Clean Power Joule recycled CO2 carbon capture ethanol

Published on May 12th, 2015 | by Tina Casey


Buh-Bye, Corn Ethanol: Joule Makes The Same Thing From Recycled CO2

May 12th, 2015 by  

The biotech company Joule Unlimited has just announced that its unique brand of recycled CO2 ethanol has successfully passed a round of third party testing, bringing it another step closer to commercializing the product in Europe and the U.S. Somewhat coincidentally Joule has just closed a $40 million round of financing, which will enable it to expand its flagship plant in Hobbs, New Mexico to commercial scale. The ultimate goal is to convert 150,000 tons of waste CO2 into 25 million gallons of ethanol per year at that facility. If you’re starting to hear a loud hammering noise, that would be another nail in the coffin of corn ethanol.

Along with our sister site we started following Joule’s solar powered, microbe-assisted recycled CO2 technology in 2009 when the company emerged from “stealth” mode, but we haven’t really checked into it since 2010. Our bad, since a lot’s been happening since then!

Joule recycled CO2 carbon capture ethanol

Sunlight + Recycled CO2 = Sustainable Ethanol

The basic idea behind recycled CO2 ethanol is to capture waste CO2 from industrial operations and convert it to liquid fuel. If that sounds a little space agey, the U.S. Department of Energy is all over waste gas-to-fuel technology.

Not for nothing, but back in 2010 MIT Technology Review named Joule’s “solar fuel” among its top ten list of “most important emerging technologies.”

Back then,  Joule was working on a pilot recycled CO2 plant in Leander, Texas, which illustrates how the “solar fuel” process works.

Here’s how we described the company’s modular, scalable technology:

The heart of the process is the company’s proprietary SolarConverter, which contains photosynthetic organisms in a bath of brackish water and nutrients, with carbon dioxide fed in.  While the concept is similar to producing algae biofuel, there are several significant twists.  The organisms are not algae, they are bio-engineered proprietary organisms [cyanobacteria] that produce and secrete fuel without the need for costly fermentation processes, extraction or refinement processes.  The system also skips the need to collect and transport large quantities of biomass.

The result is an ethanol that can be blended with gasoline, as Joule has just announced. The technology can also be applied to produce petrochemical equivalents leading to diesel, jet fuel, and gasoline among other products.

You can get the nitty gritty details in a 2011 paper titled “A New Dawn for Industrial Photosynthesis” published in the journal Photosynthesis Research. For those of you on the go, here’s couple of snippets from the abstract:

…These innovations are projected to operate at areal productivities far exceeding those based on accumulation and refining of plant or algal biomass or on prior assumptions of photosynthetic productivity. This concept, currently enabled for production of ethanol and alkane diesel fuel molecules, and operating at pilot scale, establishes a new paradigm for high productivity manufacturing of nonfossil-derived fuels and chemicals.

In there interests of cost effectiveness, the “free” energy from sunlight is big plus. Also helping things along is the process itself, which is designed as a single step, continuous-throughput system.


Recycled CO2 Ethanol For Your Audi, Anyone?

Specifically, the new recycled CO2 fuel meets the D4806 American Society for Testing and Materials standard for denatured fuel ethanol, and it likewise hits the mark for the EN 15376 German Institute for Standardization.

The certification effort is getting a huge assist from Audi, which has been working on a whole suite of alternative feedstocks to gas up its vehicles (the company is also interested in Joule’s “clean diesel” version of recycled CO2 fuel).

Audi has also been ramping up its electric vehicle efforts, so the company seems to be [wisely] hedging its bets — as much as we love EVs, it looks like liquid fuels are going to be here to stay for the foreseeable future.

A World Awash In Recycled CO2 Fuel

As for Joule’s new $40 million round of financing, puts the company at $200 million for the Hobbs expansion.

The idea is to build in phases, a strategy designed to showcase the scalability of SolarConverter. The company makes an interesting comparison to oil fields:

The catalysts, systems and processes undergoing optimization in Hobbs will form the fully-validated blueprint for future commercial plants, representing an entirely new generation of above-ground fuel wells. At full-scale commercialization, a 10,000 acre Joule plant will represent a reserve value of 50 million barrels of solar-derived fuel, equivalent to a medium-sized oil field.

