In earlier years, transmission system constraints in southwestern Minnesota were the predominant factor driving total annual wind curtailment in the Northern States Power service area, while in the future, congestion throughout the Midwest ISO and resulting Locational Marginal Pricing (LMP) in the MISO energy market are expected to be the main drivers of curtailment.
That is according to a May 22 filing by Northern States Power at the Public Service Commission of Wisconsin that was prompted by a PSC staff request for more information as part of an annual fuel review proceeding. The response was written by David Horneck, Manager, Generation Modeling Services Quantitative Risk Services at Xcel Energy Services.
“The shift in reasons driving curtailment is the result of significant transmission improvements in southwestern Minnesota that included the 825 MW and Buffalo Ridge Incremental Generation Outlet (BRIGO) projects,” said the Xcel Energy (NYSE: XEL) subsidiary. “The present transmission limit in southwest Minnesota is 1250 MW. Curtailment in this area is now expected to occur primarily during prior outage conditions while curtailments during system intact conditions should be minimal.”
NSP added: “However, in other areas of the MISO region, particularly in Iowa, a significant number of wind generation projects recently went into service or will go into service this year. These projects may affect LMP pricing in the MISO regional energy market and the Company expects that it will become more common for curtailment to occur due to regional system congestion and negative LMP in the MISO energy market.”
To better manage this congestion, MISO and the industry are moving towards a Dispatchable Intermittent Resources (DIR) system, the utility reported. DIR will influence curtailment decisions and should result in better management of wind resources.
Under this system, wind facilities will be registered as DIR, receiving set point instructions every five minutes and will use automated generation control technology, which will automatically control wind project output according to MISO electronic signals. DIR will allow wind farms to operate more like traditional generating facilities and, as a result, MISO will be able to more quickly and accurately respond to system conditions, Northern States Power wrote.
A number of transmission projects are underway that will benefit transmission capacity and should reduce the level of wind curtailment on the Northern States Power-Minnesota system. For example, the CapX 2020 Brookings County-to-Twin Cities 345-kV line is expected to increase the transmission limit in southwest Minnesota to 1,950 MW when it is completed in 2015.
In addition to transmission projects developed by Northern States Power, MISO has identified and approved 215 new transmission infrastructure projects, including 17 Multi-Value Projects (MVPs), to accommodate the planned and expected generation expansion in the MISO footprint. Several MVP projects may have a positive impact on reducing curtailment of NSP-owned and power purchase agreement (PPA) wind facilities.
“Estimating curtailment caused by regional congestion and economics and prior outages is difficult because of the many unknowns involved,” the utility said. “In addition, although transmission investment and expansion should help alleviate curtailment for existing wind projects, it is difficult to project how much additional wind generation may be added in the region in coming years and whether and to what extent it may outpace transmission expansion. Because of this, the Company believes that using the most recent 12 months of actual curtailment costs provides a reasonable estimate for the upcoming test year. However, system conditions and wind project development are dynamic and actual curtailment costs may vary from that projected based on historical curtailment costs.”