Western Electricity Coordinating Council Releases Long-Duration Storage Assessment

March 3, 2023

by Paul Ciampoli
APPA News Director
March 3, 2023

The Western Electricity Coordinating Council recently released a long-duration energy storage assessment that examines how, with 12-hour duration energy storage, an 80–90% clean energy future with high electrification load can be achieved and what effect this might have on the reliability of the bulk power system.

The purpose of the assessment was to determine whether long-duration energy storage systems mitigate challenges in reaching higher clean energy percentages, as identified in a 2040 clean energy scenarios assessment completed by WECC.

The clean energy scenarios assessment examined increasing clean energy and energy needs percentages provided by non-carbon-emitting resources in 2040 to 80, 90, and 100 percent.

The long-duration energy storage assessment initially sought to examine the impacts on the clean energy percentage of increasing energy storage duration — to 24, 48, 168, and 336 hours.

In WECC’s initial simulations, energy storage charging and discharging cycles for longer
than 24 hours were not used due to modeling options requiring use of static annual user defined
energy prices, thus resulting in lower than anticipated use of storage devices. Therefore, the study,
focused on if an 80-90% clean energy scenario, with load and generation balanced, can be achieved
with 12-hour duration energy storage, the report said.

The study explored the following reliability impacts on the Western Interconnection of these high clean energy scenarios:

• What would be the composition of the resulting renewable and storage mix to achieve 80-90%
  clean energy dispatch with load and generation balanced for an entire year?
• Can additional storage reduce “spillage” due to over generation conditions of renewable
  resources? (In many of the modeling runs, the software was not able to dispatch all of the available renewable resource generation. As a result, the software “spilled” excess renewable capacity, meaning even though the energy was generated, it could not be used to serve load, so it was wasted);
• Could transmission flows in the high energy storage and high renewable energy cases lead to
  reliability risks?

The long-duration energy storage assessment produced a number of takeaways.

One takeaway is that energy storage systems with a 12-hour storage duration modeled over a 24-hour charging and discharging cycle can mitigate daily fluctuations in loads and resource availability.

Also, different modeling tools are needed to model charging and discharging cycles longer than 24
hours.

Another takeaway is that to achieve a 90% clean energy scenario, significant capacity addition was needed for both renewable and energy storage resources. Careful balance between renewables and storage is needed to achieve the desired clean energy targets.

Also, increasing storage and renewable energy capacity also increases the “spillage” of renewable
resources.

Other takeaways include:

• Expanding storage and renewable energy capacity — to reach higher clean energy percentages —
  increases exports from the Northwest, Basin, and Desert Southwest regions due to increased
  solar and wind resource production;
• Increasing energy storage and renewable resources — to increase the clean energy percentage —
  shifts Bulk Electric System peak load from approximately 4:00 p.m. to 1:00 p.m. This shift
  is due to the increased storage charging load during mid-day, when there is a high availability
  of solar energy;
• Significant transmission system enhancements will likely be needed to accommodate the
  increasing proliferation of renewable energy and energy storage systems.

Building on the current 2022 long-duration energy storage assessment, the report said that the following opportunities will increase the understanding of potential energy storage system benefits in 2023:

• Exploring tools for modeling energy storage systems with charging and discharging cycles
  longer than 24 hours.
• Seeking ways to model designated long-duration storage systems to store renewable energy
  otherwise spilled during light-load periods—without the current limitations of the battery
  energy storage system modeling approach.
• Assessing ways long-duration energy storage systems mitigate reliability risks associated with extreme natural events including scenarios with prolonged low availability of variable energy resources or hydro generation.

Click here for the full report.

WECC is a non-profit corporation that exists to assure a reliable bulk electric system in the geographic area known as the Western Interconnection.

WECC has been approved by the Federal Energy Regulatory Commission as the Regional Entity for the Western Interconnection. The North American Electric Reliability Corporation delegated some of its authority to create, monitor, and enforce reliability standards to WECC through a delegation agreement.