Jet fuel from thin air: Aviation's hope or hype? | Hacker News Reader

Jet fuel from thin air: Aviation's hope or hype?

bbc.com

97 pointstheklub93 comments

I am involved in this project. The aim is to built a demonstration plant to show the feasibility of the process and to develop a blueprint for larger plants that can produce sustainable jet fuel economically. Producing sustainable fuels is always more expensive than fossil fuels. However, upcoming legislation and taxation (at least in the EU) will change this equation.

Someone mentioned an efficiency of around 50% in a post here and resulting pricing, that's a fairly good estimate of the overall process and what is discussed as achievable cost for renewable synthetic fuels in general. The process is in this demonstration plant is Fischer-Tropsch. Using CO2 from an industrial point source is more efficient; however, it has potential legislative issues when it comes to certification of sustainable fuels, emission certificate trading... it's a fairly complicated topic. In addition, worldwide potential for lowest renewable energy costs does not correlate necessarily with existing CO2 point sources. That's why direct air capture makes a lot of sense.

Whether CCS is a better solution depends on renewable electricity pricing vs. the CCS costs, public acceptance and feasibility at the location of a plant. These vary strongly depending on where you are in the world. In many parts of Europe there is strong opposition to it as it may prolong the exploitation of fossil sources.

Finally, an expert! I’m not, although I’ve been involved in energy for a while now.

I believe the Germans made synfuels towards the end of WWII using Fischer Tropsch when they were running low on conventional fuels. What tech is new about this project, besides the energy source?

Two decades and some ago a german company named Choren also produced SunDiesel in a similar process. They shut down this line of work quite some time ago. Not feasible.

Germany, during WWII, and South Africa's SASOL since the 1970s:

https://www.netl.doe.gov/research/Coal/energy-systems/gasifi...

They made synfuels from coal, which contains a lot of, uh, coal. So no need to capture it from the air. They didn't worry about CO2 pollution back then.

For fuel synthesis, you have two principle processes: carbon sourcing, and actually sythesizing the fuel.

Once you've got the coal sourced, most of the rest of the WWII process is directly applicable to modern carbon-capture methods.

Is the intent to economically compete with biofuel, which also gets its carbon from the atmosphere, or is there a specific niche targeted by direct CO2 capture approaches?

What is the potential to do this kind of process intermittently, to take advantage of excess energy produced by solar and wind plants during certain periods.

It wouldn't be expected to be cost effective, because there's also the capital cost to consider. Once you've built the plant, you basically need to run it as much as possible in order to recoup the investment.

Simplistically, isn't this basically using the carbon from CO2 as a "carrier" for PV hydrogen? There's certainly a substantial efficiency hit. But there are also substantial challenges to displacing aviation fuel with hydrogen.

But then, it's also arguable that PV hydrogen is itself a "carrier" for PV electricity. So then the alternative is batteries. As much as I love electricity, I doubt that battery technology will ever achieve the energy densities of hydrocarbon fuels.

More or less, yes.

Straigh molecular hydrogen is brutally difficult to work with. It is hard to store (high pressures and/or low temperatures), bulky, embrittles metals, and is violently explosive.

Synthetic analogues of fossil fuels (kerosene, petrol) are chemically virtually identical to what we've been using for the past century of powered flight (and should actually be cleaner/purer). There are few unknowns, safety is quite high, and the storage, handling, and combustion properties are well-understood and excellent for the application.

Powering FT fuel synthesis via photovoltaic or other solar processes could certainly work.

> Using CO2 from an industrial point source is more efficient; however, it has potential legislative issues when it comes to certification of sustainable fuels, emission certificate trading... it's a fairly complicated topic.

I can imagine! Considering lots of the co2 in air has fossil fuel origin, not putting the co2 capturing at a high volume co2 source seems rather dim. Regulators gonna regulate!

Maybe site the direct air capture in the middle of a german industrial city with coal plants all around...

