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The short answer is that pumped hydro is mature technology with a pretty wide range of places it can be implemented (at least in Australia[0], which has a mount

The short answer is that pumped hydro is mature technology with a pretty wide range of places it can be implemented (at least in Australia[0], which has a mountain range going down the east coast where everyone lives). A-CAES has three advantages, which are in my opinion aren't very fundamental: 1. It takes up less space on the surface than most PHES. This... is almost always a marginal benefit. 2. It doesn't require building a reservoir or dam. These are very well regulated in Australia and elsewhere, and the downsides are known so they are quite slow to get approval. 3. It's a bit quicker at 2.5 - 3.5 years as opposed to 3-7 years.[1] This is a bigger advantage than it looks if you have some tricky renewable energy targets to hit by 2030 (see our 42% emissions reductions target as well as an 82% renewable energy target) I can't see this gaining traction outside of a few locations in Australia, at least. I wouldn't be surprised if A-CAES is only briefly viable as a result of subsidies and cheap government financing. [0]: https://re100.anu.edu.au/#share=g-fa5a20c9c63f6ed6343a7e7573a05fe4 https://re100.anu.edu.au/#share=g-fa5a20c9c63f6ed6343a7e7573... [1]: https://www.csiro.au/-/media/Do-Business/Files/Futures/23-00033_SER-FUT_REPORT_RenewableEnergyStorageRoadmap_WEB_230310.pdf https://www.csiro.au/-/media/Do-Business/Files/Futures/23-00...

usrusr 2y ago
> with a pretty wide range of places it can be implemented How so? Yes, if you dammed up most valleys you could build a lot more capacity than humanity currently has, but that's because we don't really have that much. A factor of two or so might be well within range. But the total amount reasonably buildable simply isn't enough, except for some very local scopes where demand is low in both energy and in other use for the landscape that would be taken over by reservoirs. And that's before you start considering the geological realities required for actually building a dam, you don't just need the geometric shape of a valley, you need the bedrock to brace the dam against and the impermeability of the ground required to not have leakage wash out pathways for ever increasing leakage. Viable sites for pumped hydro are extremely rare and quite a few have actually been given up decades after building the dam, because the geology wasn't quite as cooperative as hoped. The promise of deep site water head CAES is that you can just throw money at the problem (excavation) and get as much capacity as you want to buy. The price per capacity is higher than that of a low hanging fruit pumped hydro site, but many of those buildable have already been built.
- gregoryl 2y ago
  Let's not forget the extreme environmental impact a dam has.
  - pfdietz 2y ago
    Those are for dams on rivers. PHES doesn't have to be on rivers.
- olau 2y ago
  The sources I've seen point out plenty of places. They may be overoptimistic. But excavation is really expensive, and in a competitive market, you cannot just throw money at the problem. It's the same reason nuclear fission is dead in many markets.
  - Intermernet 2y ago
    Australia loves excavation. If you could double up mining with pumped hydro you'd be the belle of the ball.
    - globalise83 2y ago
      It could make a nice option for huge abandoned open cast mines - build a dam across the pit, flood it and then pump water from one side to the other using solar-generated electricity, allowing it to flow back to generate electricity as and when needed. For example: https://www.news.com.au/technology/environment/abandoned-mine-sites-that-could-transform-australia/news-story/57bb855ecd9733a878b033026f323564 https://www.news.com.au/technology/environment/abandoned-min...
      - rtkwe 2y ago
        A big problem is those mines usually leave behind pretty toxic remains so the water you're pumping around is extremely hostile to the people and equipment you're thinking of putting it through/near. Then there's the chance of a dam collapse releasing that toxic water outside the mine.
denton-scratch 2y ago
Pumped hydro won't work unless you have a suitable mountain to hand. Compressed air can be built in flat country.
verelo 2y ago
I'd expand on your point (2) with these points. 1. Dams require water. Australia has suffered water supply challenges as long as I've been alive. 2. Dams can be environmental disasters. Both building, maintaining and one day destroying these has a lot of challenges and expenses that we're not great at measuring.
- rtkwe 2y ago
  Not having to build and maintain a dam and find an appropriate area to flood is a pretty large upside. Big thing in the US is that we already have a lot of dammed lakes in mountains in some places so we're really talking about making the water level more variable and adding some infrastructure instead of building net new lakes.
- pfdietz 2y ago
  Pumped hydro consumes much less water than evaporative cooling of a thermal power plant with the same energy throughput. Pumped hydro doesn't have to be on an existing watercourse, so it doesn't cause the environmental issues that come along with that.

usrusr 2y ago

> with a pretty wide range of places it can be implemented How so? Yes, if you dammed up most valleys you could build a lot more capacity than humanity currently has, but that's because we don't really have that much. A factor of two or so might be well within range. But the total amount reasonably buildable simply isn't enough, except for some very local scopes where demand is low in both energy and in other use for the landscape that would be taken over by reservoirs. And that's before you start considering the geological realities required for actually building a dam, you don't just need the geometric shape of a valley, you need the bedrock to brace the dam against and the impermeability of the ground required to not have leakage wash out pathways for ever increasing leakage. Viable sites for pumped hydro are extremely rare and quite a few have actually been given up decades after building the dam, because the geology wasn't quite as cooperative as hoped. The promise of deep site water head CAES is that you can just throw money at the problem (excavation) and get as much capacity as you want to buy. The price per capacity is higher than that of a low hanging fruit pumped hydro site, but many of those buildable have already been built.

gregoryl 2y ago
Let's not forget the extreme environmental impact a dam has.
- pfdietz 2y ago
  Those are for dams on rivers. PHES doesn't have to be on rivers.
olau 2y ago
The sources I've seen point out plenty of places. They may be overoptimistic. But excavation is really expensive, and in a competitive market, you cannot just throw money at the problem. It's the same reason nuclear fission is dead in many markets.
- Intermernet 2y ago
  Australia loves excavation. If you could double up mining with pumped hydro you'd be the belle of the ball.
  - globalise83 2y ago
    It could make a nice option for huge abandoned open cast mines - build a dam across the pit, flood it and then pump water from one side to the other using solar-generated electricity, allowing it to flow back to generate electricity as and when needed. For example: https://www.news.com.au/technology/environment/abandoned-mine-sites-that-could-transform-australia/news-story/57bb855ecd9733a878b033026f323564 https://www.news.com.au/technology/environment/abandoned-min...
    - rtkwe 2y ago
      A big problem is those mines usually leave behind pretty toxic remains so the water you're pumping around is extremely hostile to the people and equipment you're thinking of putting it through/near. Then there's the chance of a dam collapse releasing that toxic water outside the mine.

denton-scratch 2y ago

Pumped hydro won't work unless you have a suitable mountain to hand. Compressed air can be built in flat country.

verelo 2y ago

I'd expand on your point (2) with these points. 1. Dams require water. Australia has suffered water supply challenges as long as I've been alive. 2. Dams can be environmental disasters. Both building, maintaining and one day destroying these has a lot of challenges and expenses that we're not great at measuring.

rtkwe 2y ago
Not having to build and maintain a dam and find an appropriate area to flood is a pretty large upside. Big thing in the US is that we already have a lot of dammed lakes in mountains in some places so we're really talking about making the water level more variable and adding some infrastructure instead of building net new lakes.
pfdietz 2y ago
Pumped hydro consumes much less water than evaporative cooling of a thermal power plant with the same energy throughput. Pumped hydro doesn't have to be on an existing watercourse, so it doesn't cause the environmental issues that come along with that.