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A new all-weather solar cell generates "hundreds of microvolts" powered by raindrops, in addition to converting solar energy to electricity.

Solar Energy

New Graphene Solar Cell Makes Rain-Powered Electricity

A new all-weather solar cell generates “hundreds of microvolts” powered by raindrops, in addition to converting solar energy to electricity.

The Intertubes have been buzzing with news of an all-weather solar cell that produces an electrical current from falling raindrops. The research is still far from the marketplace, but it’s yet another indication that the growth potential of the global solar industry shows no signs of slowing down as new technologies bring on succeeding waves of efficiency improvements and lower costs.

All else being equal, an all-weather solar cell would expand the geographical map for cost-effective solar installations in rainy regions, including parts of the US. In fact, you get a twofer, because rain removes dust and debris from the surface of solar panels, providing a no-cost way to keep them humming along optimally during sunny weather.

graphene solar cells rain all weather

All Weather, Rain-Powered Graphene Solar Cell

The new rain-powered graphene solar cell was developed by the leading marine research institute Ocean University of China, in collaboration with Yunnan Normal University.

To wrap your mind around the all-weather concept, consider that rainwater is not pure H20. In its recently published study, A Solar Cell That Is Triggered by Sun and Rain, the Ocean University research team describes rain as a giant “salt reservoir full of positively and negatively charged ions.”

The foundation of the device is a rather conventional dye-sensitized solar cell deploying the familiar indium tin oxide formula. For those of you keeping score at home, the dye is another standard item in the solar toolkit, the ruthenium-based N-719.

That accounts for the sun-powered part of the equation. The rain-powered part comes in with a “whisper-thin” coating of graphene. When rainwater comes into contact with graphene (this stuff), its salts dissociate, as explained in this helpful rundown from

…the water becomes enriched in positive ions and the graphene becomes enriched in delocalized electrons. This results in a double-layer made of electrons and positively charged ions, a feature known as a pseudocapacitor. The difference in potential associated with this phenomenon is sufficient to produce a voltage and current.

The solar conversion efficiency of the device clocks in at a maximum of 6.53 percent for simulated sunlight. You’ll have to read the full study for details on the rain-powered output, but the abstract describes it as “a voltage of hundreds of microvolts.”

Those figures don’t sound all that impressive, but the point of early stage research is to identify promising pathways for improvement, and the team is confident that its findings will open up the solar map in new ways.

Is That The Best You Got, Koch Bros?

This is just one of many other new solar R&D projects (here’s another recent example) indicating that the solar industry can continue to look forward to falling costs and rising efficiencies.

One case in point is indium tin oxide (ITO). While ITO has been the go-to material for transparent thin film solar cells, it is relatively brittle. A team at Brookhaven National Laboratory has been noodling around with the idea of replacing it with a combination of graphene and plain window glass, so there’s that.

In the context of all this activity, it’s worth noting that the anti-solar lobby seems to have stopped trying to back up its position with any kind of solid public policy research.

The latest major effort occurred last year, when Utah State University’s Institute of Political Economy (IPE) came out with a pair of reports purporting to blow up the case for wind and solar subsidies.

Both reports have a half-hearted, paint-by-numbers feel. Here’s a snippet from the Executive Summary for the solar report, titled, “Reliability of Renewable Energy: Solar.”

…IPE determined that using tax dollars to mandate and subsidize solar power is not a worthwhile investment because the high costs of overcoming solar power’s unreliability outweigh its limited environmental benefits. First, solar power is heavily dependent on government subsidies and mandates, and the solar industry is not economically viable without them…

That subsidy argument is more than a bit disingenuous considering the massive, generations-long record of preferential treatment accorded the US fossil fuel industry, but consider the source. Back in 2012 IPE received a $1.54 million grant from the fossil-friendly Charles Koch Foundation, as reported by The Salt Lake Tribune:

The USU donation will be used to hire two tenure-track professors and pay for programs and building costs at the Jon M. Huntsman School of Business, specifically in its Institute of Political Economy and in Huntsman Hall.

Not helping things in the scholarly merit department is the author list of the solar report, which consists of Randy T. Simmons (this guy) of Utah State University, Ryan M. Yonk of Utah State University, and Jordan Lofthouse of the Koch-funded think tank Strata Policy (these guys).

Actually, all three authors are connected to Strata. Simmons and Yonk were instrumental in the founding of Strata back in 2003, with the idea of creating this:

…an environment where students would become part of an academic apprenticeship — where they would be trained as policy analysts and professional researchers — without the traditional academic restraints found in the classroom.

Maybe Strata should not have so enthusiastically thrown out the baby with the bathwater when it comes to traditional academic restraints. When Simmons’s Koch connections came to light last year, Utah State posted a permanent disclaimer/disclosure/apology on its website. Among other academic shortcomings, the post notes that Simmons seems unaware of “the most basic statistical principle: correlation is not causation.”

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Image (screenshot): via NOAA.


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Tina specializes in military and corporate sustainability, advanced technology, emerging materials, biofuels, and water and wastewater issues. Tina’s articles are reposted frequently on Reuters, Scientific American, and many other sites. Views expressed are her own. Follow her on Twitter @TinaMCasey and Google+.


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