What is Photovoltaic Glass (or solar pv glass)?
- Source:fuyangdian
- Time:2019-03-26
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1.1.1 The role of photovoltaic glass
The encapsulated glass used in solar photovoltaic modules (or custom solar panels), the current mainstream products are low-iron tempered embossed glass, the solar cell module has high requirements for the transmittance of tempered glass, which must be greater than 91.6%, and has a higher reflection for infrared light greater than 1200 nm. rate. In addition, the thickness is required to be 3.2 mm. It enhances the impact resistance of the solar module, and good light transmission can increase the efficiency of the solar module and function as a sealing solar module.
The front surface material of the PV module must have a high degree of transparency for wavelengths that can be used by solar cells in the PV module. For silicon solar cells, the top surface material must have a high degree of transparency for wavelengths in the range of 350 nm to 1200 nm. In addition, the reflection of the front surface should be low. Although the theoretical application of anti-reflective coatings on the top surface can reduce reflections, in practice these anti-reflection coatings are not sufficient to withstand the conditions of use of most PV modules. Another technique that can reduce reflection is to texture the surface or roughen the surface. However, in this case, dust and dirt are more likely to adhere to the top surface and are hard to be expelled by wind and rain. These solar modules are therefore not "self-cleaning" and the superiority of reducing reflection is quickly exceeded by the loss of dust on the top surface.
In addition to the reflective and transparent properties, the top surface material should be water impermeable, should be impact resistant, should be stable under long-term UV exposure, and have a very low thermal resistance coefficient. The ingress of water or water vapor into the PV module will corrode the metal electrodes and interconnect strips and will thus significantly reduce the life of the PV modules. In most assemblies, the top surface is used to provide mechanical strength and stiffness, so the top or back surface used to support the solar cells and wires must be mechanically steel.
There are several options for top surface materials, including acrylic polymers and glass. Tempered low-iron glass is the most common application because of its low cost, robustness, stability, high transparency, waterproof, and good self-cleaning properties.
1.1.2 Tempered glass
Tempered glass, thickness 3.2mm±0.3mm; tempering performance in line with national standard: GB9963-88, or the impact resistance of the encapsulated solar module meets the performance index specified in the national standard GB9535-88 ground silicon solar cell module environmental test method; The light transmittance should be higher than 90%; the glass should be clean and free of steam, and should not touch the two surfaces of the glass with bare hands.
Low-iron tempered suede glass (also known as white glass) with a thickness of 3.2 mm and a light transmittance of 91% or more in the wavelength range of the solar cell spectral response (320-1100 nm), and high reflectance for infrared light greater than 1200 nm. The glass is also resistant to radiation from the sun's ultraviolet light, and the light transmittance does not decrease.
Tempered glass used as a encapsulation material for photovoltaic modules has high requirements for the following performances
a). Mechanical impact strength
b). Surface light transmission
c). Curvature
d). Appearance
Tempered glass is a secondary processing product of flat glass. The processing of tempered glass can be divided into physical tempering method and chemical tempering method. Physical tempered glass, also known as quenched tempered glass (heats the metal workpiece to a suitable temperature for a period of time, then immerses it into the quenching medium for rapid cooling). This kind of glass is under internal tension and externally stressed. Once local damage occurs, stress is released and the glass is broken into numerous small pieces. These small pieces have no sharp edges and are not easy to injure people. Chemically tempered glass is used to increase the strength of the glass by changing the chemical composition of the glass surface. It is generally tempered by ion exchange. The effect is similar to physical tempered glass.
The strength of tempered glass is several times higher than that of ordinary glass, the bending strength is 3-5 times that of ordinary glass, and the impact strength is 5-10 times that of ordinary glass, which improves the strength and improves the safety. The tempered glass has a large bearing capacity and improves the fragile nature. Even if the tempered glass is broken, it shows small fragments without sharp angles, which greatly reduces the damage to the human body. The chilled heat resistance of tempered glass is 2-3 times higher than that of ordinary glass, which has obvious effect on preventing thermal cracking. Tempered glass has good thermal stability and can withstand a temperature difference of three times that of ordinary glass, and can withstand a temperature difference of 200 °C. However, the tempered glass can no longer be cut or processed, and the glass can be processed to a desired shape before being tempered, and then tempered. Although the strength of tempered glass is stronger than that of ordinary glass, tempered glass has the possibility of self-explosion (self-breaking) when the temperature difference changes greatly, while ordinary glass does not have the possibility of self-explosion (automation of tempered glass without direct mechanical external force) Explosion is called self-explosion of tempered glass.
