Electric commercial flight

[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?

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

I dunno, maybe. But in the context talked about here, which is generally speaking, drawing ever more electrical power than we currently do, then it's definitely unsolved.

And I personally still do not agree with the fact working on all fronts at the same time makes sense. Even basic project management principles are supposed to teach you that. Handling the hard tasks first is usually what's most efficient in the long run, and focusing on smaller tasks is only going to take away precious time and money.

Some of the "green-minded" people who advocate electrifying everything are still aware of that, and are mostly pushing electrification projects  (such as electric vehicles in general) as a way to push the world to massively invest in clean electricity production. I admit that's not a completely bogus approach. But it's, at the very least, overly optimistic. As we need more electricity, we're likely to cover the new needs on the short term with old and proven solutions rather than invest more in clean solutions for long-term results. This is what is already currently happening, as we may be constantly talking about green electricity all over the place, but we are still building more coal-based power plants all over the world.

[Cerebus]

@scandalscandal - to avoid indulging in mega-quoting.

The problem there is that improved agricultural efficiency has come with costs, both energetic and environmental. I don't propose to go and dig out figures, but the production of fertilizer comes with energetic and environmental costs, the mechanisation of agriculture ditto, there's biodiversity costs (which could decimate agriculture itself if it leads to collapse in populations of pollinators), intensive agriculture leads to pollution and so on.

Pointing at figures that show increased agricultural production per unit area for cereals (and there's no doubt that has happened) as if that's the solution implies that is sustainable. It is not. There is obviously a ceiling that can't be broken through - there's a physical density of crops versus available light and water that has to be reached at some point - moreover at some point the plants won't have physical room to grow. (Edited to add:) In the news at the moment is the seed of a war, as Ethiopia and Egypt start arguing over access to water from the Nile for both power and agriculture.

What this all runs up against is the old phrase "limits to growth". We keep on using more and more resources. As we run into availability problems in one area (CO₂ sink capacity of the atmosphere, fossil fuel reserves to name some) we pursue technological solutions that press resources in some other area (water, land, mineral reserves to name some). What no one wants to accept is that the only overall sustainable solution is "use less". For air travel that means less air travel for pleasure (take a boat instead), less air freight (wait a few weeks for your package from wherever, don't eat out of season fruits and vegetables flown from Peru to England). We can wait hopefully for some unrealistic technological miracle or we can do something practical and realistic now - "use less".

[sandalcandal]

@scandalscandal - to avoid indulging in mega-quoting.

The problem there is that improved agricultural efficiency has come with costs, both energetic and environmental. I don't propose to go and dig out figures, but the production of fertilizer comes with energetic and environmental costs, the mechanisation of agriculture ditto, there's biodiversity costs (which could decimate agriculture itself if it leads to collapse in populations of pollinators), intensive agriculture leads to pollution and so on.

Pointing at figures that show increased agricultural production per unit area for cereals (and there's no doubt that has happened) as if that's the solution implies that is sustainable. It is not. There is obviously a ceiling that can't be broken through - there's a physical density of crops versus available light and water that has to be reached at some point - moreover at some point the plants won't have physical room to grow. (Edited to add:) In the news at the moment is the seed of a war, as Ethiopia and Egypt start arguing over access to water from the Nile for both power and agriculture.

What this all runs up against is the old phrase "limits to growth". We keep on using more and more resources. As we run into availability problems in one area (CO₂ sink capacity of the atmosphere, fossil fuel reserves to name some) we pursue technological solutions that press resources in some other area (water, land, mineral reserves to name some). What no one wants to accept is that the only overall sustainable solution is "use less". For air travel that means less air travel for pleasure (take a boat instead), less air freight (wait a few weeks for your package from wherever, don't eat out of season fruits and vegetables flown from Peru to England). We can wait hopefully for some unrealistic technological miracle or we can do something practical and realistic now - "use less".

