An employee checks a cable on the nacelle of a Vestas A/S V136 wind turbine during operational testing at the Danish National Test Center for Large Wind Turbines in Osterild, Denmark, on Monday, April 18, 2016. "The doubling of turbine size this decade will allow wind farms in 2020 to use half the number of turbines compared to 2010," said Tom Harries, an industry analyst at Bloomberg New Energy Finance. Photographer: Chris Ratcliffe/Bloomberg