Energy storage is a good option for frequency response, a storage trade group will tell the Federal Energy Regulatory Commission this month.

Markets would be less efficient and "system costs greater than necessary if resource owners are mandated to provide frequency response service from generators more suited to provide energy and capacity,” the Energy Storage Association wrote in previously filed comments. 

The group is responding to FERC's request for supplemental comment on its November 2016 notice of proposed rulemaking (NOPR) to begin the process of revising its interconnection rules for both large and small generators. FERC’s concern was that fewer generators were providing primary frequency response.

According to ESA, requiring generators to provide frequency response could produce an oversupply of frequency response headroom, imposing additional system costs. The group noted that many generators are not well suited to provide frequency response because doing so can lower operational efficiency, which will eventually result in higher system costs. Additionally, requiring all generators to provide frequency response would fail to create a market signal.

On the other hand, energy storage, particularly batteries, are well suited to provide frequency response, ESA said. They are fast responding and do not lose efficiency by needing to reserve headroom. In its comments, ESA cited studies by the Electric Reliability Council of Texas that found 1 MW of fast responding resources could be substituted for 2 MW of primary frequency response resources during some system conditions.

Not designed to address storage

FERC’s NOPR (RM16-6-000) was not designed to address energy storage issues, but energy storage became an issue as the process wore on, spurring a call for supplemental comments in August from groups concerned about the NOPR’s effect on small generators and then an extension of the initial Sept. 14 deadline to Oct. 9.

​FERC’s NOPR cites a report by the North American Electric Reliability Corp. (NERC) that found “approximately 30 percent of generators in the Eastern Interconnection provided primary frequency response, and that only approximately 10 percent of generators provided sustained primary frequency response.”

In its NOPR, FERC proposes making it a requirement that generators, both synchronous and non-synchronous, install and enable primary frequency response capability as a condition of interconnection.

Primary frequency response should not be confused with frequency response, which could also be called secondary frequency response. Primary frequency response is an automatic, nearly instantaneous response by generators to deviations in frequency. Frequency regulation is a second line of defense in balancing the grid — at least in organized wholesale power markets, it is provided as a paid service.

For purposes of primary frequency response, frequency deviations are measured by metrics such as “droop” and “deadband.” If a generator trips offline or a large load leaves the grid, frequency can drop enough to create instability and even cascading blackouts. Generators and motors with large, heavy rotors add inertia to the grid and can help dampen the effect of dips in frequency, and many generators have mechanical or electrical governors that can help return frequency to balance. But the spread of variable speed motors, the retirement of baseload, synchronous generating stations, and the proliferation of non-synchronous electrically connected variable energy resources such as wind and solar power has resulted in a “significant decline in frequency response in the Eastern and Western Interconnections,” FERC’s NOPR states.

Frequency response not standard for renewables

FERC cites another NERC report that says almost 42 GW of synchronous generating plants retired between 2011 and 2014 and an Energy Information Administration report that nearly 14 GW and of coal and 3 GW of natural gas-fired plants retired in 2015.

While technological advances have enabled wind and solar plants to have the ability to provide primary frequency response, historically that has not been a standard feature. In addition, wind and solar plants often operate at maximum output, leaving no capacity or headroom to provide primary frequency response.

The simple response would seem to be to require all generators to be able to provide primary frequency response. FERC states that the costs are not prohibitive and not so different for large and small generators. That is disputed by some small generator interests, such as the American Public Power Association and the National Rural Electric Cooperative Association. They said their members would be disadvantaged if they had to provide the same primary frequency response ability as large generators.

In the notice seeking supplemental comments, FERC acknowledged that its original NOPR did not propose provisions specific to electric storage resources. Several commenters noted that by not taking into account energy storage’s unique characteristics, the NOPR requirements could pose an unduly discriminatory burden on energy storage resources. The ESA, in particular, said the requirements could result in “adverse impacts on electric storage resources.”

Large potential impact

If ESA's positions are supported at FERC, it could be “quite impactful” for the energy storage industry, the group's policy director, Jason Burwen, told Utility Dive.

“The simplest solution to the problem would be to let the RTOs decide” on how frequency response is provided, Burwen said. Failing that, ESA recommends that frequency response be made a compensated market product, he said.

That approach would coincide with FERC’s market-based approach, Burwen said. And it comes as the agency prepares to take up the compensation for reliability issue in another form. The Department of Energy last month charged FERC with implementing a NOPR to compensate baseload generators for reliability and resiliency.