Sub-zero water splitting marks a new dawn for solar hydrogen production
chemistryworld.com
chemistryworld.com
Nothing is a power system without efficiency figures. Otherwise it's just a chemistry experiment.
Then, powering a Raspberry Pi computing device (PRPi = 4W) for an autonomous measurement device year-round at the > Neumayer III station (70.68°S, 8.27°W, Tavg,y = −15.5 °C) would prospectively require a module area of 0.41 m2, whereas at Paranal observatory (Chile, 24.63°S, 70.40°W, Tavg,y = 0.4 °C) 0.18 m2 would suffice.
So the efficiency of hydrogen split-store-generate needs to beat the efficiency of store-release of the battery and the costs of the equipment.
But it isn't yet competitive with "store energy collected in the summer for use in the winter".
For that usecase, far more energy must be stored for far fewer dollars to make it competitive vs just having a big fuel tank and a winter-only diesel generator.
Keeping lakes of water for a few months for hydropower are also competitive - the storage capacity of a big lake on a mountain top is immense.
I've heard pumped water is like 90% efficient, but you need a gradient and space.
Does wind power decrease in winter? I also remember schemes for making a huge solar farm in the Sahara and a superconducting conduit to Europe, and that was several paradigm shifts in solar cell performance ago (15 years). But almost all large countries seem to have a sufficiently sized desert to do this with (US, Russia, China).
If solar gets good enough, and it is still on some prime parts of the economies of scale price drops, you don't care as much about long-distance transmission loss.
What we need is a proper international standard for cars to be able to interact with the grid, to be able to charge and discharge based on grid conditions and pricing.
Its stupid to have everyone coming home from work at 6pm and plugging in their cars to charge right at the existing afternoon demand peak, when solar is waning. Just getting those cars to delay charging until around midnight (allowing user override) would shift a huge amount of peak demand.
Same concept if you don't use your car during the day - it should be able to discharge right into the morning and afternoon peaks, at your control. The user should be credited for this onto their car account.
It might even make sense to have dedicated high-voltage circuitry in houses and apartment blocks, to be used for EVs, solar, etc.
And we should really figure that out immediately since EV production is ramping up right now. We can't just rely on single automakers (Tesla) to work out these societal problems.
The greenest time to charge here in Northern CA is between 11AM and 1PM, when solar production is maximum.
[0]Known, boring technology with 99.9% of the engineering warts and technical debt already solved.
The petrol in the ground is free, sunlight is free, biodiversity is free. The cost is only a human factor.
Higher efficiency on the other hand usually means lower resource consumption.
A weak proxy for cost ? Or a strong one for survival ?
A cheaper steel bike is less efficient than an expensive carbon fiber bike when your goal is to get to the mountain top before the flood submerges the valley.
Arguing that, in the judgement of process for the conversion of one form of energy (sunlight) to another (hydrogen), thermodynamic efficiency, or the measure of how well a process converts one form of energy to another isn't relevant is somewhere between obnoxiously pedantic and wishful thinking.
Funnily enough I read the article after your comment, and it is even less useful, interesting, than my initial assessment (not even direct solar to H2). It has approximately the novelty and utility of porting DOOM to <insert processor here> and running it in a refrigerator.
If you need the end product at a particular location, the transport costs can overwhelm any differences in efficiency.
The same also applies if you have excess energy in a particular location that you want to use.
In either case, the transport costs can make using the less efficient process, the more energy efficient choice overall.
This is a development that makes electrolysis practical in those regions.
It is neither a development[0] nor does it particularly make electrolysis practical in those regions[1] (or more so than it was yesterday). Unless there is something about keeping solar cells warm that is beneficial, I'm really not seeing it.[2]
>Hydrogen electrolysis is most efficient at elevated temperatures
negligibly until you get into the realm of solid oxide cells (100's of C) -20 to +40 is negligible, and moreover a moot point because of [1]
[0]>> The method works by using electrolytes with low freezing points, such as dilute sulfuric acid, to allow the use of water at lower temperatures.
