Electric commercial flight

[Rx7man]

I'll put this here since I don't really know which other place to put it, I didn't see an EV specific forum

Do you think long range commercial flight is possible? I know there are small flights that have been done with electric airplanes, but between take-off power requirements, flight speed, elevation, quick turn around times, and long distances, I don't see airliners becoming electric and economically viable for a very very long time (IE, when there just are no fossil fuels available at all)

I saw Airbus was experimenting with the E-fan X, the closest thing to an airliner I could find, they only used 1 of 4 as an electric (2MW) engine, and the project is scrapped according to their site.. I found all sorts of fancy videos with dramatic music and wind tunnel testing of an existing airframe (really pretty pointless I'd think), but no numbers.

I've got an argument going with a Green party MLA

[AG6QR]

Look up the amount of energy which may be stored in one kilogram of your favorite battery technology.  Compare it to the amount of energy which can be stored in a kilogram of jet fuel.

They're nowhere close.

My sources say Lithium-ion batteries are around 90 Wh/kg, while jet fuel is around 12000 Wh/kg.  That's more than two orders of magnitude difference!

It's true that efficiencies will vary, and the weight of required motors versus jet engines aren't equal, and an electric plane must carry its batteries for the entire flight, while a fuel-burning plane keeps getting lighter during flight as fuel burns.  Battery technologies are improving, but jet engines are also becoming more efficient.  These are all trivialities in the face of the two orders of magnitude difference.

Weight is all-important in air transport.  Around 45% of the takeoff weight of a modern long-haul airliner is fuel.  If you want to carry the same energy in the form of lithium-ion batteries, the first approximation would say that the plane must weigh around 45 times its current weight, just to hold the batteries.  But a plane that weighs 45 times as much as a current airliner will require a lot more energy in order to reach its destination.

Maybe electric power will someday play a part for certain very short flights.  But it will not be practical for intercontinental air transport any time soon.

Note that this doesn't imply we must continue burning petroleum to fuel aviation.  We could synthesize hydrocarbons using other energy sources.

For fun, estimate the wattage required to refuel an airliner during a one-hour ground stop.

[Cerebus]

Any long range commercial airflight is either a very long way off, or would look very different.

There are three possibilities as I see them.

Air liners that operate in a very similar fashion to the ones with which we are familiar. Within this category there are two possibilities, pure electric vehicles using batteries or hybrid ones using fuel cells and still requiring energy dense fuel.

To operate commercial craft in the way they are now but using batteries requires a huge improvement in specific energy density (W/kg) for reasons that have already been pointed out (based on current best Lithium battery technology versus kerosene the improvement required is about 50 fold).

The second option is fuel cell operated aircraft and that currently comes down to using hydrogen as fuel. There's no hydrogen infrastructure, and it would have to be developed worldwide, and there would be a significant acceptance barrier to it - mention 'hydrogen', 'aircraft' and the next two phrases you will hear from people are "Hindenburg disaster" and "R101 crash on maiden flight".

The third possibility would involve a significant change in the way that planes operate. All the really successful battery based electric aircraft so far have been essentially powered gliders. Upscaled, these could achieve useful commercial ranges with relatively modest improvements in battery technology (say 20 times better specific power density) but they would be slow compared to current aircraft, would require very different airports, would have much more restrictive weather conditions they could operate in and would have to take indirect routes while the pilots hunted for thermals during the parts of the flight where they essentially operated as gliders and consequently would have estimated flight times rather than schedules. Might be quite a nice way to fly though - quiet, unrushed, scenic. Probably still only ever practical for medium range over land.

Any option involving batteries requires either massive or phenomenal improvements in battery technology. This will not happen within 20 years, it might not happen in 100, it might not happen at all. However, the push towards this will continue as improvements in battery technology are useful in themselves. The hydrogen fuel cell option requires worldwide coordinated changes in infrastructure, if people will accept it. Moving to powered gliders changes just about everything associated with air travel as we know it, planes, infrastructure, speed, somewhat indirect flights and still requires a massive improvement in batteries to be practical.

Conclusion: It's not happening in my lifetime, it's probably not happening in my [putative] children's lifetime. Perhaps there will be short haul (~100 nm) electric commercial flight just within my lifetime.

[AG6QR]

Any option involving batteries requires either massive or phenomenal improvements in battery technology. This will not happen within 20 years, it might not happen in 100, it might not happen at all.

