Solar-driven water splitting at 13.8% solar-to-hydrogen efficiency

https://pubs.acs.org/doi/10.1021/acssuschemeng.1c03565

by Breadmaker • 5 years ago

249 271 5 years ago

pubs.acs.org

api• 5 years ago

Solves the energy storage problem. Just add tanks.

NoblePublius2• 5 years ago

$2 trillion of tanks and $1 trillion of pipelines, just for North America. Meanwhile, electrical grids already exist.

new_realist• 5 years ago

Electrical grids don't store energy. If you wanted to store just 10% of the U.S. electrical generation from summer to winter using lithium-ion batteries, it would cost roughly $42 trillion dollars. Yes, trillion. Storing 10% of the U.S. daily needs for less time (say, one day) is a better story for batteries: only $115 billion.

That's how un-scalable long-term battery storage is. Hydrogen is more so: you can store hydrogen in vast quantities in salt caverns, and move it around. Pumped hydro is best, but sites are limited. Compressed air is another solid contender.

nautilius2• 5 years ago

How does a grid solve a storage problem?

unchocked• 5 years ago

Great! That's cheap for what you get. As soon as we've built out a few $trillion in battery storage, we can get going on long-term hydrogen storage and distribution!

cjensen2• 5 years ago

$1 trillion of pipelines? Why?

This is about splitting water using electricity. You can create and use the fuel at the same site. Just need a water pipe and a connection to the grid. Splitting off hydrogen at a separate site is just wastefull.

pensatoio2• 5 years ago

Why can't we produce hydrogen, store it, and generate power with it?

I imagine the cost of hydrogen storage is significantly less than batteries, thereby offsetting the reduced efficiency of turning solar power into electricity. The main issue we have with solar is storage for when the sun isn't out.

Hypx_19• 5 years ago

We'll likely use underground hydrogen storage in the form of salt caverns and expended natural gas reservoirs.

viburnum• 5 years ago

That’s cheap. USA spends $8 trillion on defense every ten years.

r00fus• 5 years ago

I assume there are also costs to store and deliver hydrogen fuel? I'd like to see an EROEI comparison of electric vs. hydrogen.

meepmorp• 5 years ago

Make ammonia out of it, easier to store and transport.

toomuchtodo• 5 years ago

The closer you can get to both steel mills and pipelines, the better. Steel mills can use the hydrogen to replace metallurgical/coking coal, and the pipeline can accept ammonia for transport. Hydrogen is very hard on pipeline infra, unless mixed at low concentrations with a carrier gas.

hannob2• 5 years ago

This is the wrong question to ask.

Hydrogen is not for use cases where there is an electric alternative. Electric almost always wins. But there are use cases where there is no electric alternative or none that is available any time soon, most notably chemicals and steel.

aunty_helen3• 5 years ago

It's the wrong question to ask but it sure as shit is what it's being promoted as.

Look at the wayward Toyota, they seem to think they can navigate around chemisty to sell their EVs with a hydrogen fuel cell attached.

Hypx_19• 5 years ago

Fuel cell cars are electric cars. Since hydrogen is much more plentiful than lithium, it's nearly a certainty that the vast majority of cars will eventually switch over to hydrogen.

wiz21c• 5 years ago

high peak solar-to-fuel conversion

does it mean there's a "mean solar-to-fuel conversion" to look for ?

NoblePublius2• 5 years ago

this will be used as an excuse to expand production of hydrogen made from carbon fuel on the basis that eventually the carbon will be made sustainably. Don’t fall for it.

tuetnsuppe• 5 years ago

Before people get too excited they might want consider the life time of the cell as indicated over a 10 hour test window.

Animats• 5 years ago

Lithium iron phosphate batteries have about 95% round trip efficiency. Some manufacturers say 98%. AC-DC-AC conversion is around 98%-99% efficiency now. So batteries are way ahead on efficiency.

Tesla is switching from lithium-ion to lithium iron phosphate for fixed battery installations.[1] The energy per unit weight is somewhat lower, but that doesn't matter much for fixed installations. The safety is better, too - lithium iron phosphate batteries don't have the thermal runaway problem. BYD, which is the biggest producer of batteries in the world, sells shipping container sized lithium iron phosphate sized battery packs for large scale solar backup.

[1] https://www.utilitydive.com/news/tesla-shifts-battery-chemis...

dragontamer7• 5 years ago

Electricity-to-electricity efficiency should not be compared with solar-to-electricity efficiency.

The typical solar panel is maybe 25% efficient or less. The typical steam engine is maybe 50% efficient. Once things are in the form of electricity, we have a large variety of options for efficient transport and storage.

But sometimes electricity isn't useful. Li-Ion will never be light enough for a serious airplane for example, while hydrogen _IS_ light enough for an airplane. (But maybe too volumetric, as every practical H2 airplane engine relies upon high-pressure storage or even cryogenics to keep H2 at a small enough volume).

EDIT: If we think of it as chemistry... perhaps we can make liquid fuels out of H2 like coal liquefaction turns one fuel source into another. After all, classical fuels are nothing more than carbon + hydrogen + energy... and H2 is a very efficient form of storing energy for that reaction. Or maybe we learn to just use H2 directly? There are fuel cells and engines running on H2 today, but I'm always worried about the volume of H2 (requiring either compression or cyrogenics before you reach practicality).

aunty_helen3• 5 years ago

Great thing about Jet A, it's actually pretty hard to get burning.

Hydrogen: See Hindenburg.

I would rather not fly in a bomb. I just don't see it being viable for planes.

We're starting to see short distance small planes electrify and then long haul will probably go synthetic fuels over the next 10 years.

JumpCrisscross2• 5 years ago

perhaps we can make liquid fuels out of H2

You're describing hydrocarbons.

