Passengers using a newly retrofitted light-rail station in downtown Phoenix, Ariz., can press a button to be showered in cool air, powered by solar energy and cold water from an efficient district cooling system.

The system, which was inspired by similar installations in Dubai, uses solar power to run fans that blow cool air. The cool air itself comes from a system of chilled water that has been running in Phoenix's business district since 2001. It's called district cooling: A central plant run by NRG Thermal cools the water, which is then piped to nearby buildings to be used in lieu of less-efficient conventional air-conditioning systems.

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Car-free transport, distributed solar power, and district energy: It’s a triple play worthy of the Scandinavians, only it's happening in what would otherwise seem to be one of America's least sustainable cities. What is it about extreme conditions that turns desert communities into hotbeds of efficiency and innovation?

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