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Balance of Power

Large grids can integrate more wind—without major burdens.

Fortnightly Magazine - May 2011

be improved by 10 percent and 20 percent.

The study first determined how much operating reserve (quick-start and spinning) would be needed to meet CPS2 requirements if the 2,500 MW of wind and solar wasn’t added. Then the study determined how much additional operating reserve (quick-start or spinning) would be needed if the 2,500 MW of renewable wind and solar was added in the balancing authority (see Figure 1) .

The tables show the incremental operating reserves needed to integrate the additional 2,500 MW of wind and solar as opposed to the amount of operating reserves needed if no additional wind and solar power was added to the balancing authority. The capacity is needed in both the upward (increasing MW) and downward (decreasing MW) direction. The results are lower than they would have been if there was no diversity in the technology or the location of the wind and solar generation. The study was done with both 90 percent and 95 percent CPS2 targets. FERC’s first level violation doesn’t occur until the CPS2 value falls below 90 percent. However, many utilities have expressed a desire to target at least 95 percent for additional safety purposes. The table shows the additional amount of operating reserves in megawatts needed when attempting to achieve the 95 percent level of performance as compared to what would be needed if shooting for the FERC-indicated level of 90 percent.

The negative values in Figure 1 indicate that if improvements in load forecasts are accomplished at the same time as improvements in the ability to forecast renewables, then the renewables can be added even with reductions in operating reserves and still meet CPS goals.

The conclusion of this study is that the additional operating reserves needed are very much influenced by the ability to forecast the renewable output as well as the CPS2 target that is desired. This study also demonstrates that the diversity of the load and the added renewables can possibly cause a reduction in the need for operating reserves in comparison to a future without any new renewables, as long as a reasonable forecast can be made of the renewable generation.

Wind-Only Balancing Authority: Wind developers often run into difficulty in acquiring needed balancing services. Balancing authorities either claim they can’t perform the balancing services or state that if requested, they will file a tariff with FERC that has a very high charge for providing these services. As a result, wind developers occasionally consider forming their own balancing services and building gas-fired generation to accomplish the balancing.

Analyses performed for two such developers concluded that a wind developer can’t provide the balancing services it needs nearly as cost effectively as an existing balancing authority. First, a wind project doesn’t have retail load to include in its proposed wind-only balancing authority. Load and wind together provide a diversity that’s more effective than wind alone.

Second, balancing authorities generally have non-wind supplies already in place—such as resources that help meet planning reserve requirements. These assets can provide some of the operating reserves needed to perform any additional