The Biofuel Grind

When we enter the decline phase of conventional oil—likely before 2020—we will scramble to fill the gap with alternative liquid fuels. The Hirsch Report of 2005, commissioned by the U.S. Department of Energy, took a hard look at alternatives that could respond to the scale of the problem in time to have an impact. Not one of the approaches deemed to be currently viable in the report departs from fossil fuels. But what about biofuels? To what extent can they solve our problem? We’ll dip our toes into the math and see where a first-cut analysis leaves us.

Photosynthetic Scale

If you add up all the photosynthetic activity on the planet—accounting for virtually all life except for oddball extremophiles—you get a number like 80 TW (80 trillion watts; I see credible estimates ranging from 40–140 TW). About half is from all the plankton in the ocean (and its derivative food chain), and the other half happens on land, capturing every microbe, plant, and dependents. Compare this to human power consumption around 13 TW, and to human metabolic activity of about 500 GW (7 billion people operating on a little less than 100 W, or 2000 kcal/day).

First, note that the human industrial power scale is comparable to the photosynthetic scale. If you react by saying that 13 does not look much like 80, fair enough. But I’m impressed by the similarity in the exponent: both are within a factor of three of 3×1013 W! Of all the places the comparison could have ended up, it’s about the same order-of-magnitude.

Next, observe that humans comprise about 0.6% of the total biological activity on the planet. I oscillate between thinking that this makes us a massively dominant species (of the millions of species, for any one to account for nearly 1% is impressive) to thinking that this is a small number compared to what I sense in my human-dominated daily life. But I don’t see the vast oceans or rain forests every day.

Finally, reflect on the fact that our industrial enterprise has amplified human power by a factor of 25 or more (13 TW compared to 0.5 TW). We carry a lot of muscle, thanks to fossil fuels. Let me see those biceps!

So our first stop along the way is to notice that converting our fossil fuel enterprises to biofuels would mean commandeering (enslaving?) a substantial fraction of the Earth’s bio-activity for our purposes. Factoring in the massive energy it would take to harvest the Earth’s bounty year after year, we would have to—for all intents and purposes—take over the Earth’s ecosphere to serve our ends.

Note that the dream of continuing growth to five times the current scale, as discussed in the post on what “sustainable” means is not possible via the bio-route alone.

Photosynthetic Efficiency

On the global scale, we can say that 70% of the sunlight incident on the πR² projected face of the Earth is collected by the Earth (the rest is reflected by clouds, atmosphere and land), and 50% of the total is absorbed at ground level. At 1370 W/m² of incident power flux, this means that the Earth’s surface is absorbing about 100,000 TW of solar energy. Thus global photosynthetic efficiency is about 0.1%. Pretty weak.

Okay, in fairness to photosynthesis, the limitation on the scale of bio-activity tends to be availability of water and mineral nutrients—not incident sunlight. Plankton blooms are associated with discharges or upwellings of (often nitrogen-rich) nutrients. Our agricultural fields achieve “corn blooms” year after year thanks to the use of fossil-fuel-derived fertilizers to provide such nutrient services.

How does an individual plant fare, given adequate care and feeding? One way to estimate our way into an answer is to guess at the mass put on by a plant in its growing season or lifetime, assign a caloric value of 4 kcal/g for the carbohydrates (and cellulosic) material, and compare this to the solar flux presented to its leafy area in the same time period.

Let’s pick the carb-o-licious potato plant for an example of an energy storage machine. Let’s say that our plant produces a half-dozen half-pound potatoes (about 1.5 kg) in a growing season—plus an equivalent mass in leaves, stems, and roots for good measure. 3 kg at 4 kcal/g yields 12,000 kcal of energy storage, or about 50 MJ (see page on energy relations for conversions). Meanwhile, perhaps a 0.5 m² footprint at an average summer insolation of 350 W/m² delivers about 2 GJ of solar energy in four months (the insolation estimate factors in day, night, weather, and the fact that plants are not flat—so better at collecting light than a flat panel would be). The result is 2.5% efficiency.

