[HN Gopher] Solar-driven water splitting at 13.8% solar-to-hydro...
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Solar-driven water splitting at 13.8% solar-to-hydrogen efficiency
Author : Breadmaker
Score : 112 points
Date : 2021-11-18 19:50 UTC (3 hours ago)
(HTM) web link (pubs.acs.org)
(TXT) w3m dump (pubs.acs.org)
| eatbitseveryday wrote:
| 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 wrote:
| Probably makes more sense to do compressed or liquid methane
| for ground vehicles. Easier to synthesize and cleaner burning.
| tomas789 wrote:
| 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.
| fuddle wrote:
| Can someone please ELI5?
| jhgb wrote:
| 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. ;)
| dragontamer wrote:
| 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)
| fuddle wrote:
| Thanks, that was a great explanation.
| bhewes wrote:
| Cool on the way to sustainable liquid fuels.
| api wrote:
| Solves the energy storage problem. Just add tanks.
| NoblePublius wrote:
| $2 trillion of tanks and $1 trillion of pipelines, just for
| North America. Meanwhile, electrical grids already exist.
| unchocked wrote:
| 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!
| cjensen wrote:
| $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.
| sp332 wrote:
| Same reason that we put solar and wind power where land is
| cheap and transport the electricity to where we need it.
| new_realist wrote:
| 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.
| esturk wrote:
| Storage like all the cars we're planning to build anyway?
| Sorry, but there's something arbitrary about "summer to
| winter" that you're quoting to fit your narrative here.
| First of all, Li-ion battery wasn't made to storage energy
| that long. Second, there are flow batteries for that which
| will be far better than Hydrogen.
| cure wrote:
| > 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.
|
| Do you mean 10% of the generation on a typical summer day?
| Or 10% of the generation of an entire summer?
|
| The problem with this kind of calculation is that battery
| technology (and cost) is very much a moving target.
|
| LFP would probably be the better choice today. It's
| cheaper, safer, and can handle far more load cycles. That
| comes at a cost of a lower energy density, but that hardly
| matters for utility scale batteries. Tesla's megapacks use
| LFP already - https://cleantechnica.com/2021/05/11/tesla-
| transitions-to-lf....
|
| Like you say, there are many other energy storage options
| like pumped hydro, compressed air, etc. My personal
| favorite is the train full of concrete that goes up and
| down a hill (https://interestingengineering.com/concrete-
| gravity-trains-m...).
| mgfist wrote:
| You don't need to store that much energy. It's much more
| cost-efficient to over-provision energy sources. In a few
| decades we will see solar over-provisioned to 2-3x normal
| consumption and some battery and that will provide 100%
| uptime.
| oblio wrote:
| You're overprovisioning at the wrong time with solar,
| though. What good is 2-3x the power output during the day
| when you're at 0 during the night? You'd still need 12h
| of storage or more realistically a mixed energy
| production setup.
| u320 wrote:
| Maybe in Arizona. In places where clouds is a thing you
| are looking at _weeks_ of storage. And some of that
| stored energy would need to be collected months ahead of
| time. This is simply not doable with batteries, hydrogen
| storage is absolutely essential.
| oblio wrote:
| I think we're in agreement, maybe my phrasing was unclear
| :-)
|
| My opinion is that we need a mix of energy sources and we
| need a mix of energy storage solutions.
| u320 wrote:
| The most cost-effective way is a combination of over-
| provisioning, batteries and hydrogen storage. The exact
| mix is determined by consumption patterns and local
| wind/solar conditions. Generally though it's extremely
| expensive to rely on over-provisioning+batteries alone in
| places with unreliable weather patterns.
|
| Falling battery prices helps of course but we are very
| far from a point where we can eliminate the need for
| hydrogen.
| sdenton4 wrote:
| Another contender I noticed the other day: build transport
| cables eight time zones long...
| Weryj wrote:
| How's the gravity storage going, it looked really promising
| and simple.
