Scotland’s power sector is being criticized after it was revealed that dozens of giant turbines have been using diesel generators. The information came from a whistleblower who says the environmental-friendly windmills were only turning thanks to fossil fuels.

The revelation is now fueling environmental, health and safety concerns, especially since the diesel generated turbines were running for up to six hours a day.

Scottish Power said the company was forced to hook up 71 windmills to the fossil fuel supply after a fault on its grid. The move was an attempt to keep the turbines warm and working during the cold month of December.

South Scotland Labor MSP Colin Smyth said regardless of the reasons, using diesel to deice faulty turbines is “environmental madness.”