This is not too far from reported photosynthetic efficiencies: many plants in the world realize 0.01–0.1% efficiency, while well-tended crop plants tend to be around 1–2% efficient, and algae can reach numbers like 4–6%. I have to say that I gain much more trust in such reported numbers when common-sense estimation puts me in the same ballpark.

Case Study: Replacing U.S. Oil with Corn Ethanol

Most people have already caught on to the fact that corn ethanol is a poor substitute for petroleum in the U.S. Leaving aside corrosive challenges to storage, distribution, and politics, we’ll just look at energetics.

The U.S. uses about 7 billion barrels of oil each year, amounting to an equivalent power demand of 1.3 TW. Corn ethanol requires significant energy inputs to plant, fertilize, harvest, and process the corn mash into ethanol. Some estimates conclude a net energy loss. The more optimistic estimates put the energy returned on energy invested (EROEI) at around 1.4:1, meaning a net energy of 0.4 units for every 1.4 units harvested. Under the assumption that we use the energy derived from corn ethanol to run the whole operation, we get an efficiency of 0.4/1.4, or about 30%. Combining this with 1.5% photosynthetic efficiency for incident sunlight and 50% for a half-year growing season leaves us with 0.2% efficiency over the year.

During the growing season, and given the 3-d advantage plants have over flat panels, we’ll again use an optimistic 350 W/m² rate of insolation. Multiplied by our overall efficiency, this turns into 0.7 W/m² delivered to the ethanol product. To hit our 1.3 TW goal requires an area 1400 km on a side! The figure below illustrates just how serious this is.

Square area needed to replace U.S. oil demand with corn ethanol.

Ethanol from sugar cane can have a substantially better EROEI, somewhere in the neighborhood of 5–10:1. Brazil has pursued sugar cane ethanol in a big way, at the expense of rain forest. The resulting changes in micro-climate (desertification) and in soil quality/erosion may present significant barriers to sustaining this practice at a large scale.

Feeding the Beast

Another way to highlight how daunting a full-scale embrace of biofuels would be, consider that global oil consumption amounts to 6 TW of power (30 billion barrels per year, or 1000 barrels per second, at 6 GJ per barrel). This is about 12 times the human metabolic dietary intake—largely derived from agricultural lands. We’re not about to give up eating, so in the simplest analysis, we would have to find an additional cropland approximately ten times the area of our current cropland.

For scale, Earth’s land totals about 140 million square kilometers. About 50 million are classified as agricultural (includes permanent grazing land), and 13 million as arable. On what planet would we find enough land for sufficient biofuel crops?

Farmers work hard. Land issues aside, if we wanted to take the biofuel plunge, we would have to scale up farming efforts (and the number of farmers) by a substantial factor. Unlike solar panels, wind turbines, nuclear plants, etc., biofuels require a never-ending yearly push to plant, tend, and harvest the goods. The EROEI is poor, irrigation may not be available at scale, and bad growing seasons would seriously impact our economy.

This is why I call it the Biofuel Grind. We’ve become accustomed to living off of a fossil fuel inheritance, and we have been living like kings as a result. Transitioning to biofuels is like having to get a real job and work for the annual yield, year after year. No more freebees from nature, sitting around for millions of years waiting to be scooped up.

Cellulosic Plant Waste and Algae.

I have been treating biofuels as coming from food-crop-like sources. Some may think this to be unfair, given the potential for using agricultural byproduct, algae, etc. We’ll get to that. But first I’ll point out that virtually all the present biofuels are indeed from food crops: ethanol from sugar-cane and corn; and biodiesel from soy and vegetable oil crops. (I looked at why waste cooking oil for biodiesel is not scalable in a previous post.)

In principle, the energy stored in plant stalks and leaves could be converted to liquid fuel. Rather than sugars that can be fermented into alcohol, the cellulosic material must be broken down by other means. Termites do this in their guts, assisted by microbes. If termites (or these microbes) pooped alcohol or oil, we’d be in business—however icky their “business” might be. Many talk of genetically engineered microbes that could be coerced into making alcohol.

With genetic engineering, we can do anything. Witness the fact that we have eliminated most genetically-triggered diseases, eliminated the genes that cause cells (and people) to age, and can make a three-headed goat on demand. Or wait—that was a dream I had last night: then the goat turned into my mother-in-law. I’m eager to see us start racking up successes on the genetic engineering front, but it’s a hard, hard business, and talk is cheap. Let’s keep working on the magic microbe, but let’s also have a plan B in the works in case genetic engineering does not live up to its promise in the next several decades.