Or even better, at an airport. Then you have nil transportation cost for delivery too.

Something like this could create a large market for CO2. If the market was hot enough, fossil fuel plants might capture and sell their own emissions.

The article mentioned that the costs were high, but didn’t actually have any numbers. What do you expect the prototype’s efficiency to look like? What does that mean for the price of a liter of syngas? And how do you expect that to scale for larger plants?

But efficiency of 50% is great! What's even the problem about it?

Say, an average price of base load electricity of 43.26EUR/MWh in Germany in 2018 (and that is a very pricey market - country which has a shitload of renewable power) - will result, at 50% efficiency, of energy feed costs of 3.07EUR per gallon of fuel. That's only 1.7x the actual cost of jet fuel in EU as per IATA (https://www.iata.org/publications/economics/fuel-monitor/Pag...).

You should add the capital cost of device itself, but if it's used round the clock, it shouldn't add so much. And if it's not, electricity can be almost free because a lot of the time, renewable power is in excess and can be purchased from the high voltage grid for very cheap (if we are speaking of high throughput industrial units which will probably have hundreds of megawatts connected, and will plug into high voltage grid directly).

All in all, it may get fuel 2x more expensive but it's not such a big deal.

Be honest, isn't carbon capture a big distraction and was only mentioned for the media.

Why do you target Jet fuel/aviation specifically?

After all, there isn't so much special about Jet A: I figure a PT-6 could run just fine on automotive diesel.

Land and sea transportation can much more easily shift towards other energy carriers such as batteries. Or using electric trains instead of trucks, etc. For ships even nuclear propulsion might be an option if the CO2 price rises enough.

Aircraft, not so much. Liquid hydrocarbons have amazing energy density, both by weight and volume, and in aircraft that matters a lot.

I work in energy. With the rise of renewables, it is becoming more and more common that there are periods of insanely low or even negative spot energy prices.

Is it planned that the plant will be able to take advantage of low spot prices?

The jet fuel part of this is a distraction from the important (and hard) part - turning electricity into usable liquid fuel.

Electrolysis is easy enough, and there's plenty of places with enough water.

Then you have hydrogen. Hydrogen is not nice to work with, store or use, so you want to turn it into something else a bit nicer.

The problem is, almost all practically usable liquid or gaseous fuels contain carbon. Where do you get that from?

The obvious answer is the atmosphere. That's also the premise of carbon sequestration. The problem is that CO2 isn't actually particularly abundant. It's currently hovering around 400 parts per million - that's about 0.04% of air. To make a kg of hydrocarbon you need to process an awful lot of air to get enough CO2. That all takes energy. A lot of energy. Suddenly your round trip efficiency is practically zero. If these guys have cracked that problem, it would be fantastic. I hope they have, but I suspect they haven't.

There are lots of point sources of CO2 that don't require as much energy to extract, but your point stands: the conversion takes a lot of energy (thermodynamics is a harsh mistress).

The tech works quite well though, CRI in Iceland makes methanol (a viable liquid fuel) from CO2 and electrolyzed H2 semi-commercially, taking advantage of cheap and abundant geomthermal electricity.

I came here to say essentially this. To your point about how low (in percentage terms) the concentration of CO2 is, direct carbon capture from the atmosphere still seems a fool's errand to me. The only way I see carbon capture being at all viable for this purpose in the short term is to scrub the waste gasses from industrial processes where carbon-containing compounds are extremely concentrated.

The green beaches thing seemed quite promising https://news.ycombinator.com/item?id=20403570

right, but that's for sequestering the carbon, not turning it into a valuable product like a fuel, unless I'm mistaken

Yes, but the main benefit of turning it into a valuable product is to make the process of sequestration cost effective. If sequestration could instead be made cost effective by just being really cheap (relative to other techniques), as will hopefully be the case with the olivine beaches, that could work too.

Cement (of certain types) relies on direct carbon capture from the atmosphere to complete curing (although conventional cement only carbonizes through a finite depth during its expected lifetime), so it's definitely possible. It just takes a lot of energy.

