Solar photovoltaic applications
In principle, solar energy can be transformed into any form of energy. The conversion of solar energy into thermal energy (see Figure 1) is the most common one, such as solar water heaters used in homes. The use of light and heat is mainly for heating and cooling. Generally speaking, the black absorption surface has good solar radiation absorption performance and can convert solar energy into heat energy, but the radiant heat loss is large. The selective absorption surface has high solar absorption ratio and low emission ratio, and has good solar radiation absorption performance. The heat loss is small, and it is an ideal solar energy absorption surface.
There are many technical problems involved in the utilization of solar energy. The energy flow density of solar radiation is low. In order to obtain sufficient energy when using solar energy, certain technologies and devices must be adopted to collect, store and utilize solar energy. Therefore, according to the characteristics of solar energy, there are four common technologies, namely, solar energy harvesting, solar energy conversion, solar energy storage, and solar energy transmission.
This site mainly talks about solar energy conversion, called photovoltaic effect, which is commonly referred to as solar cell, or solar cell for short (see Figure 2~Figure 4).
Figure 1.2 Solar thermal utilization
Figure 1.3 Solar photovoltaic power generation for the lunar exploration project
Figure 1.4 Solar cell car
Figure 1.5 Solar cell aircraft
The development of solar cells
In the 1950s, the first practical silicon solar cell was born at Bell Labs in the United States, and it was soon used in the power generation system of artificial satellites. So far, thousands of aircraft in space are equipped with solar cell power generation systems. Due to the high cost of power generation at that time, the application of solar cells on the ground has been stagnant and not widely used. They are mainly used as supplementary energy in fields such as communications and agricultural irrigation. It was not until the “oil crisis” began to appear in the world in the 1970s that the large-scale application of solar cell power generation systems on the ground was not on the agenda of many countries. In the 1980s, rapid population growth and industrialization caused three global problems: energy shortage, ecological destruction and environmental pollution. Because more than 80% of the energy used by humans is provided by fossil fuels, of which coal accounts for 28% and oil exceeds 40%. Humans burn 4 billion tons of coal and 2.5 billion tons of oil every year, and this is increasing at an annual rate of about 3%. The burning of fossil fuels emits greenhouse gases and toxic substances, which drastically deteriorate the ecological environment of the earth. In addition, the burning of fossil fuels releases harmful gases such as carbon dioxide, dioxide and ammonia oxides into the atmosphere each year, which are the main factors causing the greenhouse effect and acid rain. Pollution and the destruction of ecological balance are becoming more and more serious, threatening the normal development of mankind. For mankind to survive and modern civilization to continue to develop, it is necessary to find a sustainable and clean energy path.
Solar photovoltaic power generation has the advantages of pollution-free, universality of resources and non-exhaustion, and it meets the requirements of environmental protection and sustainable development. Therefore, all human beings once again focus their attention on solar power generation, and governments of all countries attach great importance to this. For example, the U.S. government formulated a series of building regulations in 1970, and in 1978 some regulations were written into the National Energy Law as laws. It is mandatory that buildings must be integrated with energy saving, and preferential policies such as tax reduction and exemption are implemented for buyers who purchase solar energy systems; 1997 In 2010, it plans to install 3~5kW photovoltaic roofs for 1 million American homes by 2010, and announces the national photovoltaic plan and long-term plans for 2020 to 2030. The plan is ambitious and challenging. The United States compares it with the Apollo moon landing plan, and is determined to make photovoltaic technology the same as other energy technologies, and install solar panels on every house.
The core of Germany’s policy is to provide preferential loans, subsidies, and a higher standard fixed subsidy to renewable energy producers. The “Electricity Transmission Law” enacted in 1990 stipulates that medium to large power users shall pay 90% of the residential electricity price for electricity produced by wind, solar, hydropower and biomass. For enterprises investing in renewable energy, the state also provides preferential loans equivalent to 75% of the equipment investment cost at a preferential interest rate lower than the market interest rate. Germany began to implement the “100,000 rooftops” plan in 1999, and plans to fund 100,000 households to equip solar cell equipment in six years. The main method of the plan is to provide preferential loans directly to consumers by commercial banks.
The Dutch government promotes the development and utilization of renewable energy by providing a series of fiscal, taxation and financial incentives, including accelerated depreciation of enterprises, tax deductions, preferential loans for renewable energy projects below the market interest rate, and independent use of renewable energy Energy and other environmentally-friendly households grant low-interest loans, etc.; new energy power from power construction sites that have purchased new energy power in accordance with national requirements shall be sold to relevant users in a proportional distribution method to recover the cost of fuel and equipment invested accordingly; Impose energy taxes on enterprises that produce pollution but cannot be recycled; establish a green pricing plan so that consumers can get incentive subsidies when purchasing renewable energy power; develop national power standards based on renewable energy, and provide The supported enterprises make marketization efforts.
Unlike the above-mentioned countries, the United Kingdom promotes the development of renewable energy through a policy approach called “non-fossil fuel obligation”. Within the framework of the “non-fossil fuel obligation” policy, electricity suppliers must purchase a certain amount of non-fossil energy electricity.
