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Green Blackouts?

Increasing renewable generation threatens reliability.

Fortnightly Magazine - August 2010

That ex post action by a few generators—especially some deployed by the control operator where the shock originated—to restore frequency to its pre-shock position is called “automatic generation control” (AGC) or regulation and is what most control automation software provides.

In answer to the first and second questions of how the grids deteriorated and what to do about it, no sustainable, preferably market method yet has been developed to properly value or pay generators for providing very rapid governor response offset service, nor to penalize the bad control behavior by generators and load that causes very rapid and big supply/demand imbalances that trigger deployment of this service. Without such a method, the past decade and a half of steady decline in rotating mass and governor response to increasing shocks on the electric power grid, relative to the size of the grid, will continue until the interconnection cannot arrest in time a rapid power loss big enough to trigger a wide-area blackout. This brings us to an answer to the third question of how to reduce the very rapid variability in renewables’ collective output and improve their collective ability to respond very rapidly to sudden shortages on the grid.

Not all power generators are equally good at providing very rapid always-available governor response and rotating mass. Nuclear provides rotating mass but no governor response to sudden shortages. Wind, solar, and tidal are the worst: Not only do they provide no such rotating mass or governor response to shortages, but instead they are randomly contributing to an increasing extent to the very rapid supply and demand imbalances that require more rotating mass and governor response provided exclusively by all the other generators and by loads. Technology to improve the very rapid reliability of wind, solar, and tidal generators is limited and very expensive. For example, storage devices like batteries and flywheels can be used to provide very rapid substitute power for a sudden drop in output, but only once since they take a long time to recharge.

So the wind, solar or tidal generator would need an enormous spare battery capacity on hand, enough to respond to all the sudden major frequency drops that can occur during the long recharge period of a battery required to respond to a single major very rapid frequency drop, a very expensive proposition. Alternatively, renewable generators could buy very rapid response capacity and rotating mass from traditional generators. In any case, wind, solar, and tidal generators need to be charged/penalized for stressing the grid in order to incent them to buy the huge amount of very rapid response capability they need to fairly share the burden of all the other generators of responding to the very rapid stresses on the grid, including those caused by the wind, solar, or tidal power generator.

Meanwhile, deadband control technology also has been steadily contributing to the decline in the North American power grids’ ability to respond to very rapid changes in electrical frequency. Deadbanding software has been increasingly applied to the operation of governors on generators to delay/eliminate their response to