Seattle green energy startup LevelTen pulled in $20.5 million this week from a group of investors that for the most part ticked the usual social impact boxes. Except that big name associated with nuclear meltdown.

The Seattle startup took an investment from Exelon Corp., the biggest U.S. nuclear plant operator and owner of Three Mile Island, site of the worst American nuclear accident. That investment was led by Prelude Ventures, San Francisco venture capitalists who focus their investments on carbon reduction. Another investor was Equinor Energy, which touts itself as an investor in renewable energy growth companies.

A startup offering its marketplace that matches green energy sellers with buyers may not seem a natural fit with a nuclear plant operator. Still, Exelon, with $36 billion in revenue last year, provides a big thumbs up to LevelTen’s ambitions.

“The engagement in this round of several global energy partners should only further establish the LevelTen platform,” said Tim Woodward, Prelude Ventures’ managing director who is joining the LevelTen board, in the statement announcing the investment.

For its part, Prelude sees LevelTen’s technology becoming “an essential tool for corporate and industrial procurement of renewable energy,” Woodward said.

LevelTen was born out of the Seattle Techstars accelerator in 2016, and its technology seeks to create a marketplace for renewable energy, matching producers with commercial and industrial customers. It lists more than 1,600 clean energy projects in the U.S. with detailed project information including location, size and power purchase agreement price, so that buyers can compare and research before making a purchase. LevelTen sees its product opening clean-energy purchases to a wider audience, including smaller businesses.

Investors like Exelon may be drawn to LevelTen for a few purposes: one is the feel-good, image boost that comes with a clean energy investment. Another may be in getting in on the ground floor, because at least one expert says LevelTen has the field to itself right now.

“On competitive landscape, I don’t think that LevelTen has any direct competitors,” Eric Gimon, a senior fellow at Energy Innovation, told Karma in an email. He noted that while most deals are facilitated by individual brokers, LevelTen is the only online marketplace platform.

More than $1 billion of renewable energy has been facilitated by LevelTen, according to the company. The potential generating powers equals to 63% of existing wind and solar energy in the U.S., they say.

CEO Bryce Smith said the company’s platform is permitting it to make solar and wind power available to companies that in the past were too small for access. He said only a small number of Fortune 500 companies were able to sign big purchase agreements.

“This exclusionary problem is one we’re committed to addressing,” he said in the statement announcing the funding round. “With this new investment, we will open the door to an international community of buyers, sellers and service providers.”