Hydrogen fuel cells are not a source of energy, since hydrogen (H2) is not naturally found on Earth. All H2 must be generated in a process which consumes either natural gas or eletricity. Therefore H2 fuel cells are more aptly described as an energy storage system than as an energy source.
Therefore the relevant comparison is between H2 fuel cells and Li ion batteries. Batteries have much higher full cycle efficiency (energy input -> storage -> energy output), but they are large and heavy. H2 can be stored in less volume and less weight, but it is less efficient. In my opinion, batteries will be a technically and economicly superior solution for all uses other than where weight is extremely critical such as in aircraft.
> In my opinion, batteries will be a technically and economicly superior solution for all uses other than where weight is extremely critical such as in aircraft.
I was excited about the use of hydrogen in aircraft for a while but the more I looked into it the less likely it seems. I think the advantages of liquid fuels are too great and that even if there were no oil production it would still make more sense to synthesize jet fuel or some other liquid fuel for use in aviation.
This has nothing to do with feasibility (the Soviet Union had an airliner that ran on hydrogen, so hydrogen aircraft are absolutely feasible), just with lock-in effects and ease of use.
Hydrogen has a couple of "unique" properties that make it especially disadvantageous.
Namely: It'll diffuse through just about anything on a fairly short time scale if it isn't kept as a liquid at cryogenic temperatures, and it causes almost all metals to become brittle.
I think hydrogen is basically a dead-end as energy storage, except in a few niche applications where it's produced as a byproduct and can be consumed immediately.
Not to mention liquid H2 has quite a bit lower energy density than liquid fossil fuels. Many rockets have used kerosene in their first stages for this reason. Not the end of the world for aircraft, but certainly another major disadvantage.
How does that work? You run your propellor in reverse like a wind turbine?
This doesn't sound completely ridiculous but is there even any proof of concept for that? The gravitational potential energy doesn't seem all that high - most airplane fuel is burnt maintaining height, not gaining it - to justify the complexity of recovering some small fraction of it. Still, I once thought the same about regenerative braking in electric cars.
It's also prone to explode, and is a potent (indirect) greenhouse gas if it leaks into the atmosphere. Agreed that it will have some niche applications though. As well as the byproduct situation, there are likely situations where batteries wouldn't be feasible due to insufficient capacity or too great of weight. Aerospace maybe?
I think it'd be an "indirect" GG because it's electricity intensive to obtain it, and that likely comes from a carbon emitting source. The same argument is often made about electric vehicles.
In this case it's about how it interacts with OH radicals in the atmosphere, meaning other GHG stay in the atmosphere longer. So it's not a greenhouse gas, but it makes others hang around longer.
> The reaction
of hydrogen with OH radicals has a further side-effect of reducing the availability of OH
radicals with potential impacts on the build-up of greenhouse gases.
Well you don't typically get hydrogen from H2O, you get it from CH4. So your byproduct isn't oxygen, it is carbon. Unlike electric vehicles, it doesn't get greener as the grid changes to wind/solar/nuclear/hydro. There's just more hydrogens per hydrocarbon than water. Not to mention dealing with oxidation.
> Namely: It'll diffuse through just about anything on a fairly short time scale if it isn't kept as a liquid at cryogenic temperatures, and it causes almost all metals to become brittle.
Both claims are wildly wrong. Neither actually happens except at high temperatures and only with certain metals.
I am not an expert on this, but random internet searches such as [0] indicate that common materials, like high strength steel, are susceptible to both diffusion and embrittlement at room temperature
Those tests seem to be at >200˚C if I’m not mistaken. Hardly room temperature. Regardless, the main trick is to avoid using certain types of high-strength steel, line exposed surfaces with polymers, or using composites where ever possible. The problem is for the most part solved.
In the same sense all chemicals have handling issues. In practice, it is basically solved.
That's probably due to them using a vulnerable alloy, and was likely exposed to hydrogen while at a high temperatures. This is nothing like a gas tank filled will hydrogen.
Petroleum-based liquid fuels contain mixed entity hydrocarbons that match a specification; if you have the perfect feedstock and markets for the fractions you don't use this is cheap. Worst-case you have to synthesize them with Fischer-Tropsch chemistry
which is such a PITA (normally a chem E would be delighted that you can use iron as a catalyst, but it works so poorly that a desperate search of the other 91 elements found just 2 that sorta-kinda work)
The issue there is you are sticking C's onto the end of a chain and you have to deal with a network of reactions that produce products you couldn't care less for, such as petroleum jelly that gums up your catalyst, sticks up your downrisers, etc.