There will certainly be improvements in battery technology, but they'll never come anywhere near the energy per unit mass of hydrocarbon fuels.  The reason is chemistry.

Batteries require an oxidation/reduction reaction, and the battery must contain both the oxidizer and the reducing agent.  Burning hydrocarbons also involves an oxidation/reduction reaction, but the airplane can get the oxidizer from the air, so doesn't need to carry it along.  And it dumps the products of the reaction overboard as (polluting) exhaust, so it doesn't need to carry them to the final destination.  These two facts give burning hydrocarbons a huge weight advantage.

The chemicals that provide the best ratio of energy to mass are the lightweight elements near the top of the periodic table, like Hydrogen and Lithium.  Nobody is going to invent new elements in that part of the periodic table.  There may be some new heavy radioactive elements synthesized near the bottom of the periodic chart, but those large nuclei give them terrible energy per unit mass during chemical reactions.

You also mentioned fuel cells.  They have the same problem as batteries that they must carry both their fuel and oxidizer.  You correctly observed that hydrogen is the ideal fuel for a fuel cell as far as energy per unit weight goes (hydrogen is right up at the top of the periodic table), but hydrogen isn't nearly so spectacular if you consider the total weight required to contain it in a tank at a reasonable volume. You can store it cryogenically or compressed, but either of those options involves tankage that weighs more than the fuel.  The space required for storing hydrogen at a reasonable pressure leads to a voluminous aircraft, which doesn't work out well as far as aerodynamic drag.  Plus, hydrogen embrittles metal, and because the molecules are so tiny, hydrogen leaks through seemingly solid metal tanks.

The easiest way to tame hydrogen for practical transportation is to combine it with heavier atoms to turn it into a relatively dense liquid.  Carbon works nicely for this purpose.  And that brings us back to liquid hydrocarbons, the fuel with the best ratio of energy per unit mass, when you account for both the mass of the fuel and the mass of the tanks to safely transport it.

I wish it were different, because I'm very much aware of the downsides of hydrocarbon fuels.  We must get away from mass emissions of CO2, or at least if we continue emitting CO2, we must capture CO2 elsewhere so that our net emissions become zero or even negative.  That's why I think long-haul aviation will eventually move to using renewable energy to synthesize hydrocarbon fuels, for net zero carbon emissions.

There may be other possibilities for the distant future, such as nuclear powered aircraft, or using hyperloop-style long vacuum tunnels instead of airplanes for long distance transport.  Those have very serious practical engineering problems, of course, and I don't expect to see them become practical in my lifetime, but it's easier for me to imagine something drastically new like that than it is to imagine long-haul aviation being propelled by chemical batteries providing power to electric motors.

[Rx7man]

Thanks for all the replies, I'd used most of those arguments against this guy and he's just so convinced technology will get us there, And yes, someone came up with the nuclear battery, posted a link to some magazine or something that boasted this incredible energy density, but the prototypes were in the micro to milliwatt range

The only reasonable battery powered air travel I can think of is a zeppelin style as the buoyancy of the aircraft doesn't require fuel, the problem then is a long haul flight will take a week!

I don't think commercial air travel will continue forever, I think high speed rail will be more like it anywhere it's possible, and the cost of air travel will make a lot of non-essential travel cost prohibitive.. This is of course way in the future.. that's my 2 cents, coming from canada where we don't even have pennies anymore

[Rx7man]

Conclusion: It's not happening in my lifetime, it's probably not happening in my [putative] children's lifetime. Perhaps there will be short haul (~100 nm) electric commercial flight just within my lifetime.

I think Harbour Air is operating a modified Beaver on electric-only from Vancouver BC to Victoria, I'm not sure if it's truly commercial or for private use, it seems to me the FAA certs to do it carrying the public would be onerous to get.

Electric cars already have pretty poor ranges, we can't make a cell phone that works a whole day on a charge.. I'm not hopeful we'll do trans-atlantic commercial flights on the scale we do today powered by electricity

[Cerebus]

You also mentioned fuel cells.  They have the same problem as batteries that they must carry both their fuel and oxidizer.

My only quibble with what you said is with the above. Most fuel cells in current use don't use a supply of stored oxidiser but simply use atmospheric oxygen. There's an experimental fuel cell bus trolling somewhere around London (just checked, route RV1) that's hydrogen and atmospheric oxygen powered. In fact I can't think of any hydrogen fuel cell application that used stored oxidiser that wasn't in a space vehicle.

