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)

Performer Zhang Yashu from a Chinese ballet company perform during a photo shoot in front of the Australia's iconic landmarks Opera House (L) and Habour Bridge in Sydney on February 17, 2014. One of China's celebrated dance campanies is bringing one of the country's biggest ballet production to Australia for a series of performances in Sydney and Melbourne. (Photo by Saeed Khan/AFP Photo)

A bear that wandered into a University of Colorado Boulder dorm complex falls from a tree after being tranquilized by Colorado wildlife officials on April 26, 2012. Colorado wildlife official Jennifer Churchill said that the 200-pound male bear was tagged and relocated to a remote Rocky Mountain area. The bear was hit by two cars on May 3 and died. (Photo by Andy Duann)

A team of ten acrobats form the shape of a racehorse crossing the winning post ridden by Stefanie Hofer to celebrate the upcoming Dubai Duty Free Shergar Cup at Ascot Racecourse on July 29, 2014 in Ascot, England. The Dubai Duty Free Shergar Cup is the only team-format raceday in the UK and takes place on 9th August. (Photo by Ian Gavan/Getty Images for Ascot Racecourse)

Common seals are reintroduced to the wild on the beach of the island Juist, Germany, 28 July 2014. It is the first reintroduction to the wild drive of the seal breading station Norddeich this year. (Photo by Carmen Jaspersen/EPA)

Competitors in the Big Air challenge at the Proryv-2016 festival of extreme sports in Moscow, Russia on March 27, 2016. (Photo by Xinhua/Rex Features/Shutterstock)

A roadside ice-cream vendor waits for customers at a market in New Delhi, India, April 7, 2016. The Indian economy is characterized by the existence of a vast majority of informal or unorganized labor employment. (Photo by Altaf Qadri/AP Photo)

Skiers and snow boarders descend from a slope as they attempt to break the record for mass skiing in swimming suits at Rosa Khutor resort near Sochi, Russia, April 9, 2016. (Photo by Kazbek Basayev/Reuters)