The size of the full scale plant is a little off-putting in terms of land use, but there is a potential to build on brownfields and other pre-developed sites rather than ripping through ecologically valuable landscape.

According to Joule, more than 1,000 sites have already been identified around the world that could be suitable for SolarConverter development. We’re thinking most of those would be located in and around existing industrial parks, where recycled CO2 is ripe for the picking.

Water resource issues could through a hurdle in the way of site availability, but the system’s reliance on non-potable sources provides it with a good deal of flexibility and opens up the potential for recycling industrial wastewater as well as CO2.

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Image credit (image enhanced): Courtesy of Joule.

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About the Author

specializes in military and corporate sustainability, advanced technology, emerging materials, biofuels, and water and wastewater issues. Tina’s articles are reposted frequently on Reuters, Scientific American, and many other sites. Views expressed are her own. Follow her on Twitter @TinaMCasey and Google+.

  • Coley

    Could the CO2 from FF power stations be used in this process?

    • Bob_Wallace

      Could. But the cost of capturing the CO2 makes it very expensive. One doesn’t just slap a device on a coal plant smokestack, plants pretty much have to be built from the ground up.

      Overall, costs are simply too high. And we’d still be pouring CO2 into the atmosphere.

      There are better solutions.

  • NRG4All

    I don’t think this is the answer. There are forces allied against ethanol. Even E15 is being fought because it apparently degrades certain components in gas engines. There is also the problem of its effects on lawn mower, snow blower, trimmers, etc. gas engines.

    • Brooks Bridges

      That corn ethanol ever saw the light of day is testament solely to the power of our industrial agriculture lobby. Sugar cane is a far more efficient for producing ethanol .

      There may be some good uses for Ethanol independent of adding it to gasoline – I’m ignorant – but it totally sucks as a gas additive.

      • Aku Ankka

        Sugarcane is more efficient, but that’s not completely relevant given that most US acreage is not suitable for growing it. So it works well for Brazil, but wouldn’t be much of an option in the US.
        There are other possible plants that would work better, but I think the main advantage of corn really is that growing corn has been sort of perfected for the weather, soil conditions and the whole production chain.

        As to ethanol, likewise it is not a bad compound to add if:

        1. You can’t produce actual main hydrocarbon you want to burn (directly create combustion-engine gasoline, or something easily convertible)
        2. You want to end up with a solution that works well enough for engines in existence

        So the whole thing is much easier to understand if you start from endpoint of (a) having millions of cars with engines that are designed to burn specific hydro-carbon liquid and (b) also happen to have full agricultural setup optimized to produce certain crops (c) you want to replace part of primary fuel (dinosaur juice) with something producible with (b).

        Conversely, if you start from scratch, assuming everything can and needs to be built from ground up, solution would obviously look very different.

        • Bob_Wallace

          Sugarcane does well in a lot of the Southeast. And sugar beets are a major winter crop in California.

          • Larmion

            Then again, high value crops like soft fruit, ornamentals and vegetables also do very well in the Southeast. Energy crops aren’t big money spinners; they can’t compete with food crops in a favorable climate and with sufficient local demand from urban areas.

            Oh, and they’ll have to compete with cellulose crops like Miscanthus soon. Buy bye indeed.

            Sugar beets are just horrible for biofuels. Yields per acre are lower than with any other energy crop and processing costs are high. I once earned some money on the side by evaluating sugar beets as an energy crop for a struggling sugar plant looking for a new earner. Biggest dissapointment of my career, that.

        • Brooks Bridges

          I am amazed that you go to all this trouble to justify corn ethanol. It’s been so long I don’t have links but I remember clearly its net benefit is zero or so near zero it doesn’t matter. It takes as much fossil fuel energy to produce it as the energy the ethanol delivers. So what difference does it make if you grow corn efficiently? You’ve gained nothing.

          As I said, any reality based analysis of the entire process years ago would have trash canned it. Only politics and a very powerful lobby saved it. It can’t die soon enough.

          • jeffhre

            Were those dated studies biased and shown to be worst case examples?

          • Brooks Bridges

            Ok, will you trust Forbes – radical left wing publication?

            Took me about 10 seconds to google and get this.


