Plug Into a Plant: a New Approach To Clean Energy Harvesting

cylonlover writes "Millions of years have evolution has resulted in plants being the most efficient harvesters of solar energy on the planet. Much research is underway into ways to artificially mimic photosynthesis in devices like artificial leaves, but researchers at the University of Georgia are working on a different approach that gives new meaning to the term 'power plant.' Their technology harvests energy generated through photosynthesis before the plants can make use of it (abstract), allowing the energy to instead be used to run low-powered electrical devices."

Comments

The Potato Clock?

[jellomizer]

It sounds like a new approach to the Potato clock.

However I would like to point out the trade off. If you are going to produce energy with plants, (Sound green and all) but you will probably need to strip forests to give enough sunlight, as well as irrigation. For these plants that will not grow too much, because most of their energy is being taken away. You are better off growing switchgrass or other material to produce energy.

Photo synthesis is not all that efficient.

[140Mandak262Jamuna]

From what I understand the efficiency of photosynthesis used by the plants is quite poor. Just about 2% or so. Even the chemistry used in photosynthesis has a theoretical maximum of 25%. Compare that to theoretical maximum efficiency of ideal Carnot engines at around 57% for typical gas engine source/sink temperatures and the 38%(? not very sure of this number, too lazy to look up) or so theoretical maximum efficiency for windmills.

Re:Photo synthesis is not all that efficient.

[140Mandak262Jamuna]

Windmill theoretical max is 59.3%. Not 38%.

Re:Photo synthesis is not all that efficient.

[TheRaven64]

Photosynthesis isn't very efficient, but it is very convenient. If you want the maximum possible conversion rate from solar energy, it's a terrible choice. If, however, you want something that can be cheaply deployed, then something that can self-assemble from light, water, atmospheric carbon dioxide, and a few trace nutrients is quite attractive in comparison to photovoltaics.

Re:Photo synthesis is not all that efficient.

[140Mandak262Jamuna]

We clearly don't have all we need. I was just pointing to the fact "evolution has achieved the maximum efficiency" is a false statement. Usually they will play with the definition, and it is a warning sign. In this case they define "perfection" as the ability of the plants to emit an elector for each photon captured. But leaves and structures do not capture all the photons. They reflect most of it, not unlike solar cells. But in solar cell we define efficiency as the energy delivered to the wire to the solar energy incident on that surface.

OK, coming down further, plants do not use all the electrons, since they are trying to do an energy absorbing chemical reaction using that energy. Apples to solar cell comparisons show that photosynthesis is about 2% efficient in most plants, sugarcane reaches a peak of 7%.

But we can define cost efficiency to account for the cost of making it more efficient. If it is bio mass, that grows, replicates by itself and sustains itself, the cost of "manufacturing" the cell is practically zero. Cost of input energy is zero. Economically speaking bio mass, based on switch grass or algae must become cost efficient and competitive. It basically the interest on the cost of installation that determines economic viability of such projects. When other forms of renewable energy harvesting has such long history and hard data, this new fangled thing that has carbon nanotubes woven into leaf structure, is novel, interesting and might prove useful in a decade or two. But that is all that it is. A novelty. Nothing to get over excited about in the field of renewables.

The breakthrough we are all waiting for in renewables is not technical/scientific anymore. It is economic. Cheap natural gas is making coal too expensive. It is a good news bad news situation. Coal is not going to be economically viable soon. So powerplants grand fathered out of clean energy act which are steadfastly refusing to upgrade pollution control still burning coal all will switch to natural gas reducing pollution. But the bad news is, coal is replaced by even cheaper natural gas. The renewables must now beat even more cheap source of energy.

Re:Photo synthesis is not all that efficient.

[cjameshuff]

Except they're apparently harvesting the photosynthetic structures from plants and then incorporating them in something resembling a dye-sensitized solar cell using some exotic carbon nanotube substrate. That's not self-assembling, and given the lack of any cellular repair mechanisms, probably not very long-lasting.

Re:Photo synthesis is not all that efficient.

[angel'o'sphere]

Wind mills are ofc close to 100% efficient ... sigh, where do those strange numbers come from? In practice - however - they likely only yield 85%.
Note: a windmill is a mechanical beast, forget your thermodynamics bias.

Re:Photo synthesis is not all that efficient.

[jkflying]

It depends on the temperature differential. The higher the difference the more efficient the engine.

Re:So now we're stealing energy from plants?

[ArcadeMan]

The Matrix: Vegan Edition.

Not at all efficient

[cjameshuff]

Plants are nowhere near "the most efficient harvesters of solar energy on the planet". The most efficient plants, such as sugar cane, reach around 8%, on par with the very lowest efficiency photovoltaic modules. More typical efficiences are 0.1% to 2%.

Pracctical joke come true

[Errol backfiring]

When I was camping in a forest, I saw somebody who had mounted a wall socket on a tree, put his shaving mirror on top of it, and plugged his (rechargable) electric razor into it and shaved himself, so it looked like the razor was powered by the tree.

English Laurel

[PPH]

I have an English laurel hedge. I'd plug into it except it has one of those big British style receptacles and I've lost my adapter.

Article is flat-out wrong.

[Geoffrey.landis]

This statement "Millions of years have evolution has resulted in plants being the most efficient harvesters of solar energy on the planet" is flat out incorrect.

Plants come in at about 2% energy conversion efficiency. The best solar cells are over 35% conversion efficiency.

