Problem:

Systems that rely on electricity from solar panels can encounter problems during extended periods of rain and cloud and require draining power from batteries.

Solution:

Researchers from the Ocean University of China in Qingdao and Yunnan Normal University in Kunming have invented a type of solar cell that also works on rainy days.

Rain water contains ammonium, calcium and sodium, which become electrically charged ions when in solution.

This new kind of solar cell takes advantage of that . It is coated in graphene, a highly conductive material made up of layers of carbon just one atom thick that allows electrons to move freely across its surface.

When rain and water sit on top of a layer of graphene, those ions create spots of unbalanced charges. The free running electrons in the graphene bind with positively charged ions in the rain water, and generate an electric current.

A typical solar panel averages 15-20% efficiency in full sun conditions, while these  proof-of-concept panels have been able to achieve about a 6.5% efficiency in the rain.

Other scientists led by Professor Baoquan Sun at Soochow University in Suzhou, Jiangsu, China, have overcome a design flaw of solar panels by allowing them to collect energy in both the rain and sun.

Now, almost any home can install solar panels. So even if you live in a rainy area, you can use solar panels to produce electricity for your home. This innovation could change renewable energy completely. Currently, these hybrid solar panel designs are not ready for home and business use.

Researchers still need to find ways to increase the efficiency from rain and sun.

However, the efficiency of the Soochow University design was 13%, which makes it a viable alternative to standard solar panels. Comparatively, current solar panel designs convert 15 to 20 % of the sun’s energy into electricity.

Thus, the new design is a viable solar panel solution. Collecting energy from rain is something the team would like to develop further. Electricity efficiency from its triboelectric nanogenerators was not reported and again the graphene model had an efficiency from rain of around 6.5%. There is still much work to do.

Financed by the Beijing Natural Science Foundation, the National Natural Science Foundation of China, External Cooperation Program of BIC, the Chinese Academy of Sciences, the 2015 Annual Beijing Talents Fund and China’s Thousand Talents Program, researchers NanoYa Yang, Zhong Lin Wang and colleagues integrated two energy-harvesting technologies in one: a silicon solar cell and a nanogenerator that can convert wind energy into electrical output.

The solar cell component of the system delivers 8 milliWatts of power output (1 milliWatt can light up 100 small LEDs). The wind-harvesting component delivers up to 26 milliWatts.

Together, under simulated sun and wind conditions, four devices on the roof of a model home could turn on the LEDs inside and power a temperature-humidity sensor. Installed in large numbers on real rooftops, the hybrid device could help enable smart cities.

Megan Ray Nichols, “Scientists design new solarcells to capture energy from rain” EuroScientist, May 21, 2018;

Discover solution 21: The artificial leaf

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