[Cerebus]

The only reasonable battery powered air travel I can think of is a zeppelin style as the buoyancy of the aircraft doesn't require fuel, the problem then is a long haul flight will take a week!

Possibly a bit of an exaggeration. The Hindenburg took three days to travel from Frankfurt, Hesse, Germany to Lakehurst, NJ, USA, and that against strong headwinds, before it gave Herbert Morrison rather a lot to say on the radio. How the power to weight problems of doing this with batteries would slow it I don't know, but I suspect the issues are considerably less than those for heavier than air aircraft.

[Cerebus]

Conclusion: It's not happening in my lifetime, it's probably not happening in my [putative] children's lifetime. Perhaps there will be short haul (~100 nm) electric commercial flight just within my lifetime.

I think Harbour Air is operating a modified Beaver on electric-only from Vancouver BC to Victoria, I'm not sure if it's truly commercial or for private use, it seems to me the FAA certs to do it carrying the public would be onerous to get.

That's, what, 50 miles in a straight line with a six passenger seaplane? That's a route that, were it over land, nobody would consider flying. I must confess I didn't think about island service when I set my benchmark (although it was somewhere at the back of my mind*).  It does present a realistic commercial opportunity for electric flight, but it's not going to make a dent in terms of passenger miles even if every island service in the world converts to fully electric. I was thinking more along the lies of a full-sized plane on a route like London->Birmingham (UK obviously) where there flying might seem frankly a bit silly, on a route served by motorways and a main train line, but there are nevertheless scheduled flights daily.

I had a search for the flights in question and it looks like this is still at the trying to get approval stage. They've got a plane, they've run test flights and I can see lots of re-hashed press releases for that, but none for having got approval.

* I had the "World's shortest scheduled air flight" in mind, Westray to Papa Westray in the Orkneys - 90 seconds from take off to landing.

[Rx7man]

I just pulled a number out of my arse for the flight time on a zeppelin style craft... even if it's 3 days, taking a week vacation means you only spend a day at your destination... it's hardly going to be attractive for anything other than deliberately sightseeing on the trip

I also agree that short hop flights like Vancouver-Victoria isn't going to make a dent in emissions from air travel... It's only good for the politicians that have to go to victoria (BC's capital) and gain greenie points

[ve7xen]

I had a search for the flights in question and it looks like this is still at the trying to get approval stage. They've got a plane, they've run test flights and I can see lots of re-hashed press releases for that, but none for having got approval.

I don't even think they're at that stage yet. They've done some test flights, but I think it is still proof-of-concept and they need to flesh a lot of the details out before it's time to approach Transport Canada for approvals.

As to the topic in general, Airbus seems to be pursuing the hydrogen option, with 3 hydrogen-powered concepts revealed just last month: https://www.airbus.com/newsroom/press-releases/en/2020/09/airbus-reveals-new-zeroemission-concept-aircraft.html . I assume (maybe naively) that they have done sufficient basic engineering that these concepts are fundamentally viable. How ready / willing the market is to trust hydrogen fuel, and build the necessary infrastructure is another question entirely...

[nightfire]

The interesting idea is IMHO to explore the world of propeller-based Aircraft again. A Turboprop-based Aircraft has a better fuel efficiency than a jet-based one due to various reasons- and if you don't need the speed of the jet, in lots of scenarios a prop-plane is just fine or "good enough" for the things it has to do.
This mainly involves short-distance flights and usage as a cargo hauler.

So someone has to explore the idea of electric flight, and later on the best of both worlds can be combined: An electric concept with batteries enough to have maybe 30 mins of flying time, that also provide the huge energy boost needed for takeoff, and some generator/fuel cell that will provide energy in-flight for maintaining level.
With this concept a plane could use hydrogen oder maybe some synthetic fuel produced with renewable energy.

[tszaboo]

(IE, when there just are no fossil fuels available at all)

CO2 + H2O + Energy = CH4 + O2
CH4 as we speek heats millions of houses everywhere around the world.
There are 28 millions cars converted to it.
"The Boeing SUGAR Freeze airplane concept looks at many advanced technologies which combine to provide over 70% reductions in Carbon Dioxide emissions. It is an example of a partially turbo-electric architecture. This plane uses liquid natural gas instead of jet fuel, and generates electricity in flight by integrating a solid oxide fuel cell with the turbine engine. The electrical energy is then used to drive an aft propulsor at the tail of the plane in order to energize the boundary layer and reduce drag."