A common electrolyte for making H2, at room temperature and otherwise. Not novel (or interesting).
[1]>> resulting in an interior working temperature of around 10°C.
Approximately 30-40 percent inefficiency in an electrolyzer manifests as heat -- all they did here is wrap their electrolyzer in a blanket. Any electrolyzer of appreciable (read: useful) power has trouble keeping cold, not warm. The square-cube law applies here, electrolyzer power (and heat generation) scales w.r.t. volume, heat loss with area. For intuitive purposes, a device capable of fueling a car (driving 24/7) would be outputting about as much heat as that car's engine.
[2]There might be, (chemistry is my meat and potatoes, more so than physics), but I've always seen the issue being more with keeping solar cells cool.
Perhaps there might be some actual merit when the end product of your process is compressed/liquefied H2? Still reads more like the usual make up some hypothetical use case for the highly impractical niche you chose to push the boundaries of scientific knowledge. But who am I to judge, I did semantic web in multi-agent systems back when ai was symbolic.
It can be slower to produce the gasses, though. High efficiency, low throughput.
Hydrogen production (electrolysis, etc.) is only about 30% of the full system cost since you've also got storage and generation components. It's not likely that hydrogen will become competitive with battery energy storage since the full systems costs are very similar now, batteries are rapidly dropping in cost, and hydrogen storage and generation tech isn't getting much cheaper.
There could be a cost-competitive niche role for hydrogen through injection into existing natural gas infrastructure. But that infrastructure is already facing cost pressure from renewables.
Kölbach, Rehfeld, May: "Efficiency Gains for Thermally Coupled Solar Hydrogen Production in Extreme Cold", Energy & Environmental Science, 2021.
First off this seems like a really important addition to solar in general. My impression is that hydrogen is easy to make, can be a closed water cycle (uses the same water it generates to when release the energy), and the only downside is the inefficacies of compressing it to store it among the other steps.
Does anyone know if this would be a practical source of heat say at night, considering what I understood to be Hydrogens lower energy density?
For example, I was wondering roughly how big of a tank of (I am assuming) liquid hydrogen would be required to match say 50 a gallon tank of diesel.
Or am I missing something here?
What you might be missing here is that the "only downside" should be emphasized far more. Hydrogen is a bloody nightmare to store long term. It's boiling point makes the -20 C involved with this technology look like an oven and you really do want to ideally store it as a liquid since the exceptionally low molecular weight means leakage is a constant problem save for some very advanced (and expensive at scale) carbon composites.
Graphene seems to be a potentially excellent storage medium but we are still a while off from being able to manufacture that at the amount that would make it economically usable for hydrogen storage at scale.
The problem is that the density us rather low. Enough to store tritium in a nuclear warhead, but possibly a bit bulky for home use. (Also, the hydride remains flammable.)
Also, hydrogen rises quickly as it burns, instead of spreading out on the ground.
Ammonia has a higher energy density, at 12.7 MJ/L, than even liquid hydrogen, at 8.5 MJ/L. Liquid hydrogen has to be stored at cryogenic conditions of –253 °C, whereas ammonia can be stored at a much less energy-intensive –33 °C. And ammonia, though hazardous to handle, is much less flammable than hydrogen.
This doesn't even mention how elemental hydrogen weakens metals over time ("embrittlement"), which makes storage even more challenging. There are lots of other issues discussed at that link, and it's clear that NH3 will be more expensive than e.g. gasoline, at least until there is better solar power. Still, if hydrogen makes sense, ammonia makes sense.
[0] https://cen.acs.org/business/petrochemicals/ammonia-fuel-fut...
When you decide to shut down your fuel cell and the temperature of the system drops below zero, water will freeze on your micron-thick platinum catalyst; cracking it, and rendering the entire fuel cell useless.
Two of the major pain points were the erratic weather refusing to generate energy because of sun's availability and the storage of energy for particularly those cold areas where it was expected that entire energy for an year can be saved inside the batteries that can be generated in 2-2.5 months.
