Developing solar panels that use raindrops to generate power

Advances Photovoltaic (PV) Solar Panel technology

Solar panel technology has benefited from major advances over the last decade, with successful research into improving solar panel materials and storage technology resulting in better performing and more affordable renewable technology.

One country that has invested heavily in solar technology is China. They are using more and more solar panels as they aim to deal with the overwhelming problems faced by their residents, due to pollution from their high use of fossil fuels - particularly coal - over recent decades. The city of Rizhao is a flagship for what China is starting to achieve. Ninety nine percent of households in the central districts there use solar power to heat their water, and most of the traffic lights and street lights are powered by PV solar cells, illustrating how renewable energy can provide a sustainable and economically viable solution to the current reliance on fossil fuels. And this year China became the world’s leader in producing PV solar power, with 43 gigawatts of installed capacity, which is more than enough to supply all the power required in the UK.


Solar PV for areas with less sunshine and more rain

While a large part of China enjoys plenty of sunshine, here in the UK – as with many parts of the world - our sunshine is less consistent. And given that solar PV panel installations require the sun’s rays to produce electricity, this used to mean that solar PV panels provided a less reliable source of power. However, technologies such as CIS thin-film have been developed to provide a new generation of solar panels that are much better at converting sunshine to power in low light and cloudy conditions.

Exciting new research being carried out in China - at both the Ocean University of China and the Yunnan Normal University - has resulted in the recent development of a novel solar cell that can now generate power from both sunlight and rain. This is thanks to a special coating of graphene.

Graphene is a form of carbon that has atoms organised into a two-dimensional honeycomb lattice. It was discovered by good fortune in 2004, by scientists in Manchester who were using Sellotape to separate individual layers of graphite in order to study its structure under the microscope.

Since its discovery graphene has been widely studied and, as well as being easy to isolate, it has been found to have many extraordinary properties including its strength and ability to conduct. This makes it a hugely promising material that is already starting to revolutionise a range of technologies from computers to healthcare.


The science behind graphene and solar PV cells

In an aqueous solution, graphene can bind with its electrons to positively charged ions. This property has enabled scientists to obtain power from raindrops landing on prototype solar cells coated with graphene. Raindrops contain a small amount of salt impurities that can dissociate into positive and negative ions. The positive salt ions (e.g. Na+, Ca+) can bind to the graphene surface resulting in water that is enriched in positive ions and graphene that is enriched in delocalised electrons, hence forming a dual-layer pseudocapacitor. The difference in potential that is generated by this process produces a voltage and current - power. And when the sun starts shining, the existing PV properties of the solar cells can generate power.


While the development of these all-weather solar cells are still at an early stage, they hold much promise for providing future solar PV installation systems that can provide a reliable energy source in areas with a lot of rainfall, in our bid to move away from polluting fossil fuels.