Energy Storage Essentials: What is a Microgrid?

1. What is a microgrid?

A microgrid refers to a small power system consisting of distributed power sources, loads, energy storage, power transformation and distribution, and a control system.

Despite its small size, a microgrid possesses all the necessary capabilities. It is an autonomous power system capable of self-control, protection, and management. It possesses complete power generation, distribution, and consumption functions, effectively optimizing energy within the grid.

2. What is the difference between a microgrid and a large power grid?

A microgrid is not a "miniature large power grid." Instead, it is a concept relative to the traditional large power grid. Traditional large power grids primarily rely on one-way communication, with electricity flowing from power plants to consumers layer by layer through transmission lines. Microgrids, on the other hand, utilize a two-way communication model, enabling local power generation and balancing, maximizing energy efficiency.

Microgrids differ significantly from traditional large power grids in their functions, structure, and operation:

■ Microgrids primarily rely on distributed power sources, utilizing energy storage systems and control devices for regulation to meet load demand.

■ Microgrids support independent network operation. In the event of a main grid failure, they can quickly disconnect from the main grid and continue to supply critical loads independently.

■ Microgrid planning and design primarily determine the optimal system construction plan based on comprehensive energy consumption, resource distribution, and existing network conditions, meeting economic, reliable, and environmentally friendly power requirements.

Therefore, microgrids offer new solutions from the perspectives of energy conservation, environmental protection, and cost reduction and efficiency improvement.

3. Why build microgrids when traditional main grid construction technology is highly mature?

Building microgrids can effectively absorb new energy and address the key challenges associated with grid-connected operation of various distributed power sources.

Renewable energy sources such as solar and wind power are highly intermittent and random, and are significantly affected by the environment. Voltage and frequency instability are common, which can severely impact the main grid. Existing research shows that integrating distributed power sources into the grid in the form of microgrids and supporting the main grid is an effective way to maximize the efficiency of distributed power sources. Microgrids and large power grids complement each other, and they can play a greater role, especially in areas not covered by large power grids, to make up for the shortcomings of large power grids.

4. What are the functions of microgrids?

■ Local consumption improves energy efficiency. Microgrids use distributed energy sources such as natural gas, photovoltaics, and wind power. Microgrids typically have smaller capacity, dispersed power sources, and are located close to the load. This allows for local consumption and balancing of distributed energy resources. They can also exchange energy with the main grid, providing mutual support.

■ Single-point connection reduces impact on the main grid. Energy exchange between the microgrid and the grid occurs through a common connection point between the microgrid and the grid, eliminating the need for direct connection between multiple distributed power sources. Microgrids primarily provide power within a region, with no or minimal external power transmission, resulting in negligible impact on the grid.

■ Improve power supply reliability and meet energy needs. Microgrids utilize advanced control methods and numerous power electronics devices to connect distributed power sources, energy storage devices, and controllable loads, making them a controllable load within the grid system. They can operate in both grid-connected and independent modes, effectively maintaining the safe and stable operation of both the microgrid and the main grid.

5. What are the different types of microgrids?

Macroeconomic classification: Microgrids are broadly classified into two types: standalone and grid-connected.

① Standalone microgrids are independently constructed and operated, independent of the external grid. They ensure a balance between power generation and supply within the microgrid, ensuring grid-connected power supply stability.

② Grid-connected microgrids operate in conjunction with the external grid. When the external grid fails, they must be disconnected from the grid to control the power supply and energy storage systems within the grid, ensuring normal power supply to critical loads.

Microeconomic classification: Microgrids fall into the following five types:

① DC microgrid: Distributed power sources, energy storage devices, and loads are all connected to the DC bus. The DC network is then connected to the external AC grid via power electronic inverters. Using power electronic converters, DC microgrids can supply power to AC and DC loads of varying voltage levels. Energy storage devices can regulate fluctuations in the distributed power sources and loads on the DC side.

② AC microgrid: Distributed power sources, energy storage devices, and loads are all connected to the AC bus via power electronic devices. Currently, AC microgrids remain the predominant form of microgrid. By controlling switches at the PCC, microgrids can transition between grid-connected and islanded modes.

③ AC/DC hybrid microgrids: These contain both AC and DC busbars, enabling them to directly supply both AC and DC loads.

④ Medium-voltage distribution branch microgrids: These effectively integrate distributed power sources and loads based on medium-voltage distribution branches. They are suitable for supplying medium-capacity, high-reliability, and concentrated user areas.

⑤ Low-voltage microgrids: These integrate distributed power sources and loads at low voltage levels. These microgrids are typically owned by electricity or energy users and are relatively small in scale.

6. In what scenarios can microgrids be used?

At present, microgrids are mainly grid-connected and have a variety of expressions. Each expression name actually corresponds to an operating scenario, such as "source, grid, load and storage integration", "photovoltaic storage and charging (discharge/inspection)", "photovoltaic storage and data", "zero-carbon industrial park", etc.; but no matter how they change, they all rely on a relatively closed park/community/compound/gas station/charging station/data center. Combined with the electricity load level of the scenario, the surrounding new energy development conditions and the power grid conditions, a stable and reliable regional comprehensive intelligent energy management system is formed by newly building distributed new energy, new energy storage, power electronic equipment and other devices.