New solar technology mimics mother nature

In 1941, clinging burrs inspired a Swiss engineer to create the fastener now known as Velcro. In recent years, scientists have developed more aerodynamic wind turbines based on whale fins, stronger adhesives based on gecko feet and even glow-in-the-dark aquarium fish using fluorescent jellyfish proteins. Nature is filled with simple, elegant innovations. This week, Swiss inventor Michael Graetzel won this year's Millenium Technology Prize of nearly 1 million dollars for his low-cost solar cells based on the process of photosynthesis. These cells may someday turn our windows into man-made leaves.

Plant leaves create energy using chlorophyll, which absorbs sunlight and converts carbon dioxide and water into glucose and oxygen. Absorption and conversion occur in two different areas of the leaf. In conventional photovoltaic cells, both processes occur in the same silicon layer. In Graetzel's cells, a porous layer of nanoparticules becomes the leaf and a long-lasting dye acts as the chlorophyll. Dividing these tasks makes the cells more efficient while producing enough energy to power batteries, electronics and other devices. Unlike conventional photovoltaic cells, Graetzel's cells eschew silicon and are therefore cheaper to produce and result in less heavy metal waste. They are also bi-facial, which means they can absorb light from both sides and absorb more non-direct lighting than traditional cells.

"What's very exciting is that you collect light from all sides, so can capture electricity from the inside as well as the outside," said Professor Graetzel in an interview with BBC News. "You can imagine using those cells as electricity producing windows... You could think that the glass of all high-rises in New York would be electricity generating panels."

Imagine working in an office building powered by sunlight during the day and then, after dark, by its own artificial light. Windows already regulate temperature and airflow in homes; in the future, they may play an integral role in meeting our energy needs.

One downside to the dye-sensitized solar cell design is the liquid electrolyte used inside, which can freeze at low temperatures and expand at high temperatures, causing issues in power production and possibly physical damage. Still, the technology is moving forward and finding practical application on a small scale. Flexible solar panels now adorn bags, tents and jackets in addition to roofs.

Some companies involved in developing this technology include Konarka, which advertises its use of recyclable, non-toxic materials, and Dyesol, which sells equipment for printing solar cells. California based Innovalight seeks to make their solar cells more efficient at converting light into energy, as the company estimates that improving solar cell efficiency by just one percent could drive down the cost of solar energy by as much as six percent. While many balk at the present cost of photovoltaic cells, solar power is on track to becoming one of the most adaptable, inexpensive and environmentally friendly sources of energy available. Graetzel, for his part, has vowed to put his prize money back into the development of his photosynthetic cells and bring the power of the sun to people's hands.