The world needs radical new energy technologies to fight climate change. In 2016, Quartz reported that a group of billionaires—including Bill Gates, Jeff Bezos, Jack Ma, Mukesh Ambani, and Richard Branson — launched Breakthrough Energy Ventures (BEV) to invest at least $1 billion in creating those technologies.

Now, 18 months later, Quartz can reveal the first two startups that BEV will be investing in: Form Energy and Quidnet Energy. Both companies are developing new technologies to store energy, but taking completely different approaches to achieve that goal.

The way to reach the world’s climate goals is straightforward: reduce our greenhouse-gas emissions to zero within the next few decades. But the energy technologies that can help us get there tend to need lots of money and long lead times to develop. That’s why many conventional investors, who are looking for quicker returns, have burned their fingers investing in clean tech, according to qz.com.

The wealthy investors of BEV want to remedy that. Their $1 billion fund is “patient capital,” to be invested in only companies working on technologies capable of cutting global carbon emissions by at least 500 million metric tons annually, even if they may not provide returns on investment for up to 20 years, according to qz.com.

BEV’s first task was to assemble a group of experts, including academics, entrepreneurs, and industry specialists. In 2017, these experts announced a list of energy technologies they believe were both underfunded and extremely promising in emissions reduction: grid-scale energy storage, zero-carbon liquid fuels, micro grids, low-carbon building materials, and geothermal energy.

Qz saw financial documents indicating BEV’s investment in two energy-storage startups. A BEV spokesperson confirmed the investments and said the company is actively looking to invest in other companies.

The most widely used form of energy storage currently is pumped hydro. Quidnet’s technology uses water to store energy, but without the need for rivers or dams. Instead, it uses excess electricity to pump water into the underground shale rock found in new wells dug for the purpose or in abandoned oil-and-gas wells. After water fills up tiny cracks in the rock, forcing more in creates pressure, which compresses shale like a spring. When energy is needed, the pressure is let off and the water that gushes out is used to run turbines that re-generate electricity.

Before BEV’s investment, Quidnet had raised $1.5 million through the Clean Energy Venture Group and Prime Coalition. In 2016, the startup ran tests in Texas and Nevada to show that the technology can work. Next, it will use the $6.4 million raised through BEV and Evok Innovations on more field trials to develop the technology.

Also, Form Energy has raised $11 million: $2 million from MIT’s Engine Fund and $9 million from BEV, Prelude Ventures and other small investors, for a new type of battery. “Thanks to lithium-ion batteries, storing energy for less than a day is a solved problem,” says Ted Wiley, Form’s CEO. “Our goal is to find solutions to store energy for weeks, months, and maybe even across seasons at a fraction of the cost of current technology.”

Though Form won’t disclose technical details, Wiley says it currently has at least two types of chemistries he believes could enable the company to create cheap batteries capable of storing large amounts of energy for long durations. One of the candidate chemistries, Chiang confirmed, is a “sulfur-flow battery,” which he wrote about in some detail in the journal Joule in October 2017.