On the second Saturday in May, the Dutch celebrate an iconic national structure—the windmill—like these historic ones at Zaanse Schans. With hundreds of windmills across the country, many sites use the day to demonstrate how windmills work and host art exhibits. But the concept of using wind power isn’t just a historical anecdote—this renewable energy is experiencing a boom, and by 2050 is predicted to provide one-third of the world"s electricity.