Now, to be fair, plants aren't optimimized for energy conversion efficiency-- they are basically solar-powered engineering units that synthesize complex organic molecules and make self-replicating macromolecular structures out of little more than carbon dioxide and water, plus a few trace minerals... they are harvesting, mining, concentrating, and structural machines of amazing complexity. But "efficient energy conversion engines"-- no, not even close.

When the very first sentence of an article is factually incorrect, I have no interest in reading any more of it.

Re:Article is flat-out wrong.

[the gnat]

Plants come in at about 2% energy conversion efficiency. The best solar cells are over 35% conversion efficiency.

I think it depends on how you're counting. The 2% probably includes all photons hitting the leaf, which seems reasonable enough when comparing to a solar cell where nearly the entire surface is supposed to be converting photons to electricity. However, the individual proteins in plants that capture photons are indeed extraordinarily efficient. Nothing we can synthesize is as efficient on the nano-scale as Photosystems I and II - but of course since the plant is not made entirely of photosystems, the relative efficiency rate appears to be less.

Re:Article is flat-out wrong.

[Blaskowicz]

An other measure of efficiency would be to consider where the tool at hand is coming from. The solar panel comes from a big and expensive factory with all sorts of inputs, and the plant basically made itself.

Re:Article is flat-out wrong.

[Geoffrey.landis]

I think it depends on how you're counting. The 2% probably includes all photons hitting the leaf, which seems reasonable enough when comparing to a solar cell where nearly the entire surface is supposed to be converting photons to electricity. However, the individual proteins in plants that capture photons are indeed extraordinarily efficient.

No, actually they're not. Even if you're looking at the quantum efficiency of an individual photon absorption by a chlorophyll molecule, plant proteins aren't anywhere near as good as a decent solar cell, which will have very close to 100% quantum efficiency

I'm not sure where this myth that plants are extraordinarily efficient in energy conversion came from. They aren't. Energy conversion efficiency is not what they're optimized for. In evolution, "good enough" is good enough.

Re:Article is flat-out wrong.

[Anonymous Coward]

Nothing we can synthesize is as efficient on the nano-scale as Photosystems I and II

Typical solar cells now have an internal quantum efficiency well over 90% across the whole visible spectrum and slightly into near IR. Even when factoring in reflectance and issues with getting light into that region, the external quantum efficiency is over 80% from middle of blue into near IR. Photosynthesis on the other hand, has an internal quantum yield of about 10% in the red and blue regions, and dips to about 5% around the green region.

Re:Article is flat-out wrong.

[bluefoxlucid]

Plants take an amazing amount of energy to make. They require constant solar input and ground water to convert Carbon (from CO2, waste product O2) and Water (H2O) into sugars (CH2O) arranged as structure (cellulose), readily-available energy (simple sugars), and long-term storage (starches, i.e. potato). Initially a plant starts out as a seed containing a bunch of basic materials plus a bulk mass of energy (starch). Barley for example contains bulk mass starch and amylase; when wet, the amylase reacts with the starch to produce maltose, which provides the energy fuel to produce a plant capable of collecting a small amount of energy from sunlight. The plant then expends most of its resources manufacturing structure to grow and collect more energy. After it's grown enough, it expends a large amount of its own energy to produce seeds.

Plants cannot provide energy required for locomotion; some can produce tension by slow processes, such as by osmotic pressure or by generating chemicals and structures that respond to the chemicals to give one fast-twitch that takes up of 24 hours to reset (if they can ever reset--lots of one-shotters out there). Some plants are also under energy pressure due to predators stealing the structural and energy resources the plant has produced.

Plants primarily move by producing small seeds with little enough mass to float on the wind. This means the entire construction process must begin again to move one plant from one place to another--a maple seed must float on the wind several miles, then grow an entire tree. Plants accomplish this growth using only local resources, because they are expending all of their energy growing rather than driving trucks. The majority resources are water and air--redwoods are comprised of dense plant cellulose fiber, which is constructed by using carbon from CO2 and hydrogen and oxygen from H2O. All other components of plants are trace, comprising very little percentage of the mass, derived from the environment as well.

Solar panels are solid sheets of refined glass and other compounds. No energy is wasted constructing a massive redwood body to act as a substrate for a few sheets; instead, energy is wasted constructing solid silicon-based substrate at high concentrations. A plant attempting to achieve these high concentrations would require millions of years and an ungodly amount of energy expenditure.

Plants expend a lot of energy to use a lot of space to produce very little usable energy.

Re:So now we're stealing energy from plants?

[Hazelfield]

That would be a rare example of a sequel that actually makes more sense than the original.

Real numbers

[jklovanc]

The only vaguely relevant number in this article is the following quote;

The researchers say that small-scale experiments of this system have yielded a maximum current density that is two orders of magnitude larger than previously reported for similar systems.

Even that is meaningless as there is no basis for comparison. One hundred times a few milliamps at a few microvolts is still not much power.

I just love the following quote;

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.

It sounds like they are having issues keeping the thing from breaking down. Considering that the process interrupts the plant's ability to make food for itself longevity might be an issue.

As with many other "scientific breakthroughs" this looks like another "Give me more money for research" announcement.

Re:Isn't there an obvious flaw?

[cjameshuff]

They grind the plants up, extract the thylakoids from the chloroplasts in the plant's cells, and somehow bind them onto a base electrode covered in carbon nanotubes (it's not clear where the other electrode is). So no, the plant is not going to be doing anything with the energy produced. It's also not going to be doing any repair or replacement work on those extracted bits of cellular machinery, or reproducing, etc.