[Cerebus]

I'm not quite sure what you're trying to say here.

"Liquid Natural Gas" is a fossil fuel. The methane used to heat millions of homes is fossil fuel. A tiny proportion is biogas from fermenters. There is no technological process for turning CO₂ + H₂O + energy into methane without involving good old fashioned agriculture and rather a lot of waste along the way. We're running out of land for agriculture to feed people, we certainly can't afford the land to make enough methane to keep the world's planes in the air, homes heated and so on.

[SiliconWizard]

The majority of electricity serving the majority of the world's population came from burning fossil fuels, and the power plants have an efficiency of around 40%, while a jet engine has around 80% efficiency at cruising speed and altitude.

Electric plane, is thus not very eco friendly after all, unless it enables new paradigms like small group or personal hops between short locations where normally cars would have to burn a lot of fuel to wait in a traffic jam.

To me, this is go (very) small or go home.

Absolutely.
And to begin with, I don't know if people are really aware of the amount of thrust a conventional turbojet engine is able to generate. I'd be curious to see a similar electric engine generating as much thrust while being reasonable in terms of cost and weight.

Then there is of course the point of storing energy. AG6QR gave the figures. No need to go any further. We can always dream of the better battery that is going to happen, but hey. Unless we go for fuel cells of some kind, I don't think we'll be able to increase the energy density of a battery that much more. I'll be happy to be proven wrong in the future though. And fuel cells, you guessed it, will rely on some fuel, so that's just displacing the issue.

There is a current trend in thinking one alternative to batteries would be to store energy as a "carbon-free" fuel like hydrogen. Except that producing hydrogen takes electricity (back to blueskull's point), and the process is not much efficient either. But even so, I'm not sure converting hydrogen to electricity via some kind of fuel cell and use electric engines would make much sense. Wouldn't using hydrogen directly to power engines be more efficient? So, that still wouldn't be electric flight.

As I see it, unless we find the miracle solution, this is a dead-end. At least for the time being.
But since for that to really happen and not be useless, we would need means of producing huge amounts of electricity in a clean way, and since we are still very far from that goal, I think that is what we should focus (and invest) on. Not on building electric planes that make no sense at the moment. Because THAT is, IMO, actually the easy part.

[ve7xen]

There is a current trend in thinking one alternative to batteries would be to store energy as a "carbon-free" fuel like hydrogen. Except that producing hydrogen takes electricity (back to blueskull's point), and the process is not much efficient either. But even so, I'm not sure converting hydrogen to electricity via some kind of fuel cell and use electric engines would make much sense. Wouldn't using hydrogen directly to power engines be more efficient? So, that still wouldn't be electric flight.

We're going to need to make our electricity production systems renewable too, regardless of what we do for transportation, and this is a relatively 'solved' problem at this point, just requiring investment. It's also much easier for governments to subsidize / force progress there than the tragedy of the commons. It's a similar situation with EVs, and I don't really think this is a great argument against it. Hopefully any new production that is built to support increased EV use or hydrogen-powered aircraft would be renewable. Scale usually leads to improvements in efficiencies too. It seems like the most efficient way to transport large quantities of renewable energy at high enough density might be breaking water with it and storing the hydrogen.

The Airbus initiative is based on burning hydrogen in turbines similar to existing turbofans, and using fuel cells for the plane's electrical requirements. Having an electrical propulsion system I guess is probably not feasible given the power demands and weight of the equipment required to produce that much power in a fuel cell; maybe efficiency too.

But since for that to really happen and not be useless, we would need means of producing huge amounts of electricity in a clean way, and since we are still very far from that goal, I think that is what we should focus (and invest) on. Not on building electric planes that make no sense at the moment. Because THAT is, IMO, actually the easy part.

We should be tackling all these aspects of the issue simultaneously. Electrifying things makes them 'automatically renewable' once the infrastructure is in place. It's a slow process on both sides, and there's no reason at all to do it serial rather than parallel. Airbus is targeting 2035 for commercial availability, it's not like they're selling them today. As long as we continue burning jet fuel, we're doing nothing about the contribution of air travel at all. It's also probably an improvement even with fossil electricity generation, shifting the relatively dirty small-scale burning in the engines to larger, more efficient plants that can afford the weight of emissions controls, centralizing the output for carbon capture, etc. - in addition to the fact that >25% of global electricity is renewable today, and will certainly be more then.