          • Aku Ankka

            No. You make a claim (“It takes as much fossil fuel energy to produce it as the energy the ethanol delivers.”) but do not support it by anything. Even cursory glance at, say:


            would have uncovered this:

            “In the current corn-to-ethanol production model in the United States, considering the total energy consumed by farm equipment, cultivation, planting, fertilizers, pesticides, herbicides, and fungicides made from petroleum, irrigation systems, harvesting, transport of feedstock to processing plants, fermentation, distillation, drying, transport to fuel terminals and retail pumps, the net energy content value added and delivered to consumers is about 1.3 – 2 times higher than the total energy input.”


            “The net climate benefit (all things considered) was in the early 2000s between 15 and 30% net savings,[7] but have since improved and is now approaching the European wheat and corn-based ethanol with typical values of 65-67 % reduction of climate gasses. The best European production lines are however reducing climate emissions with 90-95 %.”

            That’s all there is to it. Whether it makes sense is a complex discussion with no easy answers. But you seem to be taking the easy way out, making black-and-white out of much more complicated reality.

          • Brooks Bridges

            Again, those efficiencies are terrible. Starting at 1.3? And they don’t consider all the damage done by the fertilizer, pesticide, herbicides washing into various rivers, the Gulf, the Chesapeake Bay, or the CO2 produced by the tractors and the plowing of the fields Again, check sugar cane – far more efficient. I am NOT suggesting the stupid idea that we stop producing corn and start producing sugar cane. All these bio fuels produced by conventional farming, including Palm oil, are proving disastrous to the environment. We keep getting promised cellulosic but it’s starting to look like hydrogen for fuel cell vehicles. Again the Forbes article


      • Steven F

        Ethanol is actually a better fuel additive than many previously used a datives. My second car was a 1995 Saturn SL2. I got 33 miles per gallon on the freeway. Then California demanded manufactures make cleaner burning fuels. Ethanol was proposed. However oil companies switched to MTBE. They claimed it worked better. My mileage dropped to 30 MPG and after a couple of vears it was found in aquifers and water reservoirs. Excessive contamination of drinking water caused California to ban it and the switch was made to Ethanol. Ethanol is not very toxic (it is in bear and wine) and quickly breaks down if it gets into drinking water. My milage went back up to 33MPG and there was a notable drop in pollution levels in cities. Other states reported notable drops in pollution levels after MTBE was banned nationally.

        Ethanol is also a very good octane additive and is less toxic than many commonly used octane additives. If a ocean tanker hits a rock and spills the ethanol into the ocean very little damage would occur to the environment. Ethanol dissolves in water and quickly gets diluted down to very low levels. Such spills have occurred. when the emergency clean up crews arrived There was nothing to be done. There was no smell or and everything looked normal at the surface. Underwater fish and animals closest to the spill could have be killed But after a few hours dilution the water would be safe for wildlife. Bacteria would then quickly consume it. Many people buy fuel additives to remove water from the car fuel system. Many of those additive products contain ethanol. Cars using fuel containing ethanol often don’t have water in the fuel system because ethanol flushes it out harmlessly through the engine.

        If you grade all possible fuels based on Toxicity, environmental impact. octane rating, and freezing and boiling point and number sources, Ethanol would be high on the list.

    • Steven F

      Cars made prior to 1980 often had rubber and plastic partts that degraded when exposed to Ethanol. Ethanol started to appear in gas in 1970 and from 1980 car manufactures switched to different plastics and rubber material that are very resistant to Ethanol.

      For cars made prior to 1980 can be modified to run on E85 (85% ethano fuel) or even 100% ethanol. often the modifications needed are new fuel lines and new seals in the fuel pump and making adjustments to the carburetor. Once these changes are made older cars will run reliably on high ethanol content fuels.

      the argument that ethanol damages engines is a very old argument. Today most people reporting problems with lawn mowers, snow blowers, and trimmers, ether have very old equipment or just blame any failure (even those that are not caused by the fuel) on Ethanol. In other cases manufactures of lawn equipment try to keep cost down by using cheep component. Often when gas powered lawn equipment fails it is often replaced instead of being fixed. Many cars built today have been found to work well on e85 even when E85 is not recommended by the manufactures.

  • partyzant

    what about the cost of producing fuel with this method??? is it cheapper than fossil fuel?

