Solar photovoltaic cell panels under sunny sky Photo © Ljupco Smokovski \ Fotolia

Given all the ways in which humans are otherwise smarter and better educated than plants, you’d think we would have established a bit more of an advantage in our capacity to harvest the sun’s energy.

Without any access to higher education, plants routinely synthesize between 3 and 6 per cent of total solar radiation. Humans, meanwhile, use solar photovoltaic cells to record an average efficiency of 15 per cent – not bad, but hardly an overwhelming advantage.

And the plants, to be fair, had a head start.

Presumably unsatisfied with the current state of affairs vis-à-vis human-plant competition, researchers at the University of Cambridge claim to have discovered a way to extract solar energy at nearly 100 per cent efficiency.

The key, apparently, is in the study of particles known as ‘dark’ spin-triplet excitons.

In a press release filled with science that sounds like it was made up by Michael Bay to justify a bunch of on-screen explosions, lead author Maxim Tabachnyk exclaims, “The key to making a better solar cell is to be able to extract the electrons from these dark triplet excitons.”

Until now, solar cells have used the easy-to-manage single-spin “bright” excitons created by light photons. Their cousin, the dark triplet excitons, spin in such a way that it is difficult to harness their energy. So difficult, in fact, that it was previously thought impossible. This new breakthrough has smashed a hole through the theoretical solar efficiency ceiling.

One of the reasons why this is exciting is that the advantage of renewable energies has never been in their high efficiency.

Conventional solar cells operate at a high of nearly 45 per cent efficiency. Meanwhile, wind power achieves up to 40 per cent and has a theoretical limit of 59 per cent. What renewables lack in efficiency they make up for in, well, renewableness – there’s plenty of sun and wind available as inputs.

If solar PV can dramatically boost its efficiency level – especially to near 100 per cent – that has major implications for the push to displace oil and gas from the top of the energy pyramid. Oil power generation averages an efficiency level of 38 per cent, so it’s not like fossil fuels are untouchable in terms of their ability to turn energy into power without waste.

Photosynthesis requires excitons too, but only the single-spin kind. For now, plants will have to be content to trudge along at a frankly laughable 3 per cent efficiency. Or perhaps not – scientists around the world are currently working to increase plant photosynthesis efficiency in hopes that it will boost food production, aided by such donors as the Bill and Melinda Gates Foundation.

And so that eternal struggle for solar conversion bragging rights continues. Man vs. plant. Ultimately, the more effectively we can harness energy from the sun, the easier it will be to rely on that enduring source of heat and power over the next billion years or so.

The Earth has a lot more sun than it does oil, so it would be nice to be able to use more of it.

See how Hillside music festival used a solar water heater to cut energy use by 30 per cent.

Stu Campana is an international environmental consultant, with expertise in water, energy and waste management. He is the Water Team Leader with Ecology Ottawa, has a master’s in Environment and Resource Management and writes the A\J Renewable Energy blog. Follow him on Twitter: @StuCampana.

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