Energy Storage is the Smart Choice to Meet Primary Frequency Response Needs

 By Kiran Kumaraswamy

Primary Frequency Response, or PFR, is a critical system service required to ensure the reliability and security of the electric grid. Though necessary, a recent study performed by the North American Electric Reliability Corporation (NERC) showed frequency response in the entire Eastern Interconnection is declining as increased levels of renewable generation and decreased levels of traditional generation plants no longer have enough inertia to supply the necessary system response. Little to no financial incentive exists to provide this critical service, so utilities, policy makers and regulators are now looking to resources that can cost-effectively provide this service and meet other market needs.

Over the last few months, I have been following the discussion in California and other states around primary frequency response (PFR). The Federal Energy Regulatory Commission (FERC) defines PFR service as “a resource standing by to provide autonomous, pre-programmed changes in output to rapidly arrest large changes in frequency until dispatched resources can take over.” In other words, PFR service maintains grid frequency by autonomously increasing or decreasing megawatt output of a standby resource.

PFR is a critical system service required to ensure the reliability and security of the electric grid. A study performed by the North American Electric Reliability Corporation (NERC) in 2012 showed frequency response in the entire Eastern Interconnection declining as increased levels of renewable generation and decreased levels of traditional generation plants no longer have enough inertia to supply the necessary system response. Based on this finding, earlier this year FERC approved revisions to the existing reliability standard (BAL-003) that require balancing authorities across the country to obtain sufficient PFR to maintain interconnection frequency. Regions across the country are now actively working on addressing PFR and ensuring they receive adequate frequency response from generators in their system.

In regions like California, there are several instances where the frequency response achieved from generators in the system is lower than the frequency response obligation (FRO) required based on NERC reliability standards. Because PFR is a service not currently compensated directly by markets in the U.S., there is little to no financial incentive for existing generation owners to provide this much-needed grid service.

Resources do currently exist which can cost-effectively provide this critical grid service. Energy storage can provide cost-effective PFR services and also meet other market needs. Energy storage resources provide both high quality PFR and frequency regulation (secondary control) to electric grid systems. For example, in the PJM regulation market, each megawatt of energy storage provides regulation service that is the equivalent of 2.6 megawatts of traditional generation based on accuracy and performance. AES’ energy storage projects in PJM have provided substantial cost and emission savings to customers for over four years by providing frequency regulation more efficiently than traditional thermal resources.

Energy storage projects developed by AES in Chile offer another example of how energy storage provides autonomous contingency response to maintain grid frequency. The units are programmed to sense frequency deviations and ramp to full output instantaneously to provide support to the local grid and restore frequency. These storage arrays have enhanced grid reliability while lowering overall system costs.

As a specific example, in May 2013 the grid operator in Northern Chile, CDEC-SING, experienced a loss of 640 megawatts of generation out of a maximum of 2,500 megawatts due to a substation trip. Two of AES’ energy storage arrays rapidly supplied 32 megawatts to arrest the frequency decay until other power units could be brought online. This fast response avoided a partial system outage. The batteries recharge at a lower rated capacity and the recharge period occurs shortly after the frequency has stabilized, often taking advantage of over-frequency events.

While storage has already proven itself as a reliable resource for maintaining system reliability in several markets, there is also great opportunity to deploy energy storage at a much larger scale to cost-effectively ensure enough PFR capability to maintain system reliability. A good example can be seen in California where CAISO’s proposed approach considers the use of spinning reserves for PFR; however, relying on these spinning reserves may be inadequate due to the associated timescale. Battery energy storage resources are a smarter choice for providing both frequency response and regulation, as they offer greater precision and control as compared to traditional generation facilities.

In summary, the advent of new regulations, coupled with the cost-effectiveness of advanced energy storage resources, are providing the right signals for service providers to meet the frequency response needs of the system in an economically efficient way – while also enhancing reliability. As utilities and grid operators around the world look for innovative ways to improve the reliability and resiliency of the electric grid, lower system-wide emissions and provide cost savings to their customers, looking to advanced energy storage to provide PFR is a smart choice.




Kiran Kumaraswamy, Market Development Director at AES Energy Storage, is responsible for identifying markets and applications that are attractive for energy storage development and educating potential customers on the benefits of energy storage. His work involves implementing regulatory and policy solutions that create access to key markets. In this role, he also actively monitors working relationships with electricity industry stakeholders, trade associations, and regulators. Prior to joining AES, he worked as a senior manager in ICF International advising private sector clients on wholesale power market issues. He holds an M.S. in Electrical Engineering from the University of Wisconsin, Madison and a B.S. in Electrical Engineering from the University of Madras, India.

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