Grid ‘transfers’ can account for up to 40% of CO2 — study

Source: By Carlos Anchondo, E&E News reporter • Posted: Tuesday, December 3, 2019

The carbon footprint of consumed electricity varies “significantly” by region and time of day — and electricity “transfers” between grids can constitute up to 40% of greenhouse gas emissions in some parts of the country, according to a new study from Stanford University researchers.

The paper, published yesterday in Proceedings of the National Academy of Sciences, traced the course of electricity across the continental United States throughout 2016 and found it’s possible to track associated emissions in near real time.

Overall, researchers said more than 1.8 gigatons of carbon dioxide was emitted in the United States in 2016 from 4 million megawatt-hours of electricity consumption. But finding precisely where and when those CO2 emissions occur has been too tricky to untangle — until now, according to the study.

In California, for instance, researchers found a whopping 40% of carbon emissions related to electricity consumption came from out-of-state sources like coal or natural gas power plants.

“There are more exchanges in the western grid because production and consumption are not in the same place,” said Jacques de Chalendar, a doctoral candidate in the energy resources engineering department at Stanford, via email. “California imports roughly a third of the power they consume (and thus ‘import’ emissions).”

Better understanding of shifts in CO2 — among other emissions from electricity generation — will be critical to decarbonizing the U.S. electric sector and to achieving climate goals, the study said.

Researchers tracked how emissions flow as grid operators carry out the complex, constant work of balancing electricity supply and demand. Blackouts can happen if electricity generation and consumption stray too far out of sync, so grid operators routinely borrow power from faraway generators — whether coal, wind or some other source — to make up for any shortfalls.

Experts have previously only been able to loosely track emissions data related to these routine transfers of electricity, drawing calculations based on yearly or “at best” monthly data, according to the study. But the amount of electricity consumed — and its associated carbon impacts — can vary quickly based on the needs of a given day.

Researchers analyzed hourly electricity and emissions data from the 66 balancing authorities — typically large power utilities — that collectively operate the entire U.S. grid.

In the western United States, 17% of emissions were attributable to electricity transfers, the study said, less than the comparatively small electricity transfer on the East Coast.

“Ensuring that emissions accounting methods for our electricity systems accurately capture when, where and why emissions are occurring is especially critical as they become more connected and as the role of renewables grows,” the paper said.

Two regions dominate the U.S. emissions footprint from electricity, authors said: PJM Interconnection and the Midcontinent Independent System Operator. MISO had the largest consumption-based carbon footprint, accounting for 21% of U.S. power sector emissions and 17% of the nation’s electricity use. By comparison, PJM constituted 19% of emissions and 20% of electricity.

Daniel Kammen, a professor of energy at the University of California, Berkeley, who edited the study, said the research makes “very clear” how clean energy and final end-use accounting must be linked on an electricity generation map.

“Consumption based accounting is critical because it relates direction to the drivers of consumption,” Kammen wrote over email, “as well as providing a means to check on ‘carbon wheeling,’ where a company might send the ‘green’ energy to one customer … and just make the mix dirtier elsewhere.”

People in regions that export electricity from higher-emitting generating sources suffer from a “disproportionate local air pollution burden,” the paper said. The study found that at Idaho Power Co. the carbon content of imports was “much higher” than local generation, or 625 kilograms per MWh compared with 71 kg per MWh.

In that region and several others, “almost all” of the pollution caused by power generation was not located near the actual users of that electricity, researchers found.

“This is particularly troublesome for the exporters,” the study said. “While the generated electricity physically leaves those regions through the electricity grid, these local pollutants don’t.”

Sally Benson, co-director of Stanford’s Precourt Institute for Energy and study author, said the team’s findings could help businesses or utilities make better choices about emissions tied to power they are getting — particularly if they’re making an effort to reduce pollution.

The researchers’ algorithm allows an “unprecedented” view of data on “where you’re getting your electricity from and what the carbon intensity of that electricity is,” Benson said, “based on the fact that it’s a mixture of electricity from different sources.”

Benson said the data set that’s in the paper is available now and that the team is working on a tool to make the information available in real time on the internet.