Solar Powered Chemical Processing

evileconboy writes "I found a great story about the creation of artificial porphyrin-based molecules that can absorb light like chlorophyll. The molecules absorb photons from porphyrin "antannae" charging a buckyball which acts like an acceptor. Apparently, the scientists want to use the molecule to drive other reactions. But I wouldn't be surprised if they could create a type of efficient, artificial leaf-like solar panel with these molecules. Forget silicon or other gallium based photovoltaic cells! "

Comments

Finally...

[DoorFrame]

A way to run my Mickey Mouse Clock without having to resort to the entire fascist system of "batteries."

Yes!

[konstant]

This is just the sort of thing I want to hear. Embed those puppies in my skin! I want to be green and foodless by the year 2020 goddammit!

But seriously, this is great news. Considering the shamefully small amount of money that goes into researching renewable sources of energy, I'm always delighted when they hit a new breakthrough. Solar is especially attractive - imagine running your entire home off a refrigerator-sized panel adhered to the roof. Total personal independence!

Unfortunately, there are severe limits at the moment. I recently looked into roofing a home with solar panels. Turns out that it would cost around $20k to be self-sufficient (and then only just barely). I worked it out, and it seems that with my monthly electricity costs, it would take me 103 years to pay that off.

http://www.mcn.org/a/mendom otive/Products/Unisolar2.htm

The trouble is that even the theoretical output of solar cells is low. It's bounded severely by the surface area because of the limitations of the diode materials available to us today. Turns out that even if you have full light shining on the surface, you can only get about 29% efficiency - and that's theoretical. In reality, it's less. Here's a site that explains the technical details:

http://www.nrel.gov/ncpv/documents/ pvpaper.html

Now, I have heard some clever ideas for increasing the efficiency. For example, one team discovered purely by accident that they could increase surface area by making the silicon layer extremely "spikey" on a microscopic level. The sunlight bounces around inside the spikes and is more likely to ultimately by trapped by a cell.
I think the theoretical number they cited was 40% efficiency, but right now that's still vaporware.

I wonder whether some slashdotter is brave enough to post the original ACS paper. I don't have access. I'd love to see what efficiency numbers these people are touting. Anybody?


-konstant

Re:Yes!

[scheme]

The trouble is that even the theoretical output of solar cells is low. It's bounded severely by the surface area because of the limitations of the diode materials available to us today. Turns out that even if you have full light shining on the surface, you can only get about 29% efficiency - and that's theoretical. In reality, it's less.

The best efficiencies I've seen so far is about 17% so its not that great. OTOH the efficiencies of combustion engines and power plants are only on the order of about 20-40%. I believe that maximum efficiency possible with Carnot egnine is about 40% with the current temperatures our engines run at.

Re:Yes!

[else...if]

40% is far more impressive than it sounds. That's on the same order as the efficiency of the human body, and vastly more efficient than anything else made by humans.

Re:Yes!

[Tau Zero]

OTOH the efficiencies of combustion engines and power plants are only on the order of about 20-40%. I believe that maximum efficiency possible with Carnot egnine is about 40% with the current temperatures our engines run at.

Combined-cycle gas turbine powerplants exceeded 51% thermal efficiency some years ago. And back in '92, Caterpillar was working on a new-generation diesel (insulated combustion chamber, turbo-compound energy recovery) which they claimed would reach 51% thermal efficiency without a bottoming cycle. I don't know what became of that one (fuel got too cheap, I guess).
--
Deja Moo: The feeling that

Carbon balls

[dattaway]

Here is the Nobel Prize in Chemistry given for the discovery of carbon atoms in a ball. It shows how you can make your own and play ball with them.

Coolness epitomised

[rde]

Geoff Ryman's excellent novel The Child Garden had our green-skinned descendents photosynthisising (sp?), and Ed Regis' Nano predicted the nanosuit that'd supply all our energy needs.
God, I love buckyballs. They can do anything. A beowulf cluster of these'd probably outcalculate Deep Thought.

Some questions left...

[aibrahim]

The innovation here is obviously in its early stages, but I would have liked to see some questions answered...

1. How suitable is this material for mass production ?

2. How much power can be generated per unit area ? I'd like to see the "theoretical maximum" and the actual measure of the current material. This would allow elementary comparisons between solar collector's and chlorophyll. This sounds like a great breakthrough, but exactly how good is it compared to what we have ?

3. What frequencies can the material respond to ? This question could be important to the space program, if materials can be made that convert even a fraction of the radiation from the sun to usable energy there could be a great saving in mission mass requirements ? This could come from simply replacing inert shielding with this material, thus you eliminate some power generation/fuel requirements, making the whole mission more efficient. Using this material as the membrane of a solar sail would be doubly effective, deriving propulsion as well as any energy requirements.

4. My previous inquiries beg the question, What is the tensile strength of this material ? How malleable is it ?

Again it is clear the technology is far from ready for prime time, but the possiblities are exciting.

Re:Some questions left...

[scheme]

2. How much power can be generated per unit area ? I'd like to see the "theoretical maximum" and the actual measure of the current material. This would allow elementary comparisons between solar collector's and chlorophyll. This sounds like a great breakthrough, but exactly how good is it compared to what we have ?

The energy incident on the Earth can be calculated by estimating the energy the sun emits (assume its a 5500K blackbody) and then figuring out how much is incident on a disc of the earth's diameter at ~ 1 AU away. If I remember right, the figure comes out to something like 14 W/m^2 within an order of magnitude. If we achieve the same efficiency plants do we'll be able to get about 30-40% of it in usable form (which is damn good).