The most-common element in the universe married to the most-common four-bonding element. Using solar panels to synthesize Jet A is probably a better path forward than redesigning every plane in the world to trawl a balloon or carry a pressure vessel.

There's a reason pretty much all of Earth's biology uses hydrocarbons as its fuel of choice.

dv_dt4• 5 years ago

The 25% panel efficiency isn't a particularly relevant metric, and doesn't play in storage. A cost or area metric is more relevant economically.

JulianMorrison• 5 years ago

It's already happening, see https://www.gov.uk/government/news/world-record-raf-flight-p...

Someone4• 5 years ago

Li-Ion will never be light enough for a serious airplane

Not everybody agrees with that. https://en.wikipedia.org/wiki/Electric_aircraft#Commercial_p... says over a hundred electric designs are in development.

I think some of them can be called serious airplanes.

Hypx_19• 5 years ago

The typical mono-si solar panel is about 20-22% efficiency. For poly-si this drops to about 15%, but are cheaper and therefore still sees a lot of demand. Solar water-splitting at 13.8% is well in the range of feasible competitiveness as long as it is cheap to build.

mr_toad2• 5 years ago

perhaps we can make liquid fuels out of H2

We can make methane, which is a lot easier to store than hydrogen.

https://en.wikipedia.org/wiki/Sabatier_reaction

walrus012• 5 years ago

while hydrogen _IS_ light enough for an airplane

If you do the watt-hours per kilogram calculation the very best lithium ion batteries are something like 255Wh/kg right now.

Hydrogen fuel cell systems for small to medium sized UAS are somewhere in the 700-800Wh/kg range right now, including the weight of the (rather heavy, seriously engineered) ultra high pressure carbon fiber wrapped tanks needed for it, piping, and fuel cell.

Something like a tank of Jet-A fuel is >4000Wh/kg.

Hydrogen itself is light, the tankage systems needed to reliably contain a large volume of it on an aircraft are not.

huntertwo4• 5 years ago

Batteries have much lower capacity, lower cost efficiency of storage, and lower weight efficiency of storage. They’re also slower to charge and slower to discharge.

Batteries are great for storing electricity efficiently as you say, but that only matters when electricity is marginally expensive (sourced from fossil fuels for example). However, if you have a cheap enough marginal cost of electricity, hydrogen is a better option because of the much cheaper fixed cost of hydrogen storage per kWH.

A good way to see this: what option would you choose for storage if electricity on demand was free but only during certain parts of the day? A hydrogen tank or batteries? A hydrogen tank is cheaper. And clean energy is essentially free besides the fixed cost of the windmill/solar panel.

jacquesm12• 5 years ago

They’re also slower to charge and slower to discharge.

Yes, but this is changing and there are a number of very interesting options.

https://en.wikipedia.org/wiki/Lithium-titanate_battery

Someone4• 5 years ago

Batteries are great for storing electricity efficiently

In some cases not even that. Modern Lithium-ion batteries are quite good, but self-discharge still is 2-3%/month. So, if you want to store for months (say charging a battery using the summer sun to heat a house in winter), you easily lose 10% to self-discharge, in addition to what you lose between charging and discharging.

https://en.wikipedia.org/wiki/Self-discharge#Typical_self-di... says NiMH batteries even lose 30% per month.

superjan• 5 years ago

For renewable energy, low efficiency is not a problem per se: you can make as much as you want. The article also mentions that they don’t need rare materials for the electrolyser, which means it will be cheaper. Lithium, that modern batteries require, is quite rare.

thinkcontext2• 5 years ago

There is plenty of demand for millions of tons of hydrogen for uses that batteries are not useful for, notably, nitrogen fertilizer. Thus, advances in hydrogen production are interesting irrespective of ones views of hydrogen vs batteries.

p1necone• 5 years ago

Talking about efficiency with solar seems purely academic to me. Considering it's just there, it doesn't really matter what percentage of the potential energy you're capturing, just the absolute cost per watt of extraction.

jacquesm12• 5 years ago

There is another dimension at play here: solar is about 1KW/sq meter so efficiency directly translates into less area for the same output.

rektide2• 5 years ago

The safety is better, too - lithium iron phosphate batteries don't have the thermal runaway problem.

Relatedly, LFP are just rugged as heck batteries. They tend to have double or more the life-cycle count. 5000 cycle count before getting down to 80% capacity? In many cases yes. That's pretty impressive, and a great boon to overall lifecycle/long-term costs. Even if you're getting less energy-density, or even less energy-store/$, that battery is going to live at least 2x the effective lifespan (barring accidents, major defects, &c).

In general, anything built for high current tends but lower energy density tends to have much more ruggedness. Sanyo’s UR18650E is Li(NiMnCo)O2, for example, but in one paper shows 4X the lifecycle count of the extremely well regarded O.G. of LFP, the A123 ANR26650M1-A[1]. Even though it's considered a "lithium ion". And uses some of the rarer/more expensive materials. (Edit: re-reading the paper more closely, I'm less willing to embrace this conclusion. The A123 remains around 2000 cycle count regardless of depth of discharge pattern, while the li-ion drops to 1000 around 50% DoD.)

Not that phosphorous (The P in LFP) is projected to remain cheap/available forever. 2 days ago, talking more about phosphor's availability specifically with regard to agriculture (and rather alarmistly), "Phosphorus is essential to life and the world is running out of it"[2].

