Hacker News Reader

There's a hell of a lot of denial and negotiation when it comes to the carbon-based economy.

There is a painful amount of searching for some way to keep on digging up carbon out of the ground and turn it into something green.

So far the only real solutions are to leave the carbon in the ground and switch to wind/solar/etc.

We need to get past the denial/anger/negotiation/depression phases and just hit the acceptance phase of post-carbon energy.

Yeah because in the 20th century Power with a capital P was almost wholly based on digging and pumping carbon out of the ground.

Well, also that green hydrogen is a drop in replacement for blue/grey hydrogen. The hard part is building all the infrastructure. If we can build the infrastructure on blue/grey and then gradually transition to green over time, it's an easier feat than waiting until we have economical green hydrogen before starting to build.

Except we already HAVE massive demand for blue/gray hydrogen (for fertilizer and steel), and the infrastructure for electric vehicles (cars, trains, and trucks) is FAR cheaper than it is for hydrogen. It doesn’t make sense to invest in expensive dead-end infrastructure when we know it is fundamentally, significantly less efficient from a physics standpoint.

Efficiency is not a huge concern when highly fluctuating energy from renewable sources is involved. You either have zero efficiency because it goes to waste for lack of storage, or some efficiency through hydrogen (electrolysis).

The options are not {hydrogen, waste}, they are {batteries, thermal storage, pumped hydroelectric, Sabatier process methane[0], …, hydrogen, waste}.

[0] I’m not a civil engineer and I can’t estimate the costs of upgrading existing methane pipes to cope with hydrogen, but people write about it being a thing, so this may or may not be better than pure hydrogen even if it’s less energy efficient; but the point is there are many options not just two

Not wrong! However:

- batteries: not available large-scale

- thermal storage: potentially terribly inefficient (but as I said, yes it's at least something!)

- pumped hydroelectric: where I'm from, only available to a tiny fraction of the country

- Sabatier process methane: that's a possibility I guess, more inefficient though

My point being, yes you're right, there's many more storage solutions, but hydrogen seems to trump most. Might as well use that as much as possible.

> [0] I’m not a civil engineer and I can’t estimate the costs of upgrading existing methane pipes to cope with hydrogen, but people write about it being a thing

The issue is also that the recipients would need to deal with the pure hydrogen they're getting. Residential boilers for natural gas can't, for example. New models are required.

The deal with hydrogen is that electrolyzers cost a lot of money & round trip efficiency is bad anyway, so you’ll want battery storage for daily cycling and a combination of solar, wind, and good distribution. A small amount of curtailment is fine, in fact most power plants don’t operate 24/7 even when fuel is cheap, and you could consider that “curtailment,” too, but it’s just accepted that it’s okay to idle a power plant if it’s output isn’t needed (the only difference with solar and wind is their fuel is free). But once you use batteries and good distribution, there isn’t much curtailment needed. Hydrogen electrolyzers just using “free” electricity 5% of the time is crazy expensive… it’s 20 times as expensive (from a capital standpoint) as running 24/7.

And all of this is fine until we get to ~95% clean/renewable grids. Maybe at that point it’d be worth using hydrogen fir seasonal storage. But even then, you’ll still have some curtailment because otherwise your electrolyzer is too expensive.

Check out https://model.energy for how this would work.

That's more or less the pitch of the oil industry. And they seem to be very successful in getting billions in subsidy to do it. That's on top of the subsidies they are getting to exploit fossil fuels. The problem is that this is just green washing their "lets put more co2" in the atmosphere strategy for an other few decades. Because that's exactly what this is. It legitimizes that strategy and they are lobbying hard for this.

Nevertheless, transitioning grey hydrogen to blue hydrogen is probably a good thing. There's a lot of demand for hydrogen already in various industrial applications that are currently mostly using grey hydrogen. And transitioning more of our industry to hydrogen is key to de-carbonizing it. So, whether we like it or not, the hydrogen market is going to grow a lot in the next decades and it is probably going to be mostly blue+grey hydrogen for the foreseeable future produced by oil and gas companies and only little bits of green hydrogen.

The problem with green hydrogen is that it is magnitudes more expensive than blue hydrogen, which in turn is more expensive than the grey variety. Green hydrogen requires renewable energy and green hydrogen is just not a particularly efficient application of that energy as you need rather a lot of it.

