This paper first introduces the process of the three energy revolutions and the position of solar energy in the third energy revolution. It points out that solar energy is an inexhaustible clean energy with the characteristics of being generally harmless and pollution-free. Solar energy plays an important role in the third energy revolution. Subsequently, four ways of utilizing solar energy, namely solar thermal, solar photovoltaic, solar photochemical and solar fuel, are introduced, which comprehensively demonstrates the ways in which solar energy is utilized by people. Next, the basic principles of photovoltaic power generation technology and the basic composition and classification of photovoltaic power generation systems are proposed, and photovoltaic power generation systems are divided into independent photovoltaic power generation systems and grid-connected photovoltaic power generation systems. In the following part, a large number of statistical data are cited to point out that the global photovoltaic industry is in a stage of rapid and vigorous development, and China’s photovoltaic industry is also growing rapidly and continuously, becoming the main driving force for the development of the global photovoltaic industry. In addition, the development of the photovoltaic industry in other countries is introduced . At the end of the article, it points out the important significance of photovoltaic power generation in energy conservation and emission reduction, and it will definitely play an important role in people’s production and life in the future. In the third energy revolution, the energy utilization method of photovoltaic power generation will also play an important role, which will have an important impact on people’s production and life and environmental protection.
1. The three energy revolutions and the role of solar energy in the energy revolution
Energy is a natural resource that provides energy for human production and life and allows people to do work. Historians point out that human society has experienced two energy revolutions and is currently undergoing a third energy revolution.
As early as in ancient times, humans learned to drill wood to make fire during labor, and learned to use the burning energy of wood for lighting, heating and food processing. 4,000-5,000 years ago, the Egyptians invented sails, so that even if humans did not row, the boats could move forward with the wind. More than 2,000 years ago, people learned to make water wheels and windmills, using the energy of water and wind to draw water and grind flour. In the first energy revolution, it took more than 200 years from the use of coke to smelt iron in 1709 to coal accounting for 87% of the world’s commodity energy structure in 1920.
In the 1870s, with the development of electromagnetism, people successively made practical motors and generators, marking the arrival of the second energy revolution. In this energy revolution, the main energy sources used by people were coal, oil and natural gas. After that, until 1959, oil and natural gas accounted for 50% of the world’s commodity energy, which lasted for 100 years. However, it is estimated that the reserves of oil on the earth are about 200 billion tons, which will be exhausted in 50 years and is a non-renewable energy. The total reserves of coal are 9 trillion tons , which can last for up to 260 years. In addition, in the process of using these energy sources, a large amount of carbon dioxide and harmful gases are emitted, causing greenhouse effects and air pollution.
Since the 1930s, people have been researching and developing new energy sources. These include the deep conversion and utilization of solar energy, hydropower, and geothermal energy, as well as the development of nuclear energy, ocean energy, bioenergy, hydrogen energy, and chemical synthesis energy. Most of these energy sources are renewable energy, and have the characteristics of high energy, high efficiency, easy use, and no pollution. People’s use of them constitutes the third energy revolution. This energy revolution has not yet been completed. According to statistics, renewable energy accounted for 20% of the world’s total energy consumption in 2015, and it is expected to account for 50% in 2050.
Refers to the thermal radiation energy of the sun, which is the energy released by the hydrogen nuclear fusion of hydrogen atoms inside the sun. It is an inexhaustible clean energy. It has the characteristics of being universal, harmless, pollution-free, and long-lasting. In the third energy revolution, solar energy plays an important role.
2. How to use solar energy?
The first way is to use solar thermal energy. Its basic principle is to collect solar radiation energy and convert it into thermal energy through interaction with matter for utilization.
The second way of utilization is solar photovoltaic utilization. Solar photovoltaic refers to the conversion of the sun’s radiation energy photons into electrical energy through semiconductor materials, usually called the “photovoltaic effect”. Solar cells are made using this effect.
The third method is photochemical utilization. This is a photochemical conversion method that uses solar radiation to directly decompose water to produce hydrogen. It includes photosynthesis, photoelectrochemical action, photosensitive chemical action and photolysis reaction. Solar energy photochemical conversion is being actively explored and studied.
The fourth utilization method is fuel utilization. So far, the R&D team has successfully achieved the full-process production of renewable fuel on a laboratory scale for the first time in the world . Its products fully comply with the EU’s aircraft and automobile fuel standards without any adjustments to aircraft and automobile engines.