[1] http://www.jocet.org/vol7/511-C0056.pdf

[2] https://medium.com/climate-conscious/peak-phosphorus-may-be-... https://news.ycombinator.com/item?id=29244529 (2 days ago, 2 comments)

rektide2• 5 years ago

meta-note: this post has bounced up and down, 1, 2, 1, 2, 3, 1, 2. something like that. i just find that weird. hn has some weird downvoting behaviors that i really don't understand at all. maybe there's something legit downvotable or that people don't like? this seems like an innocuous post to me. i don't see the reason for it to keep getting negged.

apologies. i know discussing meta-topics is against the rules. i just really dont understand why there's an ongoing basis against this content becoming popular. it's so weird to me. i want to believe there's genuine real authentic behavior behind the votes happening here & elsewhere, but it feels so so weird to see this kind of straightforward telling constantly bounded, rising, then flattened back down, again and again. it instills a larger sense of disbelief, feels like there are vulgar reactionary forces about, which is not at all a conspiracy mindset i want to fall into.

HWR_142• 5 years ago

You left out the solar to electric efficiency. If that's 30% (which is an upper limit if you produce the best solar cells you can) batteries have twice as efficient a round trip loop from the sun. In return, they are far less mobile and heavier to ship once loaded. Meanwhile, we can talk about moving around H2 via pipelines. Or simply higher energy storage for big uses. (Less energy spent dragging around batteries). Plus, the batteries do require lithium, which is pretty nasty stuff to get.

apendleton• 5 years ago

Other people have responded about circumstances where hydrogen-as-fuel (or fuel component) might still make sense; without commenting on that, it's important to also note that hydrogen is an important industrial feedstock, independent of its potential energy applications (it's critical to producing fertilizer, among other things), and industrial hydrogen pretty much all comes from natural gas at present. Given that we need at least some hydrogen anyway, figuring out better ways to produce it is worthwhile.

In that scenario, total levelized cost is the more important criterion that efficiency -- if these things convert solar energy less efficiently, but the contraption is cheaper than solar panels plus conventional electrolyzers because it's simpler or uses cheaper materials or whatever, it might still be the more economical bet.

fghorow• 5 years ago

And where exactly does the energy stored in a battery come from, do you imagine?

This is PV powered production of hydrogen. Yes, the PV electricity could go directly to a battery, granted. But the PV cell is only about 20% efficient in that conversion. (Lab results are up to 30%.)

There are use cases where rather than an electrical transmission line needing to span an ocean, energy could be stored chemically (e.g. in hydrogen, or hydrocarbons produced from them) and transported like LNG across an ocean.

The claim of 95% round trip efficiency is basically relevant if the the energy is to be consumed (or placed on a grid) near the point of production. Otherwise 65% (13%/20%) efficiency for chemical energy that can be physically transported is not too bad.

Hydrogen is a battery from the perspective of a renewable energy system. If it is produced as a byproduct of a fossil fuel (as is commonly done) IMHO, it is not a renewable resource at all. Producing it from solar PV is a completely different kettle of fish.

exyi• 5 years ago

yea, but batteries are still quite expensive (I mean on a grid scale) and the cost does not get better with scale. Storing H2 is much cheaper and will also probably scale sublinearly (simplified: you pay for the wall of the tank and the wall is only volume^(3/2)). Also, h2 can be transported, traded, ... whatever, batteries are impractical for this and cables also have limitations.

However, I see one big down to hydrogen. You can't tell how it was made, you rely on a promise that it's green, while it may actually be from methane... maybe with carbon storage, but you never know when that is gonna leak out. This might be a big loophole for fossil fuel corps / states

elihu• 5 years ago

Apparently there are also some major patents that have expired or are expiring soon, which I hope means that costs will drop and we'll start seeing more LiFePO4 battery manufacturers outside of China where the vast majority are made now.

cronix2• 5 years ago

BYD, which is the biggest producer of batteries in the world, sells shipping container sized lithium iron phosphate sized battery packs for large scale solar backup.

Tesla has been playing in that space too with their Megapack.

https://www.tesla.com/en_AU/blog/introducing-megapack-utilit...

There was a pretty bad fire with them in Australia. https://www.reuters.com/technology/tesla-megapack-fire-austr...

stubish• 5 years ago

It is a stretch to call it a bad fire. One of the battery containers caught fire, and caused a second to be lost for reasons I don't know. The fire didn't spread, did not destroy the facility and did not require extensive downtime for repairs. Which is pretty nice to know as the fear was that one spark would send the whole facility up in a fireball.

beerandt• 5 years ago

So batteries are way ahead on efficiency.

Conversion efficiency is a different thing than storage efficiency or transmission efficiency.

Unless your gas tank is leaking, it's efficiency as a portable energy storage device approaches 100%, especially for modern vapor sealed vehicles.

jtsiskin• 5 years ago

That's not a comparison. Hydrogen goes Sun -> storage -> DC. Solar panels go Sun -> DC -> storage -> DC. You're comparing (Sun -> storage) against (DC -> storage -> DC). You need to include hydrogen fuel cell efficiency and solar panel efficiency for a (Sun -> .. storage .. -> DC) comparison.

iso12102• 5 years ago

This method goes Sun -> Hydrogen -> DC

100kwh of Solar energy generates 13.8kWh of Hydrogen, which is about 50% efficent thus generates 7kWh of DC

Going direct to DC is 23%, and the battery layer drops that to 20%, so 20kWh - about 3 times as efficient if you are using storage.

That's not bad, there are many applications where you'll take the extra land/solar take to provide the flexibility and density hydrogen can provide. Sure not for normal grid connected and static usage, but for mobile and temporary usage.