A kilo of hydrogen is the equivalent of about 33 kwh. The market price of hydrogen varies wildly depending on how it is produced, transported and stored. The green variety is about 7$ per kilo. Or about 21 cents per kwh. Grey hydrogen (the dirty stuff) is about a dollar in the best cases. That's still about 3 cents per kwh. Grid prices for renewables vary widely but in the areas most likely to get involved with green hydrogen (i.e. middle east) they are between 1 and 2 cents per kwh for some recent renewable setups. So that's a factor of 3-21x depending on how you look at it. Blue hydrogen is somewhere in the bottom of that range.

It’s worse than that. 1kg of hydrogen may be 33kWh from a heating value perspective, but it only gets you like 60 miles of range in a car like a Mirai. Compared to a Model 3, which gets 4 miles per kWh, that puts the hydrogen at roughly 15kWh of useful energy. Also, the automotive price of hydrogen is about $13-16/kg in the only place with hydrogen fueling stations in the US, ie Southern California.

And it's even worse than that

The 33kWh per kilo of hydrogen - that's the absolute physical limit of green hydrogen production via electrolysis, assuming 100% efficient production, no leaks, no labor, no maintenance, no electricity losses, frictionless transportation and infrastructure that just magically pops up where needed. It's not the case that technology will push the price down - this is the best anyone can ever hope for

> The 33kWh per kilo of hydrogen

That's just a physical material property of hydrogen itself. It has nothing at all to do with anything else. 1kg of hydrogen has a (lower, not upper) calorific value of about 33 kWh, period. Doesn't matter where it's going, how it was made, what infrastructure was used, what any of the efficiencies involved were, ... You could magically conjure up 1kg of hydrogen from outer space and it would have that property too.

Pretty relevant what kind of practical efficiency you'd get converting it to useful work.

> that puts the hydrogen at roughly 15kWh of useful energy.

That's not the hydrogen's fundamental fault as a medium. It's the fault of the conversion process. 33 kWh of thermal to 15 kWh of work, according to your calculation. That's in the realm of highly efficient (Diesel) internal combustion engines.

As for 4 miles per kWh for a Tesla, you're already comparing apples to oranges. The Tesla feeds off batteries, where the expensive conversion part is already past. You're comparing high-exergy (battery) to low-exergy (raw hydrogen).

I don't know anything about fuel cells, but imagine they reach 90% efficiency (is that even theoretically possible? Don't know); suddenly you get 30 kWh of work out of 1kg of hydrogen. We're just starting out, and a hundred years ago ICE efficiencies were atrocious, too.

> We're just starting out, and a hundred years ago ICE efficiencies were atrocious, too.

Are we just starting out with fuel cells? They were on the Apollo missions and the Space Shuttle, and Wikipedia says they were invented in 1838 and commercialised in 1932.

Large scale, yes, I'd say so.

We are. There's a world of difference between the alkaline fuel cells that were used by NASA, and the solid oxide cells we have today.

That sounds like a confirmation of my point, not a rebuttal — it being more advanced now is also evidence we’re not just starting out.

It depends on what your intent is; if it's that the technology has been around for a long time, that's not really adding much to the conversation. It would be like saying that battery technology is centuries old, which is technically true, but meaningless in the context of advances being made in li-ion batteries today. If the intent is to say that fuel cell technology is mature and unlikely to significantly advance further -- which is how it's often presented on this topic in particular -- that just isn't true. SOFCs have only recently reached commercialization, and there are still gains to be had in, for example, manufacturing PCFCs, rSOCs, reducing platinum content of low-temperature (PEM) devices, etc. We're starting in the context of scaling up an industry, and all of the gains that brings.

You can’t ignore one of the main relative advantages of batteries (very high round trip efficiency) in this discussion and arbitrarily use the heating value of hydrogen without taking the relatively low efficiency into account. Skews the discussion.

And hydrogen is produced via electricity, so I’m not skewing the discussion at all.

Round trip efficiency of battery is 90-95% (can be higher). Round trip for hydrogen (ie electrolysis & then storage and then fuel cell conversion back to electricity), including cooling (required for fast refueling) and compression, is about 25-40%. Even when that hydrogen is already in your tank, you only get about 60% of the energy out of it in useful energy. Heck, in California, hydrogen stations typically are only 33% renewable with most of it being gray hydrogen (9.3kg of CO2 per kg of gray hydrogen, not counting liquefaction), which makes hydrogen cars even at $10-14/kg, worse for the environment than even just random electric cars (although many EVs use primarily nuclear or renewables).

