Five years after it introduced rules to curb generators’ uninstructed deviations from dispatch instructions, MISO said such departures are worse than ever and it likely needs to strengthen rules and software.
“Despite an initial increase in dispatch-following performance since the 2019 uninstructed deviation changes, the fleet is now performing below” pre-rule levels, MISO Market Settlements Adviser Mollie Dawson said at a May 23 Market Subcommittee meeting. She said the high number of departures from dispatch instructions remains attributable to renewable energy sources.
MISO said it will mount a “multifaceted approach” that may include new market rules and operational tools. The RTO said it will draft the changes in collaboration with its Independent Market Monitor and stakeholders.
“Our current rules are not meeting the challenge of the impact,” Dawson said.
Dawson said new potential fixes might include MISO introducing settlement penalties, stepped-up requirements to follow MISO-generated setpoints, capping use of manual dispatch and improving its forecast output of intermittent resources.
Dawson said MISO will consult with its Independent Market Monitor in July and bring a slate of potential solutions to stakeholders for evaluation in August.
MISO four years ago placed harsher tolerance limits on generation operators’ deviations from its dispatch orders. The rules determine a generator’s deviations by comparing the time-weighted average of a real-time ramp rate with a day-ahead offered ramp rate, while allowing for 12% tolerance from setpoint instructions. The rules at the time eliminated the RTO’s “all-or-nothing” eligibility for make-whole payments, instead allowing generators to collect full payments when they respond to dispatch instructions at 80% or higher over an hour, while excluding payouts when performance rates fall below 20%. Units operating between those two thresholds earn make-whole payments in proportion to performance.
Before then, generators in MISO were flagged when they deviated by more than 8% from dispatch signals over four consecutive intervals. (See MISO Plans for New Uninstructed Deviation Rules.)
MISO IMM David Patton last year recommended MISO improve its near-term wind forecasting to better reflect the characteristics of wind generation output. He said MISO currently uses a “persistence” forecast that assumes wind resources will produce the same amount of output as it most recently observed. MISO stakeholders have said that forecasting style is problematic when wind dies down suddenly. (See MISO Shelves IMM’s Transmission Planning Recommendation in State of the Market Report.)
After MISO implemented its uninstructed rules in mid-2019, Patton said more wind operators migrated to using MISO’s wind forecasts instead of their own, less accurate forecasts.