And that's not to mention all the other uses of hydrogen in industry that, without this method, would have to be generated by Sun->DC->Electrolysis

andrew_• 5 years ago

LiFePO batteries are also getting a lot of love from the marine community. I recently installed one on my boat to replace three lead acid and the weight savings alone will make up the difference in cost in fuel savings over the course of the year, not to mention the current generation last longer than lead acid in that environment.

newyankee• 5 years ago

I love LFP batteries and feel they are not given enough importance in the energy transition future. I was wondering by chance if there is a way to estimate the material amount used in these batteries to check if their limiting factor in scaling is lower than typical high Nickel batteries. I was wondering if Phosphate is a concern if not Lithium.

scythe• 5 years ago

The original technology is properly lithium-nickel dioxide. Elements such as manganese, cobalt and aluminum appear as minor constituents. Both Li-NiO2 and Li-FePO4 are based on conduction of lithium ions in the electrolyte ("Lead-acid" would be sulfate-ion by this naming convention; alkaline batteries are hydroxide-ion).

walrus012• 5 years ago

AC-DC-AC conversion is around 98%-99% efficiency now.

I'd really like to see some citations with specifiic BOMs of equipment that can accomplish this, because the datacenter industry would like to have something like that, but it's my understanding that the efficiency is nowhere near that 98-99% figure.

xorcist• 5 years ago

Solar cells are inefficient, and we should just get power off batteries instead?

That's not an argument for anything, and doesn't have anything to do with the article.

teekert• 5 years ago

It's also about energy/kilogram, especially in Aviation.

GuB-42• 5 years ago

Pedantry alert.

Lithium iron phosphate is lithium-ion. What Tesla is doing is changing the cathode material from Lithium nickel cobalt aluminium oxides (NCA) to Lithium iron phosphate (LFP). Other cathodes materials include LMO, LCO and NMC.

NCA has the best energy density, LFP is the best in everything else, including price, NMC is somewhat in the middle and LCO and LMO are becoming obsolete.

TomK32• 5 years ago

I might be mistaken on storing hydrogen, but all that takes in a high pressure container. I can imagine putting those solar-to-hydrogen plants up at sunny but remote places with plenty of space. Once a month when the containers are full a train comes along, unhooks cars with empty containers and goes off with the full ones. If you were to do that with any sort of battery you'd need two batteries, one be charged, one being used/discharged elsewhere, and your battery (for lack of a better term) efficiency (Total cost of usage?) basically halves.

iso12102• 5 years ago

Likewise the other way, say you need power at a building site for a couple of years, you can do that by delivering hydrogen bottles to replenish your generator, rather than having to take charged batteries and swap them out somehow.

raxxorrax2• 5 years ago

This is electrical to kinetic energy, which is an entirely different story.

The sun basically provides unlimited energy, so efficiency isn't as important.

ncmncm16• 5 years ago

This is a critical point.

All of the hottest utility-scale storage technologies have really quite poor round-trip efficiency, but it doesn't matter. Lower efficiency requirements so radically reduce the system cost that you add more cheap generating capacity on top, and come out ahead.

There is not now, and never will be, any shortage of available land area for solar panels. Almost every place you can think of to put them improves the place. On a reservoir, crop land, pasture land, canal, they reduce evaporation, and run cooler than in the desert. On crop and pasture land, they reduce heat stress and water demand in the plants, improving yield and irrigation efficiency. On roofs and parking lots, they slow sun damage. On parking lots they even keep the rain off.

fuddle2• 5 years ago

Can someone please ELI5?

dragontamer7• 5 years ago

The abstract looks simple enough? They played with some chemicals / catalysts, and have demonstrated a prototype where they made a "Solar Panel" that turns water (H2O) into 2H2 + O2... aka Hydrogen + Oxygen. The measured efficiency was 13.8%, less efficient than an electric solar panel (20% to 25% efficiency), but possibly the most efficient solar -> hydrogen design discussed so far.

Consider a 25% efficient solar panel -> 50% electrical efficiency to convert H2O into H2 + O2 == 12.5% total efficiency (and a 25% efficient solar panel is a high-end panel). So this design discussed is probably better than the status quo.

-------------

There are internet flame wars over the future of energy and energy storage.

Lithium Ion batteries are one form. Hydrogen is being proposed as a fuel of the future (with Japan showing off Hydrogen torches all over the Olympics earlier this year, as a lot of Japanese companies are pushing Hydrogen as a future fuel)

fuddle2• 5 years ago

Thanks, that was a great explanation.

ncmncm16• 5 years ago

But efficiency of immature processes only ever improves. Solar is close to maxing out, in watts/m^2, although watts/$ is still in free-fall. Space for solar panels is cheap, so the latter figure dominates.

jhgb• 5 years ago

Some people didn't like that you could combine bog-standard 20% efficient photovoltaic panels with bog-standard 75% efficient electrolyzers to reach 15% efficiency of conversion of sunlight to hydrogen, and came up with a specialized single-step device...that is only 14% efficient. ;)

solarkraft• 5 years ago

Congratulations on the advancement, but wow, that's still pretty bad. The only way this would become popular would be through being super cheap.

prox• 5 years ago

Thing is, this durable energy, and your limit is time here. As long as it is the sun doing the work here.

HWR_142• 5 years ago

Why is it still pretty bad?

tombert3• 5 years ago

I am speaking completely out of ignorance on this, so someone with a bit more familiarity with both physics and chemistry might be able to clarify.

------

From what I understand, one of the biggest issues with trying to replace commercial cross-country jets [1] with electric alternatives is due to the fact that there isn't enough energy density in a battery to make that possible, and as a result, airplanes are a huge polluter towards climate change.

Would it make more sense to try and make hydrogen jets, at least if we can make the hydrogen relatively efficiently?

[1] I know jets really only make sense with fuel, replace "jet" with "big airplane"

flatiron2• 5 years ago

Jet engines can burn hydrogen.

tombert3• 5 years ago

Then would it make sense for Delta or United or KLM or something to start investing in retrofitting their planes to hydrogen? I would think that governments could give tax incentives to do so, and as a result make planes substantially less horrible for the environment.

xxpor• 5 years ago

airplanes are a huge polluter towards climate change.