As for algae, these little buggers have some serious advantages over traditional food crops: no direct competition with food; higher photosynthetic efficiency; able to work in otherwise unproductive desert-land in bags/tubes; easier to harvest liquid systems (plumbing replaces clumsy harvesters combing untold acres).

An attractive idea is to erect towers of algal tubes/bags that would seem to make splendid use of land by building up into the third dimension. Let me caution against being overly swayed by this notion. There is only so much sunlight per square meter of land. Tilting a flat array of algal bags to face the sun is one way to make better use of a given land area, but depth in the direction perpendicular to the sun does little good: self-shielding keeps the deeper levels from being productive.

If we start with 6% efficient algae, and imagine that we could convert 50% of the stored energy into a useful form (including the energy cost of processing), then a desert location receiving an annual average insolation of 250 W/m² would produce the equivalent of 7.5 W/m² of useful energy. We would require a square about 425 km on a side, which is about the same land area as North Dakota.

The numbers for algae are certainly more favorable than for traditional (proven) biofuel sources. But keep in mind that we don’t see a clear path yet to squeeze useful juice from algae at appropriate scales/efficiencies. Much of the talk is around genetic engineering to make the algae excrete something useful in quantity. I need not repeat my case for non-complacency regarding this prospect. Also, anyone who has failed at aquarium maintenance (everyone who has tried?) knows how pernicious algae can be at clogging the plumbing and sticking to tube walls, etc. So they should also be working on genetically engineered teflon-coated algae. By that time I’ll also be able to enjoy that three-headed goat!

A Synthetic Approach

The one approach in all this mess I find I’m able to get excited about is synthetic photosynthesis. In particular, a large effort ($115M over 5 years) led by Prof. Nate Lewis of Caltech seeks to develop a solar-to-liquid process via artificial photosynthesis. I had already read about Prof. Lewis’ research, and was intrigued, when I saw a talk he gave at a recent conference. The talk was filmed and can be accessed here. Search for the word “Leaf.” (Incidentally, I also gave a talk summarizing some previous Do the Math posts: search “Expiration” if interested.)

Prof. Lewis summarizes the daunting scale of the energy challenge we face, and points out that because no other renewables come close to solar in terms of total energy availability, together with the fact that liquid fuels are by far the most energy-dense means of storage (short of nuclear), some day we will have a way to convert sunlight to liquid fuels directly. I hope he’s right, because this would indeed be a game-changer. Will we get there in time?

The bottleneck is that we do not know of a catalyst that can mediate the reaction in a way that is simultaneously efficient, robust, and cheap (pick two, Prof. Lewis says, and we can do it today). Their approach is to try every combination of up to three elements out of a total of twenty “interesting” occupants of the periodic table. Tried in a wide variety of fractional combinations and annealing processes, the combinatorics are ridiculous. But they are developing a method to screen a few million combinations at once (cleverly using LCD monitor indexing technology to measure currents in the samples deposited in a pixelized matrix). The expectation is that in 5 years, all sensible combinations will have been exhausted and tested.

There are 1350 ways that three elements out of 20 can be combined in X, XY, and XYZ arrangements. But now allow multiplicity in each element (up to 100 instances per element in the compound) and we get about 10,000 possible XmYn pairs where m and n are numbers from 1 to 100. I’m being lazy about knocking out duplicates—like X3Y6 and X11Y22 essentially being the same thing—just to get an upper bound, but I am also not considering the combinatorics of structural arrangements. In addition, there are one million combinations for any XmYnZo XYZ trio. This comes out to about a billion combinations altogether. Testing several million at a time, one set per day, allows this ensemble to be probed in a year. Allow for different annealing/preparation techniques and you have a few years on your hands.

