The Role of Energy Storage Systems in Microgrids

Energy storage is critical throughout the entire electricity value chain. It is experienced in all power generation, transmission, distribution, and even end-electricity consumers. Energy storage provides the most rational solution to the challenges of grid integration of renewables, grid stabilization, and efficient distribution system optimization. With the inclusion of energy storage in the system, effective demand-side management can be achieved, which will reduce the peak-off-peak gap, stabilize loads, utilize power equipment more efficiently, conserve electricity costs, and promote the use of renewable energy. It is also a cost-effective means for enhancing system stability, helping to regulate frequency and voltage, and balancing fluctuating loads.

Improving the Reliability of Distributed Energy

Distributed energy resources such as solar, wind, and biomass are typically under the control of external natural factors such as sunlight, temperature, wind, and weather, making the generated electricity random and unreliable. In the scenario where the microgrid is disconnected from the grid and relies on its own resources, the output power of distributed energy in the microgrid changes with fluctuation in environmental parameters, thus it is difficult to obtain stable output for loads. If used in microgrids, energy storage systems, controlled by an Energy Management System (EMS), can cooperate with distributed energy sources and the master grid to offset the volatility of distributed energy, stabilize the output, and improve the local utilization rate of distributed energy. This avoids the pressure of long-distance transmission to the master grid and reduces power loss.

In addition, energy storage systems may supply partial power to critical loads during nighttime or while the distributed energy sources are under maintenance, thus reducing downtime.

Enhancing the Power Quality of Customers

When the microgrid is supplied from the grid, its power quality must comply with national standards, and as such, the power factor, voltage asymmetry, current harmonic distortion, and voltage sags must reach some values.

As mentioned in the initial point, without an energy storage system, the inherent characteristics of the energy sources within the microgrid make power quality, especially voltage stability, difficult to maintain. Employing energy storage systems has the potential to significantly enhance the power quality of the microgrid. By regulating the Power Conversion System (PCS) of the energy storage system, it stabilizes the power output and regulates the active and reactive power output to the microgrid, eliminating voltage sags and dips.

Confronted with sudden increasing or decreasing main grid voltages, the energy storage system will provide quick power buffering, fast energy absorption, or filling energy, with active and reactive power supply for voltage variation stabilization. In addition, the energy storage system will have partial harmonic suppression functions for the microgrid.

Peak Shaving

In a microgrid, the energy storage system can store surplus energy supplied by distributed energy sources at off-peak hours and supply energy at peak hours in a bid to balance load demand. The energy storage system is critical as an energy buffer in the microgrid.

Apart from meeting the peak load requirements, the energy storage system can reduce the required capacity of generators or transformers.

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