If you've ever been to a high-school science fair, you probably know that citrus fruit can produce electricity. DDB Paris put that knowledge to clever use recently with an electric Tropicana billboard that was completely powered by oranges. Working with London production house Unit9, DDB attached 2,500 oranges to two big slabs of wood fitted with spikes of zinc and copper. The acidic juice of the oranges dissolved the metals, causing their electrons to react with each other and create an electrical current. That current powered a light panel that read, "Energie naturelle," making the point that oranges have natural energy that can spark your own personal human circuits as well. So as not to appear wasteful, the agency said it would recycle the oranges "either by composting or by anaerobic digestion," the latter surely being a curious science-fair project all its own. Check out a video below, and a few more images after the jump. Via Stratégies.