- Principle of solar photovoltaic power generation
Photovoltaic effect can occur in both liquid and solid materials, but only solid (especially semiconductor pn junction devices) have high photoelectric conversion efficiency under sunlight. Using the principle of photovoltaic effect, crystalline silicon solar cells can directly convert the light energy of the sun into electric energy. The energy converter of solar photovoltaic power generation is solar cell, also known as photovoltaic cell, which is the basis and core device of solar photovoltaic power generation system. The process of converting solar energy into electric energy mainly includes three steps:
(1) After solar cells absorb photons of certain energy, electron hole pairs are generated in semiconductors, which are called “photogenerated carriers”. Their polarity is opposite. Electrons are negatively charged and holes are positively charged.
(2) Photogenerated carriers with opposite polarity are separated by the electrostatic field generated by semiconductor pn junction.
(3) Photogenerated current carrying electrons and holes are collected by the positive and negative electrodes of solar cells respectively, and generate current in the external circuit to obtain electric energy.
Principle of solar photovoltaic power generation: when light irradiates the surface of solar cells, some photons are absorbed by silicon materials, and the energy of photons is transferred to silicon atoms to make electrons transition and become free electrons, which gather on both sides of PN junction to form potential difference. When the external circuit is connected, under the action of this voltage, current will flow through the external circuit to produce a certain output power. The essence of this process is the process of converting photon energy into electrical energy.
In the solar power generation system, the total efficiency n of the system is determined by the photoelectric conversion efficiency of solar cell modules, controller efficiency, battery efficiency, inverter efficiency and load efficiency. At present, the photoelectric conversion efficiency of solar cells is only about 17%. Therefore, improving the photoelectric conversion efficiency of solar cell modules and reducing the unit power cost of solar photovoltaic power generation system are the key and difficult points of the industrialization of solar photovoltaic power generation. Since the advent of solar cells, crystalline silicon has maintained a dominant position as the main material. At present, the research on the conversion efficiency of silicon solar cells mainly focuses on increasing the energy absorption surface (such as using double-sided cells to reduce reflection), using impurity absorption technology and passivation process to improve the conversion efficiency of silicon solar cells, ultra-thin cells and so on.
At present, solar photovoltaic power generation system is mainly used in the following three aspects.
(1) It provides power supply for non electric field cooperation, mainly provides power for the living and production of residents in non electric areas, and provides power supply for microwave relay stations and mobile phone base stations.
(2) Solar daily electronic products, such as all kinds of solar chargers, solar street lamps and solar lawn lamps.
(3) Grid connected power generation has been widely promoted and implemented in developed countries, and grid connected power generation in China is in its infancy.
- Advantages of solar power generation
Through the comparative analysis of several common new energy sources such as biomass energy, hydropower, wind energy and solar energy, it can be clearly seen that solar power generation has the following unique advantages.
(1) Photovoltaic power generation has economic advantages. The economy of solar energy utilization can be seen from two aspects: first, solar energy is inexhaustible, and there is no “tax” when receiving solar energy, which can be taken anywhere; Second, under the current level of technological development, the utilization of some solar energy has been economical. With the development of science and technology and the breakthrough of human development and utilization of solar energy technology, the economy of solar energy utilization will be more obvious. If the 20th century is the century of oil, the 21st century is the century of renewable energy (the century of solar energy).
From the perspective of the construction cost of solar photovoltaic power station, with the large-scale application and promotion of solar photovoltaic power generation, especially the maturity of upstream crystalline silicon industry and photovoltaic power generation technology, and the compound development and utilization of building roofs, exterior walls and other platforms, the construction cost of solar photovoltaic power generation per kilowatt can reach 7000 ~ 10000 yuan in 2010, which has the same economic advantages compared with other renewable energy sources.
(2) Solar energy is inexhaustible renewable energy. According to the calculation, the total amount of solar energy reaching the earth’s surface in a year is about 1.892 equivalent to standard coal × 1024 tons, 10000 times the proven reserves of the world’s main energy. The life span of the sun is at least 4 billion years. Compared with human history, the time that solar energy can continuously supply the earth can be said to be unlimited, which determines that the development and utilization of solar energy will be the most effective way for mankind to solve the shortage and depletion of conventional energy.
(3) No pollution to the environment. Solar energy, like clean energy such as wind energy and tidal energy, produces almost no pollution during its development and utilization. Coupled with the infinity of its reserves, it is an ideal alternative energy for mankind. Traditional fossil fuels (coal, oil and natural gas) emit a large number of toxic and harmful substances in the process of use, which will cause serious pollution to water, soil and atmosphere, form greenhouse effect and acid rain, and seriously endanger human living environment and health. Therefore, it is urgent to develop new and cleaner alternative energy, and solar energy, as an ideal clean energy, is receiving increasing attention all over the world.
From the current carbon emission rate (g / kW · h) of various power generation methods, the upstream links are not calculated: coal power generation is 275 g / kW · h, oil power generation is 204 g / kW · h, natural gas power generation is 181 g / kW · h, wind power generation is 20 g / kW · h, and solar photovoltaic power generation is close to zero emission. Moreover, in the process of power generation, there is no discharge of waste residue, waste, waste water and waste gas, no noise, no substances harmful to human body and no environmental pollution.
(4) The energy conversion link is the least. From the aspect of energy conversion, solar photovoltaic power generation directly converts solar radiant energy into electric energy. Among all renewable energy utilization, solar photovoltaic power generation has the least conversion link and the most direct utilization. Generally speaking, in the energy flow of the whole ecological environment, with the increase of conversion links and the extension of conversion chain, the energy loss will increase geometrically, and greatly increase the construction, operation cost and instability of the whole system. At present, the practical level of photoelectric conversion efficiency of crystalline silicon solar cells is 15% ~ 20%, and the highest level in the laboratory has reached 35%.
(5) The most economical and environmentally friendly. From the perspective of resource conditions, especially land occupation, bioenergy and wind energy are more demanding, while solar energy utilization is very flexible. If the land area occupied by solar photovoltaic power generation is 1, the wind power is 810 times that of solar energy and the bioenergy is 100 times. In terms of hydropower, the construction of a large dam often needs to submerge tens of square kilometers to hundreds of square kilometers of land. In contrast, solar power generation does not need to occupy more land. Roofs and walls can be used for solar photovoltaic power generation. It can also take advantage of China’s vast desert. By building solar photovoltaic power generation bases on the desert, it can directly reduce the solar radiation directly to the ground surface in the desert, effectively reduce the surface temperature and reduce the evaporation, so as to make the survival and growth of plants possible to a considerable extent, Stabilize and reduce sand dunes, and obtain clean and renewable energy from nature.
(6) It can be used free of charge without transportation. Human beings can convert solar energy into thermal energy or electric energy through special technology and equipment, and use it locally without transportation for the benefit of mankind. And it is free for human beings to use the inexhaustible energy of solar energy. Although different latitudes and climatic conditions cause uneven solar radiation, compared with other energy sources, solar energy is universal in most areas of the earth and can be used locally. This provides a bright prospect for countries and regions lacking conventional energy to solve the energy problem.