Regenerative breaking can already exist for trains without adding in the carbon capture [1].
Instead of adding batteries, and thus weight, the train supplies power back to the grid when it breaks. Thus, the cheaper source of energy described here can be achieved without the carbon capture, and consequently, we can use that power to power other things, reducing energy generation overall and reduce CO2 emissions.
Thus, it seems like the primary benefit here is using the train's motion to replace the fans required for carbon capture and thus piggybacking on the energy already expended by the train to move. That seems logical, though it could be deployed irrespective of regenerative breaking. Basically we should do regenerative breaking regardless as it is just more energy efficient. Regenerative breaking can primarily be deployed in electric trains anyway as you use the existing motors to break the train, and in so doing, generate electricity from those motors. Adding electric motors and a battery to diesel trains JUST for carbon capture seems foolish.
One question I had: how does this carbon capture change the aerodynamics of the train and thus its efficiency?
>Adding electric motors and a battery to diesel trains JUST for carbon capture seems foolish.
There's no such thing as a train propelled by a diesel engine.
All "diesel trains" are diesel-electric. They use electric motors for propulsion, and for braking as well. Normally, there's a big resistive grid on the roof where the power is dumped.
That's categorically untrue. Diesel-electric trains are not uncommon, but there are many, many trains driven directly mechanically or hydraulically by the diesel engines.
I stand corrected: some really backwards countries still have crappy old trains that run purely on diesel.
In America, all the freight trains and diesel passenger trains are diesel-electric, and have been for many decades. And America isn't even much of a leader in passenger rail.
I guess I shouldn't be too surprised about the UK; this is a country that still doesn't know how to make a single water faucet that combines hot and cold water.
Direct air capture is the holy grail of climate solutions. Its success would offer us a way to put the cat back in the bag, and see CO2 levels decrease.
The problem is how absurdly expensive these things are. In the next couple decades, even being optimistic, it's hard to forsee a scenario where we've plugged enough holes in our infrastructure that direct air capture will be better or cheaper than doing more capture inside some existing pollution site, or replacing more fossil fuels with clean energy.
But one day we will reach that point. And when we reach that point, anything to reduce the cost of carbon capture a little bit will help a lot.
So yes, regenerative breaking connection is sort of a distraction. But improvements to DAC efficiency are very welcome, and improving airflow by mounting the mechanism on a high-speed train seems like it offers a big improvement.
Great. Now build out the infra… adding carbon to the air.
The state of things leave little wiggle room for iterating on and disposing of one experiment after another
Reducing consumption and industrial activity is a sure fire way to reduce carbon in the air
But I expect we’ll avoid intentional figurative death for adults today and chuck the risk over the fence into the future as usual, given how people behaved when lockdown meant “no haircuts”.
Unless you're in a sufficiently carbon dense region (third world maybe) it seems exceptionally optimistic to assume the train will be able to power more than itself in either scenario. Not that it's not a good idea anyway but unless the train can cover itself with spare change leftover you're not going to be powering anything extra without creating waste.
There might be an additional benefit for fossil fuel trains. Point source capture is usually more efficient than direct air capture.
This isn't necessarily directly point source, but if the diesel exhaust is partially directed into the capture train, the CO2 concentration should be higher, and could have a more efficient CO2 capture.
If you are already adding batteries to the train to capture the regenerative breaking energy, why not use that same energy to accelerate again, therefore saving the fossil fuel energy in the diesel generator? Surely that would be more efficient than DAC in a CO2 sense?
Or just go fully electric overhead like they do in northern european countries. Some of the ore trains in the far north generate a fair bit of electricity from regenerative braking that's then used by other trains going uphill or fed into the local power system.
The flip side too is that the power generated by a braking train is more likely to be in the voltage range needed by other trains in the system. It is always better the use electricity locally and in the same voltage rather than convert it to grid power.
Thanks, I was looking for them but couldn't remember the name
> From Riksgränsen on the national border to the Port of Narvik, the trains use only a fifth of the power they regenerate. The regenerated energy is sufficient to power the empty trains back up to the national border.