Then we agree the core problem is not fundamentally land availability but rather increasing efficiency, controlling wasteful demand and developing sustainable practices? Biofuel sources that have been presented are based on harvesting from existing activities, they don't use more land, they capture more output from it. (Corn for ethanol is an entirely different matter)

The apparent problem you raised of food security as a function land availability is a fallacy, food production is clearly not driven by land use. Hyper efficient indoor factory farms are definitely a thing that seeks to solve the problems you mention with ability to use vertical space and reducing the distance of production->consumption. The overriding factor in increasing food production is greater efficiency through improved practices. The greatest threat to food production is climate change as you have provided an example of with water availability along the Nile.
https://theconversation.com/in-the-future-there-will-be-more-rain-but-less-water-in-the-nile-basin-129360

As much as there are "limits to growth" in our ability to better exploit land there are also "limits to growth" in human population and that can be clearly seen in the human population graph you posted with the precipitous drop in population growth rate and levelling of the world population.

[Rx7man]

I cannot fathom how growing indoors is going to be more efficient, you need light, and where is the power for that light going to come from? Solar panels? Why not plant the crops outside and skip the losses?  It might work alright for leafy greens, but there isn't a snowflakes chance in hell you'll actually feed people that way
Same argument can be used for electric flight that's powered by dirty energy sourcesd

I don't think the electric motors needed for flying a big aircraft is an insurmountable problem.. powering them is

[sandalcandal]

I cannot fathom how growing indoors is going to be more efficient, you need light, and where is the power for that light going to come from? Solar panels? Why not plant the crops outside and skip the losses?  It might work alright for leafy greens, but there isn't a snowflakes chance in hell you'll actually feed people that way
Same argument can be used for electric flight that's powered by dirty energy sourcesd

I don't think the electric motors needed for flying a big aircraft is an insurmountable problem.. powering them is

https://www.eevblog.com/forum/renewable-energy/vertical-farming-and-other-high-tech-agriculture/new/#new

[Cerebus]

The apparent problem you raised of food security as a function land availability is a fallacy, food production is clearly not driven by land use.

How apposite that you use the word "fallacy" while claiming by implication that land use is not driven by food production by saying the exact converse. No of course "food production is clearly not driven by land use" it's the other way around. This is getting a bit silly.

Meantime relying on vertical farms for food production is almost literally building castles in the air, especially if your vision for them apparently uses no extra land. Presumably they hover somewhere over the sea. Where do all the materials and energy for building and vertical farms come from? Resources of course, and we're back to those being limited. Vertical farms are fine for garnish, for salad crops, but ruddy useless for subsistence crops or crops suitable for biofuel production.

C'mon do you think we were all born yesterday and can't spot argument for argument's sake? I find it hard to believe that anybody with a sincere interest in the outcome would drag the argument down this alley.

[ve7xen]

I dunno, maybe. But in the context talked about here, which is generally speaking, drawing ever more electrical power than we currently do, then it's definitely unsolved.

It is solved in the sense that we have the technology to generate the electrical energy required without ongoing CO2 emissions. There are many solutions to this - hydroelectric, wind, PV, geothermal, nuclear... I'm not sure why you're arguing this. The problem here isn't a technical one, it's one of inertia, investment, and to some extent social (particularly with hydro that displaces people / ruins agricultural land, and nuclear that has lots of FUD surrounding it). From media reports at least it seems that we're near an inflection point where renewables are becoming cheaper too, at least in the developed world, though I haven't looked into that in depth enough to really trust it.

And I personally still do not agree with the fact working on all fronts at the same time makes sense. Even basic project management principles are supposed to teach you that. Handling the hard tasks first is usually what's most efficient in the long run, and focusing on smaller tasks is only going to take away precious time and money.

The tasks themselves are orthogonal and not significantly tied. Only their impact on global CO2 emissions is somewhat related. The engineers at Airbus have next-to-no influence on pushing authorities to deploy renewable energy production more widely. If anything, it would help accelerate those efforts to tie the greening of aviation to the greening of electricity production. There is no advantage to delaying the development of electricity->fuel systems for powering aircraft until the whole world is powered by renewable energy, yet it would certainly slow down the greening of that industry to wait before you're happy with the proportion of renewables in the energy supply (what is your threshold for this being worthwhile, anyway?) before starting the 30+ year project of developing and certifying new aviation technologies such as these.

Some of the "green-minded" people who advocate electrifying everything are still aware of that, and are mostly pushing electrification projects  (such as electric vehicles in general) as a way to push the world to massively invest in clean electricity production. I admit that's not a completely bogus approach. But it's, at the very least, overly optimistic. As we need more electricity, we're likely to cover the new needs on the short term with old and proven solutions rather than invest more in clean solutions for long-term results. This is what is already currently happening, as we may be constantly talking about green electricity all over the place, but we are still building more coal-based power plants all over the world.