| dragontamer wrote:
| If you count pumped hydro, gravity storage is the #1
| storage of the USA.
|
| Turns out that pumping water up-hill and running
| generators when the water flows backwards is a very
| efficient energy storage mechanism.
| thinkcontext wrote:
| Aside from pumped hydro I'm only aware of tiny, one-off
| pilot projects.
| nautilius wrote:
| How does a grid solve a storage problem?
| tuetnsuppe wrote:
| Before people get too excited they might want consider the life
| time of the cell as indicated over a 10 hour test window.
| solarkraft wrote:
| Congratulations on the advancement, but wow, that's still pretty
| bad. The only way this would become popular would be through
| being super cheap.
| HWR_14 wrote:
| Why is it still pretty bad?
| prox wrote:
| Thing is, this durable energy, and your limit is time here. As
| long as it is the sun doing the work here.
| r00fus wrote:
| 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 wrote:
| Make ammonia out of it, easier to store and transport.
| toomuchtodo wrote:
| 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.
| jsonne wrote:
| It also is how they power refrigeration in meat processing
| to keep the freezers cold. Seems like if you put it next to
| those manufacturing facilities to power the freezer trucks
| and facility itself you could save a significant amount of
| energy and reduce greenhouse gasses.
| jhloa2 wrote:
| Probably not as much as you'd think. Ammonia is used as a
| refrigerant in a closed-loop system. You'll eventually
| have some leaks and have to recharge the system, but the
| ammonia isn't a consumable item in this process.
| hannob wrote:
| 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_helen wrote:
| 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.
| zamalek wrote:
| They made a bet on hydrogen, hydrogen cars failed, and they
| are now sinking in more costs. They are a financial and
| executive failure, not a scientific one.
|
| There is still use for hydrogen outside of vehicles (and
| possibly some highly specific scenarios involving
| vehicles).
| Diggsey wrote:
| Most of the problems with hydrogen for cars comes from
| how you produce that hydrogen.
|
| Obviously, producing hydrogen from methane to power cars
| is a stupid idea if your goal is to reduce greenhouse
| gases.
|
| However, pure electric cars are only successful in some
| niches, and larger vehicles like buses and lorries just
| aren't practical yet, whilst hydrogen buses are already a
| thing. Battery technology has come a long way, but the
| energy density is still absolute garbage when you compare
| it to the energy density in any fuel.
|
| If you can produce hydrogen directly from solar power,
| then the overall efficiency may be less important: the
| advantages of greatly increased power density, and ease
| of refueling may make it more appealing.
|
| For battery-powered cars to be the long-term solution,
| and not just a stop-gap measure, there will need to be a
| massive breakthrough, to the point that energy densities
| can be compared with other fuelds.
|
| As petrol/diesel cars are phased out, there will be an
| increasing number of customers whose needs cannot be met
| by the current state of electric vehicles, and there will
| need to exist another option. At that point, maybe
| hydrogen won't look like such a bad bet...
| bryanlarsen wrote:
| Hydrogen has good energy/kg, but it has really poor
| energy/l. Buses are mostly empty space so they more
| volume limited than weight limited. Battery powered buses
| are already far more common than Hydrogen buses and the
| trend will accelerate quickly.
|
| In Europe, battery powered trucks can carry a heavier
| load than diesel trucks. The weight disadvantage of a
| battery powered truck is about a tonne. The batteries
| weigh a lot more than a tonne, but so does the engine,
| transmission and fuel in a diesel truck. The difference
| is about a tonne. In Europe, they allow battery trucks to
| weigh two tonnes more than diesel trucks, so... In
| America battery powered trucks have a 1000 pound weight
| limit increase.
|
| Green hydrogen is always going to cost about 10x as much
| as electricity. Using electricity to electrolyze water,
| compress the hydrogen, transport the hydrogen, strip off
| the electrons in a fuel cell, charge a battery and then
| drive a motor is necessarily a lot less efficient than
| using than skipping 4 of those steps to charge a battery
| directly.
