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One thing that often comes up with clean energy solutions is the fluctuations in capacity. In the minds of some this translates into a "OMG we need so much battery to survive the post apocalyptic circumstances that will surely make wind + solar insufficient". However in the real world, you can also address fluctuations by simply having over capacity.

If e.g. wind is half the cost of other solutions, you can install 2x the capacity that you need so that you still get 100% of what you need when winds drop by 2x. That of course creates the interesting problem of what to do with the extra energy that you don't need under normal circumstances. One solution is to simply transport it around by cable to places that have under capacity but if everyone puts over capacity in place, that's not going to soak up all the over capacity.

Solar has the same challenge. Having barely enough production + batteries can work. But when prices for solar + wind continue to drop you can start thinking about installing 2x, 3x or even 10x the capacity that is needed. That then creates a challenge of how to utilize that over capacity. This is not a problem but a huge economic opportunity.

Hydrogen is one of several ways to store energy and if we nail cheap & clean mass production, it becomes a very useful source of energy for all sorts of things. The German industry (i.e. Siemens + car manufacturers) are keenly interested in making that happen because there's going to be a world wide demand for components for all of this and that kind of is something they are good at. So, there's a very rational reason for bootstrapping the hydrogen economy like this in Germany.

> Hydrogen is one of several ways to store energy and if we nail cheap & clean mass production, it becomes a very useful source of energy for all sorts of things.

If we’re talking about long-term storage, hydrogen is nearly the only option available. Alternatives would be ideas like synfuels or ammonia (which both use H2 as a feedstock). You need the high energy densities of chemical fuels for this purpose. Something that other ideas, like pumped hydro or compress air, sorely lack.

What is "long term storage"? Why would you store energy for longer than it would need for the grid to provide appropriate capacity again?

On a grid level (that usually means: very large), how are H2 or chemical solutions better than simply pumping water up a hill?

This article might be of use: https://www.researchgate.net/publication/48693439_Large-Scal...

Long term means weeks to months of storage. This deals mainly with large season shifts in energy availability. Other ideas only really make sense for hours or days worth of storage. The need for this type of energy storage is well beyond what is plausible with pumping water or compressed air.

I think if we solve the hydrogen storage problem, it would also be the future for vehicles. Batteries just aren't going to cut it in the long run because of their limited power, limited charge cycles and heavy weight. I see those in a stationary role to provide capacity.

Sure, hydrogen diffuses through everything, but if we have a clean energy source that can be scaled, efficiency of conversion and loss from storage becomes secondary. Especially since fuel for cars is a short term form of storage. And it provides all the advantages fossil fuels currently have for this application.

That said, current technology doesn't provide adequate solutions for fuel cell cars en masse. Refueling is hard, fuel cells degrade quickly like batteries, distributing hydrogen is pretty hard and current production not environment friendly at all. There are some cars on the market with impressive performance, but the price is quite steep

But on the other hand, we also don't have infrastructure for batteries on scale. Imaging what the power supply for a "gas" stations on frequented roads has to look like if suddenly everyone had a electric vehicle. You would also need a lot more "buffer space". That is currently not possible to implement for any region with a large traffic density.

> think if we solve the hydrogen storage problem, it would also be the future for vehicles. Batteries just aren't going to cut it in the long run because of their limited power, limited charge cycles and heavy weight.

That was true in the past but not any more. Battery powered ev's, especially the best ones, are good enough for a large proportion of use cases, and are steadily getting better. And the infrastructure situation is also getting better at a rapid pace. To put in another way, the proportion of use cases where hydrogen fuel cells, if they ever become practical, would be superior, is shrinking every year.

I am not an expert on the hydrogen economy, but I've consistently seen a couple of important road blocks.

First, like you mention, the transport and storage of hydrogen is complicated due to hydrogen embrittlement of iron and steel. The Dutch gas companies seem to be very optimistic using the existing high-pressure pipe system crossing large parts of the Netherlands to transport H2. Question is whether long-term embrittlement might occur? how do we know? What about the smaller pipes leading to homes? The rate of embrittlement is quoted to be ten times higher. Do you have any wise words to add to this? Do you share my concerns?