I don’t mean this in a disparaging way, but it’s a lot like picking up the periodic table by its ankles, shaking vigorously (for a few years), and seeing if anything interesting falls out. I absolutely think this is what we should be doing: if we can, what possible reason would we have not to try? How will we know if it’s possible otherwise? But at the same time, it speaks to a bit of desperation. We honestly don’t know if it will work. Not everybody can be a catalyst, and one wonders why a catalyst better than any we have discovered by ordinary scientific processes has escaped our attention for this long. It could happen, and I sure hope it does. But let’s have a plan C.

Not an All-or-Nothing World

I have acted like we need biofuels to be able to completely replace our current oil consumption in the foregoing analysis. No one who is serious about the matter is proposing we do so, exactly. But I think it’s useful to appreciate limitations to ideas on our horizon so that no one is misinformed or simply assumes that any of the myriad solutions we discuss can plug the hole and make us whole. Don’t trust anyone who says that biofuels are the answer. Fine if they want to say “part of the solution,” but I’m not breathing easy at the claim that they’ll fix our wagon.

In any case, I can understand why biofuels were not considered to be a likely large-scale contributor to a crash mitigation strategy in the Hirsch Report.  While the fossil fuel solutions (e.g.,natural gas to liquids, coal to liquids) have their own scale challenges, they do not face the same sorts of bottlenecks or lack of demonstrated technologies that biofuels suffer.  Even so, the fossil fuel mitigation strategies will be hard-pressed to catch up to the decline in conventional oil, if full-scale initiation waits until the decline has started.  And in the end, the fossil fuel mitigation strategies will all face the same finite resource problems as conventional oil, and therefore can only represent a temporary solution.

So biofuels—as difficult as they are—may ultimately play a key role in applications where other options do not work. Airplanes really do need liquid fuels to keep doing what they’re doing. Trans-oceanic ships and cross-country trucks may also need whatever help biofuels can offer. Personal light-duty transport can more easily transition to electric drive—perhaps with biofuel hybrid reserve for the occasional trip. Indeed, the U.S. military is experimenting with biofuel airplanes. All I’ve got to say is that we’ll be disappointed with that choice if we continue to fight wars in desert regions!  Now if we could get our jets to fly high on opium…

For further reading (similar numbers, similar conclusions), see Helmut Burkhardt’s analysis.

46 thoughts on “The Biofuel Grind

  1. Great analysis Tom, except, like many I’ve seen, the Brazilian sugarcane bit seems tossed off with little investigation into the real effect cane cultivation has had on land use. This 2008 study in Ecological Applications lays it out well:

    Even with its expansion, cane makes up only 2.5 percent of Brazil’s agricultural land, with cultivation concentrated in the southeast and northeast coast. (The past five years are not included in their analysis.) So far, it finds, cane cultivation has not caused “any significant decline in the land cover of natural vegetation,” meaning deforestation. That doesn’t rule out cane pushing soybean farming into the Amazon in the future, but its cultivation would still need to starkly increase for that scenario to take hold.

    Cane growing in Brazil has had plenty of environmental costs — the paper goes on to lay those out thoroughly — but a look at the study shows why sustainability minded people have targeted Brazilian cane as a biomass source. Writing that it came “at the expense of rainforest” seems untrue — at least for now.

    • Thanks for the correction and information. I confess to being under-educated on this facet.

  2. Awesome article as usual. Thanks so much for sharing. Your thoughts echo mine verbatim except they are spelled out in perfect prose. I am very concerned that we are squandering our fossil inheritance at a rate that maximizes profit for a few companies.

    I really hate corn ethanol. I am willing to bet the EROI is actually negative. Care to revisit that topic on a future post?

    Another gotcha with algae is that there is an evolutionary pressure on them not to make a high energy output but rather make more algae. To anthropomorphize a bit – “they don’t want to poop oil!” This means once we had the perfect bug the population may evolve away into something that would out compete the magic one.

    So my take is bio fuels aint it but they may help a little.

    • Maybe introduce a genetically modified shrimp that will eat the algae pooping the least oil?

  3. Tom,

    I’d appreciate your analysis of this closed-system photosynthesis direct-to-diesel technology: It seems to make more sense to me than trying to go through corn, and converting that to ethanol, and having less-than-perfect efficiency at each step.

