For decades, grid operators took inertia for granted. Coal-fired, nuclear and hydro plants supplied it in abundance, their heavy generators rotating in step with grid frequency.
Inverter-based resources (IBRs) put that stability at risk. Solar panels and batteries produce DC, which inverters convert to AC, and while wind turbines do spin, their electronic converters decouple them from grid frequency.
Because IBRs do not physically synchronise with the grid, they provide no traditional rotational inertia. As they displace conventional plants, total inertia falls – most sharply during hours of low demand and high renewable output, such as late nights or sunny afternoons.
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Speed over spin
The counterweight for IBRs is Fast Frequency Response (FFR). Mechanical governors take seconds to adjust steam or water valves. Power electronics detect a frequency change and adjust output in a fraction of a second.
Operators can hold wind, solar or BESS output slightly below maximum, creating headroom, then inject power the instant frequency drops. They can programme wind turbines to draw kinetic energy from their spinning blades, lifting output for several seconds to slow a decline.
They can also fit large, non-critical industrial loads with sensors that disconnect them automatically when frequency falls below a set level.
Examples of FFR and load response solutions
Inverter dispatch: Holding IBRs at slightly less than maximum output (creating headroom) and using power electronics to instantly inject power when a frequency drop… [download the Energy & Storage Volume to continue reading]
