Applications of solar glass
Solar glass refers to special glass products used in solar energy products in the process of utilizing and converting solar energy.
Solar glass used in the field of solar cell power generation is called photovoltaic glass;
Glass used in solar thermal power generation and thermal energy utilization (such as agricultural sunrooms, solar water heaters, solar dryers, solar stoves, seawater desalination, etc.) is called solar thermal glass.
1. Photovoltaic glass
Broadly speaking, all glass products used in photovoltaic products are photovoltaic glass, including cover glass and backsheet glass applied to crystalline silicon cells, TCO substrate glass and backsheet glass applied to thin-film cells, and BIPV glass used in photovoltaic building integration.
At present, crystalline silicon cells mainly use solar ultra-white calendered glass, and thin-film cells mainly use ultra-white float glass.
(1) Crystalline silicon cell glass
Crystalline silicon cell glass is mainly used in the cover and backplane of monocrystalline silicon and polysilicon cell modules.
At present, 98% of crystalline silicon cells use ultra-white calendered coating or tempered glass as the cover, and double-glass modules with glass as the back panel are being promoted.
Ultra-white calendered tempered or coated tempered glass is used as a battery cover, covering the front of the solar cell module and constituting the outermost layer of the module.
The specific composition is as follows: tempered or coated tempered glass cover + encapsulated EVA (or POE, PVB) adhesive film + crystalline silicon cell + encapsulated EVA (or POEPVB) adhesive film + TPT (PET) plastic backing plate and aluminum alloy frame.
With the advancement of technology, in order to overcome the aging of TPT (PET) plastic backplane modules and improve the power generation performance of modules, some module manufacturers have changed the TPT (PET) plastic backplate of crystalline silicon solar cell modules to ultra-white tempered glass to make double-glass modules and double-sided modules (the backplate of double-glass modules is tempered glass processed from ordinary float glass; The back panel of the double-sided assembly is tempered glass processed from ultra-white glass, which has the function of generating electricity on both sides).
The composition of the double-glass module is: tempered or coated tempered glass cover + encapsulated EVA (or POE, PVB) adhesive film + crystalline silicon cell + encapsulated EVA (or POE, PVB) adhesive film + glass back panel (aluminum alloy frame is used according to the situation).
After 4~5 years of installation in the photovoltaic power station, the power generation power attenuation phenomenon with aluminum frame will occur, that is, the potential induced degradation (PD) effect will occur. Many experts in the industry believe that this is due to the bias voltage formed between the packaging material of a single photovoltaic module and the materials on its upper and lower surfaces, the crystalline silicon cell and the grounding metal frame of the photovoltaic array module. Although the voltage of a single battery module is relatively low, after multiple battery modules are connected in series, a higher voltage is formed, and the closer to the negative electrode, the more obvious the negative bias phenomenon of the module at the output end, under the action of high negative bias voltage (-1000V), ion migration occurs, forming a leakage current flow path.
The leakage current anode Na* is formed by EVA → the glass surface → a support for the cell → frame, and finally flows to the earth, and the negative charge accumulates on the surface of the cell, attracting photoelectric carriers (holes) to flow to the surface of N-type silicon and gather instead of flowing to the positive electrode (P electrode) as in the normal state, resulting in the phenomenon of power generation of the battery module, which is the PID effect caused by the phenomenon of surface polarization.
PID phenomenon is most likely to occur under humid and high temperature conditions and is related to the degree of humidity. The PID effect has a huge impact on the output power of solar cell modules and is the "horror killer" of photovoltaic power generation capacity. From the perspective of the composition of crystalline silicon photovoltaic cells, crystalline silicon cells, EVA and glass may cause PID phenomenon. In order to avoid this phenomenon from the glass side.
(2) Thin-film battery glass
There are many types of coating materials used in thin-film cell glass, mainly copper indium gallium selenium (CIGS), cadmium telluride (CdTe), gallium arsenide (GaAs), perovskite, non/microcrystalline silicon (a-Si), dye sensitization materials, etc.
At present, the substrate material used in thin-film batteries is mostly ultra-white tempered glass produced using the float forming process.
There are two main production methods for thin-film battery glass: online coating and offline coating.
At present, the coated glass produced by online coating technology includes heat-reflective glass, low-emissivity glass and transparent condensing oxide (TCO) coated glass.
Offline coated glass refers to the production method of using the glass produced by the float glass production line as the original sheet (also known as the base sheet) and using coating equipment in other sites. Offline coating technologies include magnetron sputtering, sol-gel, pulsed laser deposition (PLD), vacuum evaporation, chemical vapor deposition (CVD), etc. These methods can be used to produce various coated glasses such as heat-reflective coated glass, LOW-E coated glass, and TCO coated glass. Heat-reflective coated glass and LOW-E coated glass are mainly used in buildings, etc., and TCO coated glass is mainly used in electronic instruments and solar cell front electrodes.
