Oil giants Chevron Corp. and Saudi Arabian Oil Co. have joined Bill Gates and other venture capitalists in pumping more than a half-billion dollars into a handful of long-duration energy storage startups this summer. The spending spree injects critical cash into the young companies as they seek to compete with conventional pumped hydroelectric storage and lithium-ion batteries for a share of the fast-growing global market.

In separate transactions announced Aug. 25, Saudi Aramco Energy Ventures LLC participated in a $100 million series C funding for Switzerland-based Energy Vault SA, while Chevron Technology Ventures LLC helped Massachusetts energy storage hopeful Malta Inc. exceed more than $60 million in a series B round. Breakthrough Energy Ventures LLC, a firm founded by Gates, also contributed to Malta's funding.

Energy Vault and Malta are developing nonelectrochemical technologies in bids to provide days or weeks of energy storage, compared with the typical two to four hours enabled by lithium-ion battery stations.

"As the world transitions to renewable energy, there is a huge, unmet need for energy storage solutions that can manage intermittency and grid resiliency, which our current options just cannot offer," Energy Vault spokesperson Juliana Burns said in an email. While pumped storage and lithium-ion batteries dominate the electricity storage market, they face significant "scalability, economics and environmental risks," Burns added.

Energy Vault plans to use its fresh funds to begin a rollout of its large-scale gravity-based technology in the U.S. in the fourth quarter of 2021 ahead of a broader global build-out in 2022. It is offering energy storage options that range between just a few hours to a day or more of capacity.

A spinoff from Alphabet Inc.'s "moonshot factory" X Development LLC, Malta is working on a thermal energy storage approach it says can efficiently bottle up to 200 hours of energy while also generating heat for industrial uses and district heating. The company, which disclosed a co-development partnership with German engineering firm Siemens AG in July, hopes to build its first 100-MW long-duration storage project in the mid-2020s.

"Malta has the potential to be a key enabler of grid stability as renewables have become a greater portion of the energy mix," Barbara Burger, president of Chevron Technology Ventures, said in a statement.

Gates' storage bets approach big tests

Malta is one of several long-duration energy storage companies in Breakthrough Energy Ventures' portfolio that are raising large sums to accelerate their commercialization. Another company on the firm's roster is Form Energy, which announced the completion of a $240 million series D financing for its iron-air battery system Aug. 24. The first major test will be with utility Great River Energy in Minnesota, where the company plans to deliver its inaugural project in 2023.

Breakthrough Energy Ventures investment Ambri Inc. said Aug. 9 that it raised an additional $144 million to help build factories for its liquid-metal batteries. Gates' firm also invested in Oregon-based ESS Inc., a developer of iron flow batteries that intends to go public through a merger of more than $1 billion with a special purpose acquisition company before October.

ESS would not be the first long-duration storage aspirant to go public via SPAC transaction. Eos Energy Enterprises Inc., a New Jersey-headquartered company building zinc-based batteries, went public in November 2020. In July, Eos announced a $100 million investment from an affiliate of Koch Industries Inc.