About 2 MWh (thermal, or ~7GJ) per tonne of CO2 captured (not counting storing that CO2) to regenerate the chemical CO2 capturing agent. Here's a review: https://www.sciencedirect.com/science/article/pii/S095965261...

(As an aside, a gallon of gasoline emits about 10kg of CO2, so to capture that CO2 from a gallon of gasoline would require about 20kWh worth of electricity.... Typically, a gallon of gasoline gives you about as much range as 10 kWh in an electric car, so you can go 2 times as far in an electric car just using the energy it'd take to capture the CO2 from a gasoline car. And that doesn't count the electricity required to refine/crack the gasoline from crude.)

And also, on board the International Space Station, CO2 is captured from the atmosphere regeneratively. Capturing CO2 in this way takes less energy at the higher concentrations on board ISS, but is still possible.

As an aside: Much of the ISS's CO2 is converted into a hydrocarbon (methane) using hydrogen (from water and solar electricity) and, amusingly, vented to space as a waste product. The point is to recover the oxygen (again, in the form of water) from the CO2.

In case someone else is wondering about the math on the aside about how a gallon of gas (3.8kg) can emit 10kg of CO2: https://www.fueleconomy.gov/feg/contentIncludes/co2_inc.htm

> And that doesn't count the electricity required to refine/crack the gasoline from crude.

If we can figure out how to extract atmospheric CO2 and convert it into hydrocarbons efficiently, crude oil won’t be bart of the equation any longer — our atmospheric carbon supply will be part of a closed loop. As a lay person, that’s an awfully appealing prospect.

I wonder how many kWh it takes to pump, transport and process a gallon of gasoline when sources from crude.

It’s doable, it just requires energy. You are really working against thermodynamics with CO2 sequestration.

If it's an unmoving device fixed in place, I could see that capture from air wouldn't be particularly efficient.

But what if it's a device that already exists that moves through air with great speed, filtering through huge amounts of air? Like, say, a jet engine?

Okay, but producing fuel requires a lot of energy, so how are you going to power that? With a different engine onboard your jet?

The point of this device is to take energy available on the ground and store it for use in the air, and use a storage method with a tremendous amount of energy per unit weight (hydrocarbons).

Planting forests and turning the trees into biochar seems like a cost effective way of carbon capture. You even get some energy out of it.

The biochar can then be used to plant more forests, for more biochar. It’s a virtuous cycle.

> To make a kg of hydrocarbon you need to process an awful lot of air to get enough CO2

Would replacing air with wood as the input alleviate the problem? (Trees, in effect, turn atmospheric carbon into hydrocarbons using solar energy.)

Empress trees capture roughly 100 tons of carbon per acre per year. But wood's energy density is roughly half that of oil (oil and coal are decomposed algae and wood respectively) so it's effectively 50 tons of potential jet fuel per acre of forest per year. A 10 hours 747 flight apparently burns about 250,000 pounds of fuel - roughly 125 tons. So we'd need about two and a half acres of forest for a ten hour 747 flight.

There has been some speculation that people could cultivate vats of algae illuminated by blue LEDs emitting light in the optimal photosynthesis spectrum. But this is probably only feasible with effectively limitless supplies of electricity.

The fuel in a single fully-fueled 747 contains about 150 tons of carbon. A forty-year-old tree contains about 1 ton of carbon.

If the jet's fuel tanks get filled about 200 times per year, then you need to cut down about 30,000 mature trees per year to supply the carbon to keep it supplied with fuel. This probably adds up to a few thousand acres of forest to continuously meet the needs of a single jumbo jet.

Well you and the rest of the naysayers are in luck. They just burned the amazon rainforest. That probably frees up plenty carbon into the air for the process.

Not trying to be a naysayer; I just wanted to make a rough estimate of just how many trees would be involved in this method. We already have the ability to plant and cut millions of acres of trees for lumber, so this is an entirely possible future. Whether it's more or less efficient than other methods of carbon capture is the real question.

