Results from carbon emissions data compared year over year have revealed the United States electricity sector is continuing to get cleaner with coal generation decreasing and renewable energy on the rise.
Compared to the same time last year, total U.S. power generation fell by 4 percent in Q2 of 2019, and the carbon intensity of the sector, measured in pounds of CO2 emissions per megawatt-hour, dropped by 9 percent.
As has been the case since 2016 when natural gas became the largest source of electricity, coal generation in Q2 2019 was down 19 percent compared with Q2 2018. This year, power generation from coal provided 21 percent of the nation’s electricity, while natural gas provided 36 percent. Burning natural gas produces only about half of the direct CO2 emissions that coal does, per unit of energy generated.
"We're in the middle of an energy transition right now, and the biggest part of that story in the U.S. is how swiftly coal has been declining over the past decade," said Costa Samaras, assistant professor of Civil and Environmental Engineering and Power Sector Carbon Index co-director at Carnegie Mellon University. "The decline of coal can be attributed to the rise of natural gas, the continued improvement of renewables, and energy efficiency efforts."
Renewables saw considerable growth over the past year. Compared to 2018 Q2, generation from solar increased 10 percent and generation from wind increased 7 percent. Together, wind and solar accounted for 11% of U.S. power generation in 2019 Q2. Hydropower generation provided 8%. However, even with the increase, the renewable energy sector is driven largely by utility-scale projects rather than small-scale residential generation, like rooftop solar panels or individual wind turbines. That must change in order for renewable energy to become a larger part of the nation’s electricity generation.
Still, Samaras says he expects renewable sources to increase in the coming years.
"Wind and solar power are getting more and more competitive in electricity markets," said Samaras, pointing to the falling production costs as a significant driver of renewable energy.
Nuclear power remained the largest zero-carbon source of electricity in the U.S., accounting for 20% of total generation.
The Power Sector Carbon Index, which comes out of Carnegie Mellon University’s Scott Institute for Energy Innovation, relies on publicly available data, but compiles information from disparate datasets and standardizes the calculation of carbon intensity to provide a comparable baseline for policy makers, academics, industries, think-tanks, and the public.