Which just makes the train less efficient and need more power? These carbon capture systems only work when the input energy is free (both financially and carbon-wise), but it seems like there's better and more efficient for uses the dynamic breaking energy (electric or hybrid trains).
Fans are inherently pretty inefficient. If you want to generate airflow across a surface, it's more energy efficient to move the surface than it is to move the air (assuming you have negligible non-fluid friction, which trains do). Motors can be over 90% efficient. With a fan, you have the efficiency of the motor and then, on top of that, the static efficiency of the fan, which is often less than 50%. We use fans when it's not practical to move the things we want to create airflow over (which is the vast majority of the time). Otherwise, we use the object's own motion. This is the principle behind ramjets.
I still do not understand how any human-developed carbon capture techniques is going to be better or more efficient than just planting a tree. A (living, growing) tree can capture quite a lot of carbon for almost no cost, directly from the atmosphere. More generally, vegetation biomass growth is carbon (and hydrogen) capture in action on planetary scale - almost for free.
Trees capture carbon, but they don't sequester it. You need additional steps to prevent the biomass from decomposing. This isn't too hard, generally just burying plant material below enough earth will do the trick, but it's a substantial expense at scale.
And scale is really the issue. All the world's forests combined currently absorb about 20% of CO2 humans currently emit. To go neutral, you're looking at planting around 12 trillion trees. Worse still, about 30% of Earth's land surface area are already covered by forests, so you can't simply expand the forests to get the required carbon capture.
The only realistic way to achieve 100% carbon capture by biological means would be to seed algae blooms in the ocean, which for short term carbon uptake would work pretty well, but when that algae dies it is way harder to prevent it from decomposing, meaning you don't get long term sequestration. Further, you are talking about terraforming-level changes to marine environments all over the world. Beyond the catastrophic effects that can have on other species, the full effects of what that might do to us are impossible to fully predict.
Artificial carbon capture might have higher capital costs since the equipment is not self replicating, but it can be orders of magnitude more efficient in terms of energy, CO2 capture rate, and land use requirement.
Can’t you just use the wood for something instead? I’ve seen a lot of innovative use for wood in large construction projects. For example, there was a recent proposal to replace the West Seattle bridge with a timber through arch bridge, and timber skyscrapers are apparently now a thing. This is especially true since concrete is a really polluting industry, and finding ways to use less cement is a pretty solid climate action.
There simply isn't that much demand for wood. It is already used extensively as a building material, but only a tiny fraction of the world's forests are used for lumber production. Indeed lumber production doesn't even make up a large portion of trees that humans clear. For context 12 trillion trees of lumber would be enough to build 100 to 500 two story residential homes per human being on earth.
Again, this doesn't really matter since this wouldn't physically fit on the planet.
The price of lumber is currently the same as it was in 2018. The price spike during the pandemic was due to reduced saw mill capacity and subsequent panic buying. At no point in time were we running low on trees.
We would need to consume timber at about 1000 times the current rate for timber demand to equal the necessary tree planting rate for carbon capture.
Do you think there is any room for induced demand of timber? Like in 40 years we cut down a bunch of trees to sequester the carbon and people find new innovative things to do with the lumber, not just in construction but also in material science, packaging, etc.
I’m thinking about salt as an example. It is a by-product of many industries and cost have gone down a lot since the industrial revolution. I’m imagining that today’s salt demand is heftily induced as a result. I mean, it is cheap enough to spray on highways to melt the ice.
Every year humans use approximately 9 Billion tons of concrete. The mass of 12 Trillion trees is approximately 1100 years worth of concrete. This much lumber would need to be used every 200 years or so.
I see, so we are never going to be able to use trees to capture our current current CO2 emissions. However would it be possible to use trees (and other photosynthetic organisms) to capture our historic emissions in a mass global atmospheric cleanup efforts, after we’ve mostly gone carbon neutral? Or is that also like a 1000 year effort even if we became carbon neutral tomorrow?
