Business Green: Along with the chocolate teapot and the inflatable dart-board, the solar-powered torch is an oft-quoted example of inherently daft design. But while the idea might have elicited mirth in playgrounds through the years, the concept of a torch recharged by sunlight is one that is now proving highly successful. Silicon-valley start-up D.Light Design recently claimed to have improved the lives of over a million individuals thanks to the 220,000 solar lanterns it has sold in the …