It's far from useless to pursue this avenue, if it's viable. The alternative is simply that air travel will become completely unaffordable.

[tszaboo]

I'm not quite sure what you're trying to say here.

"Liquid Natural Gas" is a fossil fuel. The methane used to heat millions of homes is fossil fuel. A tiny proportion is biogas from fermenters. There is no technological process for turning CO₂ + H₂O + energy into methane without involving good old fashioned agriculture and rather a lot of waste along the way. We're running out of land for agriculture to feed people, we certainly can't afford the land to make enough methane to keep the world's planes in the air, homes heated and so on.

Of course there is>
https://www.storeandgo.info/demonstration-sites/germany/

[sandalcandal]

I'm not quite sure what you're trying to say here.

"Liquid Natural Gas" is a fossil fuel. The methane used to heat millions of homes is fossil fuel. A tiny proportion is biogas from fermenters. There is no technological process for turning CO2 + H2O + energy into methane without involving good old fashioned agriculture and rather a lot of waste along the way. We're running out of land for agriculture to feed people, we certainly can't afford the land to make enough methane to keep the world's planes in the air, homes heated and so on.

There has been since 1897 https://en.wikipedia.org/wiki/Sabatier_reaction

Also not keen on "over population, running out of land" outdated alarmism. Definitely aware of running out of historical energy resources and ever increasing energy demand + climate change but over population and food supply (apart from instability due to climate change) is not a current issue everywhere apart from Africa. Getting off topic though.

[Cerebus]

There has been since 1897 https://en.wikipedia.org/wiki/Sabatier_reaction

Name a commercial plant using it, producing gas for sale (or even on-site use) at a cost equivalent from buying it from normal sources and in commercial quantities. It has to be a practicable process, not merely possible, that operates economically at the scales of current and proposed world usage. One assumed that an intelligent person would take that as read in the circumstances under discussion. And where does one find a convenient source of concentrated CO₂ that isn't a plant burning fossil fuel to produce energy, a cement works, a brewery or a similar primary user of either energy or biomass? One might like to examine the thermodynamics of the first listed to figure out why that isn't a runner for practical purposes.

Also not keen on "over population, running out of land" outdated alarmism. Definitely aware of running out of historical energy resources and ever increasing energy demand + climate change but over population and food supply (apart from instability due to climate change) is not a current issue everywhere apart from Africa. Getting off topic though.

"Running out of" isn't the same as "have run out of" so saying it isn't a current problem doesn't solve the issue, we are discussing the future of aviation, not the now. You might not be "keen on it", personally I loathe the idea, but it is unfortunately true. Just look at these two graphs (from here) and tell me where the land to grow fuel crops will come from.

 

Add population growth:



If those three put together is not a disturbing trend then I don't know what is. Adding more land use for mass biofuel production on top of that would be a farcical idea.

Remember that all this started with someone trying to convince a "Green party MLA" that [implicitly Green] electric aviation isn't a realistic possibility at current scale for aviation, that the waving of a technological magic wand won't solve the problem. Aviation is only responsible for 2.5% of global CO₂ emissions but is still growing along with all the other sources. One can't look at just finding replacement energy sources for aviation, it won't happen in isolation. If we, say, move to massive production of biofuels for aviation won't we also have other uses for those biofuels, won't we want to produce biofuels for road vehicles, home heating and all the other uses? One has to consider the big picture before one can say that one has a realistic solution. Here, the big picture says that biofuel production for aviation isn't the solution.

Further, any claims that synthetic methane production is a feasible alternative on this scale are also unrealistic. One only has to factor in the energy cost of obtaining CO₂ from anywhere other than existing concentrated sources that all use either energy or biomass. Any diffuse source of CO₂ would be energetically uneconomic.  It's more "let's wave a technological magic wand and it'll all go away" thinking that the first mentioned Green party MLA is guilty of. As engineers and scientists one hopes that we are above pinning our hopes on that kind of thinking.

[Cerebus]

I'm not quite sure what you're trying to say here.

"Liquid Natural Gas" is a fossil fuel. The methane used to heat millions of homes is fossil fuel. A tiny proportion is biogas from fermenters. There is no technological process for turning CO₂ + H₂O + energy into methane without involving good old fashioned agriculture and rather a lot of waste along the way. We're running out of land for agriculture to feed people, we certainly can't afford the land to make enough methane to keep the world's planes in the air, homes heated and so on.

