In 1975, Danish physicist Bent Sørensen published a paper examining the possibility that his country could run on 100 percent renewable energy. Appearing in the journal Science, it could have been an important moment for beginning to look seriously at transforming the way the world produces energy.

Instead, crickets.

“It was not a loved idea at all,” said Christian Breyer, a faculty member at LUT University in Finland, in a video interview from his office.

But things have changed. In the last five years or so, as the world faces the escalating toll of climate change, the concept of 100 percent renewable energy gotten a much more serious look from scientists, policy analysts and governments.

Breyer is the lead author of a new paper published by IEEE Access tracing the development and growth of this idea, and the pushback. The concept of 100 percent renewable energy hasn’t quite reached the mainstream in most large economies, but it’s getting close, he said.

I should specify that Breyer is not a neutral party in this discussion. He and the roughly two dozen co-authors of the paper include some of the best-known researchers who focus on, and advocate for, 100 percent renewable energy. This includes Mark Jacobson of Stanford and Auke Hoekstra of Eindhoven University of Technology in the Netherlands.

The paper is a valuable primer for understanding what 100 percent renewable energy means, where these ideas have found the most support in government and what others say are the major flaws.

One of the people cited is Amory Lovins, an American physicist who wrote about the possibility of an all-renewable system in 1976. He would go on to be co-founder and chief scientist of the Rocky Mountain Institute, now called RMI.

The paper also notes that 48 countries pledged at COP 22 in 2016 to reach 100 percent renewable energy in the electricity sector.

The electricity sector is the easiest part of the economy for which to make a transition to renewable sources, which is why that’s the part that’s getting the most attention from governments right now, Breyer said.

The paper includes research on sector-specific transitions, like the power sector, and on economy-wide transitions. Some are limited to specific countries, and some are global in scope.

In most countries, a shift to renewable energy is largely driven by a combination of wind and solar power. The growth of solar is a mix of utility-scale systems and smaller installations on rooftops. Other renewable sources, including hydropower and geothermal, among others,  also may play a role.

Considering that some utilities used to say that even 10 percent renewable energy wasn’t workable, it’s not surprising that the idea of 100 percent renewable energy has faced steady criticism.

The paper says “a consensus is starting to emerge that many of those early criticisms do not hold when examined in detail.”

But there remains plenty of skepticism, including from prominent and well-regarded energy researchers. One example is a 2018 paper co-authored by Jesse Jenkins, which said a shift to 100 percent renewable energy may be possible, but the costs and technical challenges are high when moving from a mostly renewable system to an all-renewable system. The challenges have to do with building many interstate power lines and accounting for the variable nature of wind and solar, among other issues.

One of the biggest points of conflict among researchers is whether nuclear power should be a significant part of the energy mix going forward. Also, some analysts say that natural gas power plants, when paired with carbon capture technology, could be a valuable resource on the margins of a future grid.

At times, this is a debate between 100 percent renewable energy and 85 to 90 percent renewable energy, both of which would be much cleaner than what we have now.

I’m not going to delve too deeply into the specifics here, other than to say that the Biden administration is firmly in the camp that views nuclear and some fossil fuels as part of the mix. The larger point is that discussing the possibility of 100 percent renewable energy won’t get someone laughed out of the room the way it might have decades ago.

Breyer said momentum is on the side of the researchers and organizations that are looking at how 100 percent plans can be implemented.

Going forward, I’ll look to Denmark and other countries on the leading edge of the transition to see what’s working and what isn’t, and how it influences the rest of the world.

Other stories about the energy transition to take note of this week:

California to Adopt 2035 Ban on Sales of New Gasoline Vehicles: The California Air Resources Board will vote Thursday on a policy that would ban sales of new gasoline vehicles starting in 2035, one of the first such bans in the world. Daniel Sperling, a member of the board, confirmed the plans and said the measure is likely to pass, as Ella Nilsen reports for CNN. This step builds upon a 2020 executive order by Gov. Gavin Newsom that said new vehicles sold in the state by 2035 must have zero carbon emissions. “This is monumental,” Sperling said. “This is the most important thing that CARB has done in the last 30 years. It’s important not just for California, but it’s important for the country and the world.”

The New U.S. Climate Law Will Reduce Carbon Emissions and Make Electricity Less Expensive: U.S. consumers are poised to save money on their electricity bills under the nation’s first comprehensive climate law—perhaps more than $200 billion over the next decade, economists project. The potential price drop flies in the face of an argument made for years by climate action foes that a move to cleaner power will mean higher energy prices for U.S. homes and businesses, as my colleague Marianne Lavelle reports for ICN. “The clean energy tax credits will lower our cost of service, which in turn reduces the cost to customers of our energy transition,” said Lynn Good, Duke Energy’s CEO, in the company’s earnings call.

Expansion of Clean Energy Loans Is the ‘Sleeping Giant’ of the Climate Bill: The new federal climate law authorizes as much as $350 billion in additional federal loans and loan guarantees for energy and automotive projects and businesses. Those provisions are not as widely known as others in the bill, but they could be a major catalyst for helping companies involved with the transition to clean energy, as Ivan Penn reports for The New York Times. “This is a sleeping giant in the law and a real gold mine in deploying these resources,” said Dan Reicher, who was an assistant energy secretary in the Clinton administration. “This massive amount being made available is a big deal.”

Rising Fuel Prices and the Federal Climate Law Are Likely to Spur Rapid Renewable Energy Growth: The United States is now on track to get 62 percent of its electricity from carbon-free sources by 2040, a share that has risen because of the rising cost of fossil fuels and the passage of the federal climate law, according to an analysis by S&P Global Commodity Insights. Analysts said this is likely a conservative estimate of what’s to come in a rapidly changing energy landscape, as Emma Penrod reports for Utility Dive. In other words, the actual shift to clean energy could end up being faster than the ever-faster projections being made by experts.

This Power Line Could Save California—and Forever Change the American West: The American West is on the cusp of immense change because of a clean energy boom. Renewable energy projects are cropping up across the region, connected by a planned interstate power line, and driven by the power demands of cities like Los Angeles and Denver, as Sammy Roth reports in the first part of a new series for the Los Angeles Times. Some people and groups along the route of the 732-mile line are raising concerns that the project, and the wind and solar projects that would follow, would harm the character of the region.

Inside Clean Energy is ICN’s weekly bulletin of news and analysis about the energy transition. Send news tips and questions to [email protected].