1.1.3 ultra-white glass
Ultra-clear glass is a type of solar glass, and basically ultra-white glass is embossed for use on solar energy. The purpose of embossing is to increase the light transmittance. The reason is very simple. The sun shines a lot of light on a plane, so there is less to the silicon. But if you make it into a well-like shape, the reflection of light will be greatly reduced, thereby increasing the light transmittance. Therefore, the shape of the embossing will be related to the level of light transmittance, which is the reason for the commonly used ultra-white embossed glass. However, the disadvantages brought by this are as follows: 1. After embossing the glass, there are many defects on the surface of the glass. Under the long-term weathering effect, the effect of the anti-reflection is quickly weakened. 2. Because there is a concave, the dust is easy. Entry, need to be cleaned regularly; 3, the increased light transmittance is limited, because it can not be deep depressed, the role is very limited.
1.1.4 Anti-clean self-cleaning photovoltaic glass
To improve the visible light transmittance of photovoltaic glass, there are currently two directions. One is to apply an anti-reflection coating on the surface of the photovoltaic glass to improve the light transmittance of the photovoltaic glass, and the second is to use a self-cleaning anti-reflection film. Photovoltaic glass achieves self-cleaning effect while increasing penetration.
At present, most PV glass manufacturers are working hard to improve the light transmittance of photovoltaic glass. However, since the visible light transmittance of the existing ultra-white glass is already above 90%, the space for improvement is not large, and the interference principle of light is utilized. Adding a layer of anti-reflection film can only increase the effect of 3% at most, and can not fully meet the needs of the industry. In addition, since photovoltaic glass is generally installed in the wilderness, the dust and sand are large, and the surface of the glass is extremely dirty after a long period of time. After using for a period of time, the visible light transmittance of some photovoltaic glass is even only 60% of the original. It affects the power generation efficiency. If the problem of the surface of the photovoltaic glass is not solved, it will greatly restrict the development of the solar photovoltaic industry. This gave birth to the second research direction of photovoltaic glass, how to enhance the self-cleaning and anti-fouling effect of photovoltaic glass, and make it a self-cleaning glass.
Porous silica film is an ideal photovoltaic glass coating material because of its excellent light transmittance, anti-reflection performance and high thermal resistance. At the same time, it has certain water repellency and self-cleaning function, which can effectively reduce the efficiency of the overall solar photovoltaic cell performance with the use time, and avoid the performance degradation caused by surface contamination.
The principle of roll coating method for producing AR coated photovoltaic glass is to prepare nano silica sol and porous silica film by sol-gel method. First, a silica sol is prepared by using tetraethyl orthosilicate (TEOS) as a precursor and ammonia as a catalyst. The AR coating solution is obtained by diluting and adding a stabilizer, a viscosity modifier, a binder, etc., and then passing through a roll coating film. The machine applies the AR coating solution evenly to the surface of the photovoltaic glass, and after drying through the surface, heating and solidification, it enters the tempering furnace to obtain AR-coated photovoltaic glass.
1.1.5 Storage conditions of photovoltaic glass
Photovoltaic glass should be protected from light, moisture, and stacked, covered with dust cloth. The best storage conditions for glass: in a constant temperature, dry warehouse, the temperature is 25 ° C, the relative humidity is less than 45%, the glass should be clean and free of steam, not bare contact with the contact surface of the glass and EVA film, otherwise it will affect EVA Adhesion between the film and the glass layer.
1.1.6 Inspection of photovoltaic glass
1.1.7 Summary
The factors determining the performance of crystalline silicon solar photovoltaic cells are various factors related to the conversion efficiency of light energy. The most important determinant is the crystalline silicon technology in photovoltaic modules, followed by the protection of photovoltaic glass in photovoltaic modules. Photovoltaic glass is one of the best materials to protect crystalline silicon and has high self-transmission rate for a long time. Therefore, the optical properties of photovoltaic glass are an important factor outside the crystalline silicon technology. However, maintaining and improving the optical properties of photovoltaic glass is much easier and cheaper than developing crystalline silicon with higher conversion rates, so the development and production of photovoltaic glass with higher transmittance, regardless of solar module manufacturers or in the terminal market. The needs are very urgent. Porous silica film is an ideal photovoltaic glass coating material because of its excellent light transmittance, anti-reflection performance and high thermal resistance. At the same time, it has certain water repellency and self-cleaning function, which can effectively reduce the efficiency of the overall solar photovoltaic cell performance with the use time, and avoid the performance degradation caused by surface contamination.
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