2. Risk of hydrogen build-up in enclosures. Hydrogen's lighter than air property is often cited as a benefit, as it can evaporate into the atmosphere. However, in an enclosure, it might delay detection, since it is captured in the top of the building and presence might not be picked up with added odors. Some buildings open mostly at the bottom, such as distribution centers. Is this an unknown risk? We don't know, because it is actively being researched.

3. For powering vehicles, there is tremendous loss of energy from renewables due to transfer of energy and transport of gas. I think I've seen cited 30% efficiency.

4. There is an actual, continuous demand for hydrogen. However, for green hydrogen, we will need near 100% utilization of the electrolysis plants. That contradicts the premise to use excess energy from renewables to produce hydrogen. The electrolysis plants would shut down when generated electricity can be used to power industry motors directly.

5. Subsidizing hydrogen initiatives pulls subsidy away from Photo Voltaics, better electricity distribution and battery technology.

6. Long-term, we will end up with two infrastructures, with all the fixed costs associated. That might be more expensive than one (less efficient) infrastructure.

So, all in all, I am mildly skeptical on mass-scale hydrogen solutions. Perhaps you can make me more optimistic?

> Risk of hydrogen build-up in enclosures.

Allowing smoking in buildings again would stop this build-up.

1) Main strategy to avoid this is to just coat pipelines with plastic or make them out of plastic. Not all metals are equally susceptible to this process, and newer alloys are being developed that can strongly resist this phenomenon. While it is a problem, it is a solvable problem.

2) What I’ve read is that they’ll build hydrogen sensors and alarms for this.

3) This is hugely overstated for two reasons. One, just because an process contains inefficiencies, doesn’t mean the entire process is invalid. After all, gasoline powered cars throw away more than 80% of the original energy found in crude oil as waste heat. Fuel cell cars may waste more energy than battery cars, but it is less than ICEVs. Also, you do want to have excess heat sometimes.

Second, most of the sources of inefficient are solvable and/or were wildly exaggerated to begin will. Many arguments against hydrogen seem to cite some 20-30 year old source, and had some extremely pessimistic projections like hydrogen tanks leaking 20% or more of their fuel. Most of these projections haven’t been borne out.

4) Why do electrolysis plants need to run at 100% utilization rates? In a renewable world, almost nothing will have 100% utilization. This is not really a big deal since electrolyzers can be turned on and off quickly.

5) That’s true of any subsidy. One of the biggest complaints of the subsidy regime is how wasteful it is, and how poorly optimized it is for reducing GHG emissions. It will be almost a relief if hydrogen gets of those subsidies, since right now it is an important necessary technology that’s getting close to zero subsidies.

6) We don’t really need two overlapping infrastructures. Limit each infrastructure to where it is most effectively used.

Ad 1) But is that realistic, given the existing LNG infrastructure? The story being told is that we can just pump H_2 into the existing LNG pipes.

Ad 2) Yes, in processing environments. The story that is told to us is that we can replace LNG with H_2 to heat houses (with minimal investments).

Ad 3) True, ICEs are grossly inefficient. However, as I've seen it, EVs are still twice (?, reference needed) as efficient as H2. Especially for renewable, efficiency is key, as the whole production line competes with the price of oil.

4) Capital Expenditures. The YoY ROI is obviously very strongly influenced by the utility rate.

5) Green hydrogen as it stands is heavily subsidized and it needs to be. The capital expenditures for a hydrogen filling station is more than 50% covered by subsidy. And that is optimistic. So, close to zero subsidies, is not what I am seeing.

Ad 6) This might be true for industry usage, but not for consumer usage.

1) You can blend hydrogen with natural gas. To go 100% H2, you may need new pipes, but this isn't an insurmountable problem.

2) These sensors aren't that big. It'll probably be like fire alarms but for hydrogen if we go that route.