|
| And truckers don't care about fuel density, they care
| about costs.
| Diggsey wrote:
| > it has really poor energy/l
|
| Compared to fuel yes. Compared to batteries, even at
| relatively low pressures, I think hydrogen still wins
| even by volume, and at higher pressures it's an order of
| magnitude difference.
|
| > In Europe, battery powered trucks can carry a heavier
| load than diesel trucks.
|
| You mean legally? If we're discussing which option is
| technologically superior long term, then it doesn't
| really make sense to argue based on arbitrary laws today.
| Is there a particular retionale behind the law that would
| make sense for electric trucks but not hydrogen ones?
|
| > Green hydrogen is always going to cost about 10x as
| much as electricity.
|
| Possibly, but as more renewable energy sources come
| online, the problem is going to change from "can we
| produce enough energy?" to "is the energy available at
| the right time and place?". Electrical energy is very
| difficult to store and transport in any significant
| quantity. We already have to turn off renewables
| sometimes because they're simply producing too much power
| when we don't need it. That power may as well go to
| creating hydrogen than doing nothing.
|
| I don't know that hydrogen specficially will be the long
| term solution either (after all, something better could
| always materialize) but current battery technology is
| definitely not a panacea.
|
| > ... is necessarily a lot less efficient than using than
| skipping 4 of those steps to charge a battery directly.
|
| High battery/payload weight ratio means you need more
| energy to get where you're going, which is not typically
| considered when comparing the efficiency of batteries to
| hydrogen. Batteries also take a lot of energy to
| manufacture in the first place, and have a limited
| lifespan, which is also rarely considered. I think that
| with some minor efficiency improvements to a couple of
| steps, and a lowering cost of electricity at "off-peak"
| times, that the overall equation will shift.
|
| > And truckers don't care about fuel density, they care
| about costs.
|
| Costs come from a lot of places. Trucks sitting around
| charging instead of delivering goods are a cost. Reduced
| range means increased costs. Expensive batteries that
| have to be replaced every X years are a cost.
| jacquesm wrote:
| Toyota bet on the wrong horse, they just haven't publicly
| admitted yet and for now the marketing engine is still
| running on (hydrogen) vapors.
|
| There is also Hyzon, a fuel cell manufacturer that hopes to
| massively convert trucks to Hydrogen.
| tombert wrote:
| 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"
| Smoosh wrote:
| 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.
| flatiron wrote:
| Jet engines can burn hydrogen.
| tombert wrote:
| 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.
| flatiron wrote:
| Interesting idea. Supply chain issues aside I don't know if
| the current gas tanks could be retrofitted for hydrogen.
| Maybe fuel cells would be easier. Could just shoot water
| out of its little plane tush as its flying.
|
| Is there enough O2 at plane levels for fuel cells?
| xxpor wrote:
| >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.
| Manuel_D wrote:
| 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
| zardo wrote:
| 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.
| tombert wrote:
| > 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?
| zardo wrote:
| It would mean adding carbon. In order to be carbon neutral
| that carbon would need to extracted from the carbon cycle.
| divbzero wrote:
| > 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
| ampdepolymerase wrote:
| 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 wrote:
| I wonder what efficiencies look like for making hydrocarbons
| from atmospheric CO2 and water.
| lazide wrote:
| Not great, not terrible [https://en.wikipedia.org/wiki/Fisc
| her%E2%80%93Tropsch_proces...]
|
| Not price competitive with fossil fuels, but then not much
| is - hard to beat 'mega joules for free*' as it were.
| rdedev wrote:
| Came across this recently:
|
| https://en.m.wikipedia.org/wiki/Powerpaste
|
| It might pan out and reduce issues with hydrogen leakage
| Animats wrote:
| 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...
| dragontamer wrote:
| 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).
| Someone wrote:
| > 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.