Wood/biomass gasifiers were used during WW2 when gas was rationed in some areas. So they are practical, but with the current price of oil/gas I would not expect it is commercially viable. Wood is not the only source though, and there are current fuel sources that are wasted. Like it is common for farmers to burn the leftover straw after a harvest

Ammonia and hydrazine could work. I mean, as fuels, not as a PR stunt, obviously.

> The obvious answer is the atmosphere. That's also the premise of carbon sequestration. The problem is that CO2 isn't actually particularly abundant. It's currently hovering around 400 parts per million - that's about 0.04% of air. To make a kg of hydrocarbon you need to process an awful lot of air to get enough CO2. That all takes energy. A lot of energy. Suddenly your round trip efficiency is practically zero. If these guys have cracked that problem, it would be fantastic. I hope they have, but I suspect they haven't.

Isn’t biofuel precisely this?

Maybe you put your device somewhere the winds blow for you. Think of the 200mph westerlies that blow through the Drake Passage.

Aside from the distance from civilization, you've got water, power, and air movement all right there.

Wind energy through a given cross section scales with the cube of air speed; kinetic energy per particle is proportional to the square of velocity, and mass flow is proportional to velocity. This makes high wind speeds difficult to design for, and most wind turbines will apply a brake and stop in high windspeed conditions in order to avoid overheating and other issues from the high energies involved.

I was thinking more of the need to move a lot of air for DAC, wind energy was somewhat secondary.

>To make a kg of hydrocarbon you need to process an awful lot of air to get enough CO2

Thinking laterally, instead of processing a lot of air, can't we just engineer a gaseous molecule that is good at capturing CO2 and can precipitate conditionally.

Imagine something like a buckyball that would let in a CO2 molecule. While it's sufficiently hot it stays under its gaseous form. Then once cold it falls to the ground.

You then release a lot of this engineered molecule in the atmosphere where it will come into contact and absorb the CO2 then fall to the ground where you can collect it efficiently by scrubbing it of surfaces like soot for processing and recycling.

If it is bio-safe and sufficiently stable you can even let it accumulate naturally in the water where you will retrieve it even more efficiently once it's concentrated enough. That's what we do in Rouen now and everyone is fine with it /s.

>The obvious answer is...

Did you know that there are massive streams of CO2 available for the taking?

https://www.reuters.com/article/us-australia-lng-carbon-fb/f...

The US Navy is already experimenting with producing synthetic jet fuel on aircraft carriers using power from the nuclear reactor. Their concern is with reducing the logistics chain rather than environmentalism. But if the research results are made public they could be applied to commercial aviation.

It would be really interesting to see that getting applied to a fleet oiler design. A nuclear powered tanker that constantly refills itself for the DDs and CGs to use...

Let me get out my back of the envelope for some quick and inaccurate calculations ;-)

There are 10.3 kWh of energy in a litre of Jet A1 fuel.

Let's assume (generously I think) that the process is about 50% efficient, so it takes ~20 kWh of electricity to make a litre of Jet fuel.

Assuming (amortized) solar power is the same cost as grid power ~$0.1/kWh then to make your litre of fuel costs 20 *0.2 = ~$2/litre

According to my research Jet A1 costs about ~$0.50/litre.

So this is a way off at the moment, however if there was tax on fossil fuels for aviation then this could be competitive.

Depending on how capital intensive the plant is, this might still be cost competitive with intermittent low, zero or negatively priced green electricity.

Also ... renewables are always going through cycles of high and low availability. Prices vary across these cycles. If you make your fuel only at the time during the day when there is the highest delta between supply and demand, then you pay the minimum electricity cost, and the utilities are glad to have you there to balance the load.

Note that this economic strategy is already in place in other industries where electricity price is a large component of the final cost of goods sold. Aluminum smelting is a huge example of this.

