April 15, 2021
Planning for the unexpected: How energy storage can be a grid resiliency asset
This is a guest blog post from DNV, a Level 1 sponsor for #ESACon21. Connect with DNV at Virtual #ESACon21 April 21-22. Later in the year #ESACon21 will bring the industry together in Phoenix, AZ, December 1-3. Learn more about DNV’s energy storage services here.
From the rolling blackouts during California’s heatwave last summer and subsequent power cuts to mitigate wildfire risks to the recent Texas deep freeze in February, grid resiliency has become one of the industry’s watchwords. Energy storage is commonly cited as a key technology for increasing resiliency across the energy value chain.
For residential and C&I utility customers, energy storage provides short-term reliability to a single customer. Its use in these applications is straightforward: Provide power to critical loads during outages, acting similarly to an onsite backup diesel generator. Generally, the duration of this backup power depends on the size of battery and its state-of-charge when the outage occurs. For a standalone battery, a grid outage lasting a few hours to whole day may be mitigated. If paired with a rooftop solar system, the backup duration can last for weeks. For C&I customers, storage primarily provides load management services for the customer, but also may provide demand response or ancillary services to the grid. These larger batteries and sophisticated inverters create resiliency for critical operations, such as in a hospital, manufacturing plant, or data center. Likewise, aggregators might corral several residential and C&I batteries and provide similar services, with increasing access as ordered in the Federal Energy Regulatory Commission Order 2222, but in practice aggregation is not yet a mature resource for the grid.
Providing resiliency to a single customer is one thing, but on the other side of the meter, battery storage as a resiliency tool becomes more complicated. To a small degree, residential, C&I, and microgrid customers with battery storage can benefit the system, depending on willingness and agreements with the utility. In a catastrophic situation, these customers with onsite backup can help a utility distribution system respond to supply issues by shedding their load from the grid, creating islands of powered customers and reducing strain on central grid supply. To that extent, energy storage can help from the ground up.
But currently the number of customers with onsite energy storage is low. At one point in the recent ERCOT outage, almost half of the generating fleet was offline. ERCOT wound up shedding 10GW of load and for many hours—needless to say, that’s far, far more than storage could provide immediately, much less over more than a few hours without some means to recharge the batteries. Reducing this outage footprint can facilitate faster restoration, reducing the burden of cold load pickup, while potentially allowing for community resiliency hubs to provide critical support services to neighbors without power.
On the grid, energy storage projects typically serve more than one purpose. While a project provides backup reserve during a catastrophe, its purpose for the most part is to offer ancillary services and balance grid supply and demand in real time to mitigate fluctuations in frequency. Theoretically, more storage on the grid would help in a catastrophic situation, but this will require market mechanisms to value storage during the year—realizing the benefits and opportunities of storage in normal operation, while reserving capacity for grid resiliency and reserves.
More important, regulation can impede the practical and valuable use of storage in a catastrophic situation. In many jurisdictions, for example, regulation wants to classify storage as either a generation or a distribution asset, but not both. Also, the HVAC system for the battery storage itself requires power for cooling—as batteries can produce heat during operation which must be managed to maintain battery health. In many jurisdictions, storage auxiliary load must be connected to and supplied by the retail electricity provider in the region and pay retail rates for this site electric load. In an emergency situation that calls for a storage plant to act as a local resiliency asset for the grid, the local retail provider itself may be unable to provide power to the battery plant. This arrangement potentially defeats the purpose of using storage to aid in grid resiliency and restoration.
ERCOT has recently taken steps to allow for energy storage resources to self-serve and self-report auxiliary loads as part of NPRR 1020. Such systems may allow for increased grid resiliency during extreme grid stress conditions. Perhaps that is a sign of things to come.
Energy storage will prove to offer utilities larger load-shedding opportunities. But accepting the dual nature of storage on the grid—and making it easier for projects to monetize this value—will begin the process of building resiliency across systems. This will require technology to facilitate communications that help the asset respond not only to market signals but also supply and demand issues.