Grassy Clothing May Give PV Solar Better Energy Efficiency!
This is not the first time scientists have discovered something they were not looking for. Chemistry books mention that the ring structure of Benzene molecule was discovered through a dream scientist Kekule saw while sleeping at night. Now another similar discovery has been reported in December 2017 by researchers at University of Pittsburg, USA. This time it was not a night-time dream, but a daytime activity while awake and alert.
Scientists had been experimenting with optical experiments with a sheet of glass which had been etched with nano-structures. Because of their shape, the scientists called them nano-grass. While cleaning that nano-grass glass sheet with water, they observed that the hazy glass turned transparent when water was applied to it. The switch between transparency and opacity was almost 100%. How does it matter to solar cells? Apparently, not at all. Actually, both the nano-grass and the switch ability have application to photovoltaics.
Nano-Grass Catches the Eye of the Sun
Solar cells are covered with a protective glass layer through which light is expected to pass and hit the semiconductor. Unfortunately, some of the light is reflected at the surface of the glass. This reduces the utilization of the available sunlight thus adversely affecting the net conversion efficiency. Scientists have been working hard to minimize the reflection. The nano-grass actually helps improve absorption of the incident energy. The length of the “blades”, their mutual orientation, and spacing all matter, and scientists are to determine an optimum etching pattern.
Switching the Transparency
How does the switching of transparency help photovoltaics? This special glass can be used in making smart photovoltaic windows- ones that can generate electricity as well as pass light. By controlling the opacity one could block sunlight glare or control privacy as desired. Actually, this glass can let through a large percentage of light even while appearing hazy.
The application of water will make it transparent and removal will make it opaque. Actually, water enters the nan-grooves and makes an almost flat surface. As the refractive index of water ids close to that of glass, light can pass through as a plane sheet of glass. When water is removed the sheet becomes opaque again. The switching is performed in a matter of seconds. Acetone and toluene can also be used instead of water. Previously available designs of such glass do not switch so well. Their design involves electrical wires and application of electrical potentials over the entire surface to control the opacity. Those are expensive, too.
Between the Cup and the Lip
But there is always many a slip between the cup and the lip. One obvious question is: how to apply water and then remove it at will? The current proposal is to overlay a sheet of normal glass. Pumping fluid in the inter-space will make it transparent. Sucking it out will make it hazy. That is possible, but will add complexity.