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Comment by ClumsyPilot | Hacker News Reader

> We need storage and pumped storage is the only practical way to get there with current supply chains and technology.

This really cannot be enphasised enough - this is the only game in town. The solutions are needed yesterday, and must be built on a massive scale - there is no time for a 20 year R&D to production cycle of a miracle technology. Only hydro does not require any new minerals and mining.

The only other container that is even worth mentioning is conpressed gas, but it seems to have neither the capacity nor the efficiency of a large hydro deployment

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The only other contender that is even worth mentioning is compressed gas, but it seems to have neither the capacity nor the efficiency of a large hydro deployment.

The largest pumped storage station in the US has a storage capacity of 24,000 MWh:

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

There's an underground hydrogen storage project underway in Delta, Utah with a capacity of 300,000 MWh:

https://www.powermag.com/massive-utah-hydrogen-storage-proje...

It would take 22 Deltas to overtake the world's largest pumped storage plant, a massive Chinese installation with 6.6 terawatt hours of storage capacity:

https://www.pv-magazine.com/2022/01/04/state-grid-of-china-s...

Still, potential underground hydrogen capacity is tremendous, amounting to thousands of terawatt hours in Europe alone:

https://www.preprints.org/manuscript/201910.0187/v1

How does the energy in underground hydrogen get utilized? Is the capacity the combustive energy, or only the energy from the gas pressure?

It's burned as fuel in a gas turbine to generate electricity. The process is similar to burning natural gas in turbines, but some equipment adjustments have to be made when running on hydrogen. The Delta project is starting with a 30/70 blend of hydrogen and natural gas, gradually stepping up to 100% hydrogen.

Siemens currently has turbines that can burn up to 75% hydrogen and is targeting 100% hydrogen by 2030:

https://www.siemens-energy.com/global/en/priorities/future-t...

General Electric has a variety of gas turbines, accepting 50% to 100% hydrogen in the fuel blend:

https://www.ge.com/gas-power/future-of-energy/hydrogen-fuele...

Mitsubishi claims to offer turbine operation on up to 100% hydrogen:

https://solutions.mhi.com/clean-fuels/hydrogen-gas-turbine/

Also used for direct industrial heat and as a feedstock!

Eg. the Hybrit project produces iron sponge with electrolyzed hydrogen. So the process becomes

> (electricity + H2O) + Fe3O4 [iron ore] => Fe + H2O

instead of the usual

> C [coke] + Fe3O4 => Fe + CO2

No it's mostly the chemical energy in the stored hydrogen, pressure is only a small part of it (though they might insert some expander turbine somewhere in there). Pretty similar to how you'd rate a natural gas storage facility.

It should be noted that the energy stored in the pressure of gas is zero. All the energy of an ideal gas is the kinetic energy (and rotational/vibrational energy) of its molecules, which is thermal energy. Internal energy of an ideal gas is independent of pressure.

What compressed gas storage does is (aside from combustion energy of a fuel gas) to provide not a store of energy, but a store of reduced entropy, enabling otherwise unusable amounts of heat to be converted to work.

The Delta facility is in its preliminary stages. It could be expanded by something like 50x that of current listed capacity.

You are confusing energy storage and fuel storage. I am talking about CAES, it uses electricity to compress air and feed that into a container, like a metal cylinder or caverns lined with impermeable material. When you need electricity, you release the air through a generator and produce electricity.

Hydroelectric, compressed air and batteries have round trip efficiency of ~80%.

https://www.sciencedirect.com/topics/engineering/compressed-...

The facility you linked produces and stores chemical fuel, and can't even convert it back into electricity. It is really easy to store insane quantity of fuel, just like we can store loads of oil.

The kicker is that production of Hydrogen and other e-fuelds is less than 50% efficient, and converting them back to electricity is another 50% loss. Compression for storage and transportation mean further losses. So the overall round-trip efficiency is expected to be about 25% or lower.

It is probably possible to build an economy based on e-fuels, and that's what many oil companies are pushing for. They are probably the only viable way to achieve seasonal storage. It's a different set of tradeoffs.

The facility you linked produces and stores chemical fuel, and can't even convert it back into electricity.

The project includes using Mitsubishi M501JAC combined-cycle gas turbines to turn the hydrogen back into electricity:

https://www.powermag.com/aces-deltas-giant-utah-salt-cavern-...

https://power.mhi.com/products/gasturbines/lineup/m501j

This turbine has a rated combined-cycle efficiency of 64%.

