Distributed photovoltaic power generation under grid-connected operation

Distributed photovoltaic power generation from the perspective of grid-connected operation

“On a cloudy day today, the power generation capacity is only 820 kilowatts. However, in July and August when the sunshine is strongest, the maximum power of this photovoltaic power plant can exceed 1,000 kilowatts.” On November 6, Jiangsu Jiangyin City Power Supply Company's control center control operation class The squad leader Fan Min opened the 10kV Hong Kong line graph in the dispatch automation system.

The 10 kV Hong Kong line is connected to the Jiangyin Lingang International Logistics Park 2000 kilowatts of distributed photovoltaic power station. The photovoltaic power station is composed of more than 1,000 polycrystalline silicon battery panels laid on the roof of seven warehouses, covering an area of ​​41,680 square meters. Last year From December 30, grid-connected power generation. From January to October this year, the power station generated 1.17 million kilowatt-hours of electricity and the largest amount of electricity generated reached 240,000 kilowatt-hours in July.

Distributed photovoltaic power generation is an emerging industry. Its characteristics of small power generation, instability, and decentralized location make it more difficult for the dispatching department of power supply companies to manage.

In August of this year, the State Grid Corporation's corporate standard "Photovoltaic Power Generation Dispatch Operation Management Specification" held a draft review meeting. The experts from the National Electric Power Dispatch Control Center and other departments reviewed the first draft one by one and proposed amendments and improvements to the National Energy Administration for review. In terms of photovoltaic grid-connected operation management, this specification defines the related responsibilities and obligations of photovoltaic power stations and dispatching departments.

Specific to distributed photovoltaic power generation, Fan Min said: “At present, the dispatching operation management of 10 kV distributed photovoltaic power generation projects is implemented in accordance with the nature of the power supply, that is, each distributed photovoltaic power generation project regardless of the power size, for the dispatch All of these are small power supplies. After these small power supplies are connected to the grid, their operation monitoring workload is much more than the normal 10-kilovolt line. If the public grid equipment needs a power outage and maintenance, the dispatcher must first distribute the distributed photovoltaic power from the The power grid is de-listed, and after the maintenance of the public power grid equipment is over, the dispatcher then grid-connects the distributed photovoltaic power supplies one by one.

Taking into account the special nature of distributed photovoltaic power supply, as early as in the beginning of the distributed photovoltaic power station construction in Jiangyin Lingang International Logistics Park, a service team consisting of Wuxi Power Supply Company, Jiangyin City Power Supply Company's regulatory, automation, and other related professional experts took the initiative. It is suggested that in accordance with relevant technical requirements of the State Grid Corporation of China, they shall install disconnection devices that are easy to operate, can be blocked, have obvious break point, and grounding functions at the common connection points of the distributed photovoltaic power supply and grid connection, and are specially designed for the relay protection equipment. The setting calculations determine a set of safe and reliable settings.

Doing a good job of grid-connected services

In July, the “12th Five-Year Plan for the Development of Solar Power Generation” issued by the National Energy Administration mentioned that during the “Twelfth Five-Year Plan” period, the total installed capacity of distributed solar power systems in the country reached more than 10 million kilowatts, encouraging conditions. Photovoltaic power generation systems have been installed on the roofs of public facilities, commercial buildings and industrial parks in cities and towns, and a grid operation technology system and management method adapted to user-side photovoltaic power generation have been explored and established.

On October 26, the State Grid Corporation of China issued the “Opinions on the Implementation of Distributed Photovoltaic Power Grid-connected Services,” stating that it will conscientiously implement the national energy development strategy, actively support the accelerated development of distributed photovoltaic power generation, and optimize the interconnection process. Simplify the connection procedures and improve service efficiency. Some media claimed that this opinion was issued in the context of the establishment of trade barriers for China's photovoltaic products by countries in Europe and the United States. Its scope of application covers all roof photovoltaic and photovoltaic building integration projects in China and is a distributed photovoltaic power generation project. The network provided convenience and paved the way for the development of distributed photovoltaic power generation.

On November 7, the visiting team organized by the Marketing Department of Zhejiang Jiaxing Electric Power Bureau came to a solar energy company and publicized it to the person in charge of the company with “Fresh Opinions on Improving the Grid-connected Photovoltaic Power Generation Service”. Understand business needs and difficulties.

After the State Grid Corporation of China convened a video-telephone conference to service distributed photovoltaic power generation and grid-connected work, the Jiaxing Power Bureau held the implementation meeting at the first time and set up a research working group. This solar energy company is a key enterprise in the photovoltaic industry in Jiaxing City. Since the company’s investment in Jiaxing, the Jiaxing Power Bureau sent a special person to take the initiative to come to the dock to understand the demand for electricity and the scale of development of the company, open up a green channel for it, and simplify the procedures. The process will accelerate the progress of the power facilities renovation project and fully serve the distributed photovoltaic power generation and grid operation.

Exploring the Road to Management

Then, what impact does the large-scale distributed photovoltaic power generation grid-connected operation have on the distribution network? What kind of countermeasures do the operation and management of the grid need? It is understood that in Germany, where distributed photovoltaic power generation is used more often and development is better, the "Distributed Power Supply Access to Low Voltage Distribution Network Operation Management" as a national mandatory standard was officially put into effect in January this year. This management regulation provides technical guidance and also provides important information for power supply companies to ensure stable power grids and normal operation of the system.

Dr. Zhao Bo from Zhejiang Electric Power Research Institute has a more forward-looking study on the effects of a large number of distributed photovoltaic power supplies on the distribution network. According to his analysis, the impacts include voltage, abnormal islanding, and current harmonics. etc. He gave an example. When the sun is full at midday, the photovoltaic power output is usually larger. If the line is light, the photovoltaic power supply will significantly raise the voltage of the access point.

The reality is that due to distributed photovoltaic power generation is still in the initial stage of development, the power grid dispatching and transportation inspection departments are still in the exploratory stage for the operation management measures of distributed photovoltaic power point.

According to Henan Electric Power Company, since the country initiated the "Golden Sun" and "photovoltaic building integration" demonstration project, the construction of photovoltaic power generation projects in Henan province has entered the "fast track". At present, 39 photovoltaic projects have been declared in the province. Put into operation 4. In order to meet the requirements for safe, standardized, and orderly access of distributed photovoltaic power generation projects, Henan Electric Power Company combined with the characteristics of Henan Power Grid to further refine and improve the standards for grid-connected photovoltaic power generation, access, testing and acceptance, and increased the training of technicians. Strengthen the further optimization of grid-connected processes to provide the whole process of customer access system plan development, installation of electrical energy metering devices, and acceptance and commissioning of grids.

Faced with the difficulties in distributed photovoltaic power generation and grid operation and management, power supply companies are actively adopting new technologies and management measures to minimize the interaction between distributed photovoltaic power supplies and the grid, and strictly follow the “support, welcome, and service”. The working principle is to deepen the development of distributed photovoltaic power generation and ensure the safe and stable operation of the power grid.