We are still building more coal plants around the world, yet the proportion of renewables continues to increase year over year.

Since you seem to need more convincing, I also don't think anyone expects this tech to replace traditional aviation overnight - the Airbus concepts are fairly short range. The proportion of renewables is fairly regional, and many jurisdictions have commitments to reach 100% renewables by 2050 or sooner, so by 2035 when these things are optimistically expected to be available, they better be well on their way. So they buy them, and places where coal is still the primary source don't.

You could also 'just' have governments force airlines to buy clean power / equivalent offsets, which would help drive investment.

[hendorog]

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.

Metal air batteries have theoretical energy storage much higher than lithium ion.
Still very much theoretical, but in the ballpark.

Someone will bring up that Thunderbolt did a debunking if metal air. Frankly that video was unconvincing click bait.
Of course it may never be practical/cost effective when compared to the alternative. But it may be possible. Open minds required here. Recharging for example might be done quickly chemically or with a battery swap.

The net effect of air travel on climate change is apparently about 3.5% of the total human causes, so I'm not sure that justifies the massive change required.

[sandalcandal]

The apparent problem you raised of food security as a function land availability is a fallacy, food production is clearly not driven by land use.

How apposite that you use the word "fallacy" while claiming by implication that land use is not driven by food production by saying the exact converse. No of course "food production is clearly not driven by land use" it's the other way around. This is getting a bit silly.

Meantime relying on vertical farms for food production is almost literally building castles in the air, especially if your vision for them apparently uses no extra land. Presumably they hover somewhere over the sea. Where do all the materials and energy for building and vertical farms come from? Resources of course, and we're back to those being limited. Vertical farms are fine for garnish, for salad crops, but ruddy useless for subsistence crops or crops suitable for biofuel production.

Don't start trying to BS formal logic. The exact converse of "food security is a function land availability" is " land availability is a function food security" where as "food production is clearly not driven by land use" and "food production" being equivalent to "food security" is used to imply that "food security is a not a function of land availability". There's no converse statement, it is an assertion of the negation. What I should have said is "food security is a function land availability is a false statement because the negation is true (food security is a not a function of land availability)".

The point of bringing up vertical farms is that even "at some point the plants won't have physical room to grow" and "out of season fruits and vegetables flown from Peru to England" aren't absolutes. I never said we should rely on them because I doubt we will ever will due to the massive waste present and many other areas for potential improvements.

C'mon do you think we were all born yesterday and can't spot argument for argument's sake? I find it hard to believe that anybody with a sincere interest in the outcome would drag the argument down this alley.

You want to spin it like that?
I had two beefs

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.

and

We're running out of land for agriculture to feed people

When have I strayed away from trying to demonstrate those points? I see two erroneous claims that are demonstrably false and I've put up evidence and information to disprove them while you try to drag it on with anecdotes and idle speculation.

Are you sure you're not just trying to have the last word when you have nothing more to say? I has hoping to find consensus with you but it's clear to me now you don't have good will.

[Cerebus]

Are you sure you're not just trying to have the last word when you have nothing more to say? I has hoping to find consensus with you but it's clear to me now you don't have good will.

No, I'm quite happy to let you have the last say and make whatever claims you like about what I've said. It's on the record, people can read it and judge for themselves what is fallacious and what is not, I feel no need to add another datum, riposte or argument.

[tszaboo]

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.

This is a demonstration site. First I wanted to link a 40 Million EUR P2G facility that is being built in Germany.
But now I realize, it doesnt matter what I would've linked, you are just here to pick fights, and I'm not interested in that.
This shit is not just a fad that is picked up because it is trendy. There is nothing trendy about big industrial chemical plants, that's why nobody is talking about it. But the technology can be used to reverse global warming, just by using CO2 from the air to run the process.

[PlainName]

people can read it and judge for themselves what is fallacious and what is not

I thought you two were having a discussion. Didn't realise you were actually playing to the gallery.

[Cerebus]

people can read it and judge for themselves what is fallacious and what is not

I thought you two were having a discussion. Didn't realise you were actually playing to the gallery.

