Distributed photovoltaic power generation specifically refers to photovoltaic power generation facilities that are built near the user's site, and whose operation mode is characterized by self-consumption on the user side, surplus electricity connected to the grid, and balanced adjustment in the power distribution system. Distributed photovoltaic power generation follows the principles of adapting measures to local conditions, clean and efficient, decentralized layout, and nearby utilization, making full use of local solar energy resources to replace and reduce fossil energy consumption.
Distributed photovoltaic power generation specifically refers to a distributed power generation system that uses photovoltaic modules to directly convert solar energy into electrical energy. It is a new type of power generation and comprehensive utilization of energy with broad development prospects. It advocates the principles of nearby power generation, nearby grid connection, nearby conversion, and nearby use. It can not only effectively increase the power generation of photovoltaic power plants of the same scale, but also It effectively solves the problem of power loss in boosting and long-distance transportation.
The most widely used distributed photovoltaic power generation system is a photovoltaic power generation project built on the roof of urban buildings. Such projects must be connected to the public grid, and together with the public grid, provide power to nearby users.
1. Technical characteristics of distributed photovoltaic power generation
Distributed photovoltaic power generation has the following characteristics:
1.1 The output power is relatively small. Generally speaking, the capacity of a distributed photovoltaic power generation project is within several thousand watts. Unlike centralized power plants, the size of photovoltaic power plants has little impact on power generation efficiency, so it also has little impact on its economy. The return on investment of small photovoltaic systems will not be lower than that of large ones.
1.2 Small pollution and outstanding environmental benefits. During the power generation process of distributed photovoltaic power generation projects, there is no noise and no pollution to air and water.
1.3 To a certain extent, it can alleviate the local electricity shortage. However, the energy density of distributed photovoltaic power generation is relatively low. The power of distributed photovoltaic power generation system per square meter is only about 100 watts. In addition, the roof area of buildings suitable for installing photovoltaic modules is limited, which cannot fundamentally solve the problem of power shortage. .
1.4 Power generation and consumption can coexist. The power generation of large-scale ground power stations is boosted and connected to the transmission network, and it only operates as a power generation station; while distributed photovoltaic power generation is connected to the distribution network, where power generation and consumption coexist, and it is required to consume as much as possible on the spot.
2. Advantages of distributed photovoltaic power generation
2.1 The output power is relatively small
Generally speaking, the capacity of a distributed photovoltaic power generation project is within several thousand watts. Unlike centralized power plants, the size of photovoltaic power plants has little impact on power generation efficiency, so it also has little impact on its economy. The return on investment of small photovoltaic systems will not be lower than that of large ones.
2.2 Small pollution and outstanding environmental benefits
During the power generation process of distributed photovoltaic power generation projects, there is no noise and no pollution to air and water.
2.3 Alleviate the local electricity shortage to a certain extent
However, the energy density of distributed photovoltaic power generation is relatively low. The power of distributed photovoltaic power generation system per square meter is only about 100 watts. In addition, the roof area of buildings suitable for installing photovoltaic modules is limited, which cannot fundamentally solve the problem of power shortage.
3. Solutions for distributed photovoltaic power generation
3.1 Application scenarios
Application range of distributed photovoltaic power generation system: It can be built in rural areas, pastoral areas, mountainous areas, developing large, medium and small cities or near commercial areas to meet the electricity demand of local users.
Distributed photovoltaic power generation system, also known as distributed power generation or distributed energy supply, refers to the configuration of smaller photovoltaic power generation and power supply systems at the user site or near the power consumption site to meet the needs of specific users and support the economy of the existing distribution network. operation, or both.
The basic equipment of the distributed photovoltaic power generation system includes photovoltaic cell components, photovoltaic array brackets, DC combiner boxes, DC power distribution cabinets, grid-connected inverters, AC power distribution cabinets and other equipment, as well as power supply system monitoring devices and environmental monitoring device. Its operation mode is that under the condition of solar radiation, the solar cell module array of the photovoltaic power generation system converts the solar energy into the output power, and sends it to the DC power distribution cabinet through the DC combiner box, and is converted into AC power by the grid-connected inverter. The building's own load, excess or insufficient electricity is regulated by connecting to the grid.
