Physics of energy generation makes Polis’ 100 percent renewables goal unlikely

““Electric grids are complex networks and interconnections that rely on a steady supply of electricity, but that also must maintain extremely close control of the frequency of the alternating current.

America operates on 60 cycles per second, or 60 Hz. That grid frequency can vary only about 2 Hz in either direction, says Griffey. “These are small variations, but if it drops below that you start kicking off loads,” he said. “Bad things happen and your system crashes.”

The grid is so sensitive to these variations that power producers must provide both reserve capacity to deal with sudden load increases and “grid inertia” to keep the frequency stable.

“You have to have inertia on the system that helps buffer load changes, and inertia is provided by turbines that spin. Renewables don’t have inertia,” said Griffey.

Without the electrical inertia available from fuel-powered, constantly-spinning generators, the entire grid can crash unexpectedly if the wind stops blowing while the sun isn’t shining.

This means that renewables like wind and solar will always require backup generators to provide both inertia and reliable power to take up unexpected loads.

And how much backup is required increases with the amount of renewables in the system.

“The more intermittent capacity you have, or the more unreliable capacity you have, you actually have to increase that reserve margin to carry more backup,” Griffey said.

“In the case of an all-wind system you’re going to be carrying 90 percent, give or take, to back it up because [windmills] only provide 5 to 15% of equivalent capacity,” said Griffey.

By equivalent capacity Griffey means that the advertised theoretical capacity of a wind farm of say 30 megawatts, called the “nameplate capacity,” only ever actually produces a fraction of that amount, called the “efficiency factor.”

Other sources place the efficiency factor of wind generators between 25% and 40%.””
     — Scott Weiser

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Solar and wind power are not practical. The sun doesn't always shine and the wind doesn't always blow.

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