By Jason Fordney
CAISO is developing new tools to deal with the variable output from the increasing amount of renewable and non-dispatchable generation on its grid, an effort that could bring fundamental changes to California’s resource adequacy rules.
The tools are meant to deal with the highly variable output of new wind and solar generation and changes in net load on the CAISO grid. The grid operator must not only properly balance generation and demand, but also avoid reliability violations and accommodate policy objectives such as renewable integration.
“The system is evolving and the challenges are evolving,” CAISO Principal of Renewable Generation Clyde Loutan said in an stakeholder call Wednesday. He added that “we are encountering operational challenges on the system that we need to understand.”
Through its Flexible Resource Adequacy Criteria and Must Offer Obligations 2 (FRACMOO2) proceeding, the ISO is proposing to introduce new variations of its flexible resource adequacy capacity product, which is intended to increase the ramp rate of the flexible capacity fleet that is becoming more critical to integrating new renewables.
The bulk of the current proposal is designed as short-term modifications to the flexible capacity criteria to emphasize start-up and minimum run times. CAISO is exploring the use of intertie resources but does not yet have a specific proposal. It hopes to have a program in place in time for the 2020 resource adequacy year. A separate initiative will develop a long-term flexible capacity solution and a resource adequacy roadmap in conjunction with the California Public Utilities Commission.
“The proposed short-term solution is unlikely to be sustainable long-term because the forecasted three-hour net load ramps could exceed the available flexible capacity in several years under this proposal without additional enhancements,” CAISO said in its revised straw proposal.
The package is designed to address the changing characteristics of the grid as CAISO requires quicker ramping speeds within shorter time cycles. While the steepest three-hour net load ramp in 2015 was about 10,600 MW, those ramps are projected to reach about 16,800 MW by 2020, with one ISO estimate putting hourly ramps as high as 7,000 MW by that time. New flexible capacity products would be designed to address variability and uncertainty down to five-minute increments.
The proposal is divided into an operational aspect and a capacity procurement workstream, Johannes Pfeifenberger of the Brattle Group said in a presentation during the call. Brattle has been developing a proposal for CAISO’s flexible capacity procurement framework. Addressing the issue requires a better understanding of the physical capability of the system and flexible and non-flexible resources, he said.
There was broad opposition to a previous ISO flexible capacity proposal, according to a CAISO presentation. Critics contended that the plan conflated three separate drivers that should be dealt with more independently: curtailment of renewables, risk of generation retirements and maintaining a reliable grid.
During the Aug. 2 call, CAISO officials were asked if they have considered putting more limits on how quickly variable resources are allowed to ramp up or down, as is done in ERCOT.
“We are trying to look at all solutions right now,” Loutan said. But ERCOT has different operating characteristics, less non-dispatchable generation and different frequency requirements, he said, noting also that Texas is not interconnected with other regions, unlike California.
CAISO said it has been considering limiting the ramp rate of renewables to manage swings in generation output, but oversupply and minimum load requirements put more focus on flexible resources and start times of flexible capacity resources. The ISO proposed to require a flexible capacity resource have a start-up time of less than 4.5 hours and minimum run time of less than 4.5 hours.
CAISO is accepting comments on FRACMOO2 until Aug. 16, with a draft final proposal planned for December. The initiative also requires coordination with the PUC and other agencies with generation resource adequacy jurisdiction.
The ISO hopes to submit a final product to the Board of Governors next summer, followed by implementation in 2020.