Large-scale Negative, zero or below-cost renewables only happen if someone else foots the bill. And that usually means tax-payer funded subsidies. I mean sure, there will be some hours during exceptionally sunny/windy days when price is less than the production cost, but don't bet your business on it.

What does work is building the plant in a wind/solar abudant location and co-siting with large, behind-the-meter wind/solar plant. Not only do you get electricity at cost, but you cut the grid costs and taxes away too.

I think the problem in your calculation is the cost of grid power for industrial use is lower. I didn't look it up though.

Maybe the question should be how long can it stay at $2/liter? That $0.50/liter advantage may be gone in a year or two but the $2/liter synthetic fue remains or maybe slightly more.

$0.10 per kWh for solar power is a really high figure.

There's non subsidized power plants now being built for southern california, in India and in the UAE where the price for power sold to the grid is 2 to 3 cents per kWh ($0.025 to $0.030 per kWH).

My residential electricity costs about $0.12/kWh, including delivery. I don’t think that’s a realistic price for solar. Current utility-scale solar is maybe $30-$45/MWh with some estimates of $15/MWh in 2022. Obviously that doesn’t include transmission, but presumably it would make sense to co-locate fuel synthesis near generation and reduce those costs. Seems like that would make a big difference to those estimates.

> it would make sense to co-locate fuel synthesis near generation and reduce those costs

I'm not so sure about it. I believe that transmission of electrical energy is cheaper than transmission of fuel. So it would be better to collocate synthesis with airports where planes are refueled.

Jet fuel produces about 2.5kg of CO2 per litre. Since that in emitted at high altitudes, you can probably multiply this by 3 to get the actual climate impact. So a carbon tax of around $200/ton would make this competitive even with the rather high price of solar than you assume.

Cost of renewables is falling fast. Getting close to 1c per kWh.

The question should not be whether this is too costly as compared to jet fuel, but at what carbon price is it cheaper than jet fuel? Once the cost of carbon is at the long term limit, which is equal to the cost of extracting carbon from the atmosphere, then these technologies could be much more cost effective. (But if they aren't, there would be no reason to ban flying, as the carbon price would pay for the extraction of carbon that flying produces.)

By not account for how much jet fuel costs with increasing carbon pricing, and by framing the alternative to allowing climate change as banning flying, it seems like the author has completely missed the story..

I guess a more low-tech approach would be to fuel jets with ethanol. Googling a bit now, the U.S. uses about 18 billion gallons/year of jet fuel[1], and produces 17 billion gallons/year of fuel ethanol [2]. The price per gallon is about $1.5 versus $1.94 [3,4]; because jet fuel has 46% higher energy density that means that the cost per Joule would increase by a factor of 1.9.

Obviously this is only a back-of-the-envelope thing, but it seems that even if we switched to renewable fuels using the technology that are available today, ticket prices should about double. Historically, that corresponds to going back to circa-1980 prices[6], which I guess is bad, but not exactly apocalyptic.

[1] https://www.eia.gov/todayinenergy/detail.php?id=31512 [2] https://www.eia.gov/todayinenergy/detail.php?id=32152 [3] https://markets.businessinsider.com/commodities/ethanol-pric... [4] https://www.indexmundi.com/commodities/?commodity=jet-fuel [5] https://en.wikipedia.org/wiki/Energy_density [6] https://www.theatlantic.com/business/archive/2013/02/how-air...

You answered your own question.

" jet fuel has 46% higher energy density"

That's why. Few things matter more when lifting things into the air than weight.

I guess the current long routes would not work, but apparently airliner fuel efficiency improved by almost exactly this much since 1980 (https://www.greenaironline.com/news.php?viewStory=684), so it still seems that's the era we'd go back to...

The problem with ethanol is it absorbs water, which at greater altitudes (lower temperature and pressure) freezes and blocks fuel lines. For that reason aviation fuels have limits on ethanol content.