I wasn't, but one is always conscious that it's a public discussion.

[sandalcandal]

people can read it and judge for themselves what is fallacious and what is not

I thought you two were having a discussion. Didn't realise you were actually playing to the gallery.

Ah yes, nothing quite as addictive as validation from random internet strangers...

[NiHaoMike]

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.

Never heard of jet engines being that efficient, last I checked they were in the 40-50% range.

tell me where the land to grow fuel crops will come from.

Look at all the yards doing nothing useful. (Some are used to grow food but I'd imagine that's likely single digit percentages in terms of area.) Biofuel crops can grow in a lot of places, even where the soil is too polluted for growing food.

That said, biofuels from ocean algae would probably be easier to scale up.

Goes to show how inefficient factory farming really is and why we should be replacing it with sustainable farming. Factory farming also makes near ideal conditions for bacteria and viruses to multiply and potentially become particularly dangerous ones (for example, MRSA and other antibiotic resistant bacteria), but that's for another discussion.

[Cerebus]

Oh for *** sake NANDBLog, let me fix that that quoting for you so it makes some sort of sense.

(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."

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 .

This is a demonstration site. First I wanted to link a 40 Million EUR P2G facility that is being built in Germany.
But now I realize, it doesnt matter what I would've linked, you are just here to pick fights, and I'm not interested in that.
This shit is not just a fad that is picked up because it is trendy. There is nothing trendy about big industrial chemical plants, that's why nobody is talking about it. But the technology can be used to reverse global warming, just by using CO2 from the air to run the process.

Now *that* is in order and makes sense:

My frustration is with you just handwaving and effectively saying that some technological process for producing methane will solve the problem, and not saying it very clearly at that.  You start out with an unbalanced chemical equation for reforming methane and say that methane is used for heating millions of homes and that there are 28 million cars converted to use it. As if getting from the formula to heating all those houses and fuelling all those cars on reformed methane is trivial. There's a bit more to it than that.

Then we have a pilot plant, running at 56% energy efficiency using grid power. That's fine, its experimental, who cares where the power comes from for the experiment. But it uses a potted source of concentrated CO₂ that's derived as 'waste' from a bioethanol plant. The energy costs (and other costs) of that CO₂ stream aren't factored into 56%. Even if it was, this process that will require a net supply of 1.8 times as much energy as we're currently using in methane form a solution at all? Doesn't increasing power generation capacity at all sound more like a problem than a solution? They're claiming a likely efficiency of 69% for a scaled up 5MW plant, so that figure will fall to a mere input energy multiplier of 1.45, still not a figure that makes one feel sanguine is it? And the costs of acquiring CO₂ feedstock are still not factored in.

What is so difficult in understanding that while these pilot plans are all very interesting, they aren't the practical solution in the short term, and may not be in the long term?

But the technology can be used to reverse global warming, just by using CO2 from the air to run the process.

You can't "just" use CO₂ from the atmosphere without incurring massive energy costs. CO₂ is around 400ppm of the atmosphere, 0.04% - converting that into a concentrated 100% CO₂ feedstock isn't trivial. Whatever way you do it will incur a huge energy cost, concentration with zeolite type concentrators, compressing air to the point where you can extract liquid CO₂, or some other method. If you know of a technology for cheap, low energy CO₂ concentration from atmospheric air, please do tell.

These plants won't reverse global warming. I wish they would, but they won't. The energy budget for doing it from atmospheric CO₂ is huge. There's the biological capture and then fermentation route en route to producing a fuel. But that uses energy, and land. Where do you get them?

The solutions are not technological. Technology will not save us this time. It might make fixing the problems easier, perhaps less painful, but it won't fix things on its own. You sound as if you think it's all fixed, and we just have to wait for the research projects to finish and the full scale plants to be built and then it's "problem solved".

If you think that it's about point scoring or picking a fight you're wrong. It's about the complacency that so may engineers exhibit that "Don't worry, technology will fix it". Keep believing that and it's what they'll have to write on mankind's, or at least civilisation's, gravestone. Engineers ought to be the people capable of seeing the flaws in the technological "quick fixes", capable of realising that it's a massive systems problem, not just producing the next generation of products (or whatever metaphor you prefer for looking at parts of the puzzle, but not the whole problem). And don't get me started on the so called 'engineers' who can't, or rather refuse to, even see that there's a fundamental problem of global warming staring us in the face here.