Production of hydrogen is more than 70% efficient in the best current commercial electrolyzers:

https://www.nrel.gov/docs/fy04osti/36705.pdf

Round-trip efficiency is much lower than 80%, but not as low as you have written here.

Industrial-scale electrolysers will soon be well over 90% efficient.

Any terms I can search to understand these advances? I seemed to remember learning that boring old electrolysis was around 30% efficient!

https://www.nature.com/articles/s41467-022-32652-y

Presuming I understood correctly.

Another system used a hydrogen-side electrode made of foamed metal immersed in water, where the surface area presented to the water was therefore very large, and the small pore size limited the hydrogen bubbles' interference with contact between water and electrode surface.

why are turbines used in place of potentially more efficient fule cells?

Cost. Fuel cells require quality manufactured membranes that also require regular maintenance and replacement. Getting volume with them is also a hard problem.

Thermochemical hydrogen offers the best prospect for hydrogen production if it can be worked out, because the whole-process efficiency from solar or nuclear heat can exceed the practical limits of water electrolysis. Most recent work focuses on the copper chloride process (which uses an electrolytic step) [1]. The best purely thermal cycle is sulfur-iodine, but running the process sustainably has yet to be achieved due to the corrosive nature of the intermediates.

1: https://www.sciencedirect.com/science/article/pii/S019689041...

Russians did that at some point in the 70s 80s. They pumped compressed air into some salt mines and that worked well until one of the mines sprung a leak and blew the mountain up

Such hydrogen storage facilities already exist, actually. But the hydrogen the store is produced via steam reformation which emits carbon. The big issue with hydrogen storage cheaply producing hydrogen without producing CO2.

There is in fact no such issue because literally no one is even considering producing hydrogen for energy storage in that way.

Then how is hydrogen going to be stored? Electrolysis remains either inefficient or expensive.

Storage method has exactly nothing to do with production method.

Electrolysis efficiency and expense are entirely sufficient to requirements for the hydrogen storage projects are, in fact, proceeding.

Inefficiency doesn't matter if you are storing curtailed energy.

If it makes more financial sense and uses less resources to overbuild solar 3x and curtail 60% of the energy than paying for fuel, then you have 2 units of energy you have already paid for spread out over 6-8hrs/day.

As long as using your $300/kw electrolyser at reduced duty cycle is cheaper and less resource intensive than mining and shipping gas, you do it.

I thought it was missing from the list...

https://en.wikipedia.org/wiki/Grand_Coulee_Dam#Irrigation

However it seems that the pumped storage I recall hearing about as a kid has an extremely low storage capacity and is more focused on irrigation.

Ontario recently started a pumped hydro facility in an abandoned mine, and it will hold ~400 MWh of power that can be charged or released over several days. Several other sites are in planning, including one that, if it goes forward, will hold 8000 MWh. That could run the entire city of Toronto for many hours.

Such facilities should allow Ontario to run on a mix of pure nuclear, hydro and wind. Currently about 15% of the electricity supply in the province is natural gas, used at peak times when demand exceeds the constant output of the nuclear/hydro base. At other times, their surplus is sold at a loss. More pumped storage will smooth this out.

> Only hydro does not require any new minerals and mining.

Why is mining a major obstacle, provided it is economical and the environmental costs are some orders of magnitude less than those of climate change?

The environmental costs of mining are extremely localized and that’s also generally where the permitting takes place.

New mining permits in the US are magnets for environmental review lawsuits.

Depending on the type of mine, getting a new one up and running can take 7-17 years, counting planning, permitting and the inevitable lawsuits.

Copper and nickel mine runoff can be extremely toxic, especially to aquatic wildlife and wetlands. Remediation isn't really feasible once the damage is done, so plenty of groups would rather outright ban certain rich deposits from being mined at all than take the risk.

How sensitive environments elsewhere in the world fare under mines that aren't subject to safety precautions in the US is apparently an "other people" problem.

Because lots of mined metals come either from 3rd world countries like Congo with no environmental protection laws or are mined in few places like Russia where a trade war can lead to shortages.

Hydro requires the most common mayerials like steel or concrete.

And, not even concrete.

But there are numerous other storage alternatives that also do not need any special materials. We don't know yet which ones will be cheapest.

The recent appearance of hydrogen energy storage has basically refuted this argument. We can now store all of the renewable energy we want. The only problem is the lack of awareness among environmentalists and engineers.

My limited understanding was that the electrolysis tech is not yet efficient enough at scale to make this feasible. Do you have links where I could read more about the cutting edge in hydrogen production? This is a very fascinating potential tool for solving the "we don't have enough batteries" problem with renewables.

