Solar panels today work best during periods of strong sunlight, but start to wane when it gets cloudy or rainy. A breakthrough in graphene-based solar panels could change all that, by allowing solar panels to generate electricity during inclement weather.
Graphene-based solar cells, say the researchers from the Ocean University of China, would be able to derive energy from raindrops that happen to fall on the panel, by taking advantage of the various salts present within the liquid.
The graphene sheets that make up the solar cells would be able to separate the positively charged ions in rainwater, including sodium, calcium and ammonium. These positive ions bind to the ultra-thin layer of graphene to form a double layer (also called a pseudocapacitor) with the electrons already present. The potential energy difference between the two layers is what generates the electrical current.
The researchers have tested a prototype by using slightly salty water to simulate rain, and a thin-film photovoltaic cell called a dye-sensitised solar cell.
The researchers modified the cell by adding a layer of graphene, then mounting it on a transparent backing of indium tin oxide and plastic. This dual-function solar cell concept could then be used to produce power from both sunshine and the simulated rainwater.
Graphene as a material is both strong and light, and can hold energy better than graphite. It is also being developed into anti-reflection coatings for solar cells, so the integration of graphene into solar applications is not unheard of.
By extending the role of graphene to actively harvest energy from rainwater, the researchers were able to generate hundreds of microvolts from the water, and achieve a 6.53 percent solar-to-electricity conversion efficiency from the solar panel.
While these results are impressive for a conceptual prototype, there’s more work to be done in order to raise efficiency to commercially-viable levels. One particular problem is the relatively low concentrations of ions in raindrops, which make it a challenge to generate enough electricity. The researchers are also working to adjust the technology so it can handle a variety of different types of rainwater with different ion mixtures.
However, the researchers hope their findings can guide the design of future solar cells, and open up thinking about alternative electricity generating capabilities for solar cells. For example, it may be possible to create solar cells that are able to harvest energy from ambient heat and light, to boost their performance indoors.
This is of course in addition to current trends toward the wider use of solar panels, such as integrating them into roofs, walls and windows of buildings, as well as the movement to provide decentralised storage of power generated by solar panels via battery systems.