    I did some back-of-the envelope calculations, and it looks like this technology could produce about 240k barrels/year/sq mile. I had a hard time finding diesel usage statistics, but the best I could come up with was 14k square miles (or a square 120 miles on a side) would be required to make up for current US diesel usage. I’ve no idea what sort of water usage would be required for that…

    What do you think of this approach?

    • Yes Joule’s Cynobacteria approach is attractive. They claim, “15,000 gallons of diesel, or 25,000 gallons of ethanol a year on an acre of land, for as little as $20 per barrel-equivalent of diesel and 60 cents per gallon of ethanol.”[1]

      Using 20,000 gallons per acre-year requires 13 million acres (52,000 km^2) to entirely replace US oil consumption. That compares to the 60,000 sq km under till *today* for just corn ethanol in the US [2]. The method for CO2 and water sources could use some more explanation.


      • The figure I gave above for US corn ethanol acreage is incorrect and far too low; the given reference and others show the 2011 US corn acreage at 92 million acres, of which 40% goes to ethanol production in the US, resulting in 149e3 square km of acres dedicated to ethanol.

        Option C, after ethanol and Joule cynobacteria farms, might be solar PV which @30W/M^2 average over that area would produce an average 4.4TW.

  4. Unless Nate Lewis’s research turns out a miracle, how can anybody think of perpetuating “personal light-duty transport,” aka cars-first transportation? If the U.S. uses 10 percent of the humanity’s energy diet via oil (1.3TW/13TW), and if at least 75% of that is due to automobiles (the 71% for automotive fuel plus some unknown but appreciable share for the oil used in manufacturing cars and maintaining asphalt roads), and if personal cars use 60 percent of the total automotive oil, then cars-first transportation in the US eats 6% of the total human energy allowance.

    If automotive research were to yield the best imaginable advances, and if the U.S. were to compel everybody here to give up the right to own SUVs and muscle cars, this 6% might drop to perhaps 3%. So, even with this nearly unimaginable and highly unlikely outcome, personal car use in the US would require something like 3/4 of the entire per capita energy allotment (imagining that energy use somehow gets tied to a nation’s population share) here. Scale that up globally, and using perfected cars would mean humanity squandering 3/4 of its energy budget on that optional and arguably net-harmful technology. If we were to include the share of long-distance trucking that exist mainly to prevent rail movement/unionization of the relevant workforce, then the sum could approach 100 percent.

    While Nate Lewis has a 2% chance of figuring out commercially viable artificial photosythesis, there is a zero percent chance that cars-first living will make it into the extended human future. It was/is a complete pipedream, and capitalist cliff-drive. The sooner we see that, the better.

  5. A more fundamental question is: Does the Earth have the resources to sustain biofuels over the long-term? The answer is not encouraging due to one thing: Phosphorus. Phosphorus is an ESSENTIAL component of all living things. Currently, the world mines phosphate rock to provide the phosphorus to grow crops, but there is a limited amount left, and only in a few countries. This is a looming crisis that still has not appeared on people’s radar screens, but it should, because there are NO SUBSTITUTES for Phosphorus.

    • Good point, humdrum. Put another way, taking soil fertility and turning it into exhaust pipe smoke may not be a wise thing for a civilization to do.

      On a related note, I always bristle when the suits and media talk about converting “crop wastes” to energy. There are no “wastes” in nature. Whatever’s leftover after the crop is harvested should be left to decay or tilled back into the soil to feed the microbes and improve fertility.

    • Yes phosphorous is necessary for life, but unlike energy, it is never “consumed”; that is, there is just as much phosphorous on the planet today as there was 10,000 years ago. It is moved from one place to another, it may become more expensive to concentrate, but it does not go away.

      • Don’t forget entropy. When you accidentally put salt in the batter mix instead of sugar and stir, try correcting the mistake. All the atoms are still there, but that’s little consolation. Your point is a non-starter.

        • Topsoil could be recycled too, if we could find it [wink].

  6. As for energy alternatives, I liked what Stewart had to say at your recent Compass gathering re progress in nuclear fusion at Lawrence Livermore. He mentioned that at current trend, they are just one year away from sustaining 100 mS ignitions using deuterium.