| JulianMorrison wrote:
| It's already happening, see
| https://www.gov.uk/government/news/world-record-raf-
| flight-p...
| aunty_helen wrote:
| 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.
| oblio wrote:
| > I would rather not fly in a bomb. I just don't see it
| being viable for planes.
|
| As opposed to the kerosene fueled bombs we're flying in
| right now?
|
| I'm not sure comparing things to close-to-wartime tech from
| 90 years ago is a valid approach.
| dragontamer wrote:
| > I'm not sure comparing things to close-to-wartime tech
| from 90 years ago is a valid approach.
|
| You might be surprised how good WW2-era scientists were
| at chemistry and science.
|
| The earlier poster has a point. Gasoline, Diesel, and
| Kerosene have all been studied extensively (especially in
| the 1930s and 1940s BECAUSE of preparations for WW2). The
| safety of soldiers was paramount even to the Nazis.
|
| War machines: be they airplanes, tanks, or battleships,
| were all going to be exposed to enemy fire and
| explosions. These fuels (Kerosene and Diesel in
| particular) were chosen because they're extremely safe:
| high flash points and even higher auto-ignition points.
|
| That means that kerosene __literally__ can't catch on
| fire at room temperature. You need to warm up kerosene
| before its appropriate to burn (Of course, once its
| burning it will warm up the rest of the kerosene and keep
| burning. But this isn't some super-explosive volatile
| chemical we're talking about here)
|
| Gasoline is still safe, but not as safe as the other two
| (-40C Flash Point). Gasoline was safer than a lot of the
| other petroleum products that were investigated back
| then, and was still chosen as a fuel for war machines.
|
| ---------
|
| The same is not necessarily true for H2. H2 will explode
| at any temperature (even near absolute zero).
| oblio wrote:
| > You might be surprised how good WW2-era scientists were
| at chemistry and science.
|
| I'm well aware of chemical prowess in that period,
| especially on the German part. They had a bunch of Nobel
| prize winners.
|
| However, that's why I said "close-to-wartime". First of
| all, in case you weren't aware, the Hindenburg was
| supposed to use helium but due to a lack of helium in
| Germany (I think it was primarily due to American export
| restrictions), they had to use hydrogen.
|
| I don't know of other limitations for the Hindenburg, per
| se, but knowing the overall German shortages of the
| period, I wouldn't be surprised if they had other
| structural issues with the Hindenburg itself, especially
| since it wasn't designed to be used with hydrogen.
|
| On top of this, the Hindenburg design was from the late
| 20s, 1929, I believe.
|
| If materials science, modeling, etc haven't advanced
| since 1929, I'll eat a shoe. If we're somehow worse at
| managing hydrogen after almost 100 years, I'll eat the
| other shoe.
| dragontamer wrote:
| Even if H2 isn't used directly, there are likely chemical
| processes that can convert it into some form that is more
| useful.
|
| EDIT: That's what its called. H2 is a component of Syngas
| (https://en.wikipedia.org/wiki/Syngas). Syngas can then be
| further processed into kerosene, gasoline, or other fuels
| we use.
| lemmsjid wrote:
| This has some interesting comparisons between hydrogen and
| gasoline as fuel, in terms of historical experimentation as
| to the effects of rupturing or destroying tanks holding one
| or the other: https://hydrogen.wsu.edu/2017/03/17/so-just-
| how-dangerous-is.... Not my field so I'd be interested in
| if this more or less reflective of current knowledge on the
| subject.
| huntertwo wrote:
| I read something that says Hindenburg was more about the
| mix of the gas and the material of the blimp. Properly
| mixed H2 doesn't burn (it explodes quickly, which is what
| powers an ICE).
|
| I agree though, planes and H2 probably don't mix. Jet fuel
| should not be a priority to replace with H2. Priority
| should be given to static applications before trying to
| apply it to moving vehicles.
| R0b0t1 wrote:
| You are right. The issue with the Hindenberg was not the
| hydrogen. It was the coating.