Of course there is>
https://www.storeandgo.info/demonstration-sites/germany/

Which has produced "about 192.000 kWh" in "the run time of the project" (1186 hours = 49 days 10 hours). That's the equivalent of about 16 tonnes of kerosene, 19,919 litres of Jet-A1. The fuel capacity of a Boeing 737-200 is 22,596 litres. So that plant in its lifetime hasn't even produced enough fuel to fill a 737-200 once, energetically.

I'll say the same thing that I said above: "It has to be a practicable process, not merely possible, that operates economically at the scales of current and proposed world usage. One assumed that an intelligent person would take that as read in the circumstances under discussion."

Edited to add: The plant in question used grid electricity and the feed gas CO₂ was from a bioethanol facility. The overall power-to-gas efficiency was 56%, and I couldn't find a figure for the ultimate land use to produce the CO₂ .

[sandalcandal]

Name a commercial plant using it, producing gas for sale (or even on-site use) at a cost equivalent from buying it from normal sources and in commercial quantities. It has to be a practicable process, not merely possible, that operates economically at the scales of current and proposed world usage. One assumed that an intelligent person would take that as read in the circumstances under discussion. And where does one find a convenient source of concentrated CO₂ that isn't a plant burning fossil fuel to produce energy, a cement works, a brewery or a similar primary user of either energy or biomass? One might like to examine the thermodynamics of the first listed to figure out why that isn't a runner for practical purposes.

The point was a counter to the claim:

There is no technological process for turning CO₂ + H₂O + energy into methane without involving good old fashioned agriculture and rather a lot of waste along the way.

You might say you meant it differently but anyone reading it could take that to mean it just doesn't exist not it doesn't practically exist.

You can go start a new thread somewhere else if you really want to discuss population and land use.

Edit: I mostly saw that one point above that was patently false, I don't have much to comment on otherwise for the main subject.

[Cerebus]

The point was a counter to the claim:

There is no technological process for turning CO₂ + H₂O + energy into methane without involving good old fashioned agriculture and rather a lot of waste along the way.

You might say you meant it differently but anyone reading it could take that to mean it just doesn't exist not it doesn't practically exist.

Really? The context is evident from the discussion. One shouldn't need to spoon feed people every obvious qualification and exception. This is just a discussion, not a formal presentation for the public, one can hopefully presume a certain degree of 'smarts' and willingness to debate honestly from one's audience, one shouldn't have to be wary of wilful misinterpretation.

You can go start a new thread somewhere else if you really want to discuss population and land use.

Edit: I mostly saw that one point above that was patently false, I don't have much to comment on otherwise for the main subject.

No thank you, I don't want to have a general discussion about those, but one can't ignore them and develop a magic strategy for "greening" aviation in glorious isolation. I don't really believe that you are incapable of seeing that or realising that one has to be discussing solutions that are both practicable and practical at scale rather than theoretic solutions here, but perhaps I overestimate you.

[SiliconWizard]

We're going to need to make our electricity production systems renewable too, regardless of what we do for transportation, and this is a relatively 'solved' problem at this point, just requiring investment.

Is it? Really?

[Cerebus]

We're going to need to make our electricity production systems renewable too, regardless of what we do for transportation, and this is a relatively 'solved' problem at this point, just requiring investment.

Is it? Really?

Solved? No. But as doubly qualified as "relatively 'solved' ", in context, possibly. C'mon lets admit some subtlety on his behalf here.

[sandalcandal]

Cerebus

I don't disagree entirely. "Practical" electricity->fuel is problem that has not been solved and will need to be solved if hydrogen, methane or "renewably powered" aircraft are to be feasible. I'm not aware of any "practical" electric aircraft systems currently realised. However, there are options with potential merit that could be developed into. There are challenges with H20+CO2->methane systems which you've partially pointed out correctly but saying there are none then leaping back to saying there are some but they aren't practical is the point of brining up the actual existing solutions and developments. Even if they aren't 100% efficient does not mean that they do not have a net benefit.

Again, I don't agree that land availability is a problem. The problem is is sustainable and efficient land use. On the same site you've linked data from there's strong data showing the improving efficiency of land use: https://ourworldindata.org/crop-yields#the-trade-off-between-higher-yields-and-land-use

Honestly, I hope this isn't you but the only people I see peddling "Not enough land! We're all full!" are xenophobes trying to use sustainability as an excuse for their cultural intolerance which is why it drew my attention.

Edit:How do I scale the image? lol
Edit2: used [img width=700]