    I’m not -counting- on any major energy breakthroughs, but if fusion becomes workable and scalable (ten ignitions per second, sustainable), our energy future becomes a lot brighter. Think 1 gigawatt inertial fusion engines that are relatively cheap, green, and scalable.

  7. Superb article. Thanks.

    I read somewhere that in addition to the 13 TW of fossil energy consumed, we also consume about 25% of the 80 TW of photosynthetic energy as food and energy, and another 25% indirectly as fiber.

    Does this ring true to you? If not, how much of the 80 TW do we already consume?

    • On the face of it, I don’t buy this number. The human metabolism is 0.5 TW in aggregate—far short of the 20 TW this statement would imply. But if we drill deeper, we see that we live high on the food chain and eat animals that have consumed photosynthetic inputs, so that our footprint/scale is increased by some factor (of several). I could see getting to a few TW this way (2, maybe). When we eat tuna, who ate mackerel, who ate sardines, who ate plankton (I’m just making this chain up, by the way), perhaps we have a larger amplification factor. I would have a hard time believing we could bootstrap this all the way to 20 TW, but I’m not going to draw a line in the sand on this one.

  8. “Don’t trust anyone who says that biofuels are the answer. Fine if they want to say ‘part of the solution,’ but I’m not breathing easy at the claim that they’ll fix our wagon.”

    Too true. Most people who study our energy predicament conclude there’s no silver bullet, but only silver buckshot.

    In my mind, even if we implement all the viable solutions, we’re too late, and they’re all too poor a substitute for oil, for us to continue endless economic growth and our high-energy consumptive lifestyle.

    Good times!

  9. [one of three illustrative points kept]

    The conclusion in the “Synthetic Approach” section about the irreplaceable “most energy dense” “liquid fuels” I think goes to far. Of course gasoline contains 47e6 joules per kg, some 60X that of a Li Ion battery, yadah, yadah. The story does not end there. Consider: i) thermodynamics tells us that some 2/3 of that energy must be thrown away in a heat engine, and ii) because of that heat waste more volume and mass of a transportation vehicle is necessarily tasked to heat transfer and exhaust mechanisms (large radiator, water pump, exhaust system, thermal firewall for passenger compartment, etc, etc). After all the system engineering is done, we end up with a gasoline fueled vehicle that today travels about 4X further than a battery powered one, not 60X, and the gap continues to fall over time.

    • This is a bit sloppy. To go 75 miles, the Leaf (as an example of a production electric car normal people might afford) has 300 kg of battery. The same distance can be traveled on two gallons of gasoline at a mass of 5.5 kg. So actual performance is about 54:1, including thermodynamic losses, etc. Both cars have mass overheads in the engines/motors, etc. Bottom line: curb weight is the same or heavier for the Leaf (1521 kg) as for a comparable gasoline sedan (fully loaded with gas). So the mass overhead you speak of evaporates. I stand by my statement about energy density.

      • There’s also a safety issue involved. Vehicle mass is a huge factor is what happens during vehicle collisions. Let’s assume there’s a miracle that breaks the connection between electricity storage and battery mass. Who wants to be riding in a 750-pound car when it collides at 45 mph with another object that substantially out-masses it?

        • Well, we can regulate vehicle masses, so that’s an easily solved problem.

          • Cars crash into rocks, poles, trees, embankments, etc., as well as other cars and trucks.

            Meanwhile, even 750-pound cars (though almost certainly impossible, given the inherent tie between battery mass and energy storage) are massively wasteful of energy and utterly unsustainable as ordinary means of daily travel.

      • One of my points in the original post was the EV’s and combustion vehicles do not have similar “mass overheads” with respect to the drive train. For instance, the Tesla Roadster’s 200 kW (268 hp) e-motor weighs 50 kg, a 4:1 kW/kg power density. A similar capability combustion engine weighs ~300 kg (0.65 kW/kg), and that does not include the exhaust manifold, water pump, oil pump, starter motor, fuel pump, etc. Only the jet engine beats the electric motor for power density.

        • It’s a question of baselines. You can brag about “electric” cars, even ones priced at $109,000, compared to gas cars. The question remains how “electric” cars rate in comparison to other modes of travel, such as rail, bicycles, and human feet. On that front, the “electric” car is just as insane as gas autos.

