Last week, the nation of Portugal achieved something remarkable. For 107 hours—about four days—the country ran on nothing but wind, solar and hydro power.

Running a country of about 10 million people without any fossil fuels is certainly an impressive feat. The weather helped: sunny, breezy days optimized energy-collection and mild temperatures didn’t strain the grid with excessive heating or cooling needs. Of course, this figure only nods to utilities—it doesn’t include the gas-powered vehicles on streets. But it does mean that any electric vehicles that were charged during that period were truly zero-emission vehicles.

Perhaps more inspiring than the achievement itself is how much Portugal’s energy portfolio has changed from just a few years ago, thanks to major investments, according to The Guardian :