Batteries, fusion, and hydropower: Meet the 24 clean-energy startups that Bill Gates is backing

• Microsoft cofounder and former CEO Bill Gates is the second richest person in the world, with a net worth over $100 billion.
• He's invested a sizeable chunk of cash into clean-energy companies, largely through a billion-dollar fund he spearheads called Breakthrough Energy Ventures.
• Most of the startups he funds address three solutions Gates says are necessary for the clean-energy transition: Long-duration storage, nuclear energy and carbon capture, and power transmission.
• Business Insider compiled a list of the 24 clean-energy companies that Gates has invested in, using data from PitchBook.
• Visit Business Insider's homepage for more stories.

Bill Gates is rich. His net worth is on the order of $100 billion, according to Forbes' real-time billionaires list, making him the second-wealthiest person on the planet.

He's also one of the most generous, as measured by how much money he's given away. Through the Bill and Melinda Gates Foundation, Gates and his wife have dished out about $50 billion since 1994 to support public health, education, and development.

But what Gates receives less attention for is his investments in startups - of which there are dozens. Many of them fall into the category of clean energy.

"What's needed are affordable ways to bring clean energy to nearly a billion people who deserve more access to electricity," Gates said in a video that's part of his personal blog, Gates Notes. "That's why I'm making investments in clean, affordable, and reliable ways to generate electricity, and I'm encouraging others to do the same."

Gates' most public venture vehicle is a $1 billion fund he spearheaded with a coalition of other extremely high-net-worth individuals called Breakthrough Energy Ventures (BEV). Richard Branson, Michael Bloomberg, Ray Dalio, and Vinod Khosla are all investors in BEV, one of the world's most active clean-energy venture funds.

Read more: The top funds making bets on the clean-energy industry

"Our goal is to generate a financial return on our investments, each of which will have the potential of significantly reducing greenhouse gas emissions," the fund's website says.

Gates has also invested in startups through other funds including Gates Ventures, Cascade Investments, and Village Global, according to the startup finance database PitchBook.

Most startups he backs are working on one of three solutions that Gates says the world needs "for the transition to clean electricity," according to his blog.

The first is long-duration energy storage - essentially, big batteries that can store power for days or months.

"Finding ways to store that energy to use after the sun sets and the wind stops blowing is a big challenge we need to solve," he wrote in a blog post.

The second is a mix of nuclear energy and carbon capture, a seemingly unusual pairing. Citing an MIT study, he said that if the energy transition includes nuclear power and carbon capture and storage technologies - which can reduce emissions from fossil fuel plants - it would "make carbon-free electricity up to 62 percent cheaper than using renewables alone."

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Finally, he says we also need high-voltage, long-distance power lines that can send direct current from renewable energy sources to areas of demand.

"Connecting our renewable energy supply with demand will require us to build transmission lines that can handle large amounts of power over very long distances," he said.

Business Insider compiled a list of clean-energy startups that received investment from Gates or one of his investment funds, according to data from PitchBook and company statements.

The startups below are listed by how much total capital they've raised in increasing order.