Nov 16

Posted in Energy Inventions | Photovoltaic Cells | Solar Power

When we think about going solar we make a mental picture of large heavy panels adorning one’s rooftop. But researchers are trying to get rid of bulky solar panels. They are aiming to achieve this feat with the help of zinc oxide nanostructures grown on optical fibers and coated with dye-sensitized solar cell materials. Researchers at the Georgia Institute of Technology have built up a new kind of three-dimensional photovoltaic system. This three-dimensional photovoltaic system will not be heavy and it will not occupy a place of prominence on rooftops; it can be hidden from the view.

This project is financed by the Defense Advanced Research Projects Agency (DARPA) , the KAUST Global Research Partnership and the National Science Foundation (NSF) . Zhong Lin Wang, who is a Regents professor in the Georgia Tech School of Materials Science and Engineering , shares his views, “Using this technology, we can make photovoltaic generators that are foldable, concealed and mobile. Optical fiber could conduct sunlight into a building’s walls where the nanostructures would convert it to electricity. This is truly a three dimensional solar cell.”

Dye-sensitized solar cells have certain distinct advantages over traditional solar panels. They utilize a photochemical system to produce energy. Manufacturer can produce dye-sensitized solar cells cheaply. They are flexible and also mechanically robust. But they have their disadvantages too. Their conversion efficiency is lower than that of silicon-based cells. But this hurdle can be overcome. Nanostructure arrays can be expanded to enlarge the surface area. This expanded surface area can trap more sunlight to convert it into energy. This feature could assist in reducing the efficiency disadvantage. Currently the biggest advantage of Dye-sensitized solar cells is it can be gelled into anything, be it buildings, vehicles or military equipments.

Dye-sensitized solar cells are inspired by the optical fiber of the type used by the telecommunications industry to transport data. Researchers improved upon the previous model by removing the cladding layer. In the next step they went for a conductive coating to the surface of the fiber before seeding the surface with zinc oxide. Now scientists utilized solution-based techniques to grow aligned zinc oxide nanowires around the fiber. It shaped up like the bristles of a bottle brush. These nanowires are finally covered with the dye-sensitized materials that do the ultimate work, i.e. convert light to electricity.

How this whole system works? Wang is forthcoming with a good explanation, “In each reflection within the fiber, the light has the opportunity to interact with the nanostructures that are coated with the dye molecules, You have multiple light reflections within the fiber, and multiple reflections within the nanostructures. These interactions increase the likelihood that the light will interact with the dye molecules, and that increases the efficiency.” First sunlight passes through the optical fiber and into the nanowires. Once sunlight is trapped inside the nanowires here it acts together with the dye molecules to generate electricity. A liquid electrolyte is present between the nanowires. This electrolyte collects the electrical charges. The final outcome is a hybrid nanowire/optical fiber system which is six times as efficient as planar zinc oxide cells with the equivalent surface area.

Currently Wang and his research team have attained an efficiency of 3.3%. But they are aiming for the 7-8% percent after surface modifications. This level of efficiency is clearly lower than silicon solar cells. But it will prove to be a good source of practical energy harvesting. Its cheaper costs will makes its penetration deep into the market.

The researchers are attempting to overcome the lack of conversion rates by utilizing other options such as providing a larger area for gathering light. This method would lead to maximize the amount of energy produced from strong sunlight. It will also generate decent power levels even in feeble light. The amount of light entering the optical fiber could be manipulated too. It could be amplified by using lenses to focus the inward bound light, and the fiber-based solar cell have very high saturation intensity.

Wang elaborates on some more points, “This will really provide some new options for photovoltaic systems. We could eliminate the aesthetic issues of PV arrays on building. We can also envision PV systems for providing energy to parked vehicles, and for charging mobile military equipment where traditional arrays aren’t practical or you wouldn’t want to use them.”