If we stopped emmitting CO2 tomorrow, a realistic increase in number of trees (~1 trillion trees) would take about 900 years to return to pre-industrial co2 levels. The more trees you plant, the faster it goes, but even if you cover the entire planet in forest (including places like Antarctica and the Sahara), you're still looking at centuries.
Other organisms can be used as well, but again you need to sequester the carbon.
Thanks. I appreciate your answers here. This is why I love HN. Getting answers to questions on niche topics I don’t even know how to begin searching for.
Pretty much. I don't have the numbers but the phrase to always bear in mind is "fossil carbon." All that oil, gas and coal was once living bio matter (to a first approximation). Industrial civilisation has been predicated on us burning fossil carbon laid down over millions of years by earths organisms. It will take more than a few decades to remove the excess that we have pumped in, even if we reforest the earth, reduce the population and all become ascetics.
Many trees live for over 500 years (Redwoods, Cedars, Douglar Fir, Oaks, etc.). They can be part of the solution of keeping CO2 levels down while our energy system is de-carbonized. Go ahead and plant trees. They are great in many other ways also.
Again, the real deal breaker is needing 1.6 earths worth of land. No one is saying planting trees is a bad thing, but there is no escaping the need for other methods of carbon capture.
Trees tend to stop growing after about 150 years, so trees left standing longer than that will delay releasing the CO2 they've already captured, but will not continue to capture carbon. Indeed you probably want to cull trees before their growth rates start to decline around the 100 year mark to maximize your carbon capture rate.
How are you arriving at the 12 trillion trees number? I think there are some less obvious ways that trees can capture more carbon. For instance, trees build soil over time. Much of the deforested land in the world has had its topsoil washed away without trees to hold it in place. That soil is also a form of captured carbon.
Earth currently has about 3 trillion trees, this population captures about 20% of current human co2 emissions (which includes soil creation). To get to 100%, you need 5 times as many trees, which means increasing the current population by 12 trillion.
Of course this is a crude estimate, not all trees are equal and planting trees in such large numbers would undoubtedly have other effects, but no matter what you are talking about an absurdly large number.
Photosynthesis is pretty inefficient and trees release the CO2 when they rot, so they aren’t great for long term storage. At certain phases of growth, forests are actually carbon positive. DAC can bind carbon to rock or pump it deep underground where it will stay potentially forever(on any meaningful human timescale). You can also directly account for the tons of CO2 removed by DAC which makes it more used for carbon trading schemes that financially incentivize capture.
That's true, but they don't fix any more carbon after they're fully grown. I'm not against tree planting, but it's probably a bit oversold as a solution. Kelp probably presents a more interesting opportunity.
I know at least conifer trees are never "fully grown". I imagine it is the same for deciduous trees. Trees continue to add wood to there structure every year. You count the tree rings to know its age. A 500 year old redwood, cedar, or Douglas fir can be 15 or more feet in diameter. That is a lot of wood. Unlike what many people thought, studies have found that the volume of wood added to trees in a mature forest is similar to a young one.
I think the example to look at is biological nitrogen fixation, vs. the Haber-Bosch process, which operates at high pressures and temperatures and therefore has a small area footprint. You can do biological nitrogen fixation with legume (pea, bean) crops in symbiosis with nitrogen-fixing bacteria nodules, and then compost the crop to generate a nitrogen-rich fertilizer, but this means devoting large fields to the process. The Haber-Bosch process in contrast can produce much greater amounts of pure ammonia in a single location.
Haber-Bosch traditionally has relied on large fossil fuel inputs, but it's possible to get the hydrogen from the process via hydrolysis of water, powered by renewable energy (or nuclear), and use electricity instead of fossil fuels to run the high-temperature, high-pressure catalytic reaction (H2 + N2 -> NH3).