And while electric cars can have distribution losses, they’re pretty low, ie single-digit percent. But hydrogen stations are almost always refueled by truck, which has its own inefficiencies, and the stations also must constantly maintain the hydrogen at cryogenic temperatures to be ready to fuel. Also, some new stations get fuel delivered as liquid hydrogen, which is denser than compressed and therefore easier to transport, but liquefying 1kg of hydrogen (and converting it to para-hydrogen, which is normal) requires about 10-13kWh of electricity… which could send a Model 3 about 40-50 miles. So you almost can get further on an electric car on just the energy needed to distribute the kilogram of hydrogen as the hydrogen car can get by consuming that kilogram!

It’s pretty bad. Hydrogen for transport just doesn’t make much sense except for niche use cases. Maybe the last 10% of air transport that proves electrification-resistant or certain long distance ships or rockets.

> We don’t need hydrogen […] for transport

We’ll need it for aviation.

Hydrogen for aviation doesn’t solve the high altitude water emissions problem of aviation and in fact makes it potentially worse. This effect is just as bad a CO2 emissions. Battery-electric can eliminate both. In the mid-term, battery electric can serve all short haul routes, which is about half of aviation passenger miles, and probably most medium and long haul routes can be split up into short haul routes (the hub and spoke model means that you end up doing multiple flights anyway for most random city pairs and the smaller initial battery electric aircraft will be more granular, meaning you can do more direct flights, or at least more flights that go in the right direction instead of needing to double back to hubs). Long term, battery-electric can do 4000-5000km long haul routes, and perhaps even supersonic flights.

That’s just wishful thinking. So far nothing shows that batteries would allow even most current “short” flights by airliners, only some trivial extremely short regional connection flights at most.

That’s also why no major aviation company is going towards batteries for airliners.

Also, burning H2 does generate heat and water emissions, but it’s not the case with fuel cells. Those can be literally 0-emissions.

Nope. It’s not wishful thinking, it’s my day job. It pops out of analysis of what aerodynamics advances are possible, eg work by Pfenninger and others which is decades old. It’s fascinating how some confuse their own lack of familiarity with the state of the art research on this with lack of any sound ability.

Boeing and Airbus have both invested millions in startups that are working on battery electric aircraft. But beyond that, it wasn’t Toyota or VW that made the Model S and the Model 3. Why would we expect a massive, slow-moving behemoth to be at the forefront of electric flight if the massive, slow-moving behemoths of land transport weren’t at the forefront of practical long distance electric cars? Companies such as Eviation, MagniX, and Bye Aerospace have promising approaches for the roughly 1000km range, with more advanced approaches (longer wings, pressurized cabin enabling higher altitudes, better battery chemistries, etc) enabling all short haul flights. Long-haul is a much bigger challenge, but still possible.

And dropping water from high altitude will still cause water emissions. You’d need operational complexity such as freezing the water into pellets, or dumping the water occasionally at low altitudes. And compressed hydrogen has terrible energy density so you’ll want liquid hydrogen, which is still the lowest density liquid known to humankind plus is also almost the deepest cryogenic liquid, with a bunch of energy required for liquefaction and some pretty annoying/dangerous handling issues during refueling. Sure, it could be done, but it’s going to be harder than people think and the poor round trip efficiency is going to limit the economic case for it versus battery-electric.

Correct me if I'm wrong, but ultimately the energy requirement for flight boils down to optimal lift-drag ratio, doesn't it? My impression was that we were in a pretty sweet spot there already, and can only expect marginal improvements (higher aspect ratio (which comes with its own challenges - from airport suitability to structural stability), less zero-lift drag by reducing wetted area). Even if we double L/D (which would be a substantial achievement, no?), battery-electric flight would only have endurance of about an hour with current tech, and then maybe 2 hours in two decades after specific energy has doubled again, just about giving us a bit more than 1000 km (after reserves etc.).

There's also no reason to expect that an L/D improvement applicable to battery electric aircraft wouldn't also directly benefit aircraft using fossil fuels or hydrogen / ammonia. Unless you have batteries with triple the energy density to current technologies, hydrogen is still going to go further and have a faster refuel time.