Advanced energy storage technology, including lithium ion battery systems, has a number of commercially viable use cases, including frequency regulation and T&D investment deferral. A third application for which advanced energy storage is showing significant benefits is spinning reserve, where storage assets can efficiently increase the reliability and improve the responsiveness of the electric power grid. Advanced energy storage can also release traditional generation—otherwise encumbered by an obligation to provide some amount of spinning reserve— to sell more valuable energy output.
To help ensure consistent availability and reliability of electricity, utilities keep generation capacity on reserve that can be accessed quickly if there is a disruption to the power supply. For example, if a base load generator or a major transmission line delivering imported power goes down, the utility and/or grid operator will access its reserve capacity to compensate.
Typically, this reserve capacity is created by generators that are already synchronized with the power grid but are not operating at full capacity. If backup power is needed, utilities will increase the output of these generators, usually by increasing the rotation of the turbine (hence “spinning reserve”). Typically, a 10-minute response time is a minimum requirement to qualify as spinning, or “operating” reserves.
However, leveraging traditional generation assets for creating reserved capacity creates a number of inefficiencies. For example, because these generators are operated below their rated value, the utility is not maximizing their power output that could be used for base load supply. Also, it requires the use of additional fuel to ramp these generators up in the event that their reserved generation potential is needed, which increases emissions while reducing the net efficiency of the power system.
Alternatively, energy storage can be implemented onto the power grid as spinning reserve assets. These systems provide a cleaner, more efficient mechanism for utilities to compensate for disruptions to the power supply while enabling them to leverage the full capabilities of their generation assets to deliver base-load power. The most advanced storage solutions are also equipped with sophisticated monitoring and control systems, enabling them to detect disruptions in the power supply and communicate quickly with the grid to near-instantaneously discharge and provide the reserve capacity when it is needed.
Some research has shown that there is a direct correlation between speed of response and the amount of capacity needed to mitigate a negative grid operating condition. Essentially, faster response requires less capacity for equally beneficial impact.
Energy storage projects for spinning reserve are currently being deployed in various locations globally, including at a new 500MW power plant being constructed by AES Gener in Northern Chile. This is an important but remote mining region, so maintaining the stability of the electric grid through contingency services like spinning reserve is critical. The advanced storage solution will continuously monitor the condition of the power system. If a significant frequency deviation occurs—for example, the loss of a generator or transmission line—the energy storage system is capable of providing up to 20MW of power within milliseconds. This output is designed to be maintained for 15 minutes at full power, allowing the system operator to resolve the event or bring other standby units online.
The AES Gener project and others leveraging energy storage for spinning reserves showcase how more advanced solutions can reduce emissions while enabling the more efficient use of generating assets by allowing grid operators to run them at their maximum capacity, and release encumbered generation capacity to sell more valuable energy services. In addition, some markets are starting to enact rules that assign high value to this functionality, allowing the owner of the storage solution to accrue monetary benefits, which further validates spinning reserve as a commercially viable business use case for advanced energy storage.
By Chris Campbell, vice president of marketing and business development, Energy Solutions Group, at A123 Systems, a leading developer and manufacturer of advanced Nanophosphate™ lithium ion batteries and energy storage systems for the transportation, electric grid and commercial markets.