|
| The main concern for hydrogen as a fuel now is the high
| pressures. If the pressure vessel is damaged it explodes
| due to mechanical forces. This is not impossible to work
| around. Consider, for example, that gas tanks can already
| be punctured and lead to fires; it takes a fair
| accounting of the risks to really rule out hydrogen as a
| fuel.
| huntertwo wrote:
| Those gas tanks are more risky when you have constraints
| on weight and material of the tank, like in moving
| vehicles. I agree though, people unfairly disqualify
| hydrogen on this risk only.
| lizknope wrote:
| https://en.wikipedia.org/wiki/Hindenburg_disaster#Incendi
| ary...
|
| They tested the incendiary paint hypothesis on the TV
| show Mythbusters.
|
| The MythBusters concluded that the paint may have
| contributed to the disaster, but that it was not the sole
| reason for such rapid combustion.
| jjoonathan wrote:
| Right, but consider a punctured gas tank vs... well, have
| you played "spot the COPVs in the SpaceX explosion"? They
| spit fire and zoom around like party balloons. Good fun
| from a distance, but if I had to pick one to ride with
| every day, it's an easy choice in favor of the gas tank.
| R0b0t1 wrote:
| Do you know what the fuel is? Rockets are unique in that
| they carry a significant amount of oxidizer with them. A
| hydrogen container is unlikely to zoom around spitting
| fire, there's too much fuel for how much oxygen there is
| and it rises very quickly.
|
| There are still dangers, but practically I'm not sure
| they are that much worse than a gasoline fire. There are
| also systems that reduce the pressures needed, like
| activated carbon beds. Research on them stalled mostly
| because there was no good way to generate H2.
| mywittyname wrote:
| I thought the fact that H2 burns invisibly combined with
| the fact that it goes boom once the burning mixture is
| stoichiometric is the big risk with H2 over typical
| hydro-carbon-based fuels, which burn a bright orange and
| are surprisingly hard to blow up.
| R0b0t1 wrote:
| The Mythbusters did a show on this exact thing with
| spraypaint, hairspray, and propane canisters. They didn't
| explode even when wrapped with flaming rags, but
| sometimes the released material would combust. In some
| cases the gas rushing out actually extinguished the
| flame.
|
| You rarely by accident get a stoichiometric mix. With a
| slow leak into an enclosed container is usually how it
| happens. Otherwise there is too much fuel to O2 in the
| atmosphere.
|
| People really need to stop trying to sound smart by
| thinking of imagined dangers. That is what stopped
| nuclear power, it's what's stopping hydrogen as a fuel,
| it's what's stopping gene therapy research, etc. Get over
| yourself.
| dv_dt wrote:
| 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.
| JumpCrisscross wrote:
| > _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.
| Blammar wrote:
| Yes, exactly! Or any other hydrocarbon. This is a carbon-
| neutral process also, as the carbon will come from CO2 in
| the atmosphere. And we get the bonus of extra oxygen in the
| air...
| dahfizz wrote:
| Wouldn't the extra oxygen get burned up as you burn the
| fuel? It would be a carbon neutral and oxygen neutral
| process.
| xvedejas wrote:
| I think you're right, the oxygen would be sourced from
| water and water is also one major product of hydrocarbon
| combustion, which can be easy to forget.
| dragontamer wrote:
| > You're describing hydrocarbons.
|
| Well yes. But I'm also aware that H2 is a component in the
| synthetic production of those hydrocarbons. Using the H2
| directly could prove beneficial. But if not, then we can
| always convert it into some combination of C and H and burn
| that instead.
|
| Either way: producing H2 from clean sources (like this
| weird chemical solar panel thingy) is a good thing.
| elihu wrote:
| 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.
| p1necone wrote:
| 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.
| jacquesm wrote:
| There is another dimension at play here: solar is about
| 1KW/sq meter so efficiency directly translates into less area
| for the same output.
