1 . The over 48,000 orange trees that are distributed at all corners of Seville, Spain, not only fill the city's air with the pleasant smell of their flowers in spring, they also produce over 16, 500 tons of fruit every winter. Though that makes the city Europe's top orange-producing city, the fruit is too sour to be consumed fresh. While some of the produce is used to make orange juice, most of it ends up in Seville's landfills. However, that may change soon thanks to a creative idea to use the oranges to produce clean energy.

In the pilot program, juice from 38. 6 tons of oranges will be left to ferment (发酵)in an existing biogas facility. The juice is fructose (果糖)made up of very short carbon chains, and the energetic performance of these carbon chains during the fermentation process is particularly high. The gas released from the fermented liquid will be used to drive a generator to produce clean power. The officials estimate the test run will generate about 1,500 kWh of energy—enough to run a water purification plant. "It's not just about saving money. The oranges are a problem for the city, and we're producing added value from waste,^M said Benigno Lopez, the head of Emasesa's environmental department.

If successful, by 2023, the city hopes to recycle all the oranges and add the electricity generated back to its grid (电网). In trial runs, 1,000 kilos (2,200 pounds) of oranges produced 50 kWh of clean energy一enough to meet the daily electricity needs of five homes. The project team estimates that if all the fruit is recycled, it will produce enough energy to power as many as 73,000 residences.

The latest effort is among the many programs implemented in Spain to achieve the country's goal of switching its electricity system to renewable sources by 2050—and if everything goes according to plan, fully decarbonizing its economy shortly after that.