Solar cell power generation principle

Date:Apr 19, 2019

There are two ways of solar power generation, one is light-thermal-electric conversion, and the other is direct-to-electric conversion.

Light-thermal-electrical conversion

The light-thermal-electrical conversion method generates electricity by utilizing thermal energy generated by solar radiation. Generally, the solar collector collects the absorbed heat energy into a working medium vapor, and then drives the steam turbine to generate electricity. The former process is the light-to-heat conversion process; the latter process is the thermo-electric conversion process, which is the same as ordinary thermal power generation. The shortcoming of solar thermal power generation is that it is very inefficient and costly. It is estimated that its investment is at least 5 to 10 times more expensive than ordinary thermal power plants. A 1000MW solar thermal power station requires an investment of 2 to 2.5 billion US dollars, and an average investment of 1kW is 2000 to 2500 US dollars. Therefore, it can only be applied to special occasions on a small scale, and large-scale utilization is economically uneconomical and cannot compete with ordinary thermal power plants or nuclear power plants.

Light-to-electric direct conversion

Solar cell power generation is based on the optoelectronic properties of a particular material. Black bodies (such as the sun) radiate electromagnetic waves of different wavelengths (corresponding to different frequencies), such as infrared rays, ultraviolet rays, visible light, and the like. When these rays are irradiated on different conductors or semiconductors, the photons react with free electrons in the conductor or semiconductor to generate a current. The shorter the wavelength of the ray, the higher the frequency, the higher the energy, for example, the energy of ultraviolet light is much higher than that of infrared ray. However, not all wavelengths of energy can be converted into electrical energy. It is worth noting that the photoelectric effect is independent of the intensity of the radiation. Current can only be generated when the frequency reaches or exceeds the threshold at which the photoelectric effect can be produced. The maximum wavelength of light capable of producing a photoelectric effect of a semiconductor is related to the forbidden band width of the semiconductor. For example, the forbidden band width of crystalline silicon is about 1.155 eV at room temperature, so that light having a wavelength of less than 1100 nm is required to cause photoelectric effect of crystalline silicon. . Solar cell power generation is a renewable and environmentally friendly way of generating electricity. It does not generate greenhouse gases such as carbon dioxide during power generation and does not pollute the environment. According to the production materials, it is classified into a silicon-based semiconductor battery, a CdTe thin film battery, a CIGS thin film battery, a dye-sensitized thin film battery, an organic material battery, and the like. Among them, silicon batteries are further classified into single crystal batteries, polycrystalline batteries, and amorphous silicon thin film batteries. The most important parameter for solar cells is conversion efficiency. In the silicon-based solar cells developed by the laboratory, the efficiency of single crystal silicon cells is 25.0%, the efficiency of polycrystalline silicon cells is 20.4%, and the efficiency of CIGS thin film cells is 19.6%. CdTe The efficiency of the thin film battery is 16.7%, and the efficiency of the amorphous silicon (amorphous silicon) thin film battery is 10.1%.

A solar cell is a photovoltaic element that can convert energy, and its basic structure is formed by bonding a P-type and an N-type semiconductor. The most basic material of a semiconductor is "silicon", which is non-conductive, but if a different impurity is incorporated into the semiconductor, a P-type and an N-type semiconductor can be formed, and a P-type semiconductor has a hole (P type). The semiconductor has one negatively charged electron, which can be regarded as a positive charge. It has a potential difference of free electrons with the N-type semiconductor to generate current, so when the sunlight is irradiated, the light energy will be in the silicon atom. The electrons are excited to generate convection of electrons and holes, which are affected by the built-in potential, which are attracted by the N-type and P-type semiconductors, respectively, and are concentrated at both ends. At this time, if the external electrodes are connected to form a loop, this is the principle of solar cell power generation.

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