The focus of Japan’s development is solar cells and wind energy. The more prominent project is the “ten thousand roofs” plan implemented before 1997. The plan is to raise funds by imposing an additional tax on electricity consumption. All households equipped with solar energy equipment will be given a subsidy equivalent to one-third of the equipment cost. At the same time, the power department promises to buy back the solar energy equipment produced in excess of household consumption at market prices. Demand for electricity. Japan’s New Energy Law passed in 1997. The main policy measure is that the government mobilizes major energy suppliers to actively purchase electricity produced through renewable energy, and power companies must pay retail electricity prices for electricity produced by renewable energy equipment; power purchase contracts The period is 15 years. During the contract period, the electricity purchase price level is adjusted at any time according to the market electricity price.
In 1996, the United Nations convened the “World Solar Energy Summit”, which once again called for global joint action to make extensive use of solar energy and issued a series of important documents, expressing the firm determination of the United Nations and other countries in the world to develop solar energy. The European Union also issued the “Renewable Energy White Paper”, requiring the production of 6000 MW photovoltaic cells in 2010. It is estimated that the production of photovoltaic cells in the United States, Japan, and the European Union alone may exceed 15,300 MW. Since 1999, the photovoltaic industry has developed rapidly; in the last ten years, the output of photovoltaic modules has increased by nearly 10 times, while the price has dropped by 3/4. According to the report of the relevant research institutes in the United States, the photovoltaic industry will be in line with the information industry, Together, the communications industry has become one of the fastest growing industries in the world. According to the EU photovoltaic R&D roadmap published in 2004, the proportion of conventional energy and nuclear energy in the energy structure was about 80% in 2000, and the proportion of renewable energy was 20%. Among the renewable energy sources are mainly bio-energy, and the proportion of solar energy is very small, but by 2050 the proportion of conventional energy and nuclear energy will drop to 47%, and the proportion of renewable energy will rise to 53%. Among renewable energy sources, solar energy (including solar thermal utilization and solar power generation) will occupy the first place, accounting for 29% of the total energy. It is particularly worth pointing out that solar power generation alone accounts for 25% of the total energy and will account for 1/5 of the world’s total power generation. Solar energy will become an important substitute for conventional energy, as shown in Figure 5. In addition, the expansion of production scale is inversely proportional to the price of the product. With the reduction of solar cell manufacturing costs and the improvement of production capacity, the potential for further cost reduction makes it completely possible to become an alternative energy source.
The principle of solar power generation, that is, the photovoltaic effect, was the first time that Beequeeral, France, was observed in chemical cells in 1839; the first solar cell came out in 1887 with a conversion efficiency of 1% to 2%; silicon solar cells appeared in 1941: 1876 Photovoltaic effects have also been observed in solid selenium (Se) systems. In 1954, Bell Labs Chapin and others developed a monocrystalline silicon solar cell with an efficiency of 6%: silicon solar cells were first used in spacecraft in 1958. In the following ten years, silicon solar cells continued to expand in space applications, the technology continued to improve, and the cell design was gradually finalized. In the early 1970s, many new technologies were introduced into the battery manufacturing process, and the conversion efficiency was greatly improved. At the same time, silicon solar cells began to attract ground applications. At the end of the 1970s, the output of ground solar cells had exceeded the output of space cells, which led to continuous cost reductions. In the early 1980s, silicon solar cells entered a period of rapid development. Technological progress and research and development have further improved the efficiency of solar cells, continued to reduce commercial production costs, and continued to expand their applications.
From the development of cell efficiency, 1954~1960 is the first development stage: In 1954, Bell Labs Chapin and others developed monocrystalline silicon solar cells with an efficiency of 6%; in 1960, the main technology to improve solar cell efficiency was to use The preparation process of silicon materials is becoming more and more perfect, and the quality of silicon materials continues to improve. During this period, the cell efficiency is 15%. 1972~1985 was the second stage of development. Back-field battery (BSF) technology, “shallow junction” structure, texture technology, and close-grid metallization are the representative technologies of this stage. The battery efficiency is increased to 17%, and the battery cost Dropped significantly. After 1985 was the third stage of battery development. With the emergence of a variety of new battery technologies and new materials, battery performance and photoelectric conversion efficiency were improved, such as surface and bulk passivation technology, Al/P Gettering technology, selective emission zone technology, double-layer anti-reflection film technology, etc. At present, a considerable number of technologies, materials and equipment are gradually breaking through the limitations of laboratories and being applied to industrial production. The concept of high-efficiency solar cells has also been proposed.
In short, because solar power generation has the advantages of sufficient cleanliness, absolute safety, relative wideness and adequacy of resources, long life, easy maintenance and other advantages that other conventional energy sources do not have, photovoltaic energy is considered to be the most important in the 21st century. One of the new energy sources, photovoltaic power generation is of great significance to solve the human energy crisis and environmental problems.