Campaigners say the 107 hours when the country was powered by wind, sun and water show they can replace fossil fuels.
If you can keep your gaze off the hilltops, imagine away the pylons and forget the occasional tractor of an uncertain vintage coughing along the narrow roads, little appears to have changed in the valleys of north-eastern Portugal for decades, perhaps even centuries.
The gnarled alvarinho vines have been relieved of their fruit to make vinho verde, an old woman in black herds her sheep through a hamlet and hungry eagles hover over the fields, scanning the land for lunch.
But look up, past the villages, the clumps of stout ponies and the wolf-haunted forests of pine, oak and eucalyptus, and the harbingers of an environmental revolution are silhouetted against the December sky.
The 130 giant wind turbines that sprout from the peaks, slicing the air with a rhythmic sigh, have helped Portugal to a remarkable achievement. For four and a half days in May the country ran entirely on electricity from renewable sources: wind, hydro and solar power.
[Photo by Nelson L. | Flickr]