  • Ross

    Will they perfect it before we’ve converted to battery based transportation. With the low Watts per square metre perhaps this has a longer term future in more specialised use cases.

    • Larmion

      It’s really not that helpful to see batteries and biofuels as being in direct competition (barring any unforseen massive breakthrough in either field).

      Electrified transport is ideal for relatively short distances (cars, buses) or for fixed routes (rail vehicles). Biofuels, meanwhile, are ideal for aviation, shipping and heavy machinery in forestry, agriculture and construction.

      Quite apart from any technical arguments, there’s also the potential of sustainable low-density biofuels as a tool for nature conservation (look at Tilman’s work, for a US example: and for a biofuel/biochar tandem to act as a net carbon sink.

      Those positive externalities are hard to put a price on, but at least to me they are a good enough reason to support advanced biofuels (as if the economic case wasn’t enough).

      Of course, there’s a big difference between viable biofuel production and the nice little idea in the article, which appears massively oversold (either by Tina or her source).

    • Michael G

      It is not yet clear batteries will be the ultimate transportation system. I don’t know what might be better but until it is clear batteries will win, we can’t neglect anything.

      There are problems with existing batteries such as degradation over time, cold weather degradation, and cost. I expect those problems will be solved but until they are solved, it is prudent to keep alternatives waiting in the wings.

      • Joseph Dubeau

        We need a solution for the US military.

        • JamesWimberley

          The solution in Costa Rica for the army was to abolish it, in 1948. Subsequent invasions of Costa Rica: zero.

          • Joseph Dubeau

            You very well know the U.S. military protects Costa Rica.
            It’s also a tiny country with a population of 5 million people.
            Since it’s my mother’s home country, that makes me 1/2 Tico.

  • Shane 2

    Using this sort of system you still release CO2 into the atmosphere but you get more useful energy before you release the CO2. Typically you might burn coal in a power plant produce CO2, then convert that to ethanol using sunlight and then burn that in your ICE car.

  • Dreck Sheisse

    Since Bush’s ethanol subsidies (and tax-free status for ethanol) made corn expensive and very profitable, hay and alfalfa prices have gone through the roof because farmers switched to corn to get the subsidized price for corn.
    Good riddance to corn ethanol, a stupid idea if there ever was one.

    • Larmion

      Yep. Because what we need more of is cheap fodder for an already oversized cattle industry.

      First generation corn ethanol is not the best idea in the world (the economics don’t work out for a start), but it’s impact the food supply is often overstated. So far, it has almost exclusively deplaced corn and other feed crops rather than crops grown for direct human consumption. That’s not a bad thing in my book.

      • Dragon

        Erm? Isn’t corn used in almost every processed food for human consumption these days? Remember, high fructose corn syrup is… corn.

        • Larmion

          It depends slightly on where you live, but in the US the breakdown is as follows:

          – 45% fodder
          – 30% ethanol.
          – 15% export (mainly to feed European pigs and chickens)
          – 8% corn derivatives for human consumption (HFCS, modified starch, corn oil,…)
          – 2% for human consumption, and even that’s mostly for producing alcohol rather than eating.

          Percentages vary from year to year, but it’s usually in that ballpark. Globally, the percentage used for fodder is even higher (reaching 85% and over in some European countries).

          Did you honestly believe we use enough HFCS and other processed starch derivatives to use the majority of the harvest of the world’s most widely grown grain? Big food is big, but not that big.

        • Aku Ankka

          I think that the claim “uses more CO2 than saves” depends heavily on parameters used and assumptions; that is, there’s wide range of estimates on this question. Would be nice to see a meta-study on this; my understanding was that consensus was on side of savings being slightly higher, but all things considered, not very impressively so.

      • d

        Actually the US cattle industry has been dropping in numbers of cattle. As of Jan 2015 we had the second smallest cattle numbers since 1952 in the United States. These numbers are being replaced by imports from countries that may have questionable health and safety monitoring. Most of the cattle in this country (mother cows and calves) spend most or all of their lives on grasslands that are not capable of sustaining a growing crop which humans can consume, and require no added water. Most of these grasslands are managed by family ranchers who have a vested interest in maintaining the grasslands in a sustainable manner. Not mention the amount of CO2 sequestration that occurs on grasslands.

