Cognitive Classroom - Photovoltaics
Basic Knowledge of Photovoltaics
What is photovoltaic power generation? What is distributed photovoltaic power generation?
Photovoltaic power generation refers to the method of generating electricity by directly converting solar radiation into electricity. Photovoltaic power generation is the mainstream of solar power generation today, so what people often refer to as solar power generation is photovoltaic power generation.
Distributed power generation refers to the construction of photovoltaic power generation facilities near user sites, with user side self use as the main operating mode, excess electricity connected to the grid, but characterized by balanced adjustment in the distribution system. Distributed power generation follows the principles of adapting to local conditions, clean and efficient, decentralized layout, and nearby utilization, fully utilizing local solar energy resources to replace and reduce fossil energy consumption.
Do you know the historical origin of photovoltaic power generation?
In 1839, at the age of 19 in France, Becquerel conducted a physics experiment and discovered that the current of two metal electrodes in a conductive liquid would increase when illuminated with light, thus discovering the "photovoltaic effect". In 1930, Lange first proposed using the "photovoltaic effect" to manufacture solar cells, converting solar energy into electrical energy.
In 1932, Audubot and Stora made the first cadmium sulfide solar cell.
In 1941, Odu discovered the photovoltaic effect on silicon.
In May 1954, Chapin, Fuller, and Pearson from Bell Laboratories in the United States developed a monocrystalline silicon solar cell with an efficiency of 6%, which was the world's first practical solar cell. In the same year, Wick discovered for the first time that nickel arsenide had a photovoltaic effect, and deposited nickel sulfide thin films on glass to make solar cells. The practical photovoltaic power generation technology of converting sunlight into electricity was born and developed from this.
3. How do photovoltaic cells generate electricity?
Photovoltaic cells are semiconductor devices with photovoltaic and electrical conversion characteristics, which directly convert solar radiation energy into direct current. They are the most basic unit of photovoltaic power generation. The unique electrical characteristics of photovoltaic cells are the incorporation of certain elements (such as phosphorus or boron) into crystalline silicon, causing permanent imbalance in the molecular charges of the material, forming semiconductor materials with special electrical properties, Under sunlight, semiconductors with special electrical properties can generate free charges, which move and accumulate in a directed manner, resulting in the generation of electrical energy when both ends are closed. This phenomenon is called the "photovoltaic effect" or simply the photovoltaic effect.
What are the components of a photovoltaic power generation system?
The photovoltaic power generation system consists of photovoltaic arrays (photovoltaic arrays are composed of photovoltaic modules in series and parallel), controllers, battery packs, DC/AC inverters, and other parts. The core component of the photovoltaic power generation system is the photovoltaic modules, which are also composed of photovoltaic cells in series, parallel, and sealed. They directly convert the solar energy into electricity, and the electricity generated by the photovoltaic modules is DC electricity, We can use inverters to convert it into AC power for utilization. From another perspective, the electricity generated by photovoltaic systems can be generated and used immediately, or energy storage devices such as batteries can be used to store the energy and release it for use as needed.
5. What is a distribution network?
What is the relationship between distribution network and distributed photovoltaic power generation? The distribution network is a power grid that receives electricity from the transmission network or regional power plants and distributes it to various users on site or step by step according to voltage through distribution facilities. It is composed of overhead lines, cables, towers, distribution transformers, isolation switches, reactive power compensation capacitors, metering devices, and some ancillary facilities. Generally, it adopts a closed-loop design and operates in a loop, with a radial structure, The integration of distributed power sources into the distribution network results in the coexistence of power generation and consumption in the distribution system. The distribution network structure has changed from a radial structure to a multi source structure, and the size, direction, and distribution characteristics of short-circuit current have all changed.
Why is photovoltaic power considered a green and low-carbon energy source?
Photovoltaic power generation has significant energy, environmental and economic benefits, and is one of the highest quality green energy sources. Installing a 1 kW photovoltaic power generation system under average sunlight conditions in China can generate 1200 kWh of electricity per year, reduce coal (standard coal) usage by about 400 kilograms, and reduce carbon dioxide emissions by about 1 ton. According to research by the World Wildlife Fund (WWF), in terms of reducing carbon dioxide emissions, Installing a 1 square meter photovoltaic power generation system is equivalent to planting 100 square meters of trees and forests. Currently, developing renewable energy such as photovoltaic power generation is one of the effective means to fundamentally solve environmental problems such as haze and acid rain.
7. How to view the news that there are reports that "a large amount of energy is consumed in the production of photovoltaic cell modules"?
Photovoltaic cells do consume a certain amount of energy during their production process, especially in the three stages of industrial silicon purification, high-purity polycrystalline silicon production, and monocrystalline silicon rod/polycrystalline silicon ingot production, which require high energy consumption. However, photovoltaic cells can continuously generate energy during their 20-year lifespan. According to calculations, under the average sunshine conditions in China, the energy return of photovoltaic power generation systems over their entire lifespan exceeds their energy consumption by more than 15 times. The energy recovery period of the 1 kW rooftop photovoltaic grid connected system installed at the optimal tilt angle in Beijing is 1.5-2 years, which is much lower than the service life of the photovoltaic system. That is to say, the electricity generated by the photovoltaic system in the first 1.5-2 years is used to offset the energy consumed in its production and other processes, while the energy generated after 1.5-2 years is pure output. Therefore, the energy consumption of photovoltaic cells should be evaluated from a full lifecycle perspective.
8. How to view the news that there are reports that the production of photovoltaic cell modules will generate a large amount of pollution?
The production of photovoltaic cell modules includes several links in the industry chain, including polycrystalline silicon, silicon ingot silicon wafers, photovoltaic cell packs, and photovoltaic modules. The related pollution reports mainly refer to the raw materials of photovoltaic modules and the by-products generated in the production of high-purity polycrystalline silicon. The production of high-purity polycrystalline silicon mainly uses the improved Siemens method, which converts metallurgical grade silicon into trichlorosilane, and then reduces it to solar grade polycrystalline silicon by adding hydrogen gas. In addition, it forms a by-product, silicon chloride, When silicon tetrachloride comes into contact with humid air, it decomposes into silicic acid and hydrogen chloride. Improper treatment can cause pollution problems. However, the improved Siemens method currently used by polysilicon production enterprises in China can achieve closed-loop production by recycling the by-product silicon tetrachloride and tail gas, achieving clean production. In December 2010, the country issued the "Access Conditions for the Polycrystalline Silicon Industry", which stipulated that the recovery and utilization rates of silicon tetrachloride and chlorine gas in the reduced tail gas should not be less than 98.5% and 99%. Therefore, the mature and improved Siemens production technology fully meets environmental protection requirements and will not cause environmental pollution problems.
How much sunlight do we have available?
Can it become the dominant energy source for the future? The solar radiation received on the Earth's surface can meet 10000 times the global energy demand, and the average annual radiation received per square meter on the Earth's surface varies by region, ranging from approximately 1000-2000KWH. According to data from the International Energy Agency, installing solar photovoltaic systems in 4% of the world's deserts is sufficient to meet global energy demand. Solar photovoltaics have vast development space and enormous potential.
According to preliminary statistics, China's market potential for using existing building installed photovoltaic power generation alone is about 3 trillion kilowatts or more. In addition, the vast Gobi photovoltaic power generation market in the west has a potential of several billion kilowatts or more. With the technological progress and large-scale application of photovoltaic power generation, its power generation cost will further decrease, becoming a more competitive energy supply mode, Gradually transitioning from supplementary energy to alternative energy and hoping to become the dominant energy source in the future.