Could we redesign the fuel system to (safely) remove the water somehow? Or prevent the fuel from absorbing moisture in the first place?

It would have to be hermetically sealed from creation to combustion at 37,000 feet. I’m sure it’s theoretically possible but so difficult as to be untenable.

Maybe you could chill it to precipitate the ice just before loading it on the plane?

Alternatively we could use ethanol in fuel cells, and use electric motor, unfortunately it requires either finding new catalists or a cheap source of platinum https://en.m.wikipedia.org/wiki/Direct-ethanol_fuel_cell

Ground vehicles can run fine on ethanol but the increased fire risk (relative to kerosene) probably makes it impractical for commercial passenger flights.

So, here's how to kill a few birds with one rock. Make jet fuel using nuclear energy. But nuclear energy is horribly expensive, right? No, civilian nuclear energy is horribly expensive. The US Navy churns out nuclear reactors at a steady pace, and operate them perfectly safely. They've never had any incident. If the Congress mandates the US Navy to become net zero carbon emitter, they can do it. And they also gain additional logistical simplification. They say that every gallon of fuel sent to the front line in Iraq costs the DoD $100. Yes, in the oil-soaked Iraq. If you shorten the supply line, maybe this price goes down to a more reasonable level. Can you imagine that, instead of getting a war for the exorbitant price of $10 trillion, you can get one for a paltry $1 trillion? We could get 10 wars for the price of one.

> They've never had any incident.

I'm not being conspiratorial here, but if there was an incident, which would make the navy look vulnerable and weak to both the population and potential enemies, would we ever know about it?

A big chunk of incidents would be known to adversaries just by their nature.

"It sure does sound amazing. It sounds like a solution to all of our problems - except that it's not," said Jorien de Lege from Friends of the Earth.

"If you think about it, this demonstration plant can produce a thousand litres a day based on renewable energy. That's about five minutes of flying in a Boeing 747.

"It'd be a mistake to think that we can keep flying the way that we do because we can fly on air. That's never going to happen. It's always going to be a niche."

Wow, the Naysayers really know how to build a constructive argument.

This always strikes me as missing the point. The end result is fuel to burn. It doesn't matter where it comes from, only what the net carbon budget is. Continuing to burn petroleum in jet engines is fine, as long as it's appropriately offset. There's absolutely no technical reason to need to bend over to implement this kind of setup. Spend those dollars on renewables and sequestering solutions instead, clean up the last 10% of fossil fuel extraction at the end of the process.

Lots of people working on different ideas to help reduce CO2 is probably what we need though. We don't know what will be the 'winner' yet, but the more things we try the more likely we are to find the best solution(s).

Good fuels are hard to find.

The problems with petroleum (and natural gas) are twofold. One is the carbon emissions, but the other is the fact that supplies will eventually run out, and have to be substituted by something. And as we try to pursue every last fraction of petroleum, the environmental costs will rise -- increasingly hard-to-access, high-risk, or heavy-treatment options. Think deep water, Deepwater Horizons, and tar sands and fracking.

Hydrocarbons are great fuels, and for some applications, especially powered flight, there's virtually no other viable alternative. Keep in mind that the aeroplane and automobile both appeared at virtually the same moment -- the principle requirements for each were high power-to-weight engines and energy-dense fuels. Sorting out the mechanical and aeronautical problems were relatively straightforward.

(Lightweight sturctural aluminium also helped markedly, and also became available largely through the same related set of technological processes providing Otto-cycle engines and petrol-based fuels.)

Sounds very similar to Prometheus Fuels. The AMA thread on here from the founder was amazing.

To save anyone else curious the hardship of searching...

https://news.ycombinator.com/item?id=19842240

> "It'd be a mistake to think that we can keep flying the way that we do because we can fly on air. That's never going to happen. It's always going to be a niche".

Why did BBC include such a strong statement in the article, given that it's just someone's gratuitous personal opinion?

