atcllc.com Using CEMS Data to Estimate Coal-Fired Plant FORs and Scheduled Maintenance Chris Hagman

atcllc.com 2 FORs on large coal-fired plants can have a significant impact on transmission congestion. –Transmission constraints may prevent lower-cost power from getting to load when large low-cost generation is forced off. –FORs and scheduled maintenance can also vary widely on coal-fired plants –Modeling better mimics actual congestion when this variability is captured, i.e. when there is better granularity. Significant Impact on Congestion

atcllc.com 3 Generator Availability Data System (GADS) data is often used to estimate FORs –GADS data can be difficult to interpret –Under-reporting? –Not plant-specific Alternative Approach: Use hourly Continuous Emission Monitoring System (CEMS) data to estimate plant-specific: –Forced Outage Rates –Scheduled Maintenance CEMS data is publically available. GADS Data and Alternative Approach

atcllc.com 4 Method using CEMS data works for baseload plants –CEMS data provides hourly generator output. –Coal-Fired plants are typically "Baseload” and operate all of the time, but for maintenance and forced outages. Hours with zero output are considered either scheduled maintenance or forced outages. CEMS Data Provides Hourly Output

atcllc.com 5 How can we distinguish between scheduled maintenance and forced outage hours? –Summer peaking utilities typically do not schedule maintenance on coal-fired plants during the Summer (when they are needed the most). Assume hours with zero output from June through August are forced outages. –Outages lasting 14 days or longer and not during the Summer are assumed to be maintenance. –Assume the opposite for Winter peaking utilities. Hours with zero output from December through February are forced outages. Partial forced outages are not captured so FORs calculated using the CEMS method may be somewhat lower than actuals. Rules for Applying the CEMS Method

atcllc.com 6 Analyzed 65 coal-fired plants in the 2024 Common Case with Maximum Capacities ranging from 150 to 857 MW. To be conservative, used 10 years of hourly CEMS generation data (2005 to 2014). When FORs and scheduled maintenance are low, relative to actuals, coal-fired plants over-generate in the model. Analysis

atcllc.com 7 Middle Third Sorted Based on CEMS FORs

atcllc.com 8 Top Third Sorted Based on CEMS FORs

atcllc.com 9 Bottom Third Based on CEMS FORs

atcllc.com 10 Using the CEMS method, average FORs and Scheduled Maintenance outage lengths are somewhat higher than current WECC 2024 Common Case values. –Completed analysis last night--may want to refine the rules for analyzing the CEMS data. Forced outages and scheduled maintenance on coal-fired plants can have a significant impact on congestion, especially when multiple plant outages occur at the same time. Conclusion

atcllc.com 11 Questions? Chris Hagman Questions?