[Cerebus]

That said, biofuels from ocean algae would probably be easier to scale up.

That's the kind of thing that really scares me. "Look, OK, we've messed up the ecosystem by messing with the atmosphere, let's fix it by fiddling with the Oceans".

We've messed up big time by not understanding what we were doing to the atmosphere, and that was pretty much accidental. Are we really so knowledgable about the effects of messing with the Oceans that it's a safe thing to contemplate deliberately doing? I think not somehow. Every time I hear someone mention "ocean seeding" as a method of carbon capture I start to acquire a nervous tick.

[tszaboo]

The solutions are not technological. Technology will not save us this time. It might make fixing the problems easier, perhaps less painful, but it won't fix things on its own. You sound as if you think it's all fixed, and we just have to wait for the research projects to finish and the full scale plants to be built and then it's "problem solved".

If you think that it's about point scoring or picking a fight you're wrong. It's about the complacency that so may engineers exhibit that "Don't worry, technology will fix it". Keep believing that and it's what they'll have to write on mankind's, or at least civilisation's, gravestone. Engineers ought to be the people capable of seeing the flaws in the technological "quick fixes", capable of realising that it's a massive systems problem, not just producing the next generation of products (or whatever metaphor you prefer for looking at parts of the puzzle, but not the whole problem). And don't get me started on the so called 'engineers' who can't, or rather refuse to, even see that there's a fundamental problem of global warming staring us in the face here.

On some high level thinking, it doesn't matter, what is the efficiency of these plants. If the power->CH4-> power cycle is only 60% so be it. It only means that we need to install more solar panels. It's the total investment cost that matters.
And that the technology gives reason for all parties to invest in this technology.

I'm sure that fir the first decade or so, we could just carbon capture the CO2 outputs of existing power plants. Since power plants could sell CO2, they will have a reason to capture this, instead of releasing into the atmosphere. Also it reduces their cost with carbon credits.
There are already times, when solar panels generate more electricity than needed. Solar inverters actually shut down in these cases, because the voltage on the network increases and they are not supposed to work when the output voltage is too high. The price of electricity in these times is actually negative, so any industrial process you do, will generate income for you. These times will be more and more frequent.
There is always market for methane. It can be stored cheaply, with existing technologies, in bulk. There are countries that store months of their methane needs. This is a technology that we can actually build up for scale, unlike all the other proposals. Like seriously, are we going to place several powerwalls in every house, and everyone change to an electric car? We could convert half the existing car fleet to use LNG or CNG, and make it CO2 neutral. And it costs 1000-2000 EUR/car, unlike buying an electric car for about 40000.
It is the perfect middle-ground solution for the next 20-30 years. You have to understand that any solution that we want to do has to be financially acceptable for everyone. We cant ask countries like China to scale back, they are just not going to do it. But if you start buying CO2 from them, they are going to do carbon capture.

[sandalcandal]

On some high level thinking, it doesn't matter, what is the efficiency of these plants. If the power->CH4-> power cycle is only 60% so be it. It only means that we need to install more solar panels. It's the total investment cost that matters.
And that the technology gives reason for all parties to invest in this technology.

I want to support and add to that. Solar for energy capture doesn't need to be 24/7. Solar can be installed in non-arable land. Solar PV is more efficient than photosynthesis in terms of energy production.

...the maximum conversion efficiency of solar energy to biomass is 4.6% for C3 photosynthesis at 30 °C and today's 380 ppm atmospheric [CO2], but 6% for C4 photosynthesis. This advantage over C3 will disappear as atmospheric [CO2] nears 700 ppm.

