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Green Blackouts?

Increasing renewable generation threatens reliability.

Fortnightly Magazine - August 2010

Obama administration energy policy targets a 500-percent increase over the next 15 years in solar, wind and tidal power’s share of the U.S. electricity system to 25 percent. If a way isn’t found to stop the North American power grids’ declining ability to respond rapidly enough to shocks, the increase in renewable generation already underway will accelerate stress on the North American power system to the breaking point.

No amount of money spent on a smart grid or on expanding the transmission system will address this problem, while consequent administration pressure on the Federal Energy Regulatory Commission to fast track a solution risks backfiring into no solution at all.

Solar, wind and tidal renewables add stress to a power grid in two ways, as if in exchange for their zero fuel cost. One is by making very rapid random changes in the power they produce. The other is by their physical inability to very rapidly supply energy to arrest the effect on all generators of very rapid random generator output shortages before the effect grows too big on the power system, and thereby to help maintain a more stable continuous balance between supply and demand on the grid.

At the same time, the ability of the three North American power grids (called “interconnections”) serving the United States to provide rapidly enough such arresting energy ( i.e., within seconds of a disturbance) steadily has declined, on the Eastern and Western grids (which are roughly separated by the Great Plains) especially since these were opened in 1996 to wholesale electric power markets. This has been especially true on the Eastern grid (Figure 1) which includes Canada from the Prairies eastward but excludes Texas and Quebec. However the decline had begun years earlier on the grids when for plant safety reasons nuclear power plants were proscribed from suddenly increasing generation to respond to a sudden variation in energy imbalance.

How does an electric power system normally prevent higher levels of stress from reaching the breaking point? The biggest shocks on a grid consist of sudden rapid either loss or excess of power due to loss of a generator, a power line, or a load. An electric power grid defends itself proactively against these shocks by offsetting them as rapidly as possible, specifically by farming out the job to all the generators and loads on the grid—a practice unique to electric power systems among physical systems. The generators are thereby each obligated to provide simultaneously within seconds a small portion of the total offset needed to keep supply and demand steadily balanced on the grid.

One or a few of the generators alone could provide the total offset, but too slowly (by taking as long as ten minutes to ramp up a generator). That adjustment time is critical, because the