Solar Cells that Could Generate Energy from Rain

Researchers have found that graphene solar cells are capable of generating electrical current through the breakdown of salts in rain.
Robin Whitlock

Graphene has been the subject of research programs at numerous academic institutions all over the world with regard to benefits for renewable energy, such as those involving Manchester and Abu Dhabi Universities earlier this year. The material is basically a single layer of carbon atoms arranged in a lattice structure that makes it 10 times stronger than steel but 1000 times lighter than a sheet of paper. It has great potential for the development of electrical components and gadgets and other items, from sensors and batteries to ion-exchange membranes with a range of potential applications including energy, defense, and water treatment.

With regard to potential benefits for renewable energy, researchers have discovered it can hold energy better than graphite, which means it can be used for battery energy storage, in EVs, and in fuel cells. It can also be used to develop anti-reflection coatings for solar cells.

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.