Why is 6MW the benchmark? | The Past and Present of 6MW Distributed Photovoltaic Scale

In the rapid development of the photovoltaic industry, the number 6MW seems to have become an unavoidable benchmark. Whether it's the policy definition of the National Energy Administration or the technical specifications of power grid companies, 6MW serves as a key threshold, affecting the planning, construction, and operation of distributed photovoltaic power stations. Today, let's explore together why 6MW has become an important limit for the scale of distributed photovoltaics, and its "past and present."

I. Policy Perspective: The Origin and Evolution of 6MW

Looking back at history, China's definition and management of distributed photovoltaic power stations have not been static. As early as 2012, China first proposed limiting distributed photovoltaic power stations to 10kV and below voltage level access, and the capacity of a single project should not exceed 6MW. This regulation was further clarified and standardized in the "Interim Measures for the Management of Photovoltaic Power Station Projects" issued by the National Energy Administration in 2013. Subsequently, in 2019, the National Energy Administration reiterated that newly built industrial and commercial power generation projects requiring national subsidies must meet the requirements of a single point grid-connected capacity of less than 6MW and non-household use. The latest policy trends, such as the "Management Measures for the Development and Construction of Distributed Photovoltaic Power Generation (Draft for Comments)" issued by the National Energy Administration on October 9, continue to refine and regulate the scale of distributed photovoltaics.

《Comprehensive Analysis of Distributed PV Pricing Trends under the Background of Full Participation in the Electricity Market.pdf》

《Solution for Distributed PV Power Generation Projects in Steel Enterprises.pptx》

《Scheme and Application of "Four Possible" Access of Distributed New Energy in the New Power System.pdf》

The 6MW limit at the policy level is actually a balance between the scale of distributed photovoltaic power stations and the grid access capacity and management convenience. By setting this limit, the government can more effectively manage distributed photovoltaic power stations, ensuring the safety and stability of their grid connection, and also providing more policy support and subsidy benefits for small and medium-sized distributed photovoltaic projects.

II. Distribution Network Technology Perspective: Technical Constraints of 6MW

From a technical perspective, 6MW as the limit for distributed photovoltaic power stations is mainly limited by distribution network technology. In the typical design of the State Grid Corporation, the capacity range of photovoltaic power stations connected to 10kV lines is usually between 400kW and 6MW. This is based on various technical considerations. First, the 10kV distribution network belongs to the load side and is mainly used to supply power to industrial and commercial users and large public facilities. Distributed photovoltaic power stations are also based on load-side access, so their scale must match the carrying capacity of the distribution network. When the capacity of the photovoltaic power station exceeds 6MW, the grid needs to withstand a greater load, which may affect the stability of the local power supply.

Secondly, the specifications of the incoming cables and the carrying capacity of the switches are also important factors limiting the capacity of photovoltaic power stations. A 6MW photovoltaic power station needs to be equipped with high-specification cables and switching devices to meet the current requirements. When it exceeds 6MW, the load on the cables and switches will increase significantly, and the distribution equipment needs to be comprehensively upgraded, which will lead to a significant increase in costs. Finally, the distance and carrying capacity of the transmission lines are also factors that must be considered. Photovoltaic power stations of 6MW and below can be connected to the 10kV distribution network through shorter transmission lines without putting excessive pressure on the transmission system. When it exceeds 6MW, the problems of line loss and voltage fluctuation will become significant, affecting power quality and power supply reliability.

III. Grid Stability Perspective: The Reasonableness of 6MW

The access of distributed photovoltaics puts high demands on grid stability. Based on grid operation experience, 6MW is a relatively reasonable capacity limit. In terms of power fluctuation management, photovoltaic power generation is greatly affected by meteorological conditions, and the power output fluctuates significantly. For a 10kV distribution network, the power fluctuation of photovoltaic power stations below 6MW is relatively small, and it is easy for the grid to balance and adjust. When it exceeds 6MW, the impact of power fluctuation on the local grid increases, and the complexity of grid scheduling increases. In terms of voltage fluctuation and harmonic effects, the access of large-scale distributed photovoltaics may lead to voltage fluctuation and harmonic interference. Photovoltaic power stations of 6MW and below can be effectively controlled by existing voltage regulation and filtering equipment, while those exceeding 6MW require further strengthening of voltage regulation equipment and reactive power compensation devices (such as SVG), which increases the complexity and cost of grid operation.

In addition, in terms of power grid protection system design, in photovoltaic power stations below 6MW, existing power grid protection equipment can effectively cope with photovoltaic power station failures. In systems above 6MW, due to the large capacity of the photovoltaic power station, grid failures may cause more serious power outages, so the protection equipment needs to be redesigned to ensure the safety and stability of the power grid.

IV. Economic Perspective: Economic Considerations of 6MW

From an economic perspective, 6MW is also a reasonable limit for the scale of distributed photovoltaic projects. First, in terms of project investment and return, photovoltaic projects below 6MW have a moderate scale, reasonable equipment investment and construction costs, and can achieve a faster return on investment. Projects exceeding 6MW not only face problems such as equipment upgrades and increased construction complexity, but also increased approval and access costs, which will affect the overall economic benefits of the project.

Secondly, in terms of policy support and subsidies, national and local government subsidies for distributed photovoltaic projects are mostly concentrated on small and medium-sized projects. Projects below 6MW are more likely to receive financial support and tax incentives, while projects larger than 6MW may be classified as centralized photovoltaic management and cannot enjoy the relevant policy incentives for distributed photovoltaics. Finally, from the perspective of industrial and commercial user needs, a 6MW photovoltaic system can usually meet the electricity needs of medium and large-sized enterprises, helping them achieve self-generation and self-use and reduce electricity costs. Systems exceeding 6MW, on the one hand, will increase the initial investment of the photovoltaic system, and on the other hand, may exceed the actual electricity demand of the enterprise, leading to electricity waste. At the same time, the factory area and roof resources of most industrial and commercial users are limited, and photovoltaic systems below 6MW can usually make reasonable use of these resources to achieve high economic benefits. In summary, 6MW as the limit for the scale of distributed photovoltaics is the result of the combined effects of various factors such as policy, technology, grid stability, and economy. The setting of this limit ensures the safety and stability of distributed photovoltaic power stations accessing the grid, and provides more policy support and market opportunities for small and medium-sized distributed photovoltaic projects. In future development, with technological advancements and grid upgrades, this limit may be adjusted, but in any case, 6MW will leave a deep mark in the development history of distributed photovoltaics.