RADAR is to air-traffic control what eyes are to people. It allows ground controllers to guide planes around the skies without the risk of a mid-air collision. But air-traffic-control radars—which use up more than 25kW per pulse—have a hefty appetite for electricity. A big airport may use up to four separate devices: to provide a picture of the surrounding airspace, guide aircraft during bad weather, see position of aircraft and vehicles on the ground to prevent collisions, and provide weather information. Multiply that by the number of airports worldwide, add in other radars that track aircraft between airports, and you end up consuming oodles of power.

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http://www.economist.com/blogs/babba.../airport-radar