Generator content

2. Foreign research status

Energy is a powerful direct driving force for economic growth and social development. The international economy has shifted from high-speed growth to medium-to-high growth. We see the determination of the international community to develop green resources, recognizing the characteristics of high energy consumption, high pollution, high energy efficiency, low energy efficiency and serious environmental pollution. The high cost treatment of old development roads is difficult to maintain. Countries all over the world are vigorously promoting the application of photovoltaic power generation systems. Grid-connected photovoltaic power generation is the main trend of the development of solar photovoltaic power generation technology in the world. The use of photovoltaic power generation systems mainly starts from the initial investment subsidy and application layer [11]. For example, in 1998 and 1999, in order to promote the development of the photovoltaic industry, Germany has launched 1,000 roof projects and 100,000 roof projects. The South Korean government has adopted policies to support initial investment and subsidies. South Korea has built the world's largest 24-megawatt photovoltaic plant to improve power generation efficiency. The system uses the latest technology to achieve sunlight tracking, the solar panels automatically swing, and the final production efficiency is 15% higher than the fixed installation [12]. Canada has developed a series of policies. According to these policies, photovoltaic systems below 500 kW can provide excess power on grid-connected lines, so as to obtain certain benefits, under the premise of meeting their own use requirements, all systems above 500 kW can be connected to the grid to achieve profitability.

Second, photovoltaic system and photovoltaic industry analysis

1. Classification and power generation principle of photovoltaic power generation system

Solar energy systems can be divided into independent systems and grid-connected systems according to whether they are connected to the grid. The difference, however, is that stand-alone photovoltaic systems are very complex and require batteries as an energy reserve. Grid-connected photovoltaic power generation system can be directly connected to the public grid, fewer projects, simple structure.

Whether it is an independent power generation system or a grid-connected power generation system, its main components are solar panels, controllers and inverters [16]. The solar cell and the inverter work in coordination under the control of the controller. The principle of solar cells is relatively simple, and the common types on the market are usually semiconductors. When sunlight hits the surface, the photon energy is absorbed by the electrons, causing the electrons to change from P-type semiconductors to N-type semiconductors, resulting in the accumulation of electrons and holes. When the conductors are connected to form a loop, the voltage at the semiconductor contact surface will drop and the external current will drop [17]. The power generation principle of solar cells is shown in the figure. Another panel structure is emerging on the market. The organic matter is uniformly suspended on the surface of the film, which has the advantages of light weight and low cost.

2. Solar photovoltaic power generation system composition

Photovoltaic power generation system consists of solar array, charge and discharge controller, inverter, AC distribution cabinet, filter circuit and so on. Solar photovoltaic power generation can be divided into one-stage energy conversion and multistage energy conversion. The widely used energy conversion method is first order energy conversion.

There are some common parameters for photovoltaic systems. The most commonly used are installed capacity and power generation. Installed capacity is equal to the product of panel area. The average sunshine intensity and photoelectric conversion efficiency of the photovoltaic system, where the light intensity is the average light energy intensity per unit area, the unit is w/m2[20]. The power generation capacity of photovoltaic power generation system is equal to the product of installed capacity, effective sunshine time and comprehensive coefficient. The comprehensive coefficient in the formula is affected by many factors, so the Angle of photovoltaic panel, transmission loss and energy conversion loss should be considered when determining the final efficiency coefficient [21]. The installation of solar photovoltaic systems is also one of the hot issues discussed, namely the optimal location of solar panels. Depending on the regional environment, lighting direction and other factors may have different requirements for the installation position.

Third, the application of solar photovoltaic technology

1. Grid-connected inverter technology

According to the different characteristics of DC power supplies, inverters can be divided into current sources and voltage sources. Because of the simple structure of voltage inverter, the control technology is mature and reliable. Voltage inverters are more efficient than current inverters. Therefore, voltage-type inverters are usually used in photovoltaic grid-connected systems. Grid-connected photovoltaic inverters can be divided into insulated and non-insulated types. According to whether there is electrical insulation between the input side and the output side of the grid-connected photovoltaic system, the grid-connected photovoltaic inverter can be divided into power frequency insulation type and high frequency insulation type, which depends on the working frequency of the grid-connected photovoltaic inverter. Operation of insulated transformers.