          Using intricate 3,000 pound machines to accomplish most daily errands is not compatible with a decent human future.

  10. That magic bacteria that converts cellulosic plant waste and old newspapers into something you pour into your gas tank was actually just there for the picking:

    Bacteria like this have been known for a while, this one is a bit different in that it also tolerates an oxygen rich environment, making it a lot easier to use for industrial applications.

  11. Human metabolism @ 2000 kCal/day = 2.4 kWh/day or 100 Watts per hour. Just for clarity.

    • Very close. 100 W/hr does not mean what you think it means. You probably meant to say 100 W, which is already a rate of energy consumption: 1 W is 1 Joule/second. See notes on “power” on the useful energy relations page.

      • Fore more clarity, that is 100W while not doing anything. Doing physical activity can boost your metabolic output easily to 300W, and normal athlets can output at 500W. This is quite normal for cycling.

        Top athletes can peak for short durations at 1,500-2,000 W, but only for a few minutes (at most).


  12. Thanks, Dr. Murphy, for another well-reasoned and insightful analysis. I’ve found all your posts to date to be extremely enlightening. However I must also say that you’ve depressed me quite a bit by having demonstrated the colossal magnitude of the task ahead of us, and the near certainty of our failure given our current political and societal attitudes. Seems we’ve painted ourselves into a corner from which we cannot escape without being severely bloodied and bruised, if at all. But please keep posting these! We need more people like you doing this!

    • Now to depress you further – look at how many mainstream economists keep talking about growth as the be-all and end-all of their “science”. Implicitly (and some explicitly) depending on scientists to keep delivering breakthrough after breakthrough (even though we are starting to hit physical limits to what can be done) to allow the economists to keep chanting their mantra of “growth”.
      Also, note how industry (led by these economists) treat scientists. The financial rewards pale compared to many other job-functions in the company. So where is the incentive for the bright kids to work in science to create the next breakthrough when it’s a hard career path with relatively low monetary award.
      For some icing on the cake, look at how research is funded now. In this age of money-driven everything, it’s difficult to get funding for anything that does not have near-term financial benefits. “Blue sky” research, just primarily for curiousity, is hard to fund. Which is short-sighted, considering most of the truly revolutionary inventions/discoveries were initially curiousities before someone else (sometimes decades later) had that “aha” moment to put the idea to practical use (electricity, lasers etc).
      It used to be said about accountants, but I think can easily be applied to economists, that they know the price of everything but the value of nothing.

    • Exactly! Although I don’t quite have the cycling skills of the guy in the picture :-)

      Living in London, UK, the most sensible approach to transport is:
      * Walk or cycle for short distances,
      * Public transport for long distances (underground, bus, train, etc.) or when the weather is not amenable to option 1.

      However this still leaves a gap when you need to transport something that is too bulky and/or heavy for those options (photograph notwithstanding). In such cases, larger personal transport is difficult to avoid. A way to solve this problem in large cities is car clubs: cars parked in the street that you can book for a few hours, paying by the hour. I’m registered with one of them so whenever I need a car for a couple of hours, I book one and use it: it is a lot more efficient and cheaper that owning my own car (it also makes me think twice before using it as I explicitly pay by the hour and have to plan the trip in advance).

      Those are perfectly fine solutions for urban environments but become a lot more difficult to implement in rural environments where shared transport isn’t practical. Then again, if you’ve ever been to South America and taken a ride on a mini-bus, it demonstrates that shared transport can be implemented even in very remote places.

      Unfortunately, all of this means that you lose the comfort of having your own weather-proof personal transport with integrated luggage capacity that you can use when you want and for however long you want parked just next to your house. And a lot of us in the Western world are just too used to that particular comfort to give it up willingly.

  13. “biofuels require a never-ending yearly push to plant, tend, and harvest the goods. The EROEI is poor, irrigation may not be available at scale, and bad growing seasons would seriously impact our economy.”

    The same could be said for industrial agriculture in general, so perhaps it’s not a specific problem with biofuels but the model of production. In other words, if you use an industrial ag model to produce biofuels you will inherit all of the problems you state above.