The same arguments apply to carbon capture and fixation: you can do it in an industrial setting, for example the North African desert (which doesn't support much plant growth), you could use seawater as the hydrogen source and plentiful sunlight and PV/concentrated thermal for electricity to drive the carbon capture (fans etc.) and the analogous version of Haber-Bosch (Fischer-Tropsch) for CO2 - CO + H2 -> hydrocarbons.
you only can plant so much trees, with no guarantee that they even will grow old; currently we do everything but increase tree "population", because instead of going vegan we have ever rising meat consumption demanding more and more land for agriculture.
Even restoring all the forests that have existed pre the industrialization will not help much, because it only resets a small part of the emissions. All fossil fuel burned is still in the atmosphere, likewise increasingly more methane.
Additionally, it's easily used for green washing.
Plant trees -> Yai carbon is offset, can emit like before;
then trees are cut down, burn or don't even grow, and the next company can plant trees at the same land
Because trees cannot be grown just anywhere, they require specific [land, water, nutrient] conditions that also happen to be the same things that are already under pressure from our civilisation. This is caused by things like extensive monocrop agriculture, grazing etc. Furthermore, trees do not necessarily sequester carbon beyond their lifespan - the sequestration is an additional process that may or may not occur naturally. Think of old trees dying, falling down and decomposing vs old trees dying and being covered by mud.
> Specifically, a coordinated global round of unconventional quantitative easing through the issuance of a complementary currency, called the carbon coin, to be issued in proportion to the mass of carbon that is mitigated.
That is just nuts.
The result would be like every other time money is printed: Wealth flows to those that know how to game the system while inflation erodes the wealth and income of normal people.
Totally agree, woody biomass is being under utilizes these days. Gasification produces syngas which can be used to produce heat and electricity when wind and solar aren't producing. The biochar that is left over can be introduced into the soil to improve it's nutrient and bio-activity (terrapreta). This is essentially reverse mining of carbon and is stable for thousands of years in the soil. It also keeps the biomass from producing greenhouse gases from decomposition.
Beyond trees, we should also be growing algae and other plant mater to sequester more carbon and produce oils, sugars and other useful ingredients for our lives. This can be done at sea or in areas where water is scarce and normal vegetation grows poorly.
>Trees weren't designed to capture carbon, so there's every reason to think something which is can do a better job.
They weren't, but just like jets and knives require a lot of human labor to manufacture in mass quantities, any artificial solutions are likely to be the same for a while. Trees, on the other hand, are fully automatic, self-replicating machines that require almost no human labor (perhaps for initial plantings in a place where they don't already grow, or don't grow in sufficient quantities with their natural self-replication). Basically, if you plant a bunch of tree saplings somewhere suitable, you can leave it alone for 300 years and come back and find a forest.
Considering that most of the energy supply is currently going into brake pads, designing an efficient regen braking system is quite reasonable.
Once we are on renewable energy, the efficiency argument will make it undeniably efficient.
This drought is teaching us that "just grow a tree" is not always viable, and the resulting water crisis is also begging the question "with who's water?"
Who's water? Planting trees usually helps to prevent droughts because they keep water in the local climate with effects like shading the ground and containing rainwater (instead of the rain just washing down the next river). I'm that sense watering them is a good investment.
Or at least create the hydrocarbons in a factory, sucking the carbon from the atmosphere, and using energy from renewable sources or something of the sort. This would be carbon neutral at least, and still allows liquid fuels to be used. I have never seen anybody invest into this research. Somebody please correct me if I'm mistaken here.
What's the market for this? Are parts of the US unable to electrify trains for some reason? Surely the easiest way to capture the carbon is not to emit it in the first place, and if you are going to emit it, you might as well do it in a stationary power plant.
> Are parts of the US unable to electrify trains for some reason?
It basically comes down to cost. The electric infrastructure costs per mile to install, and per mile per year to maintain. The benefits come per train. If you don't have enough trains per day, it's not economical to electrify.
There are some places, like the Union Pacific around North Platte, where you'd think that electrification would be a natural. But the problem is that 90 miles east of North Platte, and 20 miles west of North Platte, the lines split, and the traffic density goes down. Switching between electric and diesel locomotives twice in 110 miles adds operating cost.
