Photovoltaics - The conversion efficiency of a photovoltaic system.

Photovoltaics - Development of Solar Photovoltaic Technology

Development of Solar Photovoltaic Technology

With the advancement of technology and the expansion of the industrial scale, the cost of energy production from photovoltaics will be further reduced and will become one of the important energy sources for sustainable development in the future.

Basic Elements of Photovoltaic Technology

The key element of photovoltaic power generation technology is the solar photovoltaic cell. The growth of solar photovoltaic cells can be roughly divided into three generations. The first generation are silicon-based solar cells; the second generation are thin-film solar cells;

At present, the mainstream is the first generation of silicon solar cells and the market share of thin film cells is gradually expanding. In addition to high power concentration cells, most third generation cells are still in the laboratory research and development stage.

Photovoltaics - Development of Solar Photovoltaic Technology

Photovoltaics - Development of Solar Photovoltaic Technology

Silicon solar cells

Among silicon solar cells, monocrystalline silicon technology is the most mature. The efficiency and cost of such cells are mainly affected by their manufacturing processes. The manufacturing process is mainly divided into various stages, such as ingot casting, shredding, diffusion, texture, screen printing and sintering. The photoelectric conversion efficiency of the solar cells produced by this common process is generally 16% -18%.

The conversion efficiency of monocrystalline silicon solar cells is the highest, but the cost is also higher. Polycrystalline silicon solar cells can reduce costs very well. The advantage is that large square silicon ingots suitable for large scale production can be made directly. The equipment is relatively simple, so the manufacturing process is simple, energy saving and silicon material The material requirements are also relatively low.

In addition to reducing the cost of materials and the cost of solar cells, it is achieved mainly through two aspects: one is the reduction of consumables, such as the reduction of the thickness of silicon plates; the other is the improvement of the conversion efficiency. Ways to improve performance include the following aspects: The first is to increase the absorption of light, such as the texture of the surface, the preparation of anti-reflective layers and the reduction of the width of the front electrode. The second is to reduce the recombination of photogenic carriers and improve the use of photons, such as emission passivation technology. The third is to reduce the resistance and increase the absorption of current through the electrode, such as doping separation and rear electric field technology.

The current record for the photoelectric conversion efficiency of monocrystalline silicon solar cells is 24,7% created by the PERL structure solar cells of the University of New South Wales. Its technical characteristics include: low concentration of phosphorus doping on the silicon surface to reduce surface recombination and avoid the presence of surface "dead layers"; of the electrode and form a good ohmic contact; the front surface electrode narrows with the photolithography process to increase the light absorption area; the front surface electrode adopts a combination of more matching metals such as titanium, palladium and silver to reduce resistance between the electrode and silicon; the front and back of the battery are made of SiO2 and point contact methods to reduce cell surface recombination. However, the technology has not yet been industrialized.

In addition to PERL technology, other technologies can also be used to improve conversion performance. Like BP Solar's suede surface groove and rear electrode (EWT) through technology. The first mainly reduces the width of the front electrode through the laser grooving process and increases the absorption area of ​​sunlight and large scale output can achieve an efficiency of 18,3%, the rear side, thus increasing the absorption area of ​​the front side , can achieve a yield of 21,3%.

Solar cells thin film

The crystalline silicon solar cells are highly efficient and continue to dominate large-scale applications and industrial production. However, due to the relatively high price of silicon materials, it is very difficult to significantly reduce its cost. In order to find alternatives to crystalline silicon cells, cheap thin-film solar cells have emerged. The main thin film batteries include silicon based thin film batteries, cadmium tellurium thin film (CdTe) batteries and copper-indium-gallium-selenium thin film batteries (CIGS).

The thickness of thin film cells based on silicon is only 2 microns Compared to crystalline silicon cells with a thickness of about 180 microns, the amount of silicon material is only about 1,5% of that of crystalline silicon cells and the cost is low. Depending on the number of PN connections involved, silicon-based thin film cells are divided into single-linker cells, double-linker cells, and multi-linker cells. Different PN connections can absorb sunlight of different wavelengths. At present, the highest yield of single-linker cells can reach 7%, and dual-linker cells can reach 10%.

Due to the good light absorption of the material, the conversion efficiency of cadmium tellurium thin film cells is higher than that of silicon based thin film cells and the current efficiency can reach 12%. However, cadmium has carcinogenic effects and natural tellurium stores are limited, which limits the long-term development of this battery.

The thin film batteries Indium copper gallium ions are considered as the future development direction of high performance thin film batteries, which can improve the rate of absorption of sunlight by adapting the manufacturing process, thus improving conversion efficiency. At present, the laboratory conversion efficiency can reach 20,1%, and the product efficiency can reach 13-14%, which is the highest among all thin film batteries.

Photovoltaics - Development of Solar Photovoltaic Technology

Photovoltaics - Development of Solar Photovoltaic Technology

Third generation battery :

The third generation cells can theoretically achieve higher conversion efficiency. At this stage, in addition to the condenser cells, most of them are still in the laboratory research stage.

The cells generally use III-V semiconductor materials, mainly because III-V semiconductors have much higher resistance to high temperatures than silicon, still have high photoelectric conversion efficiency under high illumination and the multi-link structure makes the absorption spectrum and its spectrum sunlight is close to the same and the theoretical conversion efficiency can reach 68%. Currently, three PN junctions are formed from three different semiconductor materials: germanium, gallium arsenide and gallium indium phosphorus. If large-scale production takes place, the yield can reach more than 40%.

The solar cells are packaged in solar units and the application of different solar cells depends on their own characteristics and the development of market demand. In the early days, solar energy was used mainly in communication base stations and artificial satellites, and later gradually entered the political sector, such as solar roofs. In these scenarios, the installation area is small and the energy density requirement is high, so the silicon units occupy the main market share.

With the development of large-scale solar power plants in the desert and photovoltaic buildings, total costs have gradually replaced energy density as an important factor to consider and the application of thin-film batteries is on the rise. In addition, the application of different technologies is influenced by other factors such as the user environment and climatic conditions.

Application of Solar Photovoltaic Technology

A complete solar photovoltaic system is required to convert solar radiation into electricity that can be used by humans. Solar photovoltaic cells are an important part of the solar photovoltaic system and the basis of the entire system. In addition, the photovoltaic system also includes inverters, batteries, monitors, power distribution systems, etc.

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Photovoltaics - Development of Solar Photovoltaic Technology,

Photovoltaics - Development of Solar Photovoltaic Technology,

Photovoltaics - Development of Solar Photovoltaic Technology, New photovoltaics, third generation batteries, solar cells

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