Renewables and the Big Inertia Problem

How rotational mass plays a critical role in grid resilience and how we're mimicking it to save our modern grid.

It’s 2:35 pm and boiler pressure is dropping rapidly at the Lackawanna natural gas power plant. The plant powers over a million homes in Pennsylvania, generating 1,485 megawatts. One of the three boilers going offline puts a substantial dent in the accessible power in the PJM Interconnection.

The grid needs to adjust, and to adjust it needs time—specifically, a few seconds to several minutes. This crucial buffer is afforded almost accidentally, through the design of the generator itself. The General Electric 7HA combustion turbine spins an 800,000-pound rotor that will freely spin for as much as 30 minutes after shutdown. This inertial spin provides exactly the runway needed to reallocate power and keep service uninterrupted for Pennsylvanians.

But what about those newer power sources that don't have the benefit of several hundred tons of spinning inertial force? That's one of the challenges facing the modern grid, increasingly reliant on solar, wind, and wave power.

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