The Intertubes were buzzing all weekend with news that a solar cell the size of a book could convert enough solar energy to power an entire house. That’s a matter of solar cell efficiency, of course, so let’s take a look and see what’s cooking.
Solar Cell Efficiency, Funnel Cake Style
Speaking of cooking, the new PV research comes from the University of Exeter, which describes the breakthrough as a kind of “funnel” effect:
The idea is similar to pouring a liquid into a container, as we all know it is much more efficient if we use a funnel.
If you ever watched a funnel cake being made (or, for that matter, sausage being made), the funnel effect looks simple enough.
Translating the funnel effect into solar cell efficiency, the idea is to corral an amorphous collection of electrical charges into a more precise area, where they can be transferred into use. That’s where the efficiency magic happens:
While current solar cells are able to convert into electricity around 20 per cent of the energy received from the Sun, the new technique has the potential to convert around 60 per cent of it by funnelling the energy more efficiently.
60% Solar Cell Efficiency? A Strain, Not A Stretch
So much for the big picture. The problem is how to bump the charges from points B-Z over to A without using an actual funnel. The Exeter team took a cue from the IT field, both computer and human:
Manipulating the motion of charge carriers by means of an electric field has been a stepping stone in a wide range of sectors. From electronic circuits to synapses in neural cells, the electric field control over the dynamics of charges underpins a vast range of computing, storage, sensing, communication and energy harvesting tasks.
In particular, the team zeroed in on strain. Strain is a measurement of the original length of a material compared to its length when stretched or compressed.
Engineering strain into a material can enhance its electrical properties. However, conventional materials can only be strained so far before they break apart.
That’s where 2-D materials come in. As described by the Exeter team, atomically thin materials like graphene can sustain relatively high levels of strain. The team anticipates strain levels topping 25%, compared to a peak of just 0.4% for conventional materials.
The implications for solar cell efficiency are clear:
One tantalising charge transport phenomenon that could be accessible owing to large values of strain is the funnelling of photoexcited charges away from the excitation region and towards areas where they can be efficiently extracted.
As for which material they used, graphene is a good guess but that’s not it. The Exeter team used something new on the CleanTechnica radar, hafnium disulphide (hafnium is a silvery gray transition metal).
Coal Is Dying, With Or Without 60% Solar Cell Efficiency
The Exeter team sees their research as a “gateway” for further R&D, so don’t wait around for them if you’re thinking of getting rooftop PV. Go ahead and do it now (for those of us in the US, rooftop solar is still a good deal, PV tariffs or no tariffs).
Meanwhile, here in the US the current level of solar cell efficiency is combining with other forces — natural gas and wind power, to name a few — to knock coal power plants out of the picture.
In the latest development, last week our friends over at Utility Dive noticed something that few others did. The massive Colstrip coal power plant in Montana has been suffering through an unplanned shutdown, but its electricity customers are not suffering along with it.
The Billings Gazette has the details, so do follow this link and support local journalism. The plant’s two older units were already shut down for scheduled maintenance, and while that was happening the operator had to shut down two newer units because their pollution controls were not functioning as designed.
Six utilities own a stake in the Colstrip plant, and so far they have been able to fill the gap with non-coal sources and open market power purchases:
Right now without Colstrip electricity, those utilities are buying electricity on the spot market and doing so without interruption, sometimes at prices lower than the cost of Colstrip power. All six of Colstrip’s owners own other generating facilities, ranging from hydroelectric dams to wind farms and natural gas plants.
It’s not clear if that’s sustainable over the long run, but stay tuned. CleanTechnica is reaching out to Colstrip stakeholders to see if the weeks-long closure could have implications for the plant’s economic viability over the long run.
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Image (screenshot): The funnel effect in action via University of Exeter, YouTube.