    What alternatives are there? Vertically stacked, local, animal integrated, perennial based and mineral cycling polycultures. They have much better photosynthetic efficiency due to reduced light saturation and competition and eliminate need for pesticide, herbicide, fungicide, transport, and mitigate risk of poor seasons by diversification and soil building and protection. You can also design the system to store runoff in the soil, drought proofing the farm and eliminating most need for irrigation, use wind breaks to improve crop performance, etc. This is permaculture design.

    An example is Willie Smit’s Samboja Lestari project, where they produce 5MW of electricity from ethanol produced from Arenga Pinnata palm sap in Borneo while producing other crops, local jobs and protecting endangered orangutans:

    • Sunshine is the only income we’ve got. If humans have a future on Earth, it seems like we have no choice but to maximize photosynthesis on the planet. Life is a photosynthetic process. Not always necessarily planting, but sometimes tending and always harvesting is the way of life. How can there be unemployment with the vast acreage of land in the US that is untended. It’s constant work, but then we can’t live on ipod sandwiches. Every photosynthetically captured watt is also some captured carbon.
      I try to do more good than harm.
      Before we worry too much about peak oil and peak phosphorus we have to survive peak sanity.
      Many thanks to Mr. Murphy for the numbers.

  14. Biogas, anyone?

    can be generated from most organic feedstock except wood, by a process that isn’t exactly well understood but the bacteria seem to manage just fine.
    So, foodwastes, whole plants and manure can be used to some effect.

    Germany had about 2.7GW of electrical power fed into the grid from BG plants one year ago, I assume that a bit more than half a GW has been built this year (though that will slow down next year for economic reasons)

    While it is a hassle to upgrade Biogas to pure Methan and put it into a Tank (Of a methane drive vehicle), it is doable.

    Of course, the general point about how much energy that can be gathered via biofuels holds true. What’s somewhat wrong is that only basically edible parts of plants can be converted.

  15. Hello Professor Murphy!

    I have enjoyed your articles, and I appreciate you doing the math. It prompted me to read Professor MacKay’s book, Sustainable Energy Without the Hot Air. I concluded the only available energy source capable of sustaining the American lifestyle for the entire planet’s population is nuclear fission.

    Wind, solar, bio, etc. are all too diffuse and intermittent for practicality. To replace the energy we use now with wind would require windmills everywhere you look as far as you can see; solar has the same problem. Your national battery post destroys any practicality of storing energy from these sources until needed.

    However, I was wondering about the practicality of a pumped storage national battery. How much land would we have to turn into a reservoir to provide a national battery?

  16. The problem with Nuclear Fission, apart from the usual suspects of waste handling and accident risk, is that it relies a finite fuel source so is not so sustainable after all. IT might give us breathing space to move completely to a sustainable future. The problem of course, is that it also gives us a reason not to bother for a few more years until the nuclear fuel (in whatever form it takes) starts running out.

  17. Great post, as usual, but I always hit my head against this when biofuels come up: it is the argument against _arable_ land. In short, there are a lot of fuel crops that don’t need to grow on arable farmland. Cattails & buffalo gourd are both roadside weeds, depending on your climate. Non-arable land includes hillsides, gutters of highways, & other marginal, non-flat land. Mechanized farming is the elephant in the room. If you harvest in a way that doesn’t necessitate fossil fuels, I think we may have options. But since _profit_ is always our primary driver, I think the use of non-arable/primary farmlands may not be an option, since mechanized processes require flat, prime farmlands.

    My main point is, that marginal lands can be used for fuel crops and prime lands can be reserved for foods; it doesn’t have to be all or nothing… But that always gets left out of the dialogue, much to the detriment of all. Think of “garbage” plants as weeds that may indeed be a source of photosynthetic fuel!

    • It is certainly desirable to decouple biofuels from agriculturally productive land. But it cannot be overlooked that today’s biofuels are almost exclusively food crops. That’s because we know how to convert the sugars, etc. into liquid fuel in ways that are sometimes even energetically and financially favorable. There is great hope for cellulosic biofuel, but we’re simply not there yet. At present, biofuels demand arable lands. Plenty of market pressures persuade us to use switchgrass and other rubbish, but physics don’t care. Lack of dialog is not the main hurdle here.

Comments are closed.