Watch the latest "Fareed Zakaria GPS" special, ‘Global Lessons: The Road Map for Powering America,’ this Sunday at 8 p.m. Eastern and Pacific.
By Michael Graetzel, Special to CNN
Editor’s note: Michael Graetzel is a professor at the École Polytechnique Fédérale de Lausanne, where he directs the Laboratory of Photonics and Interfaces. He has consulted for technology firm G24i. The views expressed are his own.
For two centuries, we have been burning billions of years of photosynthetic residue, better known as fossil fuel, to power our factories, homes, vehicles and cities. But we may not need to do this much longer – solar resources are great enough for all of us. Indeed, it may surprise many to learn that the amount of solar energy striking the earth in one hour is equal to the total energy consumed by all of humanity in a whole year. Learning to capture more of this resource could yield huge dividends for humanity.
Here at the École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland we have developed a solar cell technology that takes its cue from photosynthesis: dye-sensitized solar cells (DSCs). By separating the components for light absorption (which determines the cell’s color) and the transportation of electrical current, this technology is remarkably similar to natural photosynthesis and provides unique benefits for integrating solar cells into everyday life. The color tunability and transparency of the cells, as well as an enhanced efficiency in indoor light – power conversion efficiencies can reach over 12 percent at full sunlight intensity and more than 25 percent for interior lighting – afford DSCs the opportunity to extend solar power generation seamlessly and conveniently into our office buildings and living rooms.
The start-up company G24i, meanwhile, has already licensed this technology for marketing commercial products and entered into partnership with Logitech and Texas Instruments to create light-powered computer and iPad peripherals, as well as solar powered blinds and shades. (G24i has produced a short video that gives some technical insight this technology).
Standby power consumption from home appliances accounts for almost 10 percent of the power consumption in an average U.S. residence, but many of these devices contain a design element that could be replaced with a solar cell, such as the frame around a TV set or the plastic body of a TV remote. As a result, lightweight flexible solar cell technology is a potential game changer for many power consumers around the world.
But solar energy storage presents a major challenge for the burgeoning solar industry. Storing the sun’s energy – packets of photons – in the form of chemical bonds is one way to accomplish this task. Nature stores solar energy by combining CO2 and water through photosynthesis to produce plant matter and the oxygen we breathe. We hope to do something similar: produce hydrogen and other fuels from water and CO2. This starts by splitting water with the power of the sun, just the way plants do. Once hydrogen is liberated from the oxygen bond in water (2H2O à 2H2 + O2), it can be used directly in a hydrogen fuel cell, burned in BMW’s hydrogen combustion engine, or used to chemically reduce the greenhouse gas CO2.
The reduction of CO2 to form liquid fuels such as methanol, which can be burned like ethanol in a flex-fuel engine, provides a way to mitigate the ongoing release of CO2 into our atmosphere while newer, greener technologies make it to market. Note here how sustainable and remediating this cycle could be: solar energy is used to convert greenhouse gas into fuel while producing oxygen, akin to the overall process accomplished by natural photosynthesis.
Another method, the photoelectrochemical (PEC) approach, can produce hydrogen or oxygen directly on the surface of a light harvesting material. In our own laboratories, we investigate using iron oxide (rust) and copper oxide to accomplish this task. These two materials can be produced at very low cost and could be scaled up to the quantities necessary for converting huge amounts of solar energy into stored chemical energy. Additionally, PEC technology can be integrated synergistically with DSC technology to form a “tandem” setup. With this approach, we have recently demonstrated that it is possible to produce hydrogen and oxygen from water, using only cheap, earth-abundant materials.
In my vision of the future, humanity has tapped the ultimate resource that is our sun, reliably harvesting, transferring and storing its energy to provide clean and sustainable power. I can see a day when the sun powers our electronics, our cars, our homes, our cities – our whole planet. We have been working to realize this goal for more than two decades, and I believe the technology is finally coming into maturity. Solar is not a thing of the future; it is ready and waiting for us to take advantage of right now.
Governments and companies that embrace this idea early will not only help the planet, but they may also win out in the long run economically. After all, fossil fuels will burn out long before the sun ever does.