distinctive features:
- thickness and strength are higher than that of a classic window;
- there is anti-glare technology;
- high-quality polishing;
- transparency in the range of 90-91%.
Such a coating of solar cells is the least effective and most sensitive to the influence of the external environment. Because of this, the performance characteristics of the “float” modifications begin to deteriorate rapidly, in particular:
- the coefficient of light transmission is reduced due to mechanical micro-damage of polishing with solid particles of sand and dust;
- there are internal stress drops under the influence of structural changes in the material;
- the level of absorption of the electromagnetic photon flux decreases.
The whole complex of these problems leads to an accelerated degradation of cells. As a result, after 10-15 years, the initial efficiency of the system decreases by 20 percent or more, which requires a deep modernization or complete replacement of panels.
2. Tempered glass for solar panels
Provides better protection for several reasons. The main one is a special procedure for thermal hardening of workpieces at temperatures above 650 ° C. An auxiliary reason is a change in the chemical composition of the vitreous mass, due to a reduced content of iron oxide (Fe2O3) and an increased content of lead oxides (PbO) and barium (B2O3).
This results in the following performance characteristics:
- strength, allowing to maintain the integrity of the surface under the shock dynamic impact of large hail or pebbles of comparable size at speeds of the order of 90-95 km / h;
- a similar safe level of static load, approximately equal to the weight of an adult male;
- more stable crystal lattice;
- transparency 92-93%.
Such a mechanically and chemically modified coating for panels in solar power plants practically does not lend itself to deformation and retains all performance characteristics for at least 25 years.
3. Anti-glare solar glass
Protection of photovoltaic cells with sheets of this class is not only super reliable, but also has a high transparency – 94-97%. Physically, the material of the protective surface is a complex crystalline structure obtained in the following way:
- hardening of the silicon-silicate mixture according to a special schedule of increasing and decreasing temperatures;
- primary polishing;
- surface etching with a procedure for displacing calcium atoms;
- deposition of ionized potassium cobalt anti-reflective film using NSTM (Nano Selective Transmission Modeling) nanotechnology.
For comparison: technology similar to the last procedure is used in the manufacture of glass of the most prestigious brands of smartphones. The result is a material that is extremely resistant to all types of mechanical, chemical and biological influences, and at the same time is as transparent as possible.
4. “Sandwich” – double glass to protect solar panels
Otherwise, this technology is called “glass-glass”, and now it is used in all modules of the highest quality category. It differs from the previous variations in the use of two types of coverage at once.
The front side of the panel is protected by an anti-reflective sheet, and the back, instead of a standard metal or polymer base, is protected by tempered high-strength glass.
The main advantage of this design is the elimination of different coefficients of thermal expansion on the front and rear surfaces. Since both glass sheets have the same composition, thickness and physical properties, there is no distortion in the center of the panel.
This does not affect the efficiency, but the effective service life of the glass-glass modules immediately increases by 25-30%.
5. Polymer protection of solar panels
The last type of surface protection is plastic polymer coatings. They are used for flexible thin-film panels and have good transparency and strength at a multiple of their thickness than glass counterparts.
Thanks to the use of polymers, flexible solar cells of the latest generations, with a comparable nominal efficiency with the “classic”:
- 12-15 times thinner;
- 5-7 times lighter;
- 1.5-2 times more effective at high temperatures.