[Schroedingersat]

To follow up, fengning is on an existing river, uses an existing lower reservoir, has favorable geography, cost between $1.8 and $3 billion somewhere and stores 40GWh with 3.6 GW power.

This makes it better than existing batteries for ~1 day time scales and roughly on par with the upcoming generation of things like sodium batteries.

It's not a clear indicator as it's obviously optimized for power, but these all seem to be big advantages specific to the site which would indicate that an artificial reservoir would have trouble competing even against batteries.

Different sources have figures that differ by a bit (presumably projections vs actual) and most seem to have some mistakes. Here's one. https://www.nsenergybusiness.com/projects/fengning-pumped-st...

I could believe that you might improve storage/cost by a factor of 10 if you found a suitable reservoir by reducing power, but that seems to back up my initial assertion that you need specific geography and to significantly change the ecosystem fairly well.

As such it seems like it is not much better than a battery for displacing fracked methane, oil, or nuclear for mediating seasonal variability (which is what synthetic denser-than-hydrogen fuel is for as it is optimized for approximately zero cost per capacity at the expense of the highest cost per joule with competitive cost per watt).

Plus batteries still have a 10-20% efficiency benefit.

[ncmncm]

Pumped hydro, batteries, and tanked chemicals are not the only storage media.

We also have underground compressed air using existing deep cavities, and undersea compressed air. And underwater buoyancy, drawing floats down toward seafloor-mounted pulleys, using a winch and motor-generator on shore. Demand will not exceed our capacity to make cables and floats.

But the real answer is that there is nowhere even close to as great a need for long-term storage as you imagine, