The proportion of electricity the United States gets from solar and wind nearly quadrupled between 2011 and 2020. While geothermal generation remained relatively flat, the three technologies combined for an annual increase of nearly 15 percent over that stretch.

Those findings come from a report released Tuesday by the nonprofit Environment America Research and Policy Center and the nonpartisan research organization Frontier Group. The analysis also found that if the current growth rate continues, wind, solar and geothermal would meet current electricity demand levels by 2035 — which is when President Biden aims to have an entirely fossil-fuel-free grid.

“The pace of progress is continuing to pick up,” said Emma Searson, an author of the new report. “That’s exactly what we need to see in years to come.”

Using U.S. Energy Information Administration data, Searson and her colleagues calculated that the United States went from producing 125,820 gigawatt-hours of wind and solar electricity in 2011 to 470,141 gigawatt-hours in 2020. Geothermal generation stayed largely constant and, as of 2020, stood at a relatively low 16,930 GWh.

Solar generation grew particularly quickly, with the report finding a 23-fold increase since 2011. Wind, which started at a higher percentage than solar, saw an almost threefold increase. Three states — Iowa, North Dakota and Kansas — now produce at least half the amount of electricity they consume from wind and solar.

“Prices have plummeted,” Searson said, noting one driver of the surge. A National Renewable Energy Lab (NREL) survey found that from 2011 to 2018, utility-scale solar costs dropped by about 80 percent — and the NREL projects that prices will continue to decline.

“It’s really been a surprise even for people working on it,” said Greg Nemet, an environmental policy researcher at the University of Wisconsin-Madison.

In addition to falling costs, Searson said, public policies and a location’s renewable energy prospects seemed to be other significant factors in the expansion. California, for instance, is by far the national leader in solar electricity generation — nearly five times ahead of Texas, the state in second place.

“That’s no accident. California has enacted really aggressive policies,” Searson said of the role that legislation can play in supporting renewable energy. But, she added, “we’re certainly seeing states that you might not see as obvious renewable energy leaders also stepping out front.”

Many of those are areas with abundant renewable energy potential, such as sunny Arizona and windy Great Plains states like Iowa and Oklahoma, she said. For Searson, that is an indication that even if the political climate isn’t necessarily favorable to renewables, the technologies can catch on in naturally conducive regions. And, the report says, “every state in the country has enough potential from either solar or wind energy alone to supply all of its electricity needs.”

However, some say sustaining the current pace will be a tall task.

“You’ll need some fundamental shifts to continue this growth rate,” said Michael Craig, an energy systems expert at the University of Michigan. “There’s this race between declining costs and this increasing difficultly of deployment.”

Improving transmission systems, he said, will be a major factor in the future of renewable energy. So will social acceptability considerations — namely whether people are okay having solar or wind production at or near their homes.

“The past doesn’t dictate the future,” said Joseph Kane, a fellow at the Brookings Institution think tank who focuses on infrastructure and climate issues. “When you’re starting from a low starting point, that’s going to naturally lead to more optimism. … That doesn’t mean it’s going to be easy to displace some of the fossil fuels.”

According to Ember, a London-based think tank, the United States still produces only 12 percent of its electricity from wind and solar — putting it in the middle of the pack globally. The percentage in both the United Kingdom and Germany is more than double that.

Searson acknowledged that “we have a lot of work,” and she noted that keeping electricity demand in check is as critical as transitioning toward a cleaner supply. “Energy efficiency and energy conservation are just as important parts of the picture,” she said. The report found that, in 2019, efficiency programs in the United States saved 17 percent more energy than they did in 2011.

But ultimately, Searson said she is hopeful about the U.S. trajectory.

“This really visionary target of 100 percent clean electricity is no longer a wild picture,” she said. “It’s something we can imagine.”