OAKLAND, Calif. (October 24, 2019)—The increased use of renewable energy in California has not increased the overall amount of air pollution from power plants, according to an analysis released earlier this month by the Union of Concerned Scientists (UCS). The study disproves a claim—at least in California—that putting more solar and wind on the grid will increase air pollution because polluting natural gas plants are frequently tapped to provide energy during peak demand times when renewables are producing less energy.
“On grids that rely on a lot of renewable energy, if those sources aren’t available or demand for electricity is high, for example during evening hours or a heat wave, natural gas plants are often turned on to provide supplemental energy,” said Mark Specht, the study author and an energy analyst at UCS.
Starting, stopping and ramping natural gas plants up and down increases nitrogen oxide emissions (NOx) rates because the technologies to control those emissions are less effective when a plant is cycling on and off. While natural gas plants in California have been ramping up and down more frequently over the past decade to provide that supplemental energy, the UCS study revealed that NOx emissions from California natural gas plants dropped about 50 percent since 2009.
There are two reasons for the drop, according to Specht. “Natural gas generation has declined overall this past decade and older, dirtier plants are being retired. The newer plants have technology that is better able to control NOx emissions.”
NOx, the most common air pollutant produced from the burning of natural gas, is a concern because it causes respiratory problems and reacts with other substances in the air to produce ozone and particulate matter. Exposure to particulate matter is linked to both acute and chronic heart and lung ailments, asthma attacks, increased hospitalizations, lung cancer and death.
“NOx emissions in California could be even lower if power operators didn’t have to start and stop natural gas plants as often,” said Specht. The number of starts across the state at peaker plants—power plants used when there is high demand—have nearly tripled since 2009 as the increase in renewables changed the way the grid is operated. The study found that, nonetheless, in the past three years, as the number of starts has spiked, the downward trend of NOx emissions has held steady.
A North Carolina utility recently claimed its only solution to increased pollution from natural gas plant cycling was to keep its plants running up to 24 hours per day. North Carolina follows California in the amount of installed solar energy capacity.
Specht said continuous natural gas plant operations are not a viable option and instead the best solutions for grids with high amounts of renewable energy are to use less natural gas overall and reduce natural gas plant starts and stops by investing in short- and long-duration energy storage technologies and building a diverse portfolio of renewable generation technologies that can prevent power plant cycling in the first place.
“Natural gas plants do produce more air pollution when they start and stop,” said Specht. “But unlike what fossil fuels companies and utilities in other states are claiming, the solution is not to keep them on or lower air pollution standards. That would worsen the air we breathe and make our climate crisis worse. As natural gas plants are phased out, they should be operated as efficiently as possible with the least harm to people,” said Specht.