Using CEMS Data to Estimate Coal-Fired
Plant FORs and Scheduled Maintenance
Chris Hagman
12-15-15
atcllc.com
Significant Impact on Congestion
• 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.
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GADS Data and Alternative Approach
• 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.
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CEMS Data Provides Hourly Output
• 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.
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Rules for Applying the CEMS Method
• 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.
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Analysis
• 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.
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Middle Third Sorted Based on CEMS FORs
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Top Third Sorted Based on CEMS FORs
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Bottom Third Based on CEMS FORs
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Conclusion
• 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.
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Questions?
• Questions?
Chris Hagman
chagman@atcllc.com
608-877-7134
atcllc.com
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