"Solar trees," which suspend solar panels over parking spaces in San Diego, collect electricity. Generating solar power like this is just one rung on a ladder the city will have to climb to reach 100 percent renewable energy by 2035. Clare Trageser/KPBS hide caption
The Heartland Biogas facility in Weld County, Colo., is one of the country's largest waste treatment plants that converts methane to natural gas. Rebecca Jacobson/Inside Energy hide caption
Onlookers come to admire the self-proclaimed "Miracle on 34th Street" in the Baltimore neighborhood of Hampden. But not every country has as much electricity as America does. Patrick Semansky/AP hide caption
Wind turbines outside Caledon in Cape Town, South Africa. Solar and wind farms are filling in the gaps during power shortages. Nardus Engelbrecht/Gallo Images/Getty Images hide caption
A solar tower belonging to the Spanish firm Abengoa is shown near Seville, in southern Spain, on Nov. 13. The large renewable energy company, which has been heavily subsidized by the government, is in danger of becoming the country's largest bankruptcy. The company also has a large solar facility in Arizona that has received U.S. government loan guarantees. Marcelo Del Pozo/Reuters /Landov hide caption
Kevin Murphy says he is proud of what he and the other workers do at the Rosebud mine, including digging the coal and reclaiming the land afterward. Amy Martin/Montana Public Radio hide caption
United has purchased 15 million gallons of renewable jet fuel made from beef tallow, or fat, by Alt Air Fuels and plans to use the fuel this year for Los Angeles-to-San Francisco flights. Tony Ruppe/United hide caption
Renewable energy sources — such as the Eolo wind park about 75 miles south of the Nicaraguan capital, Managua — generate about half of the country's electricity. Officials predict that figure could rise to 80 percent within years. Inti Ocon/AFP/Getty Images hide caption
In Britain, a new bus running between Bath and the Bristol airport uses biomethane for power. The gas is derived from human sewage and food waste. Wessex Water/GENeco hide caption
Five industrial wind turbines form part of the Gorona del Viento power plant on the island of El Hierro. By the end of this year, the power plant is set to generate 100 percent of the energy El Hierro needs, making it the world's first energy-independent island powered only by renewables. Lauren Frayer for NPR hide caption