Not sure why AlgorithmicTime's comment is dead, so I'll reply here. Long distances are probably tricky to electrify. I don't know enough about US railroads (what little I know of US railroads comes from playing Ticket To Ride) to comment on the feasibility, but there are very long electrified railways in China and Japan, across difficult terrain. There is probably not much benefit in feeding electricity from regenerative braking back onto the overhead line if it's a very long segment with only one train (no one to use the power + transmission losses).
I wonder at which point diesel becomes the cleaner option here, if ever. One the one hand, you have to lug a lot of fuel around over longer distances (or you need refueling infrastructure). On the other hand, transmission losses can be significant.
Well, you up the voltage and go AC, losses then become manageable. The move from 1.5KV DC to 25KV AC in Europe was about that exactly (many caveats apply, but it's basically that, a solved problem).
If it's a somewhat loaded segment, someone would be there to consume the regenerated power. If it's not loaded then yes, no point in electrifying it to begin with.
Trains can be fairly easily electrified (via overhead rails) and hydridized with batteries. Generally they're diesel electric in the first place, so you're just switching electricity source which makes it a smooth transition.
So I feel this will lose to batteries, which can be use to brake at every motor, and so can be easily distributed along a train. (Though you don't need batteries for regen braking, you can feed the power back to the grid if you have a connection). And once you have a decent sized battery you can charge from overhead lines when available, which opens up other possibilities.
> The studies have revealed, for example, that a large proportion of the lines currently operated with diesel vehicles include non-electrified sections of well under 60 miles. The use of the existing catenary infrastructure allows battery-powered electric vehicles to be operated on these lines without major upgrades to the existing infrastructure. Extensive travel dynamics and energy simulations were also carried out as part of the project.
A similarly wacky concept, that I perhaps like is shipping full batteries to places where energy is expensive via train. So charge up a train battery from solar as it travels east, then feed that back to the grid as you meet a post sunset peak. Possibly wouldn't make sense if you were to do it for it's own sake, but if you already have a network of battery trains that can time their charge, you can probably save a reasonable amount of money by optimising when/where you charge based on time of use and demand response events.
Coordinated Demand Response of Rail Transit Load and Energy Storage System Considering Driving Comfort
Batteries are no-go. Typical electric locomotive is like 5MW sustained for multiple hours. It wouldn't be able to pull just its own batteries for any reasonable distance.
60 miles of catenary is way cheaper than wasting energy pulling dead weight that batteries are.
Note that batteries aren't an all or nothing thing. Just like a Prius, you can start with small batteries that just save you burning fossil fuels (even with the added weight), and help you reclaim energy when braking or going downhill and then add bigger and bigger batteries, as batteries get better, lighter, cheaper, electricity gets cheaper, greener or diesel gets more expensive.
It's already started, real battery trains are in operation in niche roles (and nearly always have been since before lithium ion) but the process will accelerate and expand over time. They complement electrification of lines, they don't compete with them as you can use one or the other based on which works best for a particular stretch of track, or task.
I think that is a Rube Goldberg idea. They’ve taken two reasonable ideas, regenerative braking and carbon capture and melded them together on a moving platform where it makes no sense.
Some of the problems:
1) The diesel train will emit much more carbon than captured so you are dependent on carbon emissions for your carbon capture.
2) The fans will slow the train speed.
3) The weight of the carbon capture car will increase the train’s load and hence the carbon usage of the train AND it will get heavier as you capture more and more carbon.
New diesel passenger trains are able to use regenerative braking to power auxiliary loads (heating cooling &lights), this wouldn’t really work with freight trains unless you were moving something that has to stay refrigerated.
If you're digging iron ore out of a mine and carting it on a one-way trip to the coast the train is always heavier on the way down than the way up. Store the energy from the downwards trip and use it to power the upwards trip, with some left over.
Mind you this drives home the reality that mining is a non-renewable resource, as there is no such thing as a perpetual energy source or mine.
