Published on May 11th, 2013 | by James Ayre


Harvesting Electricity From Plants — Plant-Based Energy Generation

May 11th, 2013 by  

Harvesting electricity directly from the best solar power plants in the world (photosynthetic plants)? Sound too good to be true? Well it may be a possibility in the near future, thanks to new research from the University of Georgia.

Image Credit: Leaf via Wikimedia Commons

Image Credit: Leaf via Wikimedia Commons

Researchers there have developed a way to “interrupt” photosynthesis and redirect the electrons before they are used to make sugars. If you’re wondering why this is a potentially importent discovery, it’s because photosynthetic plants function at nearly 100% quantum efficiency. What that means is that almost every photon of sunlight that is captured by the plant is converted into an electron. For comparison, most of the solar cells of today operate at about 12-17%. That’s a huge difference, and potentially a huge improvement in efficiency for solar energy generation. Though, of course, that’s only if the technology and economics can be worked out….

“Clean energy is the need of the century,” said Ramaraja Ramasamy, assistant professor in the UGA College of Engineering and the author of the paper published in the Journal of Energy and Environmental Science. “This approach may one day transform our ability to generate cleaner power from sunlight using plant-based systems.”

For a bit of background, during photosynthesis, the photons that are captured by the plant are used to split water molecules into the component parts of oxygen and hydrogen. By doing so, they produce electrons. The electrons are then utilized by the plant to create sugars that are then used by the plant (and the animals that eat it) for growth and reproduction.

The press release from the University of Georgia gets into the specifics:

The technology involves separating out structures in the plant cell called thylakoids, which are responsible for capturing and storing energy from sunlight. Researchers manipulate the proteins contained in the thylakoids, interrupting the pathway along which electrons flow.

These modified thylakoids are then immobilized on a specially designed backing of carbon nanotubes, cylindrical structures that are nearly 50,000 times finer than a human hair. The nanotubes act as an electrical conductor, capturing the electrons from the plant material and sending them along a wire.

As a result of the first, small-scale experiments of this technology, electrical current levels that are two orders of magnitude larger than any previously reported in similar systems have already been produced.

There is obviously a great deal that would still need to be done before such a technology could be commercialized, but it’s definitely an interesting one….

The researchers are currently working on improving the output and stability of the technology.

“In the near term, this technology might best be used for remote sensors or other portable electronic equipment that requires less power to run,” Ramasamy said. “If we are able to leverage technologies like genetic engineering to enhance stability of the plant photosynthetic machineries, I’m very hopeful that this technology will be competitive to traditional solar panels in the future.”

“We have discovered something very promising here, and it is certainly worth exploring further,” he said. “The electrical output we see now is modest, but only about 30 years ago, hydrogen fuel cells were in their infancy, and now they can power cars, buses and even buildings.”

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About the Author

's background is predominantly in geopolitics and history, but he has an obsessive interest in pretty much everything. After an early life spent in the Imperial Free City of Dortmund, James followed the river Ruhr to Cofbuokheim, where he attended the University of Astnide. And where he also briefly considered entering the coal mining business. He currently writes for a living, on a broad variety of subjects, ranging from science, to politics, to military history, to renewable energy. You can follow his work on Google+.

  • I note that Daniel have gave a wonderful account of his findings which was 3 years ago may i suggest that there new research with photosynthetic plants and the reaction to energy which is in space with a view in growing them in a different atmosphere such as on Mars as the Sun is the reason for the quantum efficiency
    it has a completely different effect when introduced to a atmosphere like Mars
    which is 141,630,000 miles from the Sun.
    I understand that Tim, Scott, and Crew are/have done research but of course the Rover on Mars does the other.
    However the idea is to change the atmosphere the Manhattan project on Mars

  • me

    hows it goin


    gyvpthank u for ur time

  • Daphne

    Hi, where can I find the whole research?

  • Jack Harkness

    But don’t just imitate the process artificially. This would not be the best
    way to utilize the technology. Use the plants themselves to generate electricity.
    If you imitate it you are making synthetic things in a lab with tons of waste
    products. This is our chance to continue our development of future electronics
    and yet be more as one with nature. Grow plants that are just plants but
    generate electricity. No more panels. No more plastic and metal. Just seed
    to stalk to power.

  • Dan

    This being something i am interested in, what’s the best way of exploring this without jumping into a degree program that might not necessarily lead in the right direction?
    What are the prerequisites i need to study before i can explore this at this kind of level? I have a-level equivalent biology and chemistry but found that university study wasn’t leading me in the right direction for studying this.