Sustainable motor fuels tend to be single entities such as 1-butanol, dimethyl ether, etc. You might need to blend something in for low temperature starting, but it's possible for a single entity fuel to be synthesized with decent yield.
General av is seen as a backwater that is barely hanging on and couldn't possibly get the lead out. The USAF has done biofuels trials, but commercial av is spooked to try anything that could leave passengers up in the air.
> It astonishes me how far behind aviation is behind surface transport when it comes to sustainable fuels. They still use leaded gas!
It's important to qualify this: jet fuel contains no lead, and constitutes the vast majority of commercial aviation, and hence of emissions.
Jet fuel itself is kerosene, with some additives that aren't superb in raw form, but nothing so durable in the environment as lead.
A sibling comment does a fine job of explaining why avgas still contains lead, and to be sure, a plan to phase that out except where absolutely necessary would be welcome.
> General av is seen as a backwater that is barely hanging on and couldn't possibly get the lead out.
The issue is infrastructure. Modern engines run fine on unleaded fuel, but the little airstrips in the middle of nowhere all have 100LL and/or jet fuel, so that's what pilots use.
I know a few pilots who are prefer to use unleaded in their Rotax engines to prevent spark plug fouling, and they have to jump through some pretty ridiculous hoops to get gas, while their buddies just fill up with whatever is on the field.
Not particularly relevant to the lead debate though as the engines are replaced after 1,500 - 2,000 hours and retrofit Diesel engines running Jet A are available on lots of aircraft (but people don’t buy them as they’re expensive and heavy)
The problem with LNG is that it's still a fossil fuel, still cryogenic, and that methane itself is a potent GHG. The first problem you could solve using synthetic methane, but the latter two still drives you towards LH2 as being the better option.
That falls under the “maybe” category. Synfuel are not easy to make, and will add a substantial layer of extra complexity to an already complex process. If it can’t be done cheaply then it might not happen or make sense. Hydrogen is not an alien substance BTW. It’s possible that we figure out hydrogen before synfuels get cheap.
Even in rockets, where weight is extremely critical, SpaceX chose to use kerosene/methane due to the problems of working with LH2 (very low density, very cold temperatures, hydrogen embrittlement).
Depending on energy density and power density requirements, I think a combination of batteries and traditional fossil fuels will win in the short term. In the long term, when we have stopped burning fossil fuels for electricity, then we can use electricity to manufacture them. Under this path, hydrogen will have limited importance.
Preventing explosions in the event of H2 leaks is difficult too. H2 has one of the lowest ignition energy curves of any gas. Electronics used in areas with H2 must follow very strict regulations (worse than medical requirements in many ways).
The explosion happens when you cross the ignition energy threshold. So having a low ignition energy threshold can actually be an advantage as then much less fuel is available to drive the explosion.
Agreed that doing intrinsic safety for H2 is hell. I did once design a LED sidelight for the relevant class with significant current (redundant electronic energy regulation). So it is possible to do stuff, it just takes more work. The tendency for modern electronics to be very low voltage helps a lot.
Pure hydrogen can’t burn without oxygen, so you generally get a tiny flare and then a flame based the size of the crack. It’s really about the same risks as using gasoline which almost never causes a significant detonation.
With vehicle, heating, rocket, or aviation applications, quantities involved are nontrivial. Hydrogen's flammable and explosive ratios with oxygen are large, and contrast starkly with other fuels; kerosene (jet/rocket fuel), bunker oil, and deisel, which ignite with difficulty, petrol, which ignites readily but not explosively, and even natural gas which deflagrates rather than explodes under most circumstances.
Add in hydrogen's extreme tendency to leak, metal embrittlement, and high pressures and/or low temperatures, and the risks are immense. Particularly at scale, in widespread use, with poor maintenance and inspections.
It’s technically explosive in many situations where the location or net energy released makes that irrelevant. Being significantly lighter than air you might hear a loud bang above the vehicle where gasoline’s foof ends up being significantly more deadly.
It’s not strictly better or worse, just different. Diesel for example can be very dangerous in a large open topped container, hydrogen just doesn’t stick around in that environment.
