Just a short drive west out of Des Moines, Iowa, amid fields of corn and soya, there's a dip in Route 44. Here, near the small community of Dallas Center, a short gravel road runs north to a cluster of houses and across the street there's a farm machinery dealer's yard. It seems to be an unremarkable corner of the Midwest, yet almost a kilometre beneath that dip in the road is something that could change the way we use wind power. If all goes to plan, it could allow the world's most appealing renewable energy source to compete head-to-head with fossil fuels as a way of generating electricity.
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