In a roundabout way, coal is solar-powered. Millions of years ago, swamp plants soaked up the sun’s energy, eating carbon dioxide in the process. They died, accumulated, and transformed over geologic time into energy-dense rock. This solar-powered fuel, of course, is far from renewable, unlike solar panels: Burning coal has returned that carbon to the atmosphere, driving rapid climate change.
But what if humans could reverse that process, creating their own version of coal from plant waste and burying it underground? That’s the idea behind a growing number of carbon projects: Using special heating chambers, engineers can transform agricultural and other waste biomass into solid, concentrated carbon. Like those ancient
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