I really don't understand how carbon capture can make sense, in terms of thermodynamics. Burning hydrocarbons releases energy, plus carbon dioxide and water vapor. Capturing the carbon dioxide back would, in some way, require an equivalent amount of energy to be spent, right? Where is this energy coming from? In this case, it's actually mentioned in the article (unlike many other carbon capture proposals): add regenerative braking to trains -- plus make the engines work harder by adding a lot of extra air resistance for the filtering system.
Meanwhile, the European electric grid -- and therefore its electric trains -- is partly ran by burning fossil fuels (not to mention the manufacturing processes for the proposed batteries and filters). So you're burning carbon in order to get carbon out of the atmosphere -- there's no way that equation comes out as a net negative for emissions, there are inefficiencies everywhere.
This is honestly one of the most compelling carbon capture proposals I have read, and it still doesn't make sense to me. What am I missing here? Why is this being taken seriously?
Artificial photosynthesis is absolutely required in several sectors, if you want to eliminate the use of fossil fuels. International air travel is the main example, so is space travel, and global shipping is a little behind. There's no way to fly passenger jets over the Atlantic and Pacific Ocean using battery power; the density is just too low. Likewise, if you want to have SpaceX continue to launch large methane-fueled or RP-1 fueled rockets without fossil fuels, capture of atmospheric CO2 and conversion to hydrocarbon fuel will be needed.
It's also a way of storing energy for long periods of time, i.e. if you're in the near pole regions of a planet, and want to capture solar energy in the summer and use it in the winter, batteries aren't going to work on those timescales. Some other means, generally a stable chemical conversion, will be needed. Converting carbon dioxide to methane or gasoline, converting nitrogen to ammonia (a bit dirty), even converting iron oxide to reduced iron, are all possible methods of doing this.
As far as converting atmospheric carbon dioxide to a form that won't eventually get back in the atmosphere, that's pretty difficult (you have to make limestone, CaCO3, or perhaps carbon fiber building materials, or even better, diamond).
I'm not against that point, as I mentioned in another comment, research into hydrocarbon synthesis is the only "carbon capture" scheme that makes sense to me, because it's not promising anything for free. "We'll use this solar/wind/nuclear energy to create fuels out of the air, and then we'll burn them later for less" makes thermodynamic sense, and as you pointed out, is necessary to continue some endeavors (and maybe to permanently remove CO2 from the atmosphere, at a huge cost).
It's these "we'll use fossil fuel energy to pull carbon out of the atmosphere and store it" schemes that smell like perpetual motion machine trickery to me.
And you are right... even worse: putting carbon emitted back into the ground requires not only the energy gained through burning, but several multitudes of that.
That's why not burning it in the first place is almost always better. Still, carbon capture is necessary, because there are things that are extremely hard to substitute.
Further, if we don't go for negative emissions, we will have at least 4 degrees of warming (even if we stop emitting now).
This seems like nonsense on a conservation of energy basis. Putting vents on trains would cost a similar amount of energy as using fans to blow large volumes of air (at ~400 ppm CO2) into carbon-capture systems, and the result would be to slow down the trains and cause them to use more fuel or electricity.
Secondly, who is going to pay for this? If CO2 is going to be a valuable commodity itself, then that's because it's going to be used in an industrial process as a feedstock for fuel or material production. In that case, train operators might find this to be an interesting proposition, if the value of the captured CO2 is a good deal higher than the resulting increase in fuel/electricity costs needed to operate these trains.
As far as industrial production, this doesn't look good either. It's far easier to just put large atmospheric CO2 capture systems right next to the chemical production system without having to haul trainloads of CO2 all over the place.
Trying to put mobile carbon capture systems on diesel trains seems absolutely foolish when electric trains exist. Just put up the damned wires, it will save money in the long run.
I always consider things like carbon-capture to be under the category of "We need to do all of the above". Capturing carbon at scale gives us more time to move to renewable energy, which is going to take longer than we have. So we need to do capture, and renewables, and reducing overall energy, and whatever else we can think of. If we had started moving to renewables and electrifying everything 30 years ago, carbon capture wouldn't be needed. But it is needed now.
