The most promising implementation of distributed photovoltaic power generation is facing many challenges
"The recent "third industrial revolution" in the world has spurred people to use energy in a distributed way, such as gas and renewable energy. I think that distributed photovoltaic power generation is the most promising." Liu Chun, director of the New Energy Research Institute of China Electric Power Research Institute, said in an interview. He also said that China plans to install 100 GW of photovoltaic capacity by 2020, of which 60 GW will be distributed generation. However, due to the well-known problems of domestic solar energy resources and power generation equipment, distributed power generation still needs to be tested in many real-world environments. The results can not be underestimated Problems can not be avoided In fact, from the second half of 2012 to the present, the grid company has issued a number of encouraging opinions to promote the development of distributed generation, which is a difficult but substantive first step for the domestic market. Taking the State Grid Corporation of China (hereinafter referred to as “State Gridâ€) as an example, since the introduction of encouraging policies, the number of distributed photovoltaic applications has increased significantly. Up to now, 585 users have been applied for, with an installed capacity of 1,151,200 kilowatts, which accounts for the installed capacity of distributed generation applications. More than 90. However, in spite of this, compared with other countries, our country's power is still very "slim." In Germany, the average PV installation capacity in 2010 and 2011 was about 7.5 GW, of which 2/3 was a small installed capacity of 250 kW or less, and China's average installed capacity was 2 MW, and they were all located in industrial parks. "China should develop more small-scale installations of 50 kilowatts or less, or 250 kilowatts or less, and we should encourage the development of distributed generation in every building and every household. Otherwise, China's distributed photovoltaics will not do much." Pure preaching. In addition, distributed photovoltaic power generation is not only limited by the environment (roof area), but also by the conditions of the power grid, compared with the centralized development of the power grid. "Distribution is connected with the load. Once an error occurs, it will have an impact on the entire distribution network," said Liu Chun. At the same time, distributed photovoltaic power generation has a disadvantage in that power generation equipment is closer to users and a series of adverse effects are more easily perceived by users. More difficult to connect to the grid Technology is still maturing From a technical point of view, the current photovoltaic power generation output is not stable, and distributed photovoltaic power generation is still in the exploratory stage, facing many technical problems and challenges. First, after distributed photovoltaic power generation is connected to the power grid, it has a greater impact on the power grid. Not only the voltage variation range of each access point becomes larger, the voltage between the access points increases, and the bus voltage fluctuation amplitude also increases. Second, due to the wide range of distributed photovoltaics, such as conventional access management, the demand for dispatching investment and personnel will greatly increase. If all access is in the form of a private network, communication investment is huge, and the existing dispatch automation system does not support such a huge amount of investment. The “Opinions on Promoting Distributed Power Supply Grid Management Work†issued by the State Grid put forward the distributed photovoltaic power generation, wind power, and ocean energy power generation projects on the 10kV access user side, and distributed power projects with 380V access. Wireless public network communication can be adopted. However, Liu Chun admitted frankly that the current R&D of this technology is entering a critical moment and faces many technical difficulties. "The major problems are big data, such as large meteorological data and large digital weather forecast data. This is a problem that we have never encountered before." Adaptive Control Technology Leading future technology trends Smart grid technology is the main way to solve distributed photovoltaic grid-connected problems. Among them, distributed photovoltaic adaptive control technology is an important development direction in the future. “The randomness of distributed PV output power is likely to cause voltage fluctuations and flicker.†Liu Chung followed an example. “Ningxia Autonomous Region plans to install 4 kW distributed photovoltaics on the roofs of 3800 rural residents in Hongsibao Town and pass 220 Volt-spread access, but because the electricity load in the region is only 1 kilowatt, the penetration rate is very high.If you must access, you can only rebuild the power grid.Otherwise, the user will obviously feel the voltage instability and the lights flickering. †For voltage fluctuations and flicker problems, many people propose to solve them by means of centralized compensation. Practice has shown that the effect of centralized compensation is not obvious on the side of the 10 kV mother line of the transformer; compensating the reactor at the end of the 400 V/220 V line will significantly increase the line loss; and changing the access system scheme will bring together the pressure boosted by 10 KV integration will affect economic efficiency. "Through centralized control and decentralized control, each household inverter performs adaptive reactive voltage regulation. This is the only feasible solution." Liu Chun said, "At present, China Electric Power Research Institute is conducting related technology research." According to his introduction, distributed photovoltaic power generation performs self-adaptive adjustment of reactive power or even active power according to the state of the grid connection point, improves the power quality of the grid connection point, and adjusts the power level according to the peak-to-valley power price. It can even provide auxiliary services such as peaking and emergency power support. Get the most economic benefits. In this process, distributed photovoltaics are no longer passive accessors but are active participants in the smart grid. After the realization of intelligence, distributed photovoltaics will have the ability of perception, information interaction, comprehensive judgment and decision-making capabilities, and can achieve adaptive control and better integrate into the entire system. However, compared to the mature technology of large power grids, distributed photovoltaic power generation is still in its infancy. How to solve the numerous difficulties it faces and how to improve its technical solutions still requires time and practice.
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