http://www.slate.com/articles/business/the_juice/2015/09/texas_electricity_goes_negative_wind_power_was_so_plentiful_one_night_that.html

In the wee hours of the morning on Sunday, the mighty state of Texas was asleep. The honky-tonks in Austin were shuttered, the air-conditioned office towers of Houston were powered down, and the wind whistled through the dogwood trees and live oaks on the gracious lawns of Preston Hollow. Out in the desolate flats of West Texas, the same wind was turning hundreds of wind turbines, producing tons of electricity at a time when comparatively little supply was needed.