There's also a few areas where combustion engines are more practical than electric ones and hydrogen engines could be used as a stop-gap solution until electric alternatives catch up; there's only so much humanity can do at once and using combustion engines with renewable fuels could reduce emissions while we take our time focusing on other areas.
There are other things to worry about.
It's also irrelevant, water is incredibly abundant in our solar system and we don't even have the largest oceans on Earth, they're just the largest ones on the surface.
Where is it?
Bottom line is that water is never in short supply. Nitrogen is likely to be the real bottleneck in our future efforts at colonisation and terraforming - at least till if/when we master star lifting of resources. At that point, mass and energy no longer make meaningful limiters and waste heat disposal becomes the primary menace to further development.
We just need to solve the simple problem of moving it from the atmosphere of Venus to where we want it to be. ;)
At a high enough altitude, both the pressure and temperature drops to Earth's equivilent. If you have a large enough structure that is relatively airtight (it doesn't need to be perfect), you only need a small temperature gradient to keep it aloft in the upper Venusuean atmosphere.
You could have cloud cities with open air balcony areas where you can walk around with only some basic protective gear and an oxygen supply to protect against the corrosive air and perhaps enjoy gliders or other airborne amusements. It's also good practice for when we decide to attempt something similar with Saturn and some of the other gas giants.
This realization does not stop us from using much more rare helium in party balloons, though.
This is a problem in the same sense that the sun going red giant is a problem.
To be fair to OP, at the point we're concerned about Exxon Valdez circa 2400 dumping an atmosphere of hydrogen into space and the Sun's expansion, we could solve one problem with the other and bring the Sun's mass over.
Plus hydrogen chemistry, as others have mentioned, will stop at least 99% of the losses you propose simply by reoxidizing in the presence of free oxygen.
Helium is inert and doesn't react, therefore is much more likely to be lost to diffusion.
It's like worrying that astronomers won't be able to enjoy the night sky after we've built a Dyson Sphere.
Theoretical max efficiency: 13.173 MJ/kg of water.[1]
Water in the oceans: 1.35E21 kg [2]
Total energy needed to electrolyze the oceans: 1.77E22 MJ
Total energy recieved by the Earth from the sun per second: 4.3E14 MJ
Time required to elecroyize the oceans using the entire available output of the Sun on Earth at 100% total efficiency: 478.67 days
It is a very silly idea to think that we could accidentally wield many orders of magnitude more energy than humanity has ever harnessed in collective history without noticing.
[1] https://physics.stackexchange.com/questions/24624/water-elec...
[2] https://mathblag.wordpress.com/2013/08/03/how-much-water-is-...
I guess, industrial magnates of 1800s would have shown the same reaction, if someone told them about dangers of burning fossil fuels.
"This is ridiculous!", "But Sun was causing fires for centuries!" and "If it gets bad, we can stop burning more coal!" — those excuses didn't age well, yet most replies to this comment repeat them almost verbatim.
Of course, instantly sending all (or most) of Earth hydrogen into outer space is impossible — at the current technology level. But wasting what little water we have to make it is still a bad idea.
Many places are already short on fresh water — the kind of water, necessary for electrolysis. We can make hydrogen from saltwater too — after purifying it, but that's not commercially viable. No one uses "free" energy from solar panels to make new lakes or refill depleting aquifers.
Most of the Earth's surface is covered by water, but we can't even purify enough to satisfy our biological needs — otherwise Sahara would be a major agricultural and economical attraction. To solve world's water problem would require near-unlimited power, and the hydrogen production is not going to do it. At best, a hydrogen boom would result in another round of colonial robbery: stealing water from people, who can't defend it, to power more air conditioners in USA and Europe.
The whole point of making hydrogen (from water) to store energy is so we can release the energy later — by oxidising it back into water. We get the same amount of water back afterwards. No one is going to be stealing water to make hydrogen.