What frequencies can the material respond to ? This question could be important to the space program, if materials can be made that convert even a fraction of the radiation from the sun to usable energy there could be a great saving in mission mass requirements ?

You can tailor its frequency response by attaching side groups to the porpyrhin rings or by changing the conjungation of some of the bonds within the rings. Most chlorophyll is most sensitive at about 720nm and 640nm since the sun's energy output peaks there.

Unfortunately this sort of material wouldn't be too effective in space without a lot of shielding. Most organics are fairly fragile and exposing it to the conditions in space would cause it to break down. Add in high energy photons(gamma, UV, x-ray) and the molecules start breaking down quickly.

Re:Some questions left...

[evileconboy]

I haven't yet read the ACS article, but I can take a stab at some of your (aibrahim)questions. (1) I'm sure they can mass produce this molecule with practice. Buckyballs are being made by everone now, and it's probably just a matter of getting the porphyrins to bond properly. (2)Since it's a theoretical paper, I doubt they talk about "efficiency" in it. All the paper is concerned about is driving chemical reactions. However, I doubt this material can do worse than our present photovoltaic cells. PV cells have at highest 29% efficiency. Chlorophyll, on the other hand, is extremely good at absorbing light (except, of course, green light). And since this new molecule uses the active light-absorbing parts of chlorophyll (porphyrins) it's probably just as good. (3) Molecule should respond to all visible light. Except "green." (4)Since this molecule has probably just been produced in small numbers and in solution, who knows what its tensile strength is? And having this material in a crystalized structure would probably just defeat its purpose. This material is good for (1) capturing light to excite electrons which jump to the buckyball and (2) giving the electron to some other mechanism. I think this could only happen in solution, much like a fuel cell.

It's still a while a way

[scheme]

Although its a greate achievement there is still a lot more to do. To actually use this you need to create a chain to transfer electrons and extract energy from it. Plants do this with photosystems I and II which generate NADPH(?) and ATP. The problem with this is that you get chemical engery out of it when you typically want electrical energy*. Although its possible to convert, you lose a significant fraction of the energy in the conversion. The technology may siimply not be viable if the energy received on a given area is too small.

(*)- Yes I'm aware you could create a system to generate a system that say generates ATP, and then uses the ATP to fuel a reductase or oxidase in order to run an electrolytic cell. This sort of system may work well for biological systems which have power consumptions on the order of 120 W (this is based on energy requirements of 2500 Kcal/day, fyi 1 Calorie in the nutrional sense equals 1000 calories in the biological sense). Photosynthetic systems work great in biology since plants concentrate energy over long periods of time, e.g. it takes 3-4 months to generate the energy required to produce a couple ears of corn.

Question: Reverse reaction?

[oren]

Is it possible to reverse the reaction to get a light-emitting device? Existing light sources are notoriously inefficient - most of the energy ends up as heat, instead of light.

Re:Question: Reverse reaction?

[ChrisDolan]

This already exists. A photodiode and a light-emitting diode (LED) are more-or-less the same piece of hardware with the voltage reversed.

Granted, they are silicon and not buckyballs, so that's boring, right? :)

Article missed a bet.

[Ungrounded Lightning]

Once you've got the pophyrins handing the electrons off to the buckyballs, why not connect the buckyballs to a chemical "wire" which is in turn connected to a metallic wire? Then you run the electrons through an external circuit (which they power), and back to the pophyrins.

The cell voltage (under light load) will be the voltage difference up which the pophyrins can push the electron (probably about the electron-volt equivalent of the associated photon), less any potential-differences the electron must travel getting from the buckys to the negative wire and from the positive wire back to the pophyrins.

Re:Other isotopes?

[Mr. Slippery]

Isotopes? ISOTOPES???

Have they redefined basic terms since I had chemistry back in high school? Different sized buckyballs wouldn't be different isotopes (different atomic weights of same element due to different neutron count), or even different isomers (different structures made of same set of atoms), they'd be different molecules. Or did someone sneak crack into my rootbeer?

Make that "porphyrins"

[Ungrounded Lightning]

(Oops. Made a consistent typo in the above post.)

Proof-of-concept only

[homunq]

This is exciting, but all the specifics will have to change before you get a practical application of this tech.

1. Manufacturability: These guys have connected 3 molecules of porphyrin to "conducting arms" and to a fourth "custom modified" porphyrin with a buckyball on it. That's a whole lot of custom reactions. Even if you could run these reactions in a vat instead of a test tube, there have to be at least a few of them where the maximum theoretical yield is pretty low.

2. Efficiency: as the article explained, real photosynthesis has to hand the electrons off many times before it can get useful work out of them. Things may get easier when you want electrons out the end instead of ATP, but this is still only the first step. And even in this step, you've already lost a lot of the energy. The reason a buckyball ion is so stable is that the charge distributes over 60 atoms of carbon. The electron is pretty happy there - it doesn't have a whole lot of oomph left to power your [wearable beowulf cluster].

Sure, this reaction may help us understand the chemistry of modified photosyntheses, but in the long run, I'd bet that the first green photocells will crib a lot more from life than just one part of one molecule. In other words, the pure chemists have to start talking to the genetic engineers a lot more than these ones have.

Re:Other isotopes?

[Mozo]

I think "allotrope" is probably the word the original poster is looking for. Graphite, diamond, and the various buckyballs are allotropes of carbon, i.e. structurally different forms of an element.

See http://www.dictionary.com/cgi-bin/dict.pl?term=all otrope