3. Principles of photovoltaic power generation technology and introduction to photovoltaic power generation systems
3.1 Principles of photovoltaic power generation technology
When light hits the photosensitive surface of a solar cell, the conversion of light energy into electrical energy relies on the photovoltaic effect. The photovoltaic effect is a characteristic of semiconductor materials. When a light field is irradiated into a semiconductor material, its internal electrons move driven by the light field to generate an electromotive force. If an external load is connected, this part of the potential can be used to do work and the light energy can be used in the form of electrical energy. stand up.
When there is no light, the circuit characteristics of a solar cell are reflected in the characteristics of semiconductor materials, and it behaves as a load. The relationship between its current and voltage satisfies the exponential law, which is equivalent to a diode:
Where V is the voltage across the solar cell, I is the current flowing through the solar cell, T is the temperature of the solar cell, and e and kB are physical constants. Based on the properties of the exponential function, we can roughly understand the volt-ampere characteristics of the solar cell under an external electric field.
Corresponding to the dark characteristics of solar cells is the response characteristics of solar cells under light irradiation. At this time, due to the photovoltaic effect, the solar cell behaves as a power source, providing electromotive force for the external load and outputting electrical energy [3].
3.2 Introduction to Photovoltaic Power Generation System
Photovoltaic power generation system is a power generation and power conversion system composed of photovoltaic panels, controllers, and power storage and conversion links. Solar radiation energy is directly converted into electrical energy through photovoltaic panels, and then stored and converted through cables, controllers, energy storage and other links to provide load use. Photovoltaic power generation systems are classified according to their relationship with the power system, usually into stand-alone photovoltaic power generation systems (Stand-Alone PV System) and grid-connected photovoltaic power generation systems (Grid-Connected PV System) [4].
4. Current status and future of photovoltaic power generation industry
4.1 Overview of the development of the global photovoltaic industry
It is predicted that the global cumulative photovoltaic installed capacity is expected to reach 1,721GW by 2030 and will further increase to 4,670GW by 2050. The photovoltaic industry has great development potential. It is estimated that the global new installed capacity will be 101.91GW, 107.01GW, 125.20GW, 140.40GW and 157.80GW in 2018-2022 respectively. According to the estimated demand for solar cell backsheets of 6.1 million square meters per GW installed capacity, the corresponding demand for solar cell backsheets in 2018-2022 will be 622 million square meters, 653 million square meters, 764 million square meters, 856 million square meters and 963 million square meters respectively.
4.2 Overview of the development of China’s photovoltaic industry
2002, China’s photovoltaic industry started to take off. During the “15th Five-Year Plan” period, China successively carried out research on key technologies of crystalline silicon high-efficiency batteries, amorphous silicon thin-film batteries, cadmium telluride and copper indium selenide thin-film batteries, crystalline silicon thin-film batteries and application systems through the “National High-Tech Research and Development Program” and “Science and Technology Research Program” in the research and development of photovoltaic power generation technology, which greatly improved the level of photovoltaic power generation technology and industry and shortened the gap between photovoltaic power generation manufacturing industry and international level. China’s photovoltaic power generation industry entered a period of rapid development in 2004, and the output and installed capacity of photovoltaic cells increased year by year.
China’s solar energy resources are widely distributed, and there are conditions for large-scale development of the photovoltaic industry. Photovoltaic power generation has become the fastest growing industry in China’s new energy industry. China’s photovoltaic industry started late but is showing a rapid development momentum. After 2010 , against the backdrop of a slowdown in demand for the photovoltaic industry in Europe, China’s photovoltaic industry has risen rapidly and has become the main driving force for the development of the global photovoltaic industry .
Since 2013, China has introduced a series of policies on the development of the photovoltaic industry. From the perspective of the industrial policy, China’s photovoltaic industry has mainly developed along the path of “subsidies to promote scale development – standardize the industry environment – develop multiple models – connect new energy power to the grid – reduce subsidies”. In 2017, China’s newly added grid-connected photovoltaic installed capacity reached 53GW, an increase of more than 50% year-on-year, and the cumulative grid-connected installed capacity reached 131GW, ranking first in the world.
