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Duke Energy Application Points Finger at Solar for Increased Pollution!!!

image credit: Photo: Duke Energy

This recent article published by the North State Journal ( states "increase solar power might be leading to an increase in the very emissions alternative energy sources aim to reduce."

This assertion is connected to cycling of Duke Energy natural gas plants as they "must scale back electric generation to accommodate solar energy surging onto the system when the sun rises, and power back up when the sun sets and solar energy dissipates."

This and any other assertion that plant cycling is caused by any specific driver needs to be demonstrated by a cycling causality study. Such a study has been documented in a report from Renewable Impacts LLC and is a available free by contacting Jim Schetter, President Renewable Impacts LLC at 303-726-4828 or email at .

James (Jim) Schetter's picture

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Bob Meinetz's picture
Bob Meinetz on Aug 26, 2019 7:05 am GMT

Jim, it seems that power plant data might be a more reliable indicator than a hypothetical "cycling causality study". If accurate, Duke's evidence is conclusive:

"Without any solar power in the mix, “a typical combined cycle combustion turbine emits NOx at approximately 9-11 lb/hr, assuming 24 hours of ‘normal’ operation,” Crawford said. That is equivalent to 264 pounds of NOx emissions daily. When those same plants are operated to supplement solar power facilities, daily emissions more than double to 624 pounds a day, based on a table in Duke’s application.

If DEQ agrees to Duke’s alternative operating scenario, a combustion turbine would emit 381 pounds of NOx daily — still 44% more pollution than operating without any solar power on the grid."


James (Jim) Schetter's picture
James (Jim) Schetter on Aug 26, 2019 8:05 pm GMT

Hi Bob,

Correct me if I am wrong. Are you agreeing that the predicted doubling of NOx emissions is 100% due to solar resouces?


James (Jim) Schetter's picture
James (Jim) Schetter on Aug 27, 2019 8:05 pm GMT

Just for the record, a "cycling causality study" is not hypothetical as it uses actual publicly reported power plant and load hourly data to identify all drivers within a balancing authority responsible for power plant cycling. As a result, cycling causality analysis is actually more reliable than the article comparisons for the following reasons:

1. The conclusions found in the article are the result of a classic "with" and "without" sceanrio comparison which is often used in modeling work. In this case, the "with" scenario is to include solar and the second "without" scenario does not include solar resources. The weakness in this approach is that the "with" and "without" sceanrio comparisons defined here control for only one variable - solar. Any suggestion that this is the only reason (cause) for any scenario differences is a simplistic approach to a complex grid issue. Professionals in the industry understand that there are many interrelated drivers regarding cycling and any resulting emission changes. Two key cycling drives missing from this comparison are system load and wind which certainly should be part of any analysis involving cycling induced emissions claims. Cycling causality analysis can simultaneously include system load, wind, solar and any other cycling drivers that may be defined and would clearly be a more reliable and complete analysis.

2. I view the "typical" and "normal" conditions defining the CC emissions to be hypothetical. Cycling causality analysis uses actual publicly reported generation and load data making it a more reliable indicator than data defined as "typical" or "normal."

3. Our cycling causality methodology was used to study the CAISO system and is described in our free white paper download available here:

Bob Meinetz's picture
Bob Meinetz on Aug 28, 2019 7:17 pm GMT

James, thanks for your reply, and yes - the assumption that a single factor is responsible is not conclusive, or even that the data provided is accurate. Duke could either be dishonest, or inept in interpreting gathered data.
The cycling causality on CAISO is consistent with my own, less rigorous estimates. With your permission I'd like to forward your white paper to associates in CA energy who would be interested, and hopefully in a position to offer you some business?

James (Jim) Schetter's picture
James (Jim) Schetter on Aug 29, 2019 12:48 am GMT

Hi Bob,

Good to hear from you and to learn you have developed cycling causality estimates. I would be interested to talk with you about your approach down the road. Our cycling causality white paper is for public consumption/comment so please feel free to distribute it to your associates. Happy to discuss power plant cycling impacts and causality anytime.





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