The lack of awareness I am talking about also applies to electrolysis. The current state of electrolyzer technology is already good enough to do the job. Future advancements will make this a no-brainer. This is similar to the rise of photovoltaics a decade (which also caught many 'experts' by surprise).

Some recent advancements:

https://www.energymonitor.ai/tech/hydrogen/toshiba-claims-hy...

https://newatlas.com/energy/hysata-efficient-hydrogen-electr...

https://energynews.biz/idaho-national-lab-and-bloom-energy-p...

The problem with electrolysis was not its efficiency, the problem was capital cost of the electrolysers (so they could be paired effectively with intermittently overproducing renewables.) Efficiency was more of the concern when it was imagined expensive nuclear power would be driving electrolysers 24/7.

Hydrogen leaks like crazy and corrodes storage cannisters. It isnt especially practical.

The world produces and uses 700 cubic kilometers (at STP) of hydrogen annually. Hydrogen has been used on a mass scale industrially since the 1800s. The US has over 1000 miles of hydrogen pipelines.

There are obviously off the shelf components for dealing with hydrogen. This is not some hand wringing unsolved problem.

It can be used there are just better, cheaper options. Same for compressed air, molten salt, tidal power or a litany of other working tech that doesnt hit the right price/performance point.

Better cheaper options for seasonal leveling of a 100% renewable grid, or backing up the grid against rare prolonged renewable outages? Pray tell me about these.

> this is the only game in town.

There is another game in town. Emphasis on "is", as in present tense, not future. Natural gas power plants. They emit much, much less CO2 than coal. If we use them to only generate electricity when solar and wind are not enough, we end up with much lower emissions than what the trees remove from the atmosphere. We also end up needing to overbuild solar and wind by only about 30%, not by a factor of 3 or 4. The capital cost of maintaining the current, existing, natural gas power plants is basically zero. The capital cost of building new pumped storage is huge.

Here, let me do it for you. Lifting 1 kg to a height of 1 m requires about 10 Joules (more precisely 9.8, as every high school student hopefully knows). One billion kg, or one million tons is 10 giga-joule, or giga-watt-seconds. Increase to 360 million tons, and you get one GigaWatt-hour. One ton is one cubic meter of water, one million is a square of 1km2 area and 1m height, and 360 megatons is a square of horizontal width and length of 6 km and a height of 10 meters. A fairly big lake. Building an artificial one would qualify as a mega-project. It would cost multiple billions of dollars. It would be able to generate one gigawatt of power for one hour. Of course you'd raise it to a certain height, let's say 100 meters, and that would generate the 1GW of power for 4 days. If you have 100% efficiency. Which you don't have, because you lose energy both when you pump up, and when you let the water come down. Assuming an optimistic 25% overall round-trip efficiency, you get 1GW power for one day. If you want for one month, well, you multiply this by 30.

Or you can just keep around a 1GW natural gas power plant, and use it when you need it.

To explain the economics of pumped storage, you must first understand it.

Pumped storage round-trip efficiency is not, in fact, 25%, but routinely above 70%.

Nobody pumps water up just 10 meters. It is, instead, pumped (say) a thousand meters up to a reservoir commonly 10 meters deep. A 10m-deep reservoir needs only a cheap earthen dike. A dike is hardly a "megaproject", even if km long. Dikes are low tech.

The energy is extracted at the bottom end of a penstock. Each ton of water in a reservoir 1000m up stores 10MJ. One just 100x100x10 meters thus holds 100,000 tons, 1000 GJ, >270 MWh, 6 hours at ~40 MW.

Nobody needs 30 days' storage. If your hydro storage runs low, and local fuel tankage looks like it might, too, you order out for LNG or, soon, NH3 or LH2 from solar farms in the tropics.

Few would need or want a 1km x 1km reservoir. Smaller ones distributed where the power is needed are more useful.

An underground cavity, where it exists, can be used instead of a hilltop reservoir, or with one.

Burning NG once in a while is no big deal, but NH3 will be cheaper in the near future.

I concede the 70%. I agree with your calculations too.

But you also concede that you can use LNG from time to time. Which we can later switch to H2 or NH3.

Right now, all the natural gas power plants in the US produce about 12% of the total (gross) emissions. If we use these plants only when there's not enough electricity from solar, wind, hydro and nuclear, we'll reduce their emissions by a factor of 10.

What is the point in building thousands of reservoirs then? To reduce that 1% to 0%. Which we'd reduce anyway once H2 or NH3 become cheap and abundant enough?