In the future, as China’s photovoltaic technology gradually improves, China’s photovoltaic industry still has huge room for development. It is predicted that by 2030, the global cumulative photovoltaic installed capacity is expected to reach 1,721GW, and by 2050 it will further increase to 4,670GW. The photovoltaic industry has great development potential. Under the relatively strong demand from emerging countries such as the United States, the European Union and India, the global new installed capacity is expected to be 125.20GW, 140.40GW and 157.80GW in 2020-2022 respectively. According to the demand for solar cell backsheets per GW installed capacity, it is estimated that the demand for solar cell backsheets will be 6.1 million square meters, and the corresponding demand for solar cell backsheets in 2020-2022 will be 764 million square meters, 856 million square meters and 963 million square meters respectively.
Chinese photovoltaic manufacturing companies currently have an overwhelming advantage in technology and cost. At present, China’s photovoltaic industry is in an era of intensified competition. Photovoltaic companies are “reducing costs and increasing efficiency” and are now in the stage of accelerating the research and development of advanced production technologies. Many advanced crystalline silicon cell technologies have broken world records many times. For example, high-efficiency crystalline silicon cell technologies such as passivated emitter rear surface passivation (PERC) technology, N- type silicon bifacial cell technology , and multicrystalline black silicon cell technology have improved the conversion efficiency of cells . The output of each link in China’s photovoltaic industry chain accounts for more than 50% of the world’s total, ranking first in the world[8].
4.3 Overview of photovoltaic industry development in other major countries
The number of Chinese companies in the top ten global production scales increased from 4 in 2011 to 8 in 2017, while the number of American companies decreased from 2 to 0. From 2011 to 2017, the module production capacity gradually increased from the original 35GW to the current 105.5GW, with mainland China accounting for about 72% of the production capacity.
In 2007, photovoltaic power generation accounted for 14.2% of the entire power generation industry in Germany. By the end of 2010, Germany’s photovoltaic power generation installed capacity had reached 17.193 million kilowatts, and by 2020 it will reach 51 million kilowatts. At present, Germany has formed a complete photovoltaic industry chain and established the German Aerospace Research Center Solar Energy Laboratory, whose goal is to provide technical support for the development of the first solar thermal power station project in Europe, gradually reduce the cost of solar thermal power generation, and study the chemical storage of solar energy.
The development status in France is as follows: In 2009, the world’s first solar power plant that can “track” the sun was officially put into operation in the small town of Matilda, France . The area of its photoelectric receiving and conversion device reached 3,500 square meters, and the conversion efficiency increased by 20%-40%.
Spain ranks among the world’s top countries in solar power generation and is one of the fastest growing photovoltaic countries in the world . At the end of 2010, its installed photovoltaic capacity was 3.784 million kW, and it is expected to reach 8.7 million kW in 2020.
The world’s largest solar power plant with a generating capacity of 500,000 kW and an area of 1,000 acres is under construction in the Negev Desert in southern Israel. Its first phase will have a generating capacity of 100,000 kW and will reach 500,000 kW when completed in 2012, accounting for about 5% of the country’s electricity production.
As one of the world’s largest manufacturers of solar cell templates, India formulated a US$70 billion national solar plan in 2009, with an expected power generation capacity of 20GW p by 2022.
5. The significance of photovoltaic power generation in energy conservation and emission reduction
Solar energy is a very stable energy source. In today’s energy shortage, solar energy brings hope to people. People can achieve sustainable use of energy and improve production and life through photovoltaic power generation.
The photovoltaic industry is an industrial chain with different manufacturing sectors centered on the comprehensive utilization of solar energy. It consumes energy and produces energy. The energy generated by photovoltaic power generation applications is far greater than the energy consumed from the extraction of silicon materials to the production of photovoltaic modules. It is generally believed that the service life of a photovoltaic system is 25-30 years. In addition to the energy recovery period of about 4 years required for the construction of the entire photovoltaic system, there is at least 21 years of net energy production period. With the development of technology and further improvement of production conditions, the energy consumption per ton of photovoltaic module production will decrease, and the further improvement of solar cell conversion rate and the extension of battery life will further improve energy production efficiency.
In terms of pollutant emission reduction, the photovoltaic power generation system utilizes clean and pollution-free solar energy resources. Compared with traditional energy sources , it has a significant effect in reducing emissions of pollutants such as carbon dioxide, sulfur dioxide, and nitrogen oxides. Therefore, energy utilization with photovoltaic power generation as the core is of great significance for promoting the construction of a low-carbon economy and achieving the goal of energy conservation and emission reduction. With the improvement of related process flows and technological progress , the energy conservation and emission reduction effects of the development of the photovoltaic industry will become more apparent.
