Peak Outage Forecasting Delayed
Stakeholders learned Wednesday that MISO will delay for another year a plan to account for previously un-forecasted planned outages at times of peak demand after getting mixed feedback from market participants.
Speaking at an April 11 Resource Adequacy Subcommittee meeting, MISO Resource Adequacy Coordinator Ryan Westphal said the RTO will wait until the 2020/21 planning year to implement a new, unspecified calculation that accounts for planned outages during peak demand, which could increase the RTO’s planning reserve margin requirement.
MISO had proposed to factor the effects of planned and maintenance outages on peak in its loss-of-load expectation (LOLE) study by the 2019/20 planning year. (See MISO RASC Zeroes in on Priorities.)
Westphal said some stakeholders asked the RTO investigate further before making any changes to the LOLE study. Others urged it to define “safe” periods during the summer months to take planned outages.
Director of Resource Adequacy Coordination Laura Rauch said MISO would delay accounting for planned outages on peak until it develops solutions based on a more comprehensive conversation about the RTO’s shifting resource availability. (See MISO Looks to Address Changing Resource Availability.)
Some stakeholders expressed frustration that the RTO first presented the issue as requiring expeditious treatment, then moved it into a discussion about resource availability and needs, only to again this month single it out to proceed separately. (See MISO to Fold Outage Forecasting into Larger Resource Effort.)
Reprieve for Out-year Import and Export Limit Estimates
MISO is taking a cue from stakeholders and switching gears on a previous proposal to discontinue its practice of forecasting long-term capacity import and export limits, instead proposing to modify the process that produces the forecast.
MISO’s Matt Sutton said the RTO expects by early 2019 to revise its process for predicting capacity transmission limits for its 10 local resource zones. It had proposed in February to altogether scrap out-year import and export limits, saying results were too unreliable and volatile, but stakeholders countered that the limits provided useful information. (See “Scrapping Out-Year Import and Export Limit Estimates?” MISO Resource Adequacy Subcommittee Briefs: Feb. 7, 2018.)
While the RTO still plans to compile the long-term limit estimates, it will use more zone-specific information, including data from past Planning Resource Auctions and the Organization of MISO States-MISO annual resource adequacy survey.
Sutton said the RTO would not commit to annual restudies for capacity zones that don’t experience notable changes.
“If a zone could potentially bind, a study isn’t necessary every year unless a significant supply or transmission change occurs,” he said. “The number of studies is being reduced significantly. … We’ll have fewer zones to review.”
The selective study process will allow MISO to focus on zones that could bind on their import and export limits or carry capacity surpluses beyond their export capability, Sutton said.
The more thorough process to estimate out-year limits should spark discussions around new transmission and generation projects and the impact of external system changes on capacity zones, he said, not just the usual conversations about transfer limits, constraints and redispatch options.
MISO will pass its recommendations for improvements to its stakeholder-led Loss of Load Expectation Working Group, which will produce a new prediction methodology for stakeholder review as early as September, Sutton said. He asked stakeholders to submit written comments on the RTO’s plan by April 27.
Different Method for Economic Uncertainties in LOLE Study?
MISO is exploring how to improve its modeling of economic load uncertainties in the LOLE study.
For the 2018/19 planning year, the RTO relied on a GDP growth comparison to account for the uncertainties, which increased the annual planning reserve margin by 0.2 percentage points year-over-year.
In June, MISO will have a 17.1% planning reserve margin, which represents the extra generation the RTO should have on hand to meet a probability of shedding load no more than one day in 10 years. MISO maintained a 15.8% planning reserve margin in the 2017/18 planning year.
MISO staff have attributed the increase to an upswing in generation outages and a change in the dispatch model for demand resources, but it was partially offset by reduction in anticipated load growth. The RTO last year also added the new modeling step to capture economic load uncertainty that increases risks associated with high peak loads, which also boosted the reserve margin. (See MISO Planning Reserve Margin Climbs to 17% for 2018/19.)
“We’re reviewing our methodology and investigating other approaches for the 2020/21 planning year model,” MISO Resource Adequacy Senior Engineer William Buchanan said.
In future years, the RTO may model economic uncertainty using a calculation based on comparisons between forecasted and actual demand in past years, Buchanan said.
— Amanda Durish Cook