GRAVITY IS emerging as the best bet in solving renewable energy’s biggest problem — intermittency. As countries step up renewable energy capacity addition, there is growing urgency to develop long-duration energy storage systems that could be installed alongside green power generation to balance out the variability in renewable power, given that green generation is not always in sync with the electricity demand cycle. Energy Vault, a developer of utility-scale storage technology backed by Japan’s SoftBank Group and the venture arm of Saudi Aramco, is offering a solution that promises to deploy utility-scale energy storage solutions, including proprietary gravity-based storage, to...