TCO coated glass is a transparent conductive oxide film uniformly coated on the surface of flat glass by physical or chemical methods in an online or offline manner, and the conductive oxide film mainly includes In, Sn, Zn and Cd oxides and their composite multiple oxide films. TCO conductive film glass can be divided into three types: tin oxide tin oxide tin clear conductive film glass (ITO), tin fluorine fluorine transparent conductive film glass (FTO) and aluminum zinc oxide aluminum transparent conductive film glass (AZO).
Transparent conductive oxides (TCOs) play a crucial role in thin-film solar cell applications, as the intermediate semiconductor layer has little lateral conductivity, so TCO glass must be used to efficiently collect the current from the cell, while TCO films have high transmission and anti-reflection capabilities, allowing most of the light to enter the absorbing layer. All mainstream thin-film solar cells, such as amorphous silicon/microcrystalline silicon stacks, cadmium telluride, use TCO materials (mainly aluminum-doped zinc oxide ZnO:AI, or AZO) as transparent conductive layers. Most offline coatings use magnetron sputtering to deposit this material.
2. Photothermal glass
(1) CSP glass
The principle of solar thermal power generation (CSP) is: the ultra-white float glass substrate, a plated mirror, and a curved reflecting condenser (i.e., heliostat) that is bent and tempered to reflect the sunlight once or twice, and the sunlight is converged and reflected to the molten salt or oily liquid flowing in the heated glass tube on the vacuum glass tube concentrator. Raise its temperature to more than 300'C, a heat exchange tank that conducts heat energy from molten salt or oil to the water storage, a heat exchange tank that generates high temperature and high pressure water vapor through heat exchange, and drives the turbine generator to generate electricity, and the principle of concentrated photovoltaic (CPV) power generation is basically similar to that of solar thermal power generation, using an optical system (heliostat tracking), converging solar energy onto a high-magnification concentrating solar cell chip [the representative cell is gallium arsenide (GaAs)], Then use the photovoltaic effect to convert light energy into electricity. In the industry, it is regarded as the third generation of photovoltaic technology that can replace part of the crystalline silicon market (the first and second generations are crystalline silicon technology and thin film technology respectively).
The concentrating glass used in the above-mentioned CSP and concentrating photovoltaic power generation is called CSP glass.
(2) Photothermal utilization glass
Photothermal utilization glass is the use of solar energy to heat the substances in the glass container, so that it can be converted into heat energy, which is used by people, such as flat panel solar collectors, solar smart agriculture, solar drying rooms, solar evaporators, seawater desalination devices, etc
Solar collectors are devices that absorb solar radiation and transfer the generated heat energy to a heat transfer medium. The foreign solar collector market is dominated by flat panel collectors. Although the initial investment of flat panel collectors is high, they have the characteristics of simple structure, reliable system operation, low maintenance cost, strong pressure bearing capacity, large heat absorption area, no pollution of water quality and long system life.
Under the same area, the lighting area of the flat panel collector is larger than the lighting area of the traditional vacuum glass tube collector, so the water output of the flat panel collector solar water heating system is higher than that of the vacuum glass tube collector system of the same area, and is conducive to the realization of the combination of solar energy system and buildings, saving floor space, not only can meet the usual bathing, but also can provide heating and domestic hot water for winter, because there is still a certain gap between the current domestic flat panel solar collector and the foreign advanced level, so it is still dominated by vacuum glass tube water heaters. Flat panel solar collectors are in their infancy.
In the future, after the improvement of selective coating, optimized design and production process of flat panel solar collectors, flat panel solar collectors will be used in a large area in China, and the main component of solar panel collectors that can effectively transmit sunlight and protect solar panel collectors is ultra-white calendered glass.
Solar smart agriculture is a very large (about 70,000m2 each) sunroom built by light steel structure and solar calendered glass, in which various crops can be planted, and computer technology is used to control them automatically: control solar energy entry, heat energy absorption, oxygen synthesis, fertilization, watering, pest control, etc. In the future, with the maturity of solar smart farming technology and the reduction of costs, it will replace the current plastic film greenhouses and provide us with safe, hygienic and pollution-free agricultural products.
Solar dryer is a drying device that uses the heat energy of solar radiation to evaporate and remove water from wet materials (such as grain, fruits, leafy crops, cotton, Chinese herbs, wood, etc.). The principle of solar dryer drying is that the heat-absorbing body, cover, insulation layer and shell form a box or shed type with a transparent roof and a blackened inner layer in a confined space to form a solar air collector, the heat-absorber first absorbs solar radiation, converts the radiation energy into its own heat energy, and its own temperature rises. A typical solar air collector is a flat air collector, and the ceiling used is ultra-white calendered glass.
