Global Wind Day: The power of wind

These windmills in Nashtifan, northeastern Iran, are among the oldest in the world. Made of clay, straw and wood and standing up to 20 meters (65 feet) tall, they've been catching the area's strong winds to grind grains into flour for centuries. One of the few such windmills still in operation, they were registered as a national heritage site by Iran's Cultural Heritage Department in 2002.

Early Persian models inspired the classic windmills of Europe, which have become a symbol of the Netherlands. Used to power industry and pump water out of the lowlands, there are still around 1,000 Dutch windmills left today. Sails can be used to convey messages, such as a death in the family, a happy occasion or a period of inactivity. Sail signals were even used to warn against Nazi raids.

Modern wind turbines are used around the world to provide a clean, sustainable source of energy, such as here in Palm Springs, California. Wind energy is the largest renewable energy source in the US, providing more than 7% of the country's electricity in 2019. In the European Union, wind energy accounts for around 15% of total supply, mostly generated in Germany, Spain, the UK, France and Italy.

Wind turbines aren't just restricted to windswept fields and coastlines. Modern structures have also begun adding them as an alternative way to generate electricity, though the idea isn't widespread just yet. The Strata building in London, which opened in 2010, is the world's first building to integrate wind turbines into its design. They generate 8% of the tower's energy needs.

This floating version, tested on a small lake in Lower Saxony in April 2020, could end up bobbing off the coasts of Europe in the coming years. The new model is tethered with a line to the seafloor, rather than anchored with steel frames, reducing costs and allowing it to be used in waters up to 100 meters (330 feet) deep. Energy company EnBW and Aerodyn Engineering are behind the project.

Smaller wind turbines haven't generally been worth the expense. But the Wind Tree, introduced by French green tech company NewWind in 2015, uses small, leaf-shaped turbines — some outfitted with solar panels — to produce around 80% of the average household's electricity needs. Quiet and stylish, they don't need much of a breeze to get going. But they're pricey: a basic model costs nearly €50,000.

The lifespan of the average wind turbine is around 20 to 25 years. After that, they're decommissioned and usually end up in landfills — the blades, longer than the wing of Boeing 747, are made of resistant fiberglass and difficult to recycle. But this playground in Rotterdam found a home for at least five old blades, creating a maze-like climbing structure complete with slides and climbing nets.