Bill Gates’ $1bn Breakthrough Energy Ventures (BEV) has announced it is expanding its renewable portfolio, with a series of investments into clean energy technology startups selected for their promise of tackling climate change.

The investment amounts have not been disclosed, though BEV’s total investment to date totals $100m.

Among the startups chosen is California-based Fervo Energy, which is looking to harness fracking techniques for the geothermal industry to convert the earth’s heat into a source of clean energy. The group is planning to apply such techniques to boost electricity production in existing geothermal sites, as well as new locations.

The firm said it will use the investment money to progress in the field deployment stage of testing, working to refine its ‘enhanced geothermal systems’.

Geothermal power is an attractive low-carbon energy alternative as it is a constant source of power, unlike wind and solar which rely on atmospheric conditions and time of day.

BEV also chose grid-storage startup Form Energy, solid-state battery firm QuantumScape, MIT’s Commonwealth Fusion Systems, biofuels firm DMC Biotechnologies, and Pivot Bio, a firm looking to develop an alternative to nitrogen fertiliser.

CarbonCure, which works to store carbon dioxide in concrete, pumped hydro storage firm Quidnet, and Zero Mass Water, which created technology to extract water from the air, also received investments.

BEV receives its funds from billionaire patrons such as Amazon’s Jeff Bezos, former New York City mayor Michael Bloomberg, Virgin’s Richard Branson, Alibaba’s Jack Ma, and SoftBank’s Masayoshi Son.

BEV executive director Rodi Guidero told Quartz: “We are a unique fund with investors who are patient and flexible,

“Our goal is to find the companies that will have the greatest impact on accelerating the energy transition and help them in whatever way we can.”

To be selected for BEV investment, startups need to demonstrate their technology is scientifically sound and is a viable means of reducing greenhouse gas emissions by a minimum of 500 million metric tonnes.

The venture, which was first set up in 2015, made its first two investments in June this year. These were in battery storage company Form Energy, and Quidnet Energy, the latter of which is working to develop a technology based on hydropower methods, pumping water into subsurface shale formations.