California ISO to address frequency response amid renewable power gains

It may not be the infamous “duck curve” coming to life, but the California ISO has crafted a proposal to improve the frequency response of the California ISO power grid amid the high penetration of renewable resources.

The performance of frequency response, or the ability of grid operators to match supply and demand amid fluctuations or disturbances in power generation and load, has declined each year from 2012 through 2015, and the trend continued in one event analysis in 2016, the California ISO said in its proposal to address the situation.

In the draft proposal to improve frequency response, the California ISO said it has reviewed its performance trend “and observed increasingly poor performance.”

In a Feb. 9 presentation, California ISO staff noted that when there is a drop in frequency on the power grid, generators directed by the plant’s governors will increase output within seconds to restore system frequency. The California ISO proposal focuses on how the grid operator and its member balancing authority areas respond to restore frequency within the first minute after a frequency event.

“Operations identified the main driver of this trend is largely the result of the increased proportion of renewable generation,” the California ISO said in the proposal, adding that the renewable generation levels will continue to rise as the state reaches its renewable energy goals.

The challenge for the California ISO is that NERC’s frequency response grid reliability standard (BAL-003-1) calls for compliance to begin Dec. 1, and that standard requires grid operators to demonstrate sufficient frequency response capabilities due to disturbances or a loss of generation contingency, according to a Feb. 9 California ISO staff presentation on the proposal.

In its most recent assessment of frequency response performance, spanning 25 events during 2015 and January 2016, the California ISO said it met reliability standard requirements in four of the 25 events.

“Given this trend, the ISO finds its projected performance insufficient to meet BAL-003-1 or support system reliability,” according to the proposal.

Among the solutions in the draft proposal to address the situation are revising the California ISO tariff to clarify internal generator requirements so that governor controls are required to be frequency responsive in accordance with good utility practice with minimum governor performance settings, according to the California ISO staff presentation.

The draft proposal also would have the California ISO propose to transfer a portion of its frequency response obligation to external balancing authority areas through a request for proposals process.

“A second phase of this initiative will evaluate more comprehensive market solutions to procure frequency response such as a market product,” California ISO said in the proposal.

The draft proposal was posted for comments, with a comment deadline of Feb. 23, in anticipation of filing it with the California ISO board for the board meeting March 24-25, according to the California ISO staff presentation.

The draft proposal is solely designed to address compliance with a NERC standard and not in response to the high levels of renewables being added in California, a California ISO spokesperson told TransmissionHub Feb. 12.

“Yes, we have to take into account the frequency response capabilities of renewables,” but the NERC standard is driving the proposal and it is not to address operations associated with the “duck curve” chart, the California ISO spokesperson said.

Dating back several years, the California ISO’s “duck curve” chart was an illustration of how large amounts of solar photovoltaic resources could challenge the grid operator’s ability to match supply and demand during the course of one day.

The California ISO spokesperson emphasized that frequency response is what takes place after an event or disturbance, and is not based on the output of renewable resources alone.

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The Clarion Energy Content Team is made up of editors from various publications, including POWERGRID International, Power Engineering, Renewable Energy World, Hydro Review, Smart Energy International, and Power Engineering International. Contact the content lead for this publication at

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