PS: Consider what it would take to make a large hydrogen fuel air bomb that’s as effective as it’s hydrocarbon equivalent.
> Even in rockets, where weight is extremely critical, SpaceX chose to use kerosene/methane due to the problems of working with LH2 (very low density, very cold temperatures, hydrogen embrittlement).
That and they have very few missions where the increased ISP from LH2 would actually benefit them. The other upside of LH2 and LOX is that you can run it in engines, but you can also run it in fuel cells directly and generate a surprising amount of electricity from a very small package -- the other benefit there is that the Fuel Cells produce pure water as a byproduct.
The Space Shuttle had three fuel cells which provided more than enough power for a full mission. Most missions could be run on two without any compromises. Also, when it was visiting the ISS, it was a convenient means of supplying water to the station.
On non ISS missions, so much water is generated that they have to dump it overboard.
> Hydrogen fuel cells are not a source of energy, since hydrogen (H2) is not naturally found on Earth. All H2 must be generated in a process which consumes either natural gas or eletricity. Therefore H2 fuel cells are more aptly described as an energy storage system than as an energy source.
100% this.
IMHO, this is by far the biggest misconception about hydrogen among people.
To my understanding, natural discoverability of H2 gas on earth surface is very low due to the gas being very light and buoy itself up the atmosphere, possibly escape the planet entirely.
Hydrogen is being created and consumed on a vast scale on Earth. The possibility that there are huge pockets of hydrogen gas trapped under impermeable rock layers cannot be ruled out. For one thing, natural gas pretty often contains hydrogen as a constituent.
But current battery technologies need elements that require mining and other environmentally taxing processes. Recycling batteries can be energy consuming too. With hydrogen the cost structure of the whole fuel lifecycle is much clearer. Hydrogen also depletes along the trip unlike battery which will be massive dead weight for planes & ships.
FWIW I upvoted you just because the question is reasonable, but I think you're wrong in balance. Last I looked all the current processes for making hydrogen are in fact more environmentally taxing (and worse, CO2 emitting) than the one-time cost of mining lithium.
A LiOn battery is good for many many cycles, and can then be recycled. Hydrogen must be produced and then consumed, and is usually produced from natural gas, itself a greenhouse gas that is on the main a byproduct of the oil industry.
Green hydrogen is the long-term option, which makes hydrogen the much less resource demanding option. People who keep on repeating the 'hydrogen = fossil fuel" argument is just the same kind of argument leveled against battery powered cars such as "coal powered cars."
Yes, the cost structure is very visibly more expensive. The problem is the huge amount of additional energy needed to generate the hydrogen. Hydrogen storage is also very expensive. The weight reduction is pretty neglectible, as hydrogen is the lightest element in the universe.
How important is weight in their designs though? They're cars, so they don't have to hold themselves up, and they probably both have regenerative braking
You are right, weight isn't extremely important, especially with regenerative braking. It is only interesting in the comparison with battery electric cars - if the hydrogen car is even heavier, then there is basically no advantage left for the hydrogen car.
You'd still have to compare it to the equivalent usage of the same energy into a LiOn battery, and in many cases it wouldn't fare well.
Maybe there's a future world in which we can do it all in orbit -- harvest comets, produce hydrogen in space using solar power or nuclear, and efficiently drop it down to earth in some safe way. That would definitely alter the equation. But by the time we figure that out, it'll probably be too late.
Yes this is because there isn't enough grid storage yet. Massive amounts of stationary storage need to be produced whether that be pumped hydro or lithium ion battery or some other means of energy storage.
I recently worked out that the UK's installed capacity of pumped hydro is around 28GWh. This is around the worldwide total production of lithium batteries per year circa 2016 (realistically it may have doubled since then).
Personally I don't going into competition with laptops, mobile phones and car battery manufacturers as a viable long term strategy for grid scale storage.
I think your numbers are outdated, that's about the production numbers of Tesla alone, not counting the other manufacturers. And Tesla just announced their plans to move towards 3 TWh/year production rate towards 2030.
Any electric car plugged in is a great buffer for surplus electricity production.
In theory yes, in practice, which electric car charger has a built in 3kw inverter for backfeeding? Have you seen how large a 3kw inverter is? They are also not cheap. Secondly, most homes aren't metered in both directions. What is the ROI of one car plugged into the grid in this system? How much does it depend on how long the vehicle is actually plugged in and whether it is plugged in at useful times.
