Solar Power Can Increase Air Pollution

Solar Power Can Increase Air Pollution

Duke Energy has determined that solar power on the grid results in increased emissions of nitrogen oxide (NOx), and that it’s possible solar power will also increase carbon dioxide (CO2) emissions.

The data, provided by Duke Energy, showed that when solar power usage increased on the grid, it was necessary for natural gas power plants to throttle back and operate less efficiently.

It also showed that when solar was at its maximum output, more NOx pollution was  released than if no solar had been used and natural gas had been relied on entirely.

The Duck curve illustrates what’s happening. First, natural gas power plants have to scale back in the morning as the sun rises and then rapidly increase output in the evening when the sun sets. 

Since solar power is intermittent on cloudy days, the natural gas power plants must throttle up and down during the day which results in even greater inefficiencies and greater release of NOx.

Duck Curve developed by CAISO

Duke Energy is requesting the North Carolina Department of Environmental Quality (DEQ) to revise it’s air quality permits to allow Duke to run its natural gas plants more efficiently.

Duke said, that 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, and that is equivalent to 264 pounds of NOx emissions daily.” Based on information provided by Duke, NOx emissions increase to 624 pounds per day when those same plants ran with solar power on the grid.

If DEQ agrees to Duke Energy’s request, a natural gas plant would emit 381 pounds of NOx daily which is only a 44% increase.

Once again, we find unintended consequences from mandating the use of solar power on the grid.

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