Cal-ISO seeking input on storage examples, usage limitations

Because energy storage and distributed energy resources have the potential to alleviate grid congestion in California, the California ISO (Cal-ISO) wants to make sure any market barriers or operational limitations of those resources are addressed, the Cal-ISO said in documents leading up to an April 4 webcast on the issue.

The first phase of the Cal-ISO’s energy storage and distributed energy resources (ESDER) proceeding was conducted in 2015, culminating in the Cal-ISO board in February 2016 approving a proposal that supports improved integration of storage and demand response resources in the Cal-ISO wholesale market.

Phase Two of the ESDER proceeding is now underway, with an issue paper released in March and a webinar held April 4, according to the Cal-ISO presentation for the webinar.

The main focus of the ESDER initiative is to lower barriers and enhance the ability of transmission grid-connected energy storage and distributed energy resources to participate in the Cal-ISO market, the grid operator said in the March 22 issue paper. The issue paper defined distributed energy resources as those on the distribution system on either the utility side or customer side of the meter, including rooftop solar, energy storage, plug-in electric vehicles and demand response.

“The number and diversity of these resources are growing and they represent an increasingly important part of the resource mix. Integrating these resources is expected to help lower carbon emissions and add operational flexibility,” the Cal-ISO said in the issue paper.

The Cal-ISO ESDER proceeding followed efforts by the California Public Utilities Commission (CPUC) to address energy storage matters, including directing utilities to procure different levels of storage resources. In a previous rulemaking, the CPUC examined opportunities for storage to displace upgrades to the transmission grid.

In the April 4 presentation, the Cal-ISO noted that transmission investment is mainly driven by peak load conditions, which may not be reduced by adding distributed generation (DG), and that new DG resources do not offset the cost of transmission that was previously approved and is currently in service.

As the power industry is learning how different storage technologies behave and are best managed, it is likely that there will be operational limitations and that the grid operator may need to consider different types of modeling for non-generator resources (NGR), the Cal-ISO said in the presentation. Examples of possible limitations could be the minimum number of charges or discharges of battery storage devices and different ramping rates or charging/discharging times based on the state of charge of batteries, the presentation noted.

Current Cal-ISO modeling of NGR assumes that all resources perform consistently within charging and discharging operations, but that consistency might not apply for certain storage technologies or resources that perform differently across different regions, the grid operator said.

The Cal-ISO “is seeking input to better understand the physical use limitations that storage resources may have and invites stakeholders to provide storage technology-specific examples and use cases that could be considered for NGR modeling,” according to the presentation. Comments on the issue paper are due April 18.

The CPUC has identified multiple-use applications of storage resources in the scope of its energy storage rulemaking, and to avoid redundant and potentially divergent efforts, the Cal-ISO will address that topic by participating in that CPUC proceeding, according to the April 4 presentation. If the CPUC proceeding identifies issues that should be addressed in a Cal-ISO initiative, or develops proposals that the Cal-ISO should consider adopting, the Cal-ISO can begin a new initiative or expand Phase Two of its ESDER proceeding, the Cal-ISO said.

The CPUC and Cal-ISO are planning to hold a joint workshop on May 2-3, according to the presentation.