Xin-Guang Zhu, Stephen P Long, Donald R Ort, What is the maximum efficiency with which photosynthesis can convert solar energy into biomass?, Current Opinion in Biotechnology, Volume 19, Issue 2, 2008, Pages 153-159, (http://www.sciencedirect.com/science/article/pii/S0958166908000165)

Most sources quote practical efficiency closer to 1%
Edit: "solar energy conversion efficiencies for crop plants in both temperate and tropical zones typically do not exceed 1%"
Blankenship, Robert E.; Tiede, David M.; Barber, James; Brudvig, Gary W.; Fleming, Graham; Ghirardi, Maria; Gunner, M. R.; Junge, Wolfgang; Kramer, David M. (2011-05-13). Comparing Photosynthetic and Photovoltaic Efficiencies and Recognizing the Potential for Improvement. Science. 332 (6031): 805–809. doi:10.1126/science.1200165

This has turned into (or probably always has been) a discussion on solar to fuel conversion.
A 2017 overview of Solar to Hydrogen here: https://link.springer.com/article/10.1007/s40243-017-0088-2


Very recent (Sept 2020) paper on Solar to Hydrocarbon.

A.C. Lourenço, A.S. Reis-Machado, E. Fortunato, R. Martins, M.J. Mendes, Sunlight-driven CO2-to-fuel conversion: Exploring thermal and electrical coupling between photovoltaic and electrochemical systems for optimum solar-methane production, Materials Today Energy, Volume 17, 2020, 100425 (http://www.sciencedirect.com/science/article/pii/S2468606920300447)

In response to some people suggesting biological solar to fuel generation methods, I'd say such processes appear to be immensely inefficient.

[Cerebus]

On some high level thinking, it doesn't matter, what is the efficiency of these plants. If the power->CH4-> power cycle is only 60% so be it. It only means that we need to install more solar panels. It's the total investment cost that matters.
And that the technology gives reason for all parties to invest in this technology.

There you go again: "It only means that we need to install more solar". There is a cost in resources, materials and energy to make those solar panels. That has to come from somewhere. It's no good examining this stuff in isolation - one must think about the costs as part of a whole system.

I'm sure that fir the first decade or so, we could just carbon capture the CO2 outputs of existing power plants. Since power plants could sell CO2, they will have a reason to capture this, instead of releasing into the atmosphere. Also it reduces their cost with carbon credits.
There are already times, when solar panels generate more electricity than needed. Solar inverters actually shut down in these cases, because the voltage on the network increases and they are not supposed to work when the output voltage is too high. The price of electricity in these times is actually negative, so any industrial process you do, will generate income for you. These times will be more and more frequent.
There is always market for methane. It can be stored cheaply, with existing technologies, in bulk. There are countries that store months of their methane needs. This is a technology that we can actually build up for scale, unlike all the other proposals. Like seriously, are we going to place several powerwalls in every house, and everyone change to an electric car? We could convert half the existing car fleet to use LNG or CNG, and make it CO2 neutral. And it costs 1000-2000 EUR/car, unlike buying an electric car for about 40000.
It is the perfect middle-ground solution for the next 20-30 years. You have to understand that any solution that we want to do has to be financially acceptable for everyone. We cant ask countries like China to scale back, they are just not going to do it. But if you start buying CO2 from them, they are going to do carbon capture.

Methane reformation as a battery during times of solar overproduction? OK, that actually maybe makes sense as an energy storage medium. As long as you understand that there has to be more than three times as much energy available to to do the reformation as the plant produces for consumption (pesky thermodynamics, reformation is hoped to be 67% efficient at scale, natural gas generating plants are 45% efficient, coal 32% [Source: EIA]).  And obviously as soon as that stored energy is released, its CO₂ is back in the atmosphere.

The questions to ask on that are: Does it use less or more resources than making batteries to do the same job? Does it result in a net CO₂ reduction overall or just flatten the growth curve a bit, remembering that fossil fuel is still being burned, moving carbon from the ground to the atmosphere? Is there enough 'green' electricity overproduction to practically support it? If it does produce enough gas to produce a net CO₂ reduction is there a practical way to store that gas?

To use a metaphor it's clearly a temporary dressing, not a cure. Is it a big enough temporary dressing for the size of wound, or is it a band aid on a gushing chest wound? Just looking at that 3x energy multiplier for reformation without adding any of the other resource costs, I suspect that it's a non-runner.

[Siwastaja]

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.

Why would you compare these? I mean, these are secondary, or internal parameters. Raw materials that don't get you anywhere. There is correlation, but the matter is greatly oversimplified.

The simplest flaw in your comparison is ignoring efficiency completely. Instead of comparing:

E_density_jetfuel
vs.
E_density_battery

you would need to compare:

Eff_jet_engine * E_density_jetfuel
vs.
Eff_electric_enginer * E_density_battery.