Taking the number above for installed capacity of pumped hydro. You are looking at nearly half a million cars and homes to match the capacity (assuming 50kwh per vehicle), before considering the plugged in factor.
At say a nice round £1000 to upgrade each home you are already looking at a cool half a billion. Already around the cost of the Dinorwig pumped hydro station before you figure out how to compensate electric car owners for the extra wear on their batteries or the fact that when they leave for work their car is flat because it has been powering your neighbors electric showers.
Yes, in those rather short time periods, energy prices are free. But for those periods, batteries are the better storage solution, as the total amount of "free" energy is rather small. Electrolysis plants would have to run basically 24/7 to be viable.
More battery electric cars on the roads also mean a lot of storage for excess electricity. Just use the top 10 to 20 percent of the capacity to absorb production peaks.
I think its not as bad as you make it out to be. Any battery that will be used in flight might have nickel in it but that's about the only thing that's problematic. The anode will likely be silicon.
Pretty much all battery research is targeting materials that are common. The DoD made a large bet on Lithium-Sulfer batteries.
Battery recycling can be energy intensive if you go for the full metallurgical extraction. But pretty much all car manufacturing plants want to just 'disassemble' the battery and use other far less energy intensive processes to get battery grade materials out. Also, at least in the west, these factories are generally located in location where there is cheap green energy or at least there is the potential. That is both Tesla/Panasonic and Northvolt (Europe) plan.
With batteries you can reload the battery from your gravitational energy. That is actually quite a significant range extender but it might be a regulatory issue.
> But current battery technologies need elements that require mining and other environmentally taxing processes
But hydrogen requires production, either from fossil fuels, or electrolysis, both can be environmentally taxing. It requires transport. It requires either liquefaction or compression. It require mining to manufacture suitable storage tanks - which will become brittle and have to be replaced pretty often.
> Hydrogen also depletes along the trip unlike battery which will be massive dead weight for planes & ships.
This is indeed a major difference.
Frankly, if you want to burn hydrogen, you're better off synthesizing something like methane. It's a far more effective storage mechanism. After all, if you are willing to spend the massive amount of resources required to do large-scale electrolysis, you might as well go the extra step and setup some sabatier reactors. You'll recapture the CO2 too.
Does "less efficient" mean less energy dense, or our current methods for converting its energy to electricity aren't good?
If the former, then what does "H2 can be stored in less volume and less weight" mean? I would assume you would want to compare the mass required to store the same amount of energy, in which case it sounds like H2 takes up more space and weight than Li-ion?
If the latter, then isn't it just a matter of improving our technologies? Or is there some law of nature that makes efficient conversion to electricity impractical?
It’s admittedly been a while since I’ve looked at it, but I recall that the creation of H2 using existing processes takes quite a bit more energy than you ultimately extract back from it. For example, electrolysis of H2O to H2 is a pretty lossy process (I think around 60-70% of the input power is used to break the H2O bond and the other 30-40% is released as heat).
I'm a total noob in that area, but I always thought that hydrogen was super efficient when converting it from water + oxygen and then back. Why battery is better?
Do you know what’s the (current practical and maximum theoretical) roundtrip efficiency of hydrocarbons (gasoline, alcohol, methane, ...)? Could be a better alternative than H2 (and longer lasting than batteries, even if lower efficiency).
Elektrolysis isn't very efficient, neither are fuel cells, when you compare it to batteries. On top of that you have the energy usage for transporting and most of all compressing the hydrogen for storage.
Bear in mind -- a fueling infrastructure includes a lot of potential points of inefficiency outside of the chemical conversions that are taking place during generation and consumption.
Your fuel of choice also must be transmitted from the point of generation to the point of consumption. For electricity, this is easy, you can run it down a wire. For gasoline, you need a tank that can hold liquid. For hydrogen, you need to cool it to −253°C and compress it in a cryogenic tank.
And water scarcity is expected to be a growing issue for many parts of the world. I guess we could use sea water, but then the shipping you mention comes into play.
Just a side note, you could ship it in hydride tanks.
The weight factor also makes it easier to transport. In off-grid use-cases, it could make a lot of sense to get hydrogen delivered instead of setting up solar/wind + battery.