I know that it's good journalistic practice to include sceptical opinions, but couldn't they find someone who is sceptical while at the same time being able to back their opinion with some sort of evidence or arguments?

Edit: it's also possible that this person's contribution was a longer text, and that it was cut short due to the article length limits. Maybe the original text included better arguments? It would be unfortunate if that was the case.

Whatever happened to Prometheus? I haven't heard anything since their launch [0]. The website doesn't have any updates [1]. Complete radio silence.

[0] https://news.ycombinator.com/item?id=19842240

[1] https://www.prometheusfuels.com/

I envision a future (not too far away) where we can literally turn anything into anything else reasonably efficiently.

CO2 in the atmosphere with hydrogen and oxygen from water, waste into each of its base component atoms, whatever into whatever else.

Something like global recycling of everything, if that makes any sense.

On Saturday, Elon Musk said that SpaceX will use direct air capture to make fuel from air on Earth: https://youtu.be/sOpMrVnjYeY?t=3852

In partnership with Climeworks, one of the leading DAC companies, I just launched a campaign on Kickstarter using carbon materials to make a bracelet made of captured atmospheric carbon dioxide. Check out the video! https://www.kickstarter.com/projects/go-negative/negative-br...

Sounds like some kind of Fischer–Tropsch process. Starting with CO2 sounds like it would require an obscene amount of electricity though.

> Starting with CO2 sounds like it would require an obscene amount of electricity though.

It could still be worth it, depending on how/when it was made and how it interacted with the grid. There's an increasing problem right now of too much solar supply during the day and not enough power storage; projects like this could be used to soak up excess power and it would still come out carbon-neutral.

Germany is paying other countries to absorb spikes. Anything that creates value instead looks like a win to me.

In the synthetic fuel world, how much renewable energy capacity would we need globally? We need to replace all current electricity generation with renewables, then we need to add more to power electric cars, and then some more to produce synfuel. That sounds like a lot of capacity.

"This demonstration plant can produce a thousand litres a day based on renewable energy. That's about five minutes of flying in a Boeing 747"

Why not just process biomass?

The article says those are costly, and the cost would have to be passed onto the consumer.

Honestly this feels like it's a feel-good piece "look, we're doing our part!" when the technology is still a long ways away. Better than saying that the airlines are working on teleportation, but I don't know by how much.

There isn't enough.

Even for aviation alone, which is about 6% of US fossil fuel consumption, using a process Boeing had lauded as a "breakthrough" a few years ago, essentially using a salt-water pickleweed (halophytes), you'd need the entire states of Kansas and Oklahoma, plus considerable chunks of Nebraska and surrounding states, to meet present US demand.

We use a lot of fossil fuels. Mind-boggling amounts. And those accumulated slowly over immensely long periods of time, though that's due to inefficiencies both in what ancient biomass was kerogenised in the first place, and the losses in keroginisation (essentially: petroleum formation). Jeffrey S. Dukes, "Burning Buried Sunshine" (2003), lays this out for coal, oil, and gas.

For petroleum, we're presently burning about 5 million years of accumulated fossil biomass every year. Or, alternatively, we burn through a full ancient year's biomass accumulation every 6.3 seconds.

All biomass, roughly, equates all human and livestock feed, plus some construction materials waste-streams (mostly wood and forestry products). When you say "use biomass", you're really saying "go through the leftovers of humans and livestock". And quite simply, there's not all that much there. Maybe 5-10% of current total energy use if you could efficiently capture the entire wastestream (and keep in mind that it is very widely distributed.

In practice, you could probably power waste water treatment plants off of captured biomass, with some surplus left over. But not much more than that.

"It sure does sound amazing. It sounds like a solution to all of our problems - except that it's not," said Jorien de Lege from Friends of the Earth.

"If you think about it, this demonstration plant can produce a thousand litres a day based on renewable energy. That's about five minutes of flying in a Boeing 747.

This is the same people that have faith in that technology in renewables can improve to one day surpass nuclear.

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