More Efficient Solar Panels, Thanks To Eye Of Moth And Leaf Of Lotus

When scientists at the Oak Ridge National Lab went rifling through nature’s drawers on their hunt for a more efficient solar panel, they missed the eye of newt, but they did find inspiration in a couple of other natural ingredients, the moth’s eye and lotus leaf. The result is a “revolutionary” souped-up superhydrophobic coating that could mean an increase in solar conversion efficiency in the range of three to six percent.

That may not sound all that awesome, but the new solar panel coating hits the trifecta when you count in brownie points for two other factors that contribute to the overall cost of solar energy, which would be manufacturing costs, and maintenance and operating costs.

Group Hug For More Efficient Solar Panels

Oak Ridge is part of the Energy Department’s network of national laboratories, so let’s pause here while US taxpayers get a nice group hug for chipping into the research project.

You can get all the details about the new coating in the Royal Society of Chemistry’s Journal of Materials Chemistry C under the impressive title “Monolithic graded-refractive-index glass-based antireflective coatings: broadband/omnidirectional light harvesting and self-cleaning characteristics,” but for those of you on the go it all boils down to a specialized, ultra-thin layer of porous glass.

Here is a snippet from the abstract:

…The coatings comprise an interconnected network of nanoscale pores surrounded by a nanostructured silica framework. These structures result from a novel fabrication method that utilizes metastable spinodal phase separation in glass-based materials….the fabricated nanostructured surfaces are found to promote a general and an invaluable 3–7% relative increase in current output of multiple direct/indirect bandgap photovoltaic cells.

As a side note, the Energy Department’s press materials have the upper range at six percent, not seven, so we’ll settle for that.

The boost in solar panel efficiency is enabled by the antireflective property of the coating. It can also be tweaked to make it superhydrophobic (that’s fancyspeak for impressively water repellant) and resistant to fog. Did we mention that the new coating is extremely durable, too?

…Moreover, these antireflective surfaces also demonstrate superior resistance against mechanical wear and abrasion. Unlike conventional counterparts, the present antireflective coatings are essentially monolithic, enabling simultaneous realization of graded index anti-reflectivity, self-cleaning capability, and mechanical stability within the same surface…

The Biomimicry Road To More Efficient Solar Panels

In case you’re wondering where the witches’ brew of inspiration comes in, the lotus leaves are the easy part: they repel water like gangbusters, using rain for self-cleaning.

The trick for superhydrophobicicity is to get the surface angled so that drops of water hit at an angle of about 150 degrees. Oak Ridge came thisclose, in the range of 155-165. At that angle, water “literally bounces off, carrying away dirt and dust.”

The thing about the moth’s eye is a bit more complicated. Here’s the Oak Ridge team leader waxing enthusiastic on the topic:

…a moth’s eyes are antireflective because of naturally covered tapered nanostructures where the refractive index gradually increases as light travels to the moth’s cornea…

Here’s how it translates into modern fabrication methods that produce precisely engineered nanoscale structures (from the abstract):

These structures result from a novel fabrication method that utilizes metastable spinodal phase separation in glass-based materials. The approach not only enables design of surface microstructures with graded-index antireflection characteristics, where the surface reflection is suppressed through optical impedance matching between interfaces, but also facilitates self-cleaning ability through modification of the surface chemistry.

If you caught that thing about meastable spinodal phase separation, that produces a highly durable, heat-resistant surface. In contrast, conventional coatings are fabricated from powders or polymers, which tends to make them more fragile.

We’ve been focusing on the benefits in terms of more efficient solar panels, but the research team also sees a whole slew of applications in other fields aside from photovoltaics, including all sorts of optical instruments and light sensors.

They’re also looking at applying the coating to ships’ hulls, to prevent biofouling (that refers to buildup of barnacles and other sea creatures, which erodes fuel efficiency).

One Down, One To Go

Here in the US, coal power plants are shutting down like ninepins, and though it would be nice to give competition from solar power the credit, to a great extent the availability of low cost natural gas is factoring into the demise of coal.

So, are we going to be stuck with natural gas forever? Not necessarily.

Low-cost gas appears to be on its way out. If the busted natural gas drilling boom leads into yet another cycle of rising prices, it will be helped along by two new factors emerging in the US: the export of more natural gas under the Obama Administration (though see here and here and here for some important caveats) and the use of more natural gas in domestic plastics production.

Meanwhile the installed cost of solar power is already spiraling downward, and Oak Ridge’s new coating for low-maintenance, more efficient solar panels is a good indication that solar costs will continue to sink like a stone.

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Image Credit (cropped): Courtesy of Oak Ridge National Laboratory.

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