In case you have read my last month’s guest post about harvesting solar energy in rust, you would be delighted to know that there has been yet another breakthrough in our attempt to harness solar energy. For many years, solar energy has been targeted for being unavailable at night and during rains. The problem of utilizing solar energy at night can be resolved with the help of metal oxide cells as elaborated in my above post (do read it, if you have not done so already). And now researchers at the Ocean University in China have addressed the second problem and developed solar cells that can actually use rain drops to generate electricity.
Published in the German journal Angewandte Chemie, the paper titled, A Solar Cell Triggered by Sun and Rain, opens a new realm of possibilities when harnessing solar energy. Coating the solar cell with a thin film of graphene allows the cell to function even when it is raining. Graphene is nothing but reduced form of graphite that consists of a honeycomb arrangement of carbon atoms in a two dimensional matrix. Although known to us for over 50 years, graphene was rarely studied until recently in 2004, where it was studied in greater depth and its abundant properties were brought to the fore. A good conductor of heat and electricity, it is almost transparent and yet stronger than steel. Showing bipolar transistor effect, graphene has also found its way into modern electronics such as computers, smartphones, TVs etc. and is making strides in biological research to be used as a biosensor for detecting cancers and also as electrode to engage with neurons.
|Rain drop creating a difference in potential when it impacts the graphene layer, |
thus acting as a pseudocapacitor. Image credit: www.wiley-vch.de
Prof. Qunwei Tang and his team of researchers used graphene’s property of binding to positively charged ions to generate minute amounts of electricity from their modified solar cell. Raindrops carry some impurities with them as they descend from the sky. These impurities are usually in the form of certain salts that are made up of common elements such as sodium, calcium, ammonium etc. When dissolved in water, these salts dissociate into their respective ions and upon impact with a solar cell containing a thin graphene layer, form a pseudocapacitor, that has positively charged ions of water on side and the negatively charged electrons of graphene on the other, creating a potential difference (in microvolts) that is sufficient to generate electric current and hence electricity.
The experiments done by the researchers are still in their early phases but have managed to convert 6.53% of solar energy into electricity. Although this might not sound like a lot, considering the fact that rain drops were deterrent to working of a solar cell, this is huge accomplishment and paves way for further work to be done to increase the effectiveness of solar cells. As mentioned in our previous post about solar cells, currently solar cells are able to convert 10-15% of solar energy into electric energy and a simple layering of graphene on them should enable boosting of this capacity.
But this is not all. Researchers at University of Surrey were also able to use graphene to utilise the diffused sunlight that we get inside our homes and never utilise. Coating walls with graphene films could also help us harness more solar energy than we ever have.
Tang, Q., Wang, X., Yang, P., & He, B. (2016). A Solar Cell That Is Triggered by Sun and Rain Angewandte Chemie DOI: 10.1002/ange.201602114
Anguita JV, Ahmad M, Haq S, Allam J, & Silva SR (2016). Ultra-broadband light trapping using nanotextured decoupled graphene multilayers. Science advances, 2 (2) PMID: 26933686