3) The gap is shrinking over time, as fuel cells and electrolyzers get better. Batteries are basically maxed out on efficient so they won't improve by much. Loosely spoken, the gap should shrink to about a 50% advantage for the EV in the long run. That means EVs may always make sense for short ranged trips, but for anything that needs big batteries the cost of the batteries probably will outweigh electricity savings.

4) If electrolyzers get really cheap this may not hold. I suspect that optimizing to 60-70% utilization is more than good enough.

5) Relative to the competition, it is tiny. We're subsidizing wind, photovoltaics, batteries, etc., to the tune of tens of billions, but for hydrogen it was in the hundreds of millions. Though this is starting to change as well speak as hydrogen is starting to get bigger subsidies.

>Why do electrolysis plants need to run at 100% utilization rates? In a renewable world, almost nothing will have 100% utilization. This is not really a big deal since electrolyzers can be turned on and off quickly.

The problem is capex. I am not at all an expert here, but from what I have read electrolyzers are at present very expensive, so to pay off their capex they need to be run continuously. Perhaps that will change in the future.

I'd imagine it should change in the future. We're looking at something like a 10,000x increase in production so current models won't hold in the future.

There is already a lot hydrogen use by German industry. Including a 240km pipeline built and in operation since the 30s.

The first step will be replacing hydrogen from fossil sources with renewable. This also provides industry which cannot be electrified a path to low carbon emissions.

> Barring sources like steam methane reformation from landfill-reclaimed methane

You got this reversed: as a general purpose energy carrier, methane is far more useful than hydrogen. Because it is so much easier to handle (as you said), and because so much infrastructure is already in place.

But you can't produce methane from surplus electricity without having hydrogen as an intermediate step. All this talk about hydrogen is just about skipping the inefficient methanization step. Methanization would also have a hard scaling limit in how much concentrated CO2 can be captured. Ambient concentrations are far too low for methanization and carbon fuel applications like aerospace won't ever be able to capture.

Right now, the UK is getting 7% of its electricity from burning biomass, primarily woodchips. CO2 capture there seems eminently doable, as a source for methanization of hydrogen.

It seems unlikely that hydrogen will be a viable fuel for commercial aircraft, given the difficulties of keeping hydrogen liquid or storing it compressed without excessive mass. Liquified natural gas (primarily methane) is however a viable fuel: https://www.wired.com/2012/03/boeing-freezes-design-with-liq...

If we can generate hydrogen from wind and capture CO2 from biomass, and use them to generate methane, this seems a viable way to power aviation going forwards. For most other things, batteries or direct hydrogen use seem viable, but aviation is hard.

Wouldn't aircraft H2 storage just be low pressure insulated tanks that self maintain their temperature by the boiling of the H2? Insulation is mostly air and as a result is light.

Any vented excess H2 isn't a big issue. You can just dump it straight into the atmosphere with no environmental consequence. If that turns out to be unsafe in some situations you can run it through some sort of heated auto lighting burner.

The energy loss of liquefaction is worse than that of methanization. If you add liquefaction of methane it gets close and H2 might even be slightly ahead, but LNG handling would be so much easier. 190K and 33K are very different temperatures.

You are pretty much describing the end-game scenario I had in mind: the use cases where CO2 capture would be hard or impossible are mostly the same as the use cases where direct use of H2 (without methanization or even further synfuel steps) is prohibitive. Mobile (mostly aviation) and decentralized (upgrading distribution networks for H2 capability down to individual kitchen gas stove seems almost as unlikely as upgrading the stoves to capture).

A post-fossil energy economy that combines H2 (where feasible) with methane (where necessary) won't see much if any of the methane's carbon captured. In a post-fossil economy CO2 sufficiently concentrated for methanization could easily be a limiting factor. Photosynthesis is the only scalable way to concentrate carbon from an atmosphere where CO2 is measured in hundreds of PPM, so all the post-fossil methane has to come either directly from biological processes or from biomass burning capture + H2.