In the effective utilization of solar energy, solar power generation system is the fastest developing and most dynamic research field in recent years, and it is one of the most high-profile projects. Solar energy is a kind of radiant energy, and the use of solar energy to generate electricity is to convert sunlight into electricity. At present, there are two ways of solar power generation: one is light-heat-electricity conversion, and the other is light-electricity direct conversion. To this end, people have researched and developed solar cells, designed and built independent, grid-connected light-to-electricity direct conversion solar power generation systems. Some experts believe that solar power generation will eventually account for 20% of the power supply.
(1) Light-heat-electricity conversion method.
It is to generate electricity by using the thermal energy generated by solar radiation. Generally, the solar collector converts the absorbed solar energy into the thermal energy of working medium steam, and then drives the turbine generator to generate electricity. The former process is a light-heat conversion process, and the latter process is a heat-electricity conversion process. The power generation process is similar to that of ordinary thermal power generation. The disadvantage of solar thermal power generation is that the efficiency is very low and the cost is very high. It is estimated that its investment is at least 5-10 times higher than that of ordinary thermal power plants. A 1000 MW solar thermal power station requires an investment of 2 billion to 2.5 billion US dollars, with an average investment of 1kW. $20002500. Therefore, it can only be applied to special occasions on a small scale at present, and it is very uneconomical to use it on a large scale. Therefore, solar thermal power generation cannot compete with ordinary thermal or nuclear power plants.
(2) Light-electricity direct conversion method.
It uses the photoelectric effect to directly convert solar radiation energy into electrical energy. The basic device for photoelectric conversion is solar cells. A solar cell is a device that directly converts solar energy into electrical energy based on the photovoltaic effect. It is a semiconductor photodiode. When the sun shines on the photodiode, the photodiode will convert the solar energy into electrical energy. generate current. Many solar cells are connected in series or in parallel to form a solar cell array with relatively large output power. Solar cells are a promising new type of power source with three advantages: permanence, cleanliness and flexibility. Compared with thermal power generation and nuclear power generation, solar photovoltaic power generation will not cause environmental pollution; solar cells can be large, medium and small, ranging from a medium-sized power station of 1 million kilowatts to a small independent solar power generation system that only supplies electricity for one household. These features are unmatched by other power supplies.
Like transistors, solar cells are also made of semiconductors. Its main material is silicon, and there are also some other alloy materials. The high-purity silicon used in the manufacture of solar cells has to undergo a special purification process. The working principle of solar cells is the photovoltaic effect of the semiconductor PN junction. The so-called photovoltaic effect is that when an object is illuminated, the state of charge distribution in the object changes to generate electromotive force and current. When sunlight or other light irradiates the PN junction of the semiconductor, photogenerated electron-hole pairs are generated. Under the action of the built-in electric field, the photogenerated electrons and holes are separated, and the opposite charges accumulate at both ends of the solar cell, that is, the “photogenerated voltage” is generated. “, which is the “photovoltaic effect”. If the electrodes are drawn on both sides of the built-in electric field and connected to the load, the load will have a “photo-generated current” flowing through, thereby obtaining electrical power output.
Solar cells can convert light energy into electrical energy as long as they are irradiated by sunlight or lights, and solar cells can emit electricity equivalent to 10% to 20% of the received light energy. Generally speaking, the stronger the light, the more electricity is emitted. In order to minimize light reflection and convert light energy into electrical energy, solar panels are generally covered with a film that can prevent light reflection, so that the surface of the solar panels is purple.