  • Ronald Brak

    For something to be about 100% efficient at absorbing light it’s going to have to either be black or extremely close to it. There’s no way around that. Leaves tend to be green, so we know they’re not doing that. Leaves also let light get absorbed by accesssory structures instead of just chlororplasts. (Our eyeballs do the same thing, so it’s not as if we’re any better.) Basically its a matter of how much light gets to where it actually needs to go, which is kind of bad in a plant, but the efficiency once it gets where it needs to go is pretty darn high. Our solar cells are quite good at absorbing light, generally being blue black, but their quantum efficiency isn’t as high. Overall our solar cells are much more efficient than photosynthesis, but I can’t grow a crop of solar panels by sticking single cells in the ground and watering them.

  • Pingback: San Diego Loves Green – Harvesting Electricity From Plants()

  • Daniel Wilcox

    I think we need to be careful about saying photosynthetic plants are “the best solar power plants in the world.” There are certainly many things going for plants, including high quantum efficiency. What needs to be remembered is that quantum efficiency is not the same thing as energy efficiency: the electrons come out with much lower energy than the photons going in.

    At the end of the day, energy efficiency is almost always more important than quantum efficiency, and by that metric commercial solar cells have a clear advantage.

    For background: I do ultrafast research on photosynthesis, motivated in part because of its high quantum efficiency and the potential implications for solar power.

    • CarlMN

      So, Daniel, what is the difference between typical solar cells and this photosynthetic process in terms of electrical power efficiency? And what determines the electrical efficiency of each process?

      There are many ways to evaluate what might be judged as “best.” Considering the environmental impacts of mining and processing solar cell components, photosynthesis seems to be “best” in terms of being “greenest” in more ways than one.

      If you’re doing ultrafast research, I suspect you must be way ahead of most everyone else in the field (of green). 😉

      • Daniel Wilcox

        It’s hard to get really good power-efficiency numbers out of photosynthesis alone, since plants do so many different things.

        On the other hand, we can get a basic idea of the theoretical maximum power efficiency of both a silicon solar cell and photosynthesis using some relatively simple arguments.

        If you take a hypothetical crystalline silicon solar cell with well-engineered antireflection coatings or structure, then it will absorb pretty much all the sunlight with a wavelength shorter than about a micron. The internal quantum efficiency of crystalline silicon solar cells is often really close to 100%, so essentially all of the absorbed photons are turned into electrons, each of which carries about 1.1 electron-volts of energy. For comparison, most visible-light photons have somewhere between 1.5 and 3 electron-volts of energy, so there are two sources of energy loss here. First, all of the photons with longer wavelengths than about a micron are not absorbed. Second, most of the absorbed photons are converted to electrons that have lower energy than the original photon. Put everything together with the actual solar spectrum, and you come up with 31% being the theoretical efficiency limit of a crystalline silicon solar cell (if memory serves).

        Photosynthesis is more complicated, since as Ronald points out below, a lot of light is simply not absorbed. Also, in bright sunlight the internal quantum efficiency drops (the 100% quantum efficiency number is only true under low illumination). Finally, the electrons that photosynthesis produces are rather lower in energy than those of a silicon solar cell. Strictly speaking, photosynthesis doesn’t produce electrons so much as produce chemical reactions (turning water into oxygen, for example), so it’s even harder to really gauge energy efficiency. If you do something like the article suggests and take the electrons straight from the photosynthetic centers, then the energy of the electrons will strongly depend on exactly where in the photosynthetic chain the electrons were taken from. Putting everything together, I would hazard a guess that natural photosynthesis alone is 5-10% energy efficient, based on the above facts and based on the fact that whole plants are limited to 3% or 4% total energy efficiency (in terms of converting sunlight into plant mass).

        In terms of theoretical limits, if you were to take Photosystem II and directly collect its electrons at their most energetic point (which would be really hard), I’d guess around 15% total efficiency to be the limit. The bandgap is about 1.8 electron-volts at the highest-energy point which corresponds to a theoretical Shockley-Queisser efficiency limit of about 28%, but I’m guessing only about half the incident photons with more energy than 1.8 electron volts will be absorbed.

        • FactsAreFun

          Great reply. FYI, I remember reading that the theoretical limit for the thermodynamic efficiency of photosynthesis is around 6%. Actual chemical conversion efficiency of the best plant species in agricultural use seems to be less than 1%. Add to that the limited thermodynamic efficiency of converting sugars, starch or plant oils back to electric or mechanical energy, plus the energetic cost of agriculture and processing, and the total thermodynamic efficiency of plant based energy is on the order of 0.1%, or some 100-200 times less efficient than ordinary silicon cells. In other words… solar panels on the barn roof can produce as much net energy as a small farm can, in total.

        • CarlMN

          Thanks for your explanation, Daniel, I appreciate the effort you put into it and enjoyed learning from you about this. Since “The researchers are currently working on improving the output and stability of the technology,” it will be interesting to see what might come of this … if anything. Is there something that current theory doesn’t know or understand that might allow for photosynthetic electricity being made a practical reality, or is this all just interesting laboratory experimentation?

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