Regardless of what 2025 was like in the U.S., the transition to clean energy is still progressing, both abroad and at home. It is not, however, advancing at the same pace across all clean energy sectors.
As part of our annual survey of energy world insiders, Heatmap asked dozens of climate experts which key decarbonization technologies they thought were furthest from widespread deployment.
By far the most common answer — with about two in five experts agreeing — was fusion energy.
As Heatmap’s Katie Brigham has reported, even the technology’s most optimistic proponents don’t expect fusion plants to hit the grid for at least another decade. And even if fusion becomes commercially ready, bringing down its cost to a level where it can compete with existing renewable sources of electricity will be yet another challenge.
“Even though scientifically we may get there in the next few years, I don’t know if it will result in a rapid shift in our power sector in a decade,” Ilaria Mazzocco, an expert in China’s energy policy, told Heatmap. “Can we restructure our entire power sector to deal with this completely novel technology then? And on top of that, can we make it cheap enough so that it makes sense?”
Another respondent who works in energy policy was more skeptical. “I won’t believe it ’til I see it,” they said.
Costa Samaras, the director of the Scott Institute for Energy Innovation at Carnegie Mellon University, named fusion as his pick, but said he hasn’t given up hope that it will one day come to fruition. “Having been part of the fusion energy leadership team at the White House,” Samaras said, “I'm a firm believer we should ramp up federal efforts to accelerate the fusion development timeline.”
Though sustainable aviation seems to be closer to deployment than fusion, experts don’t expect that industry to take off anytime soon, either. Both sustainable aviation fuel and electric aircrafts face significant challenges to getting off the ground — so to speak. SAF relies on scarce feedstocks, requires a lot of energy to produce, and costs far more than petroleum-based jet fuel. And batteries are heavy, making them impractical for commercial air travel.
Respondents also beefed, so to speak, with lab-grown meat and were reluctant to gas up on hydrogen. Cultivated meat technology has advanced rapidly, but key members of the Trump administration have no love for the product. Hydrogen has struggled to bring its cost in line with other energy sources such as natural gas, and the Trump administration has rolled back federal support for the technology.
There are a few companies, however, that are making advances in some key decarbonization technologies. When Heatmap asked experts which looked the best to them, geothermal energy companies took the top two spots: Fervo Energy, which is slated to open a 100-megawatt enhanced geothermal system next year, and Zanskar, a startup that utilizes artificial intelligence to find naturally-occurring reservoirs. Quaise Energy, which uses a process known as millimeter-wave drilling that involves using very high frequency radio waves to heat and vaporize rock, also scored a mention.
Respondents named more than two-dozen companies in total. Answers spanned an array of industries, from nuclear energy (Kairos Power and Westinghouse — “While they are a legacy company, if they engage successfully to scale their proven nuclear design, the impact could be massive,” Armond Cohen, executive director of Clean Air Task Force, told us), long-duration energy storage (Form Energy, Hydrostor, Antora Energy, and Rondo Energy), and grid software (GridAstra, which has created a digital platform to alleviate grid congestion, and ConnectDER, which manufactures meter socket adapters to accelerate clean energy device connection), to sustainable agriculture (Nitricity, which produces plant-based fertilizer, and Pivot Bio, which makes microbes that deliver nitrogen to plants).
Rather than naming just one company, one solar advocate chose the half-dozen leading Chinese solar panel and battery manufacturers. “These guys are together producing more energy now than the Seven Sisters of the oil industry,” they said.
Despite President Trump’s full-throated support, the U.S. oil industry hasn’t significantly boosted production in the past year. Faced with steep tariffs on supplies and equipment and increased production from OPEC+ countries, crude oil prices sank in 2025, which means that U.S. companies aren’t exactly rushing to ramp up drilling.
Editor’s note: This story has been updated to correct Samaras’ professional affiliation.
The Heatmap Insiders Survey of 55 invited expert respondents was conducted by Heatmap News reporters during November and December 2025. Responses were collected via phone interviews. All participants were given the opportunity to record responses anonymously. Not all respondents answered all questions.
