A microgrid is a small electric power system that can serve a neighborhood, campus, hospital, military base, or remote community. It uses local energy sources such as solar panels, wind turbines, and sometimes generators, along with batteries and controllable loads. Microgrids matter because they can keep critical power flowing during storms, wildfires, cyber disruptions, or failures on the larger utility grid.
They also help communities use more renewable energy close to where electricity is needed.
In normal operation, a microgrid often stays connected to the main grid and exchanges power through a point of common coupling. Smart controls balance generation, battery charging, and electricity demand many times per second to keep voltage and frequency within safe limits. If the main grid fails, switches can isolate the microgrid into island mode, where local generation and storage must supply the connected loads.
When the utility grid is stable again, the controller resynchronizes voltage, frequency, and phase before reconnecting.
Key Facts
- Power balance in island mode: P_generation + P_battery discharge = P_load + P_losses
- Electrical power: P = VI for direct current or single-phase ideal circuits
- Energy stored in a battery: E = P × t
- Solar panel output changes with sunlight, panel area, angle, temperature, and efficiency.
- A microgrid connects to the utility grid at the point of common coupling, often abbreviated PCC.
- Before reconnection, the microgrid and main grid must match voltage, frequency, and phase.
Vocabulary
- Microgrid
- A microgrid is a local electric power system that can operate connected to the main grid or independently in island mode.
- Island mode
- Island mode is the condition where a microgrid is electrically separated from the main grid and powers its loads using local resources.
- Point of common coupling
- The point of common coupling is the electrical connection where a microgrid links to the larger utility grid.
- Battery energy storage system
- A battery energy storage system stores electrical energy chemically and releases it when generation is low or demand is high.
- Load
- A load is any device or building that uses electrical power, such as lights, motors, computers, or EV chargers.
Common Mistakes to Avoid
- Assuming a microgrid is always disconnected from the utility grid is wrong because most microgrids normally run grid-connected and island only when needed.
- Ignoring energy storage is wrong because solar and wind output can change quickly, so batteries help maintain power balance and reliability.
- Treating power and energy as the same quantity is wrong because power is the rate of energy use in watts, while energy is the total amount used in watt-hours or joules.
- Reconnecting an islanded microgrid without synchronization is wrong because mismatched voltage, frequency, or phase can damage equipment and trip protection systems.
Practice Questions
- 1 A campus microgrid has a 500 kW solar array producing 350 kW, a wind turbine producing 120 kW, and buildings using 600 kW. If losses are 20 kW, how much power must the battery discharge to keep the microgrid islanded?
- 2 A battery rated at 800 kWh supplies an average load of 200 kW during an outage. Ignoring losses and minimum reserve limits, how many hours can it supply the load?
- 3 Explain why a microgrid controller might reduce EV charging or turn off noncritical loads during island mode even if solar panels are still producing power.