This is true on a relative basis: flying across the US puts out a lot of CO2 for a single person.

But on an absolute scale, it's pretty tiny: 2% of total CO2, 12% of transportation CO2.

fulafel2• 5 years ago

Just the CO2 numbers aren't giving you the right picture, as the other effects multiply the emissions effects of air travel on warming (for example radiative forcing).

That's also why an air travel emissions factor is used by policymakers when talking about its effects.

(Also, US transportation emissions in other sectors, especially road, are enormous in comparison to other countries, for context on the relative comparisons: https://www.statista.com/statistics/1201189/road-transport-s...).

zardo2• 5 years ago

Airbus has dangled the hydrogen jet concept, but hydrogen presents a lot of problems (low density, cryogenic, leaks through solid metal causing embrittlement).

It probably makes more sense to just synthesize longer hydrocarbons.

tombert3• 5 years ago

It probably makes more sense to just synthesize longer hydrocarbons.

Sorry, ignorance on my end is showing again; wouldn't a longer hydrocarbon still emit CO2 as a by-product since carbons are part of its makeup? Or does a longer hydrocarbon mean that there's a higher hydrogen-to-carbon ratio and therefore the pollution is less horrible?

ncmncm16• 5 years ago

Embrittlement is a product of high-pressure high-temperature storage. LH2 has its own difficulties, but they don't worsen with time.

ampdepolymerase• 5 years ago

Elemental hydrogen has this problem: it is hard to store. You need low temperatures, high pressure, and corrosion resistant containers. But there is one weird trick: if you bind hydrogen to carbon atoms, then you get best of both worlds. The fuel remains energetic and yet is relatively unreactive outside of combustion and is easy to store. Perfect for aviation.

worker767424• 5 years ago

I wonder what efficiencies look like for making hydrocarbons from atmospheric CO2 and water.

ncmncm16• 5 years ago

H2 is not hard to store in liquified form, LH2. You just need good insulation. Earth is excellent insulation.

For aviation, sticking on a carbon that outweighs your hydrogens by almost 8x gives up a huge efficiency advantage. The efficiency advantage overcomes inconvenience of handling cryogenic LH2. My bet is the tanks will be nacelles slung under the wings alongside the engines.

Smoosh• 5 years ago

Not my area of expertise either, but I gather that hydrogen is difficult to store in quantity, requiring large heavy pressure vessels, and it has relatively low energy density. Both of which count against using it for commercial flight.

ncmncm16• 5 years ago

No one would bother with heavy, high-pressure hydrogen containment for large aircraft, so that is a moot point. The clear choice for aircraft is LH2, where it is fantastically more efficient than hydrocarbons.

Manuel_D• 5 years ago

Short answer: yes, hydrogen jets are probably the future. Electrochemical batteries fundamentally lack the required mass to energy ratio necessary for air travel. But there's a lot of challenges to actually powering an aircraft via hydrogen, and it's probably not going to happen for a while.

The long answer:

* The question is moot until we have widespread decarbonization of the energy grid. Currently, our hydrogen mostly comes from steam reformation - splitting methane, CH4, into 2H2 + CO - which emits carbon dioxide. Once our electrical production is carbon-free, then we can think of producing hydrogen and powering vehicles with that. Electrolysis can serve as a carbon-free source of hydrogen, if the electricity is produced from a carbon-free source. There are more efficient forms of hydrogen production, like thermochemical hydrogen production with heat provided by nuclear reactors.

* Once carbon-free hydrogen production becomes available, then there's the question of building hydrogen powered vehicles. Hydrogen is the most energy dense fuel by unit of mass, except for nuclear fuels, but it's about half the energy density by unit of volume compared to hydrocarbons. Substituting fossil fuels with hydrogen is probably more feasible in container ships than aircraft. Hydrogen containment, be it pressurized or liquid-cryogenic, scales better at higher capacities as there is a better volume to surface-area ratio. Aircraft wings (long and skinny) are basically the worst shape for hydrogen containment. Past examples of hydrogen powered aircraft stored it in the fuselage [1], which would sacrifice cargo and passenger space.

* Lastly, for aircraft there's also the question of making engines that don't produce greenhouse gases. High-temperature hydrogen gas turbines will also produce nitrous oxides, which are greenhouse gases. This can be mitigated by running turbines at lower temperatures, but that reduces efficiency. There's also the idea of using hydrogen fuel cells to produce electricity to run turbines, but fuel cells and electrical motors don't have as good power to weight ratios as combustion turbines.

I'm much more optimistic about converting maritime transport to hydrogen fuels than aircraft. That said, the military is very interested in hydrogen planes. One of the limiting factors in modern naval warfare is fuel to fly planes. With hydrogen powered planes, a carrier could produce hydrogen with its nuclear reactors giving carriers an effectively unlimited source of aviation fuel. If they figure it out, hopefully the tech propagates to civil air transport.

1. https://en.wikipedia.org/wiki/Tupolev_Tu-155

ncmncm16• 5 years ago

The natural form for aviation fuel is liquified hydrogen, LH2, sidestepping worries about embrittlement. LH2 is so much more efficient as an avaition fuel, despite problems handling ultra-cold liquids, that kerosene-powered aircraft will be simply unable to compete anywhere LH2 craft are in use. The rate of collapse in value of kerosene aircraft will be limited only by the rate that we can build out new or retrofitted LH2 aircraft.

It is not clear whether existing aircraft or designs can be usefully retrofitted for LH2. Existing wing tanks are, in any case, useless for LH2. You need much more room for LH2 tankage, and you might not want a big LH2 tank inboard; there are safety reasons for the fuel in current aircraft being out in the wings. So, maybe the LH2 is carried in nacelles slung under the wing, next to the engines. We will need to build up a great deal of aerogel manufacturing capacity to insulate them.

