Wedges of an orange generate enough current and electrical juice – 3.5 volts – to power an LED. The fruit’s citric acid helps electrons flow from galvanized nails to copper wire in this 14-hour exposure. This image was published in September’s Visions of Earth, a trio of photos that appear in each issue of National Geographic. (Photo by Caleb Charland/National Geographic)

A man (2nd L) takes pictures as visitors run away from a wave caused by a tidal bore which surged past a barrier on the banks of Qiantang River, in Hangzhou, Zhejiang province August 14, 2014. (Photo by Reuters/Stringer)

An installation of Canadian artists Caitlind Brown and Wayne Garrett is displayed during the Lumina Light Festival in Cascais September 14, 2014. Lumina Light Festival shows artworks of artists from several countries, which are displayed during a tour around Cascais. (Photo by Rafael Marchante/Reuters)

A model models shoes at the Chloe Gosselin Presentation during Fall 2016 New York Fashion Week at Lori Bookstein Fine Art on February 14, 2016 in New York City. (Photo by Ilya S. Savenok/Getty Images)

A woman is supported by two men while crossing a river, north of Idomeni, Greece, as migrants attempt to reach Macedonia on a route that would bypass the border fence, Monday, March 14, 2016. Hundreds of migrants and refugees walked out of an overcrowded camp on the Greek-Macedonian border Monday, determined to use a dangerous crossing to head north. (Photo by Vadim Ghirda/AP Photo)

A devotee is smeared with a vermillion powder while celebrating the “Sindoor Jatra” vermillion powder festival at Thimi, in Bhaktapur, Nepal, April 14, 2016. Devotees mark the festival by playing traditional drums, singing, dancing and carrying chariot of various deities around town while throwing vermillion powder to welcome the advent of spring and the New Year. (Photo by Navesh Chitrakar/Reuters)

Somalis remove the body of a man killed in a blast in the capital Mogadishu, Somalia Saturday, October 14, 2017. A huge explosion from a truck bomb has killed at least 20 people in Somalia's capital, police said Saturday, as shaken residents called it the most powerful blast they'd heard in years. (Photo by Farah Abdi Warsameh/AP Photo)

A massive, 8 metre tall sculpture of Marilyn Monroe, frozen with her dress blowing up, was on display at a shopping mall in downtown Dalian city, northeast China's Liaoning province, on Tuesday, November 14, 2017. The sculpture is a replica of Seward Johnson's Forever Marilyn in Chicago. (Photo by Imagine China/Rex Features/Shutterstock)