    • d

      A couple of notes on your “expensive corn”. 1st, corn is now less than half the cost is was 2 years ago. ($8.00 in 2012 less than $4.00/bu 6/2015). Prices of hay and alfalfa are very much determined by location, but have also dropped in price by more than half since 2012. Granted 2012 was a terrible drought throughout the center of the country. ($200-300/ton in 2012 and $90-100 ton today)

  • Does this need a nearby fossil plant for CO2 input, or it can get the CO2 out from the air itself?

    • joshua

      It needs a nearby fossil plant, concentrating the CO2 from the air is too energy intensive to be economical.

      • No way

        Or even more interesting, a biomass plant.

  • sjc_1

    Buh-Bye…not really. Cellulose ethanol in Kansas and Iowa produces 100 million gallons per year, this not so much.

    An acre of corn costs a few hundred dollars to plant, yields more than 100 bushels of corn grain and 200 gallons of cellulose ethanol per acre . This requires millions of dollar per acre, but they don’t mention what the nutrients are nor what they cost.

    • just_jim

      The company’s website claims 25,000 gallons/acre at a cost of $1.25/gallon.
      I know, company claims – salt, but at least potentially we are talking about much more productivity per acre at competitive cost.

      Maybe more of a bridge fuel than shale gas, but not the silver bullet for CO2 neutral.

      • Mint

        Coskata claimed $1/gallon production costs for cellulosic ethanol, and they basically gave up.

        Corn ethanol also has the benefit of being able to sell most of the leftover materials as high protein distillers grain to feed livestock, so it’s gonna be tough for any other method to match it in price. I don’t think algal methods stand a chance, but I guess this has more potential.

        The title of the article is pretty laughable, though. The US produces ~15B gallons of corn ethanol per year. This plant is less than 0.2% of that, and isn’t even built yet. It’s akin to saying the gigafactory means bye-bye gasoline.

      • sjc_1

        The capital cost is the issue, an acre of corn might take $200 to plant, fertilize and water, an acre of this could cost $1 million.

        With cellulose and grain you could get 500 gallons per acre and this maybe 10,000 (remains to be proven).

        If the ethanol can sell for $2 wholesale and it takes $1 to make it, who will payback sooner. (hint the farmer does in 1 year, this would take 100 years.

      • joshua

        At that rate things would out to ~17 W/m^2

        Note: this is the ideal chemical energy present in the fuel, not taking into account transportation costs, or the ~25% efficiency of automotive engines.

    • joshua

      “1 acre produces 122 bushels of corn per year, which makes 122 × 2.6 US gallons of ethanol, which at 84 000 BTU per gallon means a power per unit area of just 0.02W/m2” – Sustainable Energy Without The Hot Air, page 284

      .02 W/m^2 = not worth the use of the land imnsho

      “In a sunny spot in America, in ponds fed with concentrated CO2 (concentrated to 10%), Ron Putt of Auburn University says that algae can grow at 30 g per square metre per day, producing 0.01 litres of biodiesel per square metre per day. This corresponds to a power per unit pond area of 4W/m2” – Sustainable Energy Without The Hot Air, page 285
      (watts / meter^2 is the average power output over the course of a year)

      So the biggest difference might be that the algae is 200X as efficient with respect to land use, while also using excess CO2 (or cyanobacteria, I imagine that the algae in my case would actually be WORSE that what is being proposed here). I can’t comment on the actual cost of the fuel produced however, since necessary numbers aren’t mentioned.

      I would try to do a similar calculation for the facility mentioned here, but the words:

      “At full-scale commercialization, a 10,000 acre Joule plant will represent a reserve value of 50 million barrels of solar-derived fuel, equivalent to a medium-sized oil field.”

      don’t make sense to me, after all, the facility doesn’t “use up” it’s resources, so the idea of “reserve value” doesn’t make sense to me.

      • Otis11

        Thanks for this – I was just digging up those numbers myself. Also wanted to add, solar is between 120-240 W/m^2. Even with a 10% transmission loss and 90% round trip efficiency for batteries (which is a gross underestimate), we’re looking at 25-50x better than their improved yields.

        While I do see a future for this tech in the chemical precursor industry (cosmetics, plastics, etc), and maybe niche fuels (like Jet fuel), the foreseeable future is in batteries and electrified transportation.