It is possible that existing wing tankage can be used to carry NH3 to inject, in small proportion, to minimize NOx pollution. Given a bit of surplus N, the N prefers to make N2, and the O prefers to make H2O. E.g., existing natural-gas plants inject NH3 to reduce their NOx output.

For shipping, anhydrous ammonia is probably a better choice of fuel. Existing engines can burn it, so you need only new room-temperature ammonia tanks and new plumbing.

divbzero• 5 years ago

I know jets really only make sense with fuel, replace "jet" with "big airplane"

‘Jets’ could make sense even without fuel if you consider that jet propulsion [2] is the generation of thrust using a fast-moving stream of fluid. Today’s jet engines are already turbofans [3] where only part of the propelled air passes through the fuel combustion chamber.

[2] https://en.wikipedia.org/wiki/Jet_propulsion

[3] https://en.wikipedia.org/wiki/Turbofan

rdedev• 5 years ago

Came across this recently:

https://en.m.wikipedia.org/wiki/Powerpaste

It might pan out and reduce issues with hydrogen leakage

hannob2• 5 years ago

The powerpaste is magnesium oxide. One magnesium atom weights around as much as 24 hydrogen atoms.

Thus for every hydrogen molecule you have to carry around 13 times the weight in magnesium oxide. Aka: This stuff is very heavy. Not exactly the thing you want on planes.

zz865• 5 years ago

One big electricity storage problem is seasonal - eg cold sunless winters. Eg batteries are great for daytime charging your car - but they aren't great for storing up a whole summer's worth of energy to burn in the winter. Hydrogen could do that.

bryanlarsen3• 5 years ago

A 3x overbuild of solar+wind in an optimal mix, along with a continental grid and 3 hours worth of batteries is all you need for 99.99% reliability over an entire year.

https://www.nature.com/articles/s41467-021-26355-z

kolinko• 5 years ago

According to the paper you cited, such setup in Germany would cause 100-500 hours of blackouts each year.

pensatoio2• 5 years ago

or...

we could use space rocks to heat water.

just saying.

ncmncm16• 5 years ago

You probably want a 6x overbuild to account for round-trip losses in your storage system. Cost of storage falls very fast as your efficiency requirements are relaxed, which becomes attractive as raw generating cost plummets.

lostmyoldone• 5 years ago

I would assume that many/most countries in climates where power interruptions quickly turn into deaths to avoid building in a dependence on an extra-territorial grid for base-level power supply.

It's already a problem in Eurasia with nation states using eg. natural gas delivery as a means to apply political pressure on other states, and this while it is still (relatively) easy to solve energy needs as carbohydrates can be easily transported.

If all border crossing energy/power delivery is through a physical network of cables, adapting if delivery is cutoff would be almost impossible unless all gas/coal/oil plants were kept at/near operating condition.

Hence, yes, the buildout must be some X times necessary power, as much as possible locally. A significant fraction of that generated power should be used to create a) industrial feedstock b) to generate liquids/gas that can be easily used and transported.

The latter in the case some nation is being pressured by energy blockades where the existing grid can not supply enough energy through transmission lines from other bordering states.

alliao• 5 years ago

what about those salt brine slurry energy storage? wonder how they're doing now..

https://www.osti.gov/etdeweb/servlets/purl/21390211

jillesvangurp3• 5 years ago

There are plenty of other storage solutions that are cheaper than lithium ion batteries and vastly more efficient than hydrogen. Even just cabling energy around is an option. E.g. the UK is looking at a solution for getting a few GW of Moroccan solar energy connected to their grid to supplement their wind power (which they have throughout the year) and modest amounts of solar which is a bit more seasonal.

The fallacy in your argument is assuming there's a need for seasonal storage. That need would only exist if you rely exclusively on solar energy. Which of course people up north don't tend to do and people closer to the equator could actually feasibly do throughout the year.

Plenty of places get by mostly powered by different combinations of renewables. E.g. Norway (wind, hydro), Iceland (geothermal, wind), Scotland (wind, tidal wave power), etc. without a lot of storage.

Swenrekcah2• 5 years ago

Geothermal and Hydro are steady sources, not intermittent, so that’s why you don’t need a lot of storage. The hydro dam is the storage. Geothermal also isn’t renewable unless used very very sparingly, most installations I know of will deplete the source in a few decades, perhaps a century.

bhewes• 5 years ago

Cool on the way to sustainable liquid fuels.

eatbitseveryday• 5 years ago

We see the value in fuels like diesel being highly energy-dense. If we used the sun to create fuel like hydrogen or electricity, what is against simply creating (purified in some sense) man-made diesel and continue to use combustion engines?

We would not be contributing to the overall contribution of greehouse gases. Some arguments are diesel and friends are safer in storage and transportation than hydrogen.

maxerickson• 5 years ago

Probably makes more sense to do compressed or liquid methane for ground vehicles. Easier to synthesize and cleaner burning.

mr_toad2• 5 years ago

what is against simply creating (purified in some sense) man-made diesel and continue to use combustion engines?

Mostly it’s just economics. Either the costs need to come down, or oil prices need to rise.

The way oil prices are headed, that might not take long.

kumarvvr• 5 years ago

The more complex the chemistry, the less economically viable.

Hydrogen is just H2. Diesel is a complex hydrocarbon.

A viable future, would be a highly distributed network of hydrogen stations, with Hydrogen generated from solar energy, with enough reserve capacity to act as a base load plant.

Extracting energy from hydrogen is a well understood process.

tomas789• 5 years ago

I did not investigate it properly but at first glance the efficiency is obtained via low current density of the electrolyser. That means high efficiency but low volume. That translates to more hardware needed to produce a unit of power.

