In North Carolina, when the word “solar” is mentioned, everyone takes a close look. It was no different recently when some media articles advanced the idea that solar power is actually causing more air pollution.
The basis for this was an air permit Duke Energy submitted for some of our gas combustion turbines that ramp up and down more since additional solar has been added to the energy grid.
But to say solar is causing more air pollution? That may be some faulty logic. It's like saying an electric vehicle is bad since it will increase your electric bill, while neglecting to mention the cost savings of not buying gasoline. There are many positive aspects of solar energy. It contributes about 5% of North Carolina’s energy needs with no greenhouse gases, and more is on the way.
North Carolina is #2 in the nation in solar capacity, behind only California. That’s due to favorable policies that prioritize clean energy and a lot of hard work by many. We’ve got more than 3,000 megawatts of solar in the Carolinas to date, and we expect a total of about 7,000 megawatts of solar coming onto our system by the end of 2025.
The increase in solar capacity is a sign of the very positive transition that’s under way to deliver the cleaner energy our customers want. That increase in solar has increased the need for operational flexibility for some of our gas plants to compensate for solar’s intermittency. Gas units are cleaner burning and more flexible resources than coal, which means we can more easily ramp them up and down as needed to balance out renewables. However, ramping gas units emits slightly more air emissions because they were designed to run at a steady load.
We are seeking permit modifications at some gas units to maintain the reliability our customers expect under the new operating conditions we’re experiencing today. Combustion turbines, for example, are uniquely positioned to meet system demands as we add more solar. They come online quickly and can adjust load much faster than other generation sources. These units were permitted at a time when we served customers with much more coal, and they were intended to run primarily during times of peak demand.
We’re in a different place today, and we must operate our system differently. Our customers expect nothing less.
We are pursuing these permit changes to reduce the need to curtail solar facilities and to avoid dispatching coal units to meet peak customer demand when combustion turbines are at or near their permit limits. If we can’t ramp down gas units, then we’d have to export excess energy to other regions through limited transmission capabilities (which will only exacerbate over time) or turn down our nuclear units. Nuclear’s slower ramp rate could create challenges meeting customer load, and it risks higher carbon emissions to supplement that energy.
Since 2005, Duke Energy has decreased carbon dioxide emissions by 31%, sulfur dioxide emissions by 96% and nitrogen oxide emissions by 74%. This comes from a power facelift – adding advanced air controls, retiring nearly 6,200 megawatts of coal and replacing that with more efficient natural gas and zero-emitting renewables. We expect to retire more than 1,200 megawatts of additional coal by 2025.
So while a slight increase in emissions may occur at individual units, our fleet will continue to see an overall decrease in air emissions from this transition to solar and other cleaner energy resources.