Again, it's kind of stuck in the middle: energy density by volume sucks compared to hydrocarbons, and if it isn't cryogenic, it really sucks, and cryo is expensive. Transporting fuel by truck is volume limited, not weight limited.
If we're comparing to batteries, then... ok, but you kinda only have to move the batteries once, and then you can either recharge on site with solar or connect to grid. With hydrogen, you have to keep bringing it, and you may as well have hydrocarbons at that point.
The lack of carbon emissions on-site is what makes it tempting, but it's just easier to work around this problem in various ways than it is to pay the hydrogen penalty on an ongoing basis. To a first approximation, all commercial hydrogen is cracked off of methane anyway, and electrolysis is a pretty inefficient way to use renewable electricity, so even that just displaces emissions to fossil fuel plants unless none of those exist anymore.
In theory you can also transport hydrogen through the pipes used for gas. I personally think you’ll run into problems with leaks really quickly but who knows.
It’s environmentally friendly to mine asteroids, so in a way, it will always be “cheaper” to pollute an unlivable rock rather than our only sustainable habitat.
It'll take like 100 year to get to that point. That's 100 yeard of space engineering simply polluting Earth and then maybe another 100 years to break even?
Once in orbit, it takes very little energy to go to an asteroid and to launch that asteroid to a parking orbit compared to dredging mountains of soil and rock on Earth. The yields would be extremely high; there's more gold and platinum in some Inner Belt asteroids than we've ever mined on Earth so far, and it's just floating there for you to grab and bite chunks out of.
> Once in orbit, it takes very little energy to go to an asteroid and to launch that asteroid to a parking orbit compared to dredging mountains of soil and rock on Earth. The yields would be extremely high; there's more gold and platinum in some Inner Belt asteroids than we've ever mined on Earth so far, and it's just floating there for you to grab and bite chunks out of.
This is not true at all. This is laughably absurd. Getting from Earth's surface to LEO takes about 9.8km/s of delta-v but then getting from LEO to another destination requires more delta-v. To get to the Moon requires another 6km/s of delta-v on top of the 9.8km/s you needed to get from the ground into orbit. There's a reason the Saturn V was a giant rocket with a teeny tiny capsule mounted on top. Getting places in space requires a lot of propellant.
Here's a nice list of NEAs and the delta-v required to reach them (one way) from LEO[0]. The list is very helpfully sorted by delta-v requirements. You'll notice that the easiest NEA (2018 AV2) requires an additional 3.758km/s of delta-v. The easiest to reach NEA on the least requires more than half the delta-v that it would take to land on the Moon. Once you rendezvous with an asteroid you need to come home which requires yet more delta-v (thus more propellant). Moving an asteroid to orbit Earth is not in any way as simple as you might think from reading science fiction.
So there's nothing "very little" about the energy required to land on an asteroid let alone land on one, mine anything useful, and then return it to Earth. There's also the complexity of the vehicle needed to do the mining. Platinum (pure platinum mind you) goes for up to $37k per kg.
Even if we pretended that all of the technology existed and was donated and we just paid for a Falcon Heavy launch (about $150m to get about 17t of payload to an asteroid) we would need to ship back 4t of pure platinum to Earth just to break even. Even if you assumed that in the best case platinum was a thousand times more abundant in an asteroid than Earth's crust[1] that's still only 5ppm! You'd need your asteroid miner to process about eight million tons of ore (if my math is right) to get that 4t.
If our asteroid miner is 17t or so how long do you think it will take to process that much ore? The loan for the Falcon Heavy would have defaulted long before it would be even close to finished. There's just nothing asteroids have that ends up being worth the cost to mine them instead of mining them on Earth. Don't forget besides raw ore Earth also has lots of landfills literally filled with stuff than can be recycled and valuable materials extracted.
Materials in space are only really useful to an entirely space-based industry and the only way to bootstrap a space-based industry is to launch it from Earth which is basically just lighting money on fire.
Therefore the relevant comparison is between H2 fuel cells and Li ion batteries. Batteries have much higher full cycle efficiency (energy input -> storage -> energy output), but they are large and heavy. H2 can be stored in less volume and less weight, but it is less efficient. In my opinion, batteries will be a technically and economicly superior solution for all uses other than where weight is extremely critical such as in aircraft.