Solar Cells that Could Generate Energy from Rain

More recently, researchers from the Ocean University of China in Qingdao have discovered that graphene can also help to generate energy from raindrops. It can achieve this because rain doesn’t consist entirely of water, it also contains a number of salts that can be split into positive and negative ions. This, in turn, means that a simple chemical reaction can be used to harness power, using graphene to separate the positively charged ions, which includes sodium, calcium, and ammonium, in order to generate electricity. Normally when a raindrop sits on the surface of a solar panel, the various salts within it mean that it can generate a number of unbalanced charges. The electrons binding with positively charged ions creates an effect known as the Lewis acid-base interaction.

In theory, given that although solar panels still generate on cloudy days, the amount of energy generated is less than on sunny days, if researchers can develop an all-weather solar cell which generates electricity from rain, this would greatly help to boost current solar panel efficiency.

Testing is still at an early stage thus far, but the results have been promising. The researchers managed to generate hundreds of microvolts during the research, achieving 6.53 solar-to-electric conversion efficiency from a customized solar panel. The process involved adding a layer of graphene to a sensitized solar cell which was then put onto a transparent backing of indium tin oxide and plastic. This enabled the cell to generate power from both sunshine and rain.

In essence, what happens is that the positive ions bind to the graphene forming a double layer known as a pseudocapacitor. The energy difference between the two layers can be used to generate an electric current. The problem is that the ions are present in raindrops in low concentrations, so there is a question there about how to generate enough electricity from such low concentrations. The researchers are now working on this as well as looking at how the technology can tackle the variety of ions found in rain.

Other ways of using graphene to boost the amount of renewable energy from solar include the creation of a material that can absorb ambient heat and light. This, in turn, could enable solar panels to generate electricity from diffuse sunlight indoors.

The current study is available for scrutiny in the journal Angewandte Chemie.