        • joshua

          That is true,

          but when calculated in a method similar to my first post, a PV solar farm would average ~5 W/m^2 over the course of the year.

          Therefore the claimed production of the proposed system is actually BETTER than a PV farm, albeit producing a lower quality energy (chemical vs electrical energy).

          • Otis11

            How do you figure the ~5 W/m^2?

            If we’re going for efficiency per land area, we wouldn’t use tracking (though even that gets a minimum of 12W/m2 by any reasonable calculation I can come up with…) but rather solid, South facing solar panels. Or actually flat panels if really optimizing for area, but that would be uneconomical… (or at least less economical, and I can’t think of an area with high enough land prices to justify that…)

          • joshua

            Those numbers are for this
            German solar park (Germany is cloudier, I know)

            I didn’t run those numbers personally (they are from the excellent book “Sustainable Energy – Without The Hot Air”, which is available free online)

            For a more well known plant in the US, the Topaz Solar Farm

            It puts out 1,100 GWh / year, and takes up 25km^2

            1,100 GWh / 25 km^2 * year = 5.023 W/m^2

            Interestingly, this plant is fixed rather than tracking, so I expected slightly better numbers.

            These numbers are worse than expected because they take into account the total footprint of the plant, not just of the solar panels. The numbers could obviously be improved, but I think that this is a fair comparison given these being real world examples of how these things are built.

          • Otis11

            While this is true, most of these are placed in areas where land is cheap so optimizing the solar (which is fairly easy to do) is not worth it economically. You end up getting more energy per land area, but less energy per panel. Most of the other technologies don’t scale to be more dense as readily. That said, either of these new technologies can be build on marginal or otherwise unproductive land, so that’s not too much of an issue… (Not that i’m for taking huge swaths of desert as “unproductive” as it does matter to the wildlife there, but as long as it’s done intelligently, we can minimize our impact.)

            Nice to see someone with solid numbers and research chops though – thank you!

  • JamesWimberley

    Perhaps they could reduce the land take by stacking the production cells vertically, as plants learned to do 500 million years ago.

    Cyanobacteria are the oldest form of life on Earth. Once the upstart photosynthetic eukaryotes got going and polluted the atmosphere with oxygen, the cyanobacteria retreated to weird extreme habitats like undersea volcanic vents. You have to hand it to them as sheer survivors.

    Purists will object that Joule’s technology relies on the continued existence of concentrated fossil fuel burners, so it’s not sustainable in the long run. But we will certainly still have some of these for quite a while.

    • Larmion

      You’re confusing Archaea with Cyanobacteria.

      Cyanobacteria are actually the original photosynthetic organisms that started ‘polluting’ the atmosphere with oxygen. Indeed, they were responsible for the extinction event that drove so many Archaea underground.

      Eukaryotes only acquired the ability to do photosynthesis when a proto-algae engulfed an ancestor of modern Cyanobacteria, which then eventually evolved into the much reduced endosymbiont we call a chloroplast.

      • JamesWimberley

        Touché! Memo to self: don’t comment just from memory.

      • nakedChimp

        like your comments James and Larmion, always nice to read some rumblings from people that do this by profession.

        • JamesWimberley

          Can’t speak for Larmion, but I play in the amateur league. Glad you like our contributions!

    • joshua

      “Perhaps they could reduce the land take by stacking the production cells vertically, as plants learned to do 500 million years ago.”

      The real power input here is solar, so as soon as you decrease the amount of light hitting the organisms, their output will likely fall off linearly or worse. Unless you’re talking about a solar tracking sort of option, but that actually uses more land area for the same amount of energy. (but produces more energy for every m^2 of “panel” compared to a ground mounted option).

      • Larmion

        Not per se. Plants achieve a leaf area index of up to 10, which means they have 10m2 of leaf area per m2 of ground covered.

        By arranging your leafs (or their synthetic equivalant) in an efficient stacking pattern, i.e. a Fibonaci spiral, you can achieve stacking without significant loss of output per module/leaf. Conifers take it even further by bouncing light between their needles, which capture light omnidirectionally.

        Without using any sort of tracking mechanism (which plants actually have), you can get an LAI of about 3. Still pretty decent if you ask me.

