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EPRI Develops Better Methods for Calculating Reserves

Grid operational changes that improve reliability typically increase costs. An EPRI study of Hawaii’s Oahu grid reveals that grid operators can have their cake and eat it too: More robust methods for quantifying the necessary capacity of operating reserves can increase reliability and reduce costs.

Increasingly, operators rely on reserves to accommodate intermittent renewable energy generation. The challenge is to determine the optimal reserve capacity needed based on anticipated conditions. Too much can be costly, and too little can make the system less reliable. Many of today’s methods for calculating reserve capacity are “static” and do not adequately account for changing system conditions. Consider this simple example: At night when there is no solar generation, operators do not need reserve to account for a potential decrease in solar output.

EPRI identified potential enhancements in the methods used by Hawaiian Electric to determine reserve for Oahu. Researchers proposed new dynamic methods that can calculate real-time reserve needs based on historical system variability and uncertainty, then guide the on/off cycling of power plants throughout the day (rather than run them 24 hours a day). Simulations demonstrated that the methods can improve reliability by reducing the risk of being short on capacity during contingency events. Simulations also showed that the more efficient use of reserves could save Hawaiian Electric more than $21 million annually, given Oahu’s high penetration of renewables. The utility is planning to test EPRI’s methods in its grid operations.

EPRI has developed software (called Dynamic Assessment and Determination of Operating Reserves, or DynADOR) that grid operators can use to calculate reserves, incorporating the advanced methods demonstrated in the Hawaii study. Other utilities are evaluating the use of these methods for operations and for planning studies as they prepare for increasing penetration of renewables.

Key EPRI Technical Experts:

Erik Ela
For more information, contact techexpert@eprijournal.com.

Artwork by James Provost