State of the art electrolyzers are run at 1000x current densities. That roughly means 1000x installation cost.

mountainboy• 5 years ago

so how would a person go about making one of these for use at home?

lysp• 5 years ago

There are videos on youtube with various home-made h2 generators/splitters.

The issue with doing something useful with it is compression and storage.

While compression is easy, purification is an issue. With certain lower percentages of purity (from very rough memory under 92%, but could be in the 99s) it becomes an explosion risk.

jp0d• 5 years ago

This is not too bad. I'd prefer hydrogen fuel cells over massive toxic batteries that we're going to have to dispose safely in a few years, from all those used Teslas! I don't know about other countries, but most of the electricity generated here in Australia is from Coal and Natural gas. That's an unfortunate fact. I don't see any reason to buy an electric car until that changes. In the meantime if the solar driven hydrogen production efficiency increases then we can have an even cleaner future.

MaKey• 5 years ago

What is toxic about lithium-ion batteries? After their life in a car they can still be used for stationary energy storage and can be nearly fully recycled afterwards.

jiveturkey• 5 years ago

A google search tells me there are far more efficient processes available, one almost at 25% efficiency. None of them commercially viable yet.

nanomonkey• 5 years ago

Two things are hardly ever spoken about when splitting water:

The pure oxygen is just as useful of a product and can be used to gasify woody biomass, plastics and other waste streams into more useful fuel sources such as syngas, or liquid fuels using the fischer-tropsch process. It is also useful for medical processes.

Second, natural gas lines can utilize something like 10% hydrogen...so we can store a large quantity in our existing infrastructure for use later that day, or in other locations.

fulafel2• 5 years ago

Natural gas pipelines will have to ramp down with fossils though.

woranl• 5 years ago

People often say how battery cars are more efficient than fuel cell cars, and we should focus our resources to the former. Some even called fuel cell cars dumb. This is short sighted in my opinion. If fuel cell cars are more popular, it encourages more green hydrogen production and investment. Once there are more green hydrogen, then we can truly decarbonize the chemical and industrial sectors. There are so many industrial processes requiring hydrogen as a reactant. Fuel cell cars can be a catalyst to decarbonize sectors well beyond the auto industry.

laserbeam• 5 years ago

Anyone who says thay one is better than the other completely misses the fact that we have enough researchers on this planet to work on both. You never know what applications will make sense for each of the techs.

mlindner2• 5 years ago

People are usually talking about being against having tax payer subsides for hydrogen powered consumer vehicles being inexplicably higher than those for battery powered vehicles.

jillesvangurp3• 5 years ago

The challenge is cost of energy production, which translates directly into cost per mile when it comes to hydrogen powered vehicles. That matters because when the choice is pay 1x or 3-5x per mile, it's going to be an easy choice for most and hydrogen is going to lose every time. Hydrogen is simply too expensive per mile relative to other options.

That's why battery EVs are so popular; they are clearly cheaper to drive per mile. Especially if you charge them cheaply from your own solar panels, using off peak grid rates, etc. You are basically driving almost for free. In some cases grid operators literally pay consumers to plug their cars in so they can offload excess energy. It's cheaper than shutting down gas powered peaker plants and having to restart them a few hours later.

The article is interesting because it proposes a way that gets production to less than 2x the efficiency difference relative to using solar panels to generate energy in terms of efficiencies (12-15% vs 20-25%). That's impressive. However, it says nothing about the cost of hydrogen because this is an academic article and not an actual product. However it suggests an improvement. For reference, producing hydrogen from wind energy would use about 3-4x the kwh in generated electricity to produce 1kwh of hydrogen.

That's not bad. But even (wrongly) assuming all of that would be converted to motion, that would be about a 3x cost per mile difference already vs. just putting the wind energy straight in your battery. Burning hydrogen has inherent inefficiencies (you produce heat and noise) similar to burning other fuels (20-30% efficiency would be pretty good). And even fuel cells are not that efficient; 60% efficiency is pretty good apparently. And if you are using hydrogen for fueling vehicles, what matters is the cost per mile. So, on top of the production that would be another loss of about 1.5 - 5x on top of the production inefficiencies.

The fantasy of hydrogen in cars and trucks is that it is needed and that the cost doesn't matter. The reality is that there are battery equipped vehicles in almost every weight and vehicle class being produced already with pretty awesome cost per mile that are going to be pretty hard to compete with using hydrogen. It's a no-brainer choice already for a lot of drivers and fleet operators. Sure, their range is not always that impressive. But at about 3-5x the cost per mile difference that's an inconvenience that can be worked with.

The other fantasy is that hydrogen is carbon neutral. The vast majority of hydrogen produced is grey hydrogen. If you want to save some carbon, fuel your car using methane instead of hydrogen. You'll produce a lot of co2 but a lot less than when you use that methane to produce hydrogen which you then burn or use in a fuel cell. That's the sad status quo of hydrogen on the road right now. What little there is neither green, efficient, or cheap. Making it green will raise the prices. Making it less inefficient is going to be a long battle, and until that is done, it will be inherently more expensive.

Green hydrogen when production of that is going to be more meaningful is still going to be useful elsewhere (aviation, shipping, heavy industries). And with wind and solar intermittency that basically means there are going to be surplusses (rather than shortages) because people will over provision to compensate. Hydrogen is a great way to use such excess energy. There's going to be plenty of demand for it. Just not on the road.

rdevsrex• 5 years ago

I don't get why people are acting like it's an either or scenario. That said, one pro for hydrogen, is should be easily burnable in the current natural gas plants, which should easily cover off peak times without the need for batteries.

Another thing. I think we should question any plan that requires more mass mineral extraction than necessary. It's not as if mining is an environmentally neutral thing, and there is more to restoring our planet that just getting surviving climate change.

diordiderot• 5 years ago

The UK is going to mix hydrogen and natural gas through the current infrastructure. They're currently building dozens of hydrogen plants and each one that comes online will increase the hydrogen until it's 100%.