3.3 Program Features
The systems are independent of each other and can be controlled by themselves to avoid large-scale power outages and high safety;
Make up for the lack of stability of the large power grid, and continue to supply power when an accident occurs, becoming an indispensable and important supplement for centralized power supply;
It can monitor the quality and performance of regional power in real time, which is very suitable for supplying power to residents in rural areas, pastoral areas, mountainous areas, developing large, medium and small cities or commercial areas, greatly reducing the pressure on environmental protection;
Low or no power transmission and distribution loss, no need to build a distribution station, reduce or avoid additional transmission and distribution costs, and low civil engineering and installation costs;
Good peak shaving performance, simple operation;
Since there are few systems involved in the operation, the start and stop are fast, and it is easy to realize full automation.
4. Development of distributed photovoltaic power generation in various countries
The German Renewable Energy Law stipulates the subsidy method for photovoltaic power generation. For various application modes of photovoltaic power generation such as rooftop photovoltaic and ground photovoltaic, the scale and subsidy intensity are different.
According to the country's latest revised law in 2012, the on-grid electricity price for photovoltaic power generation ranges from 17.94 euro cents per kWh to 24.43 euro cents per kWh. The country also stipulates that if the installed capacity exceeds 3.5 million kilowatts in the next 12 months, the on-grid electricity price will be reduced by 3%; if it exceeds 7.5 million kilowatts, the on-grid electricity price will be reduced by 15%. Distributed power sources requiring more than 100 kilowatts must be installed with remote communication and control devices, so that the dispatcher can understand its output in real time and can be dispatched.
The country has begun to take some indirect measures to meet the requirements of distributed power generation access to the distribution network, such as upgrading and transforming the upper-level transformer at the access point, reconfiguring the voltage conditions and control equipment of the feeder, etc.
Spain requires that the capacity of distributed power installed in a certain area be less than 50% of the peak load in the area, and reverse power transmission of distributed power should be avoided as much as possible.
China began to implement concession bidding in 2009 to promote the construction of large-scale photovoltaic power plants on the ground.
Wu Xinxiong, deputy director of the National Development and Reform Commission and director of the National Energy Administration, pointed out that it is necessary to promptly implement the requirements of the State Council's guidance on promoting the healthy development of the photovoltaic industry, vigorously develop the distributed photovoltaic power generation market, and promote the healthy development of the photovoltaic industry.
He also emphasized that all localities should fully understand the importance of photovoltaic power generation, accurately grasp the development situation of the photovoltaic industry, seize the development opportunities of the photovoltaic industry, and take vigorously promoting the application of distributed photovoltaic power generation as an important task. Focus on selecting industrial parks in economically developed areas with high prices for online shopping, large peak-to-valley differences in power loads, relatively few subsidies, large power consumption, and stable loads, and carry out distributed photovoltaic application demonstrations in accordance with the principle of "spontaneous self-use and local consumption".
5. The main impact of distributed photovoltaic power generation
5.1 Impact on grid planning
The grid connection of distributed photovoltaics increases the difficulty of load forecasting in its area and changes the existing load growth model. The access of a large number of distributed power sources makes the transformation and management of the distribution network more complicated.
5.2 Different grid connection methods have different impacts
Off-grid distributed photovoltaics have no impact on the grid; distributed photovoltaic power generation that is connected to the grid but does not transmit power to the grid will cause voltage fluctuations; grid-connected and grid-connected methods that transmit power to the grid will cause voltage fluctuations and affect the relay Protected configuration.
5.3 Impact on power quality
The important impact of distributed photovoltaic access is to change the voltage distribution on the feeder, and the magnitude of the impact is closely related to the access capacity and access location. Photovoltaic power generation is generally connected to the power grid through inverters. Frequent switching on and off of such power electronic devices is prone to harmonic pollution.
5.4 Impact on relay protection
Most of China's distribution network has a single-power radial structure, and most of them adopt the form of quick-break and time-limited quick-break protection, which does not have directionality. After the distributed power supply is connected to the distribution network, its injected power will reduce the protection range of the relay, which cannot reliably protect the overall line, and even cause the relay protection of the distributed photovoltaic installation to malfunction when other parallel branches fail.