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Bloom Energy Corporation

A maker of solid-oxide fuel cells, Bloom Energy builds the Bloom Energy Server — boxy units that quietly turn natural gas, biogas, or hydrogen into electricity without burning anything, powering data centers, factories, and utilities. Its roots trace to founder K.R. Sridhar's NASA work on making oxygen for Mars; when that mission was shelved, he flipped the idea to make power on Earth. The fuel-cell stacks are built from cheap sand-like materials, and the company's name hints at the idea of clean energy "blooming" wherever it lands.