Characteristics of distributed photovoltaic power stations
The basic principle of distributed generation is to primarily address users' electricity needs based on the building surface, and to compensate for and transmit power supply gaps through grid connection.
I. Advantages of distributed photovoltaic power stations:
1. Photovoltaic power sources are located on the user side, generating electricity to supply local loads. They are considered as loads, which can effectively reduce dependence on grid power supply and reduce line losses.
2. By making full use of the building surface, photovoltaic cells can also be used as building materials, effectively reducing the footprint of photovoltaic power stations.
3. It has an effective interface with smart grids and microgrids, operates flexibly, and can operate independently of the power grid under appropriate conditions.
II. Disadvantages of distributed photovoltaic power stations:
1. The power flow direction in the distribution network will change in a timely manner. Reverse power flow will cause additional losses, and related protection will need to be re-set. Transformer taps will need to be constantly changed, etc.
2. Difficulties in voltage and reactive power regulation: Controlling the power factor after the connection of large-capacity photovoltaic power presents technical challenges, and short-circuit power will also increase.
3. A unified load management system is needed at the distribution network level in the case of large-scale photovoltaic integration. This places new demands on secondary equipment and communication, increasing the complexity of the system.
Characteristics of centralized photovoltaic power stations
The basic principle of centralized power generation is to make full use of the abundant and relatively stable solar energy resources in desert areas to build large-scale photovoltaic power plants and connect them to high-voltage transmission systems to supply long-distance loads.
I. Advantages of centralized photovoltaic power stations:
1. Due to more flexible site selection, the stability of photovoltaic power output has increased, and the positive peak-shaving characteristics of solar radiation and electricity load are fully utilized to play a role in peak shaving.
2. The operation mode is more flexible. Compared with distributed photovoltaic, it is easier to control reactive power and voltage, and it is also easier to participate in grid frequency regulation.
3. It has a short construction period, strong environmental adaptability, does not require the supply of raw materials such as water and coal transportation, has low operating costs, is easy to centrally manage, is less restricted by space, and can be easily expanded.
II. Disadvantages of centralized photovoltaic power plants:
1. It relies on long-distance transmission lines to deliver power to the grid, and at the same time, it is also a major source of interference to the power grid. Problems such as transmission line losses, voltage drops, and reactive power compensation will become prominent.
2. Large-capacity photovoltaic power plants are achieved by combining multiple conversion devices. The coordinated operation of these devices requires unified management, and the technology in this area is not yet mature.
3. To ensure grid security, large-capacity centralized photovoltaic grid connection requires new functions such as LVRT, which often conflicts with islanded grid connection.
Centralized large-scale grid-connected photovoltaic power plants are large-scale photovoltaic power plants built by the state to utilize desert areas. The generated electricity is directly connected to the public power grid and then connected to the high-voltage transmission system to supply loads at long distances. Distributed small-scale grid-connected photovoltaic systems, especially building-integrated photovoltaic (BIPV) systems, are the mainstream of grid-connected photovoltaic power generation in developed countries due to their advantages such as low investment, fast construction, small footprint, and strong policy support.