OK, getting better. Better as in, closer to the truth instead of an agenda.

Then again, why would you only count the weight of the fuel? While some parts of the aviation system are (mostly) energy source independent (like wings, flight surfaces, etc.), some parts exist solely for that particular fuel system. So instead of comparing:

weight of fuel
vs.
weight of batteries

as a denominator in energy density, you should use:

weight of fuel + weight of jet engines + weight of complete fuel system
vs.
weight of batteries + weight of electric engines + weight of complete power delivery and management system.


and NOW we are getting somewhere.

The result is likely the same, with electric not being viable especially in longer routes for quite some time, but the story might get more interesting for very short hauls, which are relevant in Europe. Might, as in, it does in my quick&dirty napkin calculations. Do the math for yourself and see. For some weird reason, Europeans routinely travel some 500 kilometers using flights instead of building a system of cheap, fast and reliable train network like seen in China or Japan.

My sources say Lithium-ion batteries are around 90 Wh/kg,

You have some interesting sources. I mean, this number would be literally from very early 1990's, with the very first commercial li-ion cells and packs by Sony.

Even as an individual, you can easily buy cells easily exceeding 250Wh/kg and I'm sure 300 Wh/kg is available to those inside the industry. The error here is already almost half an order of magnitude.

Your "two orders of magnitude" becomes approximately one order of magnitude after correcting for the trivial shortcomings. Which is still a lot, but the difference might not be even an order of magnitude when looking at very short hauls, where different aspects get a much higher coefficient of interest, for example:
* taxiing consumption
* engine and fuel system weight you have to carry around all the time (the exact same argument that you have to carry around batteries!)

You can make any point with the numbers, and your conclusion will be likely correct anyway, but try to be mentally honest.

[Clear as mud]

I happened to see this in a recent issue of Discover magazine:
The Other Solar Power: How Scientists Are Making Fuel From Sunlight and Air.

It mentions a couple of other demonstration plants that start with the same basic reaction being discussed, take CO2 and H2O, add energy, get methane; which then can be converted to other hydrocarbons through the addition of more energy.  The difference here is these projects are getting the energy from the sun directly, instead of the power grid.  I realize it may be impracticable to scale these up to anything truly useful.

[Rx7man]

true, an entire system analysis really needs to be done to get the whole picture, I'm not sure how the weight of the power control systems, motors, etc will compare for electric, but delivering 10MW isn't going to happen with 10ga wire.. and if google steered me wrong when I searched for energy density on them, I'm sorry.. However, a conventional aircraft still gets lighter and thus more efficient as it flies, and this isn't insignificant

I think for short hops it will be become viable to use electric, I really doubt it for trans-atlantic and similar long haul flights

Also Europe does have a pretty darned good electric rail system, especially compared to north america.. I know you can get pretty much anywhere in Switzerland quickly and efficiently on rail, Japan seems to be really good as well.. North america is essentially in the 3rd world on this

[Siwastaja]

Also Europe does have a pretty darned good electric rail system,

It is pretty good AFAIK, but looking at the horrific result of everybody flying so much, it's evident something's not right. I don't know what and it's beyond the scope of this thread.

You know, with all that security theatre at the airports, flying short hauls isn't that quick or fun, the average speed (accounting for travel-to-airport, security theatre, board the plane, taxi, takeoff...) remains well below that of Asian bullet trains of 1980's.

But there must be a reason why people fly the short hops over the continental Europe. And this could be rectified.

But, electric aviation is one interesting option if the root cause for having to fly such stupid short hops over the continent can't be avoided. Once you can design the plane for a range of some 1500 km max, (some 1000km actual + 500km safety for holding and going to alternative airports), the numbers for actual energy density are quite different than those calculated for 5000km

[Rx7man]

Just a thought, but perhaps it's partly because of booking systems.. If you're going to fly anyhow might as well fly all the way.

When I was a service tech that went around north america, I actually preferred booking to the small airports close to where i had to be, not to save driving, but because the security theater on small airports that only had one or two flights per hour was much easier to deal with.. if you were there 1 hour before your flight you were fine, unlike big airports where you HAD to be at least 2 hours early