Plants take sunlight, water and carbon dioxide and use these simple ingredients to make sugars. Scientists hope to imitate plants by designing a system that takes the same set of ingredients to produce liquid fuel. This approach is called artificial photosynthesis; and although it's still in its infancy, some researchers hope the technology will eventually play an important role in replacing fossil fuels.
Current sources of energy rely on nonrenewable fuels, such as coal and oil. Liquid fuels produced through artificial photosynthesis, however, would depend only on carbon dioxide, water and sunlight, all of which are plentiful. Since production of artificial fuels would consume carbon dioxide while combustion of these fuels would release it, the process would also be environmentally-friendly because greenhouse gases produced by consumption would be recycled back into fuel through production.
Many other proposed sources of renewable energy are incompatible with current infrastructure. Your car, for example, would need to be altered before it could run on 100 percent ethanol. Electricity from wind farms and photovoltaic cells is also renewable but cannot be directly used to power your car unless it's electric. Artificial photosynthesis, by contrast, would produce liquid hydrocarbon fuels that you could burn in modern car engines without making any alterations.
Researchers have been able to make hydrogen from water and sunlight on a small scale in labs, but for these processes to work they must be practical on a large scale. No one has, as yet, been able to design a system robust enough that it can be deployed on a commercial scale. Successful designs must also be able to survive years of exposure to direct sunlight and still continue to work efficiently.
Another major disadvantage of artificial photosynthesis is the cost. Catalysts, such as platinum metal, are not cheap and would be required to split water with the aid of sunlight. Researchers are currently working on cheaper catalysts and processes, but these are still in the experimental stage. Artificial photosynthesis could be more efficient than photosynthesis in plants; but if production of biofuel from plants and algae turns out to be more cost-efficient, it might have the advantage in the short run.