Why Plants Are Green: US Air Force Behind New Solar Cell Research Breakthrough

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If President-elect Donald Trump is serious about tamping down progress in the renewable energy market, he’ll have to go through the US Air Force. The Air Force has been an important funding partner for foundational solar research, and the latest development has the potential for reducing the installed cost of solar power while boosting solar cell efficiency.

Why Are Plants Green?

It only took a few billion years or so, but Mother Nature developed solar energy converter systems that operate seamlessly and efficiently with minimal inputs, aka photosynthesis.

Scientists have been hammering away at the same problem and they have made a lot of progress in just a few generations, particularly in the last several years. However, there is still a lot of room for improvement.

Photosynthesis offers a pathway to achieve even greater efficiencies with lower costs. The problem is that the mechanisms involved have yet to be identified and described in sufficient detail.

For example, until recently little research has been done into a fairly obvious question: why are plants green?

Why Plants Are Green

That’s the question that intrigued physicist Nathan Gabor of the University of California-Riverside back in 2010.

It took six years and a “deep dive” into biology for the answer to come back, but eventually it did. You can get all the details from Gabor’s UC-Riverside research team in the journal Nano Letters, under the title “Natural Regulation of Energy Flow in a Green Quantum Photocell.“

For those of you on the go, here’s a snippet from the abstract:

Under erratic solar irradiance conditions, unregulated power fluctuations in a light-harvesting photocell lead to inefficient energy storage in conventional solar cells and potentially fatal oxidative damage in photosynthesis.

Did you get all that? Basically the research team set out to find out how plants manage to absorb enough solar energy to grow, while rejecting wavelengths that can damage or even kill them, all while dealing with fluctuating energy inputs.

Here’s the rundown from UC-Riverside:

The goal of the UC Riverside teams was to design the simplest photocell that matches the amount of solar power from the sun as close as possible to the average power demand and to suppress energy fluctuations to avoid the accumulation of excess energy.

They ended up designing a photocell that absorbs two different colors of light. The two wavelengths balance each other out, switching back and forth as the input fluctuates from high to low and back again.

The final result is a photocell that absorbs a spectrum of light that appears “nearly identical” to that absorbed by green plants.

One key color missing from the new photocell equation is green. The research team found that green light provides no self-regulating benefit:

The findings led the researchers to propose that natural regulation of energy they found in the quantum heat engine photocell may play a critical role in the photosynthesis in plants, perhaps explaining the predominance of green plants on Earth.

The findings also mesh with other research indicating that certain chlorophyll (think: green) molecules could play a role in preventing excess energy buildup in plants.

If all this is starting to sound a bit familiar, a solar cell research team at Israel’s Technion has been pursuing a pathway for absorbing and reclaiming energy that is otherwise lost in the form of heat.

US Air Force Hearts Solar

All this stuff is years away from influencing commercial solar cell design, but that doesn’t seem to bother the Air Force or, for that matter, NASA, which chipped in with support from its Fellowships and Internships in Extremely Large Data Sets (FIELDS) research center at UC-Riverside.

That’s just one example of foundational solar research supported by the Air Force that can benefit the US solar industry (here’s another recent example) eventually.

The impact on solar costs could be huge. Conventional solar arrays require converters and regulators to deal with fluctuating energy levels. Replacing them with less expensive devices — or eliminating them altogether — would make a big difference in the installed cost of solar power.

Meanwhile, the Air Force has been very busy at the shovels-in-the-ground end of things. The Air Force was an early adopter of utility scale solar at its bases, and this year it has partnered up with the US Army’s team of solar experts to accelerate those efforts.

The Air Force has also been an early adopter of vehicle-to-grid technology, so stay tuned for more on that.

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Image (cropped): “In a light harvesting quantum photocell, particles of light (photons) can efficiently generate electrons. When two absorbing channels are used, solar power entering the system through the two absorbers (a and b) efficiently generates power in the machine (M)” by Nathaniel Gabor and Tamar Melen.