It is one of evolution's crowning achievements - a mini green power station and organic factory combined and the source of almost all of the energy that fuels every living thing on the planet. Now scientists developing the next generation of clean power sources are working out how to copy, and ultimately improve upon, the humble leaf. The intricate chemistry involved in photosynthesis, the process where plants use sunlight to convert water and carbon dioxide into sugar, is the most effective solar energy conversion process on Earth. And researchers believe that mimicking parts of it could be the ticket to a limitless supply of clean power. The untapped potential for using the sun's rays is huge. All human activity for a whole year could be powered by the energy contained in the sunlight hitting the Earth in just one hour. Harnessing even a small amount of this to make electricity or useful fuels could satisfy the world's increasing need for energy, predicted to double by 2050, without further endangering the climate. Most solar power systems use silicon wafers to generate electricity directly. But although costs are coming down, these are still too expensive in many cases when compared with fossil fuels such as coal, oil and gas. Scientists are keen to develop more efficient and cheaper alternatives sources of energy. At Imperial College London, researchers have embarked on a 1m project to study, and eventually mimic, photosynthesis. Part of a project called the artificial leaf", involves working out exactly how leaves use sunlight to make useful molecules. The team then plans to build artificial systems that can do the same to generate clean fuels such as hydrogen and methanol. These would then be used in fuel cells to make electricity or directly to power super-clean vehicles..