        • joshua

          I do agree with you on the point of conifers making use of reflected light, many tiny vertical tubes of cyanobacteria would be able to capture more light than a flat panel (or thin pond). Solar panel designs have been proposed that do the same thing, but with nanotubes. However, this only takes into account reflected light, which won’t lead to the 10X improvement mentioned above.

          The leaf area index is simply the surface area of leaves in a unit area, it does not take into account self shading, and therefore does not mean that having a value of 10 means you get 10m^2 of light for every 1m^2. It is used for measuring how dense foliage is in an area, and calculating plant respiration rates.

          stuff like this:
          isn’t done more widely because it is meant for decoration rather than efficiency

          • Larmion

            Oh, I’m certainly not suggesting the LAI is a perfect measure. However, the decrease in light capture is minimal up to a value of roughly four (it can be 2-5 depending on the exact leaf architecture of the species in question, but four is a good ballpark). For an erectophile crop like maize, the most shaded leaves still manage to capture 90% of what they could capture if fully free-standing at an LAI value of 3.

            James’ suggestion of vertical stacking isn’t entirely absurd. With a properly designed lay-out, you should be able to stack two or three layers without significantly hampering the bottom layer. Going much above that would require some elaborate and uneconomical contraption with lots of moving parts.

          • joshua

            You have convinced me that vertical stacking would be good, but I think that simply making a deeper pool of the stuff would accomplish the same outcome without additional expense and complexity

            The corn example is based on the fact that plants cannot take advantage of more than ~100 W/m^2 of light

            “Photosynthesis increases linearly with light intensity at low intensity, but at higher intensity this is no longer the case (see Photosynthesis-irradiance curve). Above about 10,000 lux or ~100 watts/square meter the rate no longer increases. Thus, most plants can only utilize ~10% of full mid-day sunlight intensity.[6] This dramatically reduces average achieved photosynthetic efficiency in fields compared to peak laboratory results. However, real plants (as opposed to laboratory test samples) have lots of redundant, randomly oriented leaves. This helps to keep the average illumination of each leaf well below the mid-day peak enabling the plant to achieve a result closer to the expected laboratory test results using limited illumination.”

            The higher LAI exists because the leaves hit with maximum light cannot take full advantage of it, and more leaves are placed below to catch the diffused light.

          • Larmion

            – A deeper pool wouldn’t work well. It seems fair to approximate the pool as a marine ecosystem, in which case the euphotic zone principle would apply: even in the absence of vegetation, light only reaches 50m deep. Given the high density of both organisms and nutrients in the growing medium, expect that to reduce by an order of magnitude at least. That puts a pretty hard cap on how deep you can go.

            – The limit you refer to is an inherent limit of the photosynthetic process that applies not just to the plant, but also to the Cyanobacteria involved here. Or maybe inherent isn’t the right word: we plant breeders have been able to increase it quite a bit and there are experiments going on that push it much, much higher.

          • joshua

            I don’t think its fair to approximate the pool as such. I would approximate the pool as a tall plant with a high LAI (I’m only talking about deep enough for 10s of cyanobacteria to be stacked vertically, not meters deep).

            The top organism get’s its % of the light, and the rest passes through it’s thin body, subsequent layers get less light, but still output near maximum because the light hitting them is still at or above the maximum amount they can use.

            Basically, I agree with you in theory, some sort of stacking method can improve efficiencies of cyanobacteria, algae, or plants. Where I disagree is in method, I don’t think some sort of stacked tray/pseudo leafs full of cyanobacteria will add anything, I think the effect that we are talking about will already be achieved by the pool of cyanobacteria. I am assuming that the pool isn’t a single organism thick, but also thin enough that light still filters down to the lowest layers.

            TLDR: The effect you are describing with LAI already takes place in any practical implementation of algae/cyanobacteria biofuel production.

          • Todd McKissick

            Missing from this excellent discussion on maximum usable flux density is wavelength. I don’t know what it is for these organisms but for most plants, there are only 3 colors of which they make use of. Due to this, a high efficiency solar cell producing 25% electricity from the sun can then power 3 LEDs focused on just the effective colors and actually gain ‘solar footprint’ because the flux of those three colors collectively is now higher than the original solar input.

            This leads to the possibility of deep wells, tanks or stacks being lit at optimum flux density of optimum color wavelength for raised footprint capacity. Not suggesting anything about economics but technically, it’s doable.

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