Really brilliant as the UK will be way ahead in global production.

There's a good YouTube video explainer, search "just have a think blue hydrogen"

Here's government link

https://www.gov.uk/government/news/uk-government-launches-pl...

ncmncm16• 5 years ago

Stupendously massive production capacity of H2 will be needed for every plausible climate disaster mitigation scenario. If you want to synthesize CH4 or other hydrocarbons from captured CO2, or to synthesize NH3 for fertilizer, or for fuel, or for storage, you need H2 first.

To fuel aircraft efficiently, you want a great deal of LH2. Anywhere LH2 aircraft fly, kerosene-fueled aircraft will be simply unable to compete. That will start on major international routes, with airports synthesizing LH2 on demand from grid power, banking it when spot price is lowest. The only thing that will save carriers loaded up with kerosene craft is the limit on how fast the LH2 aircraft can be manufactured.

Carbon-neutral steel production will depend on really huge amounts of H2, in place of coal or natural gas. Existing fertilizer production lines can inject H2 with the natural gas, and increase its fraction as more becomes available. At some point, as the carbon fraction decreases, electric heating will become more economical than burning injected gas for heat. Ultimately, improving catalysts will make the whole process more efficient than ever.

NH3 made with green hydrogen is a likely fuel for retrofitted long-distance shipping, where ships need only new fuel tanks and plumbing to switch over. Probably legislation will be needed to drive this change fast enough.

Cars with high-pressure H2 tanks are beginning to be practical, and are much lighter and cheaper to make than lithium-battery cars. When the car is lighter, the motor and drive train can be lighter too, and it takes less energy to accelerate them. In the short term, though, batteries are clearly winning. It is hard to be sure which will win, long term, but batteries have a huge first-mover advantage.

You can burn H2 directly in a natural-gas plant, or mixed into natural gas. So, as H2 production capacity grows, an increasing fraction of gas input to these systems will be H2. Ultimately, fuel cells driven from pure H2 will start to take over as prices of improved catalysts fall.

For utility-scale storage, bulk underground H2 is a much simpler and more reliable proposition than millions of battery cells, even though round-trip efficiency is poor. As top-line generating cost plummets, efficiency matters less. All the hottest storage systems (iron-air, hydrogen) are low roundtrip-efficiency.

habosa2• 5 years ago

A lot of the discussion here is around hydrogen fuel cells for cars and aviation. Which would be cool. But the real reason we need “green” hydrogen now is for making steel and cement: https://www.vox.com/energy-and-environment/2019/10/10/209042...

ncmncm16• 5 years ago

It's a good point: can any imagined use of hydrogen for cars even begin to compete with all the other demands for it? They might always outbid the car owners.

For aviation, LH2 has such fantabulous efficiencies that we can expect to see all serious air transport switched over by 2050 (providing civilization doesn't collapse first).

mlindner2• 5 years ago

Aviation won’t be using LH2. The volume required makes it not feasible. Not to mention the cooling requirements. Look at the volumetric energy density of it compared to other fuels.

twic2• 5 years ago

That article shows a graph of cement cost increases from alternative energy use, and says:

As you can see, every low-carbon alternative raises costs more than 50 percent above baseline. The only ones that don’t raise it more than 100 percent are CCS (of the heat source only), blue hydrogen, or resistive electric in places with extremely cheap and plentiful carbon-free energy.
The alternative that climate hawks would most prefer, the carbon-free option that would work best for most applications, is green hydrogen. But that currently raises costs between 400 and 800 percent. Ouch.

Green hydrogen is by far the most expensive option. 3-4 times more expensive than electric heat. That's the direct opposite of "the real reason we need “green” hydrogen now is for making [...] cement".

This new work will hopefully make green hydrogen cheaper. But if you're using electricity to make that hydrogen, i don't think it can ever be cheaper than electric heating.

habosa2• 5 years ago

Sorry I didn't mean it was more viable for that purpose, I meant it's more essential. We already know how to make good electric cars and power them with green-ish energy. For cement and steel we have barely even started making them "green" and they make a huge amount of our total greenhouse gas input.

dopkew• 5 years ago

Apart from the humanitarian catastrophe, does anyone else feel vexed, at the enormous resources and man-hours lost because of the bombing campaigns in conflicts? One could argue, that efforts towards achieving inter-national harmony is also vital in reducing humanity's carbon footprint.

twic2• 5 years ago

The headline is "solar-driven water splitting", but they do this by building an photovoltaic cell and connecting it to an electrolyser, just like everyone already does.

Moreover, the innovation here is that neither the solar cell nor the electrolyser require rare elements. As they say:

Sustainable water electrolysis requires that the anode and cathode catalysts are noble metal free and contain small amounts of other metals in order to lower system costs and facilitate recycling.

As for efficiency:

The measured [solar-to-hydrogen] efficiency is improved compared to all previous electrolyzers driven by low-cost [perovskite solar cells] that used solely Earth-abundant electrocatalysts but lower compared to the highest performing perovskite/Si tandem devices that uses noble metal electrocatalysts, which reached an initial efficiency of 17% [solar-to-hydrogen].

So this setup is less efficient than what we already have. But it doesn't require rare elements.

jakozaur• 5 years ago

The best way to understand hydrogen is Liebreich Hydrogen Ladder: https://www.rechargenews.com/energy-transition/liebreich-oil...

The best use cases for hydrogen are fertilser or in hydrocracking. We currently use primarily natural gas to produce hydrogen.

Urban or commuter cars are one of the worst use case for hydrogen. Electricity and batteries are way better.

Solar-driven water splitting at 13.8% solar-to-hydrogen efficiency

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