By the way, the EIA made a handy comparison table for various power plants [1].

A "combustion turbine - industrial frame" is by far the plant with the cheapest capital cost, only $785/kW. Conventional hydro is listed at $3083/kw, with a fine print footnote that this cost is the least expensive plant that could be built in the Northeast (where the geography permits).

So, the cheapest possible conventional hydro is 4 times more expensive than an brand new natural gas power plant. My point is, we don't need a brand new one. We can just keep existing ones (and we don't even need to keep them all).

[1] https://www.eia.gov/outlooks/aeo/assumptions/pdf/table_8.2.p...

> Right now, all the natural gas power plants in the US produce about 12% of the total (gross) emissions. If we use these plants only when there's not enough electricity from solar, wind, hydro and nuclear, we'll reduce their emissions by a factor of 10.

Concluding that we'd only need 2% of the current emissions from this is a bit misleading. The overwhelming majority of emissions currently don't come from electricity and the only way to replace many of them is via electrifying them.

Some can be turned into opportunistic loads, but there will still be a major need for 4-100 hour storage in addition to the seasonal storage (which will be largely achieved via hydrogen or ammonia).

Off river PHES seems to currently be cheaper than other storage, but chemical batteries have a lot of other advantages and may become cheaper.

It also has at least one advantage over conventional hydro in that sites can have a lot more head. This allows the power room to be a lot smaller, and there are many brown field sites where one or both reservoirs are mostly complete (which may make it cheaper in spite of needing two reservoirs).

It's hardly 'the only game in town' though, and it's unclear whether the gap between 'batteries have much lower cost per watt' and 'ammonia has much lower cost per joule in storage' is big eough that 'a hole has zero long run cost' the marginal efficiency gain over electrolysis is worth it.

Let's say you want to reduce emissions by the equivalent of a 1GW natural gas power station.

Option 1: Build enough solar and wind to replace the electricity generated by the power station; in fact overbuild by let's say 30%. You can afford that because solar and wind are cheap. And then build pumped storage to be able to add an extra 300 MW for a few weeks, when you need that. Decommission the natural gas power station.

Option 2: Don't build the pumped hydro. Build instead twice as much solar and wind as in Option 1 above (for less money than in Option 1, because pumped storage is so expensive compared to solar and wind). When they can't provide 2 GW of electricity, fire up on natural gas power station to make up the deficit. Decommission one natural gas and keep one in partial use. Achieve more emissions reductions for less money.

Which option do you choose?

And, costs for everything are shifting throughout, with new technologies appearing randomly. The right answer today might be wrong tomorrow.

My point is that pumped hydro is hardly being built, but battery storage is growing very fast even at much higher costs (due to the other advantages). Step zero is, as always, build wind and solar but once you reach step one (and some places have) pumped hydro is hardly 'the only game in town', and it's not even obvious if it will remain a good option even if you have an excellent site.

Battery storage being built today is, correctly, almost all for shifting afternoon collection to evening usage, where batteries are best suited by their unlimited charge and discharge wattage, and their high cost per MWh stored matters least.

For storage beyond 4 hours, other considerations become important, particularly cost per MWh stored. You still need to extract plenty of wattage, but charge rate matters less. So, you need big or many turbines, but pumps can be slower. And, of course, retrofitting the many existing reservoirs is cheapest, so you do that before building anew.

Fuel storage similarly takes advantage of existing combined-cycle turbines, which are being adapted to burn a gradually increasing fraction of hydrogen. It remains to be seen whether they can be made to burn ammonia directly, or if the ammonia must first release its hydrogen. Stored fuel has the great advantage that it can be shipped, bought, and sold.

Most of the value in pumped hydro storage, as for chemical batteries, is in load-shifting, particularly from daily collection to evening load. You use it every day, so opex should be minimal.

For tertiary, occasional use, efficiency doesn't matter much, and other considerations dominate. Gas and steam turbines need expensive periodic maintenance after operating for some period, so you avoid running them too much. Fuel costs money, too. (Unless you synthesized it yourself; but what you burn you cannot sell.) But storing liquid fuel is cheap. Shipping it, too.

Transmission lines complicate choices, in large part because they go both ways, and because must be scheduled long in advance to maximize usage because they cost a lot to build. The power they carry might be free at the source.

Pumped hydro has 70-80% efficiency. I just looked up the number for a local one (smallish, ~180MW) and it claims 77% It operates on a weekly cycle, pumping up at night and weekends.

You do need a hill to build one, though. But you don't need Putin.

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