Solar Can Work in Cloudy Cities

Wednesday, April 23, 2014 @ 11:04 AM gHale

Cloudy skies means solar energy just won’t cut it, right? Wrong. There is a way to make perpetually gloomy cities like London and Seattle – and it is organic photovoltaics.

Unlike traditional solar panels, made of silicon, organic photovoltaics (OPV) cells consist of organic semiconductors, which can end up 3D-printed or coated over large areas.

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The promise of OPV’s isn’t necessarily that they’d produce more power than traditional panels, but that they’re more efficient at generating power from limited lighting.

Silicon cells require direct sunlight (rays must shine at a minimum of 90 degrees) before they start outputting energy. But newer technologies like OPV generate energy regardless of the angle of the rays. On a cloudy day, though there is less sunlight overall, rays still hit the earth at multiple angles. Thus, OPV cells can produce energy for a larger portion of the day.

In places like the UK, where strong direct sunlight is rare, OPV devices could end up generating more energy than conventional silicon panels, said the UK National Physical Laboratory’s Dr. Fernando Castro, a leading researcher on this subject. The efficiency of this technology already climbed rapidly from 5 percent in 2008 to 12 percent in 2013. Conventional solar panels average about 15 percent efficiency, with the best commercial products coming in at around 20 percent.

But according to Castro, those efficiency numbers do not necessarily reflect how traditional and OPV cells would stack up to each other in real life, and especially in cloudy places.

Currently, OPV products are struggling to compete in a marketplace built around traditional silicon panels. The billion-dollar industry relies on an efficiency rating system that judges a panel based on its performance under simulated lab conditions — which is to say, the strong, direct lighting silicon panels end up optimized for.

“A technology that is very efficient in direct light as simulated in the lab will get a high efficiency rating, even if it is inefficient under indirect (e.g. early morning/late afternoon) or diffuse sunlight (e.g. cloudy conditions),” Castro said. “But a technology which is designed to be better under sunlight coming from many angles, as is the reality on cloudy days, may get a very low efficiency rating.”

“So even though OPV devices may be more useful for certain regions, the current rating system would brand them as ‘low-efficiency,’ deterring potential investors and customers. The fact that OPVs are thinner, more flexible, and cheaper to produce than conventional cells (and can also come in different colors, shapes, and levels of transparency) means opportunities for commercialization are aplenty, if only they can prove their efficiency.”

That is why Castro continues working with other OPV researchers and developers to come up with a new metric for PV efficiency based on the power output generated by solar cells during real operation, instead of the peak efficiency obtained in a lab.

Castro said the need for international partners to agree on measurement standards slows things down a bit, but he expects significant progress within three years.

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