The thing I don't like is that people keep acting like we're going to avoid a climate catastrophe. We're not; it's already too late. We might as well get used to the idea that things are going to get really, really bad in the next few decades. The only way to avoid it is to completely stop the things we're doing right now, all over the planet, and that simply isn't going to happen.
After reading this article, I was wondering if a similar approach could be used on cars? Could the braking energy be used in a similar way? What about for trucks?
Surely it is more efficient to store the braking energy in cars for acceleration, which then reduces the amount of fossil fuels burned in the first place? (AIUI this already exists)
In fact i'm not sure why that wouldn't also apply to the trains...
I assume the issue is trains that aren't electric, and I assume even most electric trains don't have significant energy storage on the train itself, so might not really have much to do with energy from breaking.
It probably especially makes sense that freight trains running off fossil fuels won't even consume much electricity at all (just enough to operate instruments in the locamotive?), though presumably passenger trains could make use of it.
Maybe there are barriers to electrification of some trains in some areas.
Most electric trains only have a small service-and-emergency battery and don't have significant energy storage. For AC electric locomotives it's now standard to return electricity to the grid when using regenerative braking; that's harder with DC electric traction but is done in some circumstances (in others, the generated electricity is dumped into heat via a resistor bank).
The main barrier to electrification is the high upfront capital cost of the electrification works, set against the longer-term per-train return in lower fuel and locomotive/multiple unit costs. Lines which are not intensively used are difficult to justify electrifying on a financial-returns basis, and that probably includes most of the world's long-distance freight lines.
Nearly all fossil-fuel burning train engines (I think the exception being a handful of hydraulic engines in Germany?) are diesel-electric, which use the diesel engine to turn an electric generator to power electric traction motors. (Dynamic breaking is when those traction motors are used as generators, but that electricity is usually dissipated as heat immediatly.)
Tramway are regenerating power and injecting them back in the grid when they brake. I think electric trains do it as well, the resistor grid is only used when not enough power in generated
Modern electric passenger trains do - they can dump power back into the grid, and have enough motors to do a good chunk of braking with them (And e.g. for the German high-speed trains they plan the braking points such that they try to avoid using lossy brakes in normal operation).
If you don't have a grid as "storage", you need to carry it, and that's a problem. And freight trains obviously only have motors in the locomotive(s) and do the distributed braking on the cars mechanically, so a good chunk is lost even if the locomotive can do it.
For the rest, they don't because of lack of storage.
A diesel locomotive has a huge engine block, a generator, a large radiator, and electric motors on the axles. You can turn the motors into generators when you want braking, but where are you going to put the electricity? All the space (and weight) is already used.
Yes, they have batteries - enough to crank the engine when it has been turned off. Not enough to run the electric motors on the wheels, though.
Bring back the tender[0], but fill it with batteries instead of coal. Or better yet, intermodal container shaped batteries that could be swapped for pure electric long distance trains.
If I remember correctly, in the movie it was hinted that the train’s mechanic (Wilford) invented a perpetual motion machine. I’m not sure if the original graphic novel or the TV shows suggests something similar.
Instead of adding batteries, and thus weight, the train supplies power back to the grid when it breaks. Thus, the cheaper source of energy described here can be achieved without the carbon capture, and consequently, we can use that power to power other things, reducing energy generation overall and reduce CO2 emissions.
Thus, it seems like the primary benefit here is using the train's motion to replace the fans required for carbon capture and thus piggybacking on the energy already expended by the train to move. That seems logical, though it could be deployed irrespective of regenerative breaking. Basically we should do regenerative breaking regardless as it is just more energy efficient. Regenerative breaking can primarily be deployed in electric trains anyway as you use the existing motors to break the train, and in so doing, generate electricity from those motors. Adding electric motors and a battery to diesel trains JUST for carbon capture seems foolish.
One question I had: how does this carbon capture change the aerodynamics of the train and thus its efficiency?
[1] https://www.ctc-n.org/technologies/regenerative-braking-trai....