Inertia and the power grid: A guide without the spin

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The power grid is evolving to include ever-higher levels of wind and solar generation—which do not provide inertia, historically a key source of grid reliability. Should system planners and operators panic? A new video and guidebook from the National Renewable Energy Laboratory (NREL) explain why not.

What Is Inertia in the Power Grid?

Inertia in power systems refers to the energy stored in large rotating generators and some industrial motors, which gives them the tendency to remain rotating. This stored energy can be particularly valuable when a large power plant fails, as it can temporarily make up for the power lost from the failed generator. This temporary response—which is typically available for a few seconds—allows the mechanical systems that control most power plants time to detect and respond to the failure.

Why Does Grid Inertia Matter?

Historically, in the U.S. power grid, inertia from conventional fossil, nuclear, and hydropower generators was abundant—and thus taken for granted in the planning and operations of the system. But as the grid evolves with increasing penetrations of inverter-based resources—e.g., wind, solar photovoltaics (PV), and battery storage—that do not inherently provide inertia, questions have emerged about the need for inertia and its role in the future grid.