In 1920, a young German engineer named Albert Betz peered down at his calculations. Although interest in renewable energy was a long way from reaching its peak, he’d been exploring how wind turbines capture energy from the air. In the process, he had come up with a calculation for the greatest possible efficiency of any wind turbine: a shockingly tidy sixteen twenty-sevenths, or 59.3 percent. Since then, this number has been known as the Betz limit, serving as a virtually impossible goal for efficiency—until now. “In order to make that calculation, [Betz] had to make some simplifying assumptions,” says John Dabiri, a professor of mechanical engineering at the California Institute of Technology. In particular, he chose to approximate all wind as perfectly steady. “Now, we know that’s untrue because the wind is turbulent,” says Dabiri. “If I’m standing on a wind farm, there will be gusts so the wind won’t be a fixed value.” Further complicating the situation, popular propeller-style tu
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