MISO 2026/2027 Capacity Auction Preview — Offer Window Opens March 26
MISO's 2026/2027 Planning Resource Auction offer window opens March 26 and closes March 31, with results expected April 28. The grid operator projects a 2 GW increase in load for the planning year, requiring a reserve margin of 137.5 GW against a coincident summer peak forecast of 124.7 GW. Preliminary accredited capacity stands at just 135.6 GW, signaling a potential 1.9 GW shortfall. Midwest commercial buyers in Illinois (Ameren), Indiana, Michigan, and Minnesota should prepare for capacity cost pass-throughs.
The Reliability-Based Demand Curve (RBDC)
The 2026/2027 auction will use the Reliability-Based Demand Curve (RBDC) for the second year, following its debut in the 2025/2026 auction. The RBDC replaces the old vertical demand curve with a sloped curve that better aligns economic incentives with grid reliability needs. Under this framework, capacity prices increase as available supply tightens relative to the reserve margin target, providing clearer price signals to generators considering retirement or new investment.
Seasonal Reserve Margins
| Season | PRM (%) | Risk Level |
|---|---|---|
| Summer | 7.9% | Highest |
| Fall | 11.6% | Elevated |
| Winter | 18.9% | Moderate |
| Spring | 23.4% | Low |
Note: The Summer PRM of 7.9% is extremely tight by historical standards, meaning MISO needs essentially all accredited capacity available during peak summer months.
Why the 1.9 GW Gap Matters
With preliminary accredited capacity at 135.6 GW versus a 137.5 GW requirement, MISO enters the auction with an apparent deficit. While additional resources may register before the offer window, the tight balance means:
- Clearing prices could surge: The RBDC is designed to produce higher prices when supply is tight. If the gap persists, Zones in the Midwest could see clearing prices rival PJM's recent record.
- Load growth is structural: The 2 GW increase is driven primarily by data center development in Indiana, Illinois, and Michigan — load that is unlikely to be curtailed.
- Seasonal risk shifting: Higher winter PRMs relative to summer suggest growing concern about cold-weather reliability, a trend accelerated by ERCOT's Winter Storm Fern experience.
Impact on Midwest Commercial Rates
MISO capacity costs are passed through to commercial customers as part of their supply charges. If the auction clears at elevated levels:
- Illinois (Ameren territory): Downstate IL customers are in MISO and will see capacity costs reflected in their supply rates starting June 1, 2026.
- Indiana, Michigan, Minnesota: All major utilities in these states pass through MISO capacity costs directly to commercial customers.
- Lock rates before April 28: Suppliers will begin pricing MISO capacity risk into fixed-rate contracts as the auction approaches. Contract offers available today may not include elevated auction results.
Key Dates
| March 26, 2026 | PRA offer window opens |
| March 31, 2026 | PRA offer window closes |
| April 28, 2026 | Auction results published |
| June 1, 2026 | 2026/2027 planning year begins |
Lock Your Rate Before MISO Auction Results
Fixed-rate supply contracts executed before April 28 may not include elevated MISO capacity clearing prices.