For four and a half remarkable days in May, the country of Portugal ran entirely on renewable energy — wind, solar, and hydropower, reports Sam Jones for The Guardian.

As Jones writes, “Despite fears of a blackout, the lights stayed on for a record 107 hours between 6.45am on Saturday 7 May and 5.45pm the following Wednesday.”

Clean energy advocates are heralding this achievement as proof that renewables can reliably replace fossil fuels to power the Iberian country. While many acknowledge that circumstances were particularly favorable — the fuel-free period fell over a weekend (when demand is lower), and weather that was both sunny and windy — supporters argue that the achievement was more than just luck. António Sá da Costa, managing director of the Portuguese renewable energy association Apren, argues it was the result of years of investment and cooperation:

“It was the coming together of three factors, without which none if it would have been possible,” he says. “The first was that we had the power plants in place to take advantage of the natural conditions during that period; second, it was only possible because of the wind, water and sun. The third was that we had the operational grid capability – in terms of both distribution and transportation – to manage this type of situation.”