The next wave in making solar panels more energy efficient is finding a way they can produce energy when it's cloudy or dark out. Researchers from Ocean University of China think they've found their answer: rain.

Rain isn't just simply water. It contains salts that have positive and negative ions. Researchers have turned to graphene to help separate those ions and essentially create energy from rain. In early tests, the team has achieved a respectable 6.5% energy conversion - which is nearly what solar panels themselves first started at more than thirty years ago. The hope is that applying the graphene on top of solar panels will boost the efficiency of the panels and help create energy when the sun isn't out.

It's not the first time graphene has been used to boost solar energy technologies: earlier this year, a team from the UK was able to create a graphene-based materialthat's very effective at absorbing ambient heat and light, and which could eventually lead to solar panels that can work with the diffuse sunlight that finds its way indoors.

If these scientists get their way, in the future, photovoltaic cells may not be hampered by a lack of direct sunshine at all.

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