| bee_rider wrote:
| An interesting bit about the original paper linked -- from
| the abstract:
|
| > The trimetallic NiFeMo electrocatalyst takes the shape of
| nanometer-sized flakes anchored to a fully carbon-based
| current collector comprising a nitrogen-doped carbon
| nanotube network, which in turn is grown on a carbon fiber
| paper support. This catalyst electrode contains solely
| Earth-abundant materials, and the carbon fiber support
| renders it effective despite a low metal content.
|
| I don't know anything about chemistry so I'll have to take
| their word on the fact that the elements they use are
| abundant.
|
| The two concerns for area are:
|
| 1) The cost of panels to cover the area
|
| 2) The cost of the area itself, and the availability of a
| ton of empty space in a convenient location
|
| If they are using abundant materials, the first is not as
| much of a concern, compared to photovoltaics. Since they
| are producing some sort of fuel rather than directly
| producing electricity, transmission efficiency is not
| really a concern*. So maybe we could plop a bunch of these
| things down in some sunny middle-of-nowhere desert.
|
| * I guess is we consider vehicles to transport fuel, which
| must themselves burn fuel, to in some sort of abstract
| sense be part of the transmission efficiency, this
| computation could be pretty complicated.
| lazide wrote:
| To answer your question regarding commonality/ready
| availability -
|
| Carbon, Nitrogen, and Iron are cheap and easy (you're
| likely within body length of a large quantity right now).
| 32% of the earths mass is estimated to be Iron. $1/lb or
| less in massive quantities.
|
| Nickel and Molybdenum are slightly harder to find, but
| not by much - nickel makes up 1.8% of the earth by mass
| and is a reasonably common metal in everyday
| manufacturing. It's currently at $3.97/lb spot price at
| tonne quantities. Moly is in everything from greases to
| steels, and while typically not used in large bulk
| quantities alone, is available for such
| [https://tradingeconomics.com/commodity/molybden] at
| looks like $23/lb give or take.
|
| So all commonly available elements, albeit (nanotubes)
| not necessarily in the form desired just yet.
| dv_dt wrote:
| Area isn't a particularly limiting factor for most
| applications.
| lazide wrote:
| It is one of the most limiting factors for solar, when
| everything is accounted for.
|
| You either put it really far away (increasing
| transmission losses and right of way issues for the much
| longer lines), or you put it closer and then have to deal
| with expensive land or difficult environmental reviews.
|
| It is not AS BIG of an issue as it could be - for
| instance 30% efficient cells vs 23% efficient cells, the
| lower efficiency's cost vs space usually favors the lower
| efficiency, but it's still very strong overall.
| jacquesm wrote:
| That's opposite of my knowledge about this but I'm a
| decade+ out of date, so possibly this isn't as much a
| factor as it used to be, but the cost of the ground was a
| substantial factor in solar installations in days past.
| caoilte wrote:
| I think cost of installation / maintenance per sq meter is
| the real kicker. There's actually a lot of still available
| space for solar panels (reservoirs being the favourite one
| I just discovered).
| apendleton wrote:
| 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 wrote:
| 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.
| HWR_14 wrote:
| 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.
| huntertwo wrote:
| 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.
| Someone wrote:
| > 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.
| jacquesm wrote:
| > 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
| huntertwo wrote:
| Very cool, there are definitely use cases where batteries
| are necessary (like moving vehicles) and it's great to see
| advancement in battery tech.
|
| EDIT: These batteries seem to be even less energy dense
| than Li-ion which is one of the weaknesses of batteries in
| comparison to hydrogen.
| rektide wrote:
| > _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)
| superjan wrote:
| 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.
| thinkcontext wrote:
| 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.
| exyi wrote:
| 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
| zz865 wrote:
| 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.
| bryanlarsen wrote:
| 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
| wiz21c wrote:
| > high peak solar-to-fuel conversion
|
| does it mean there's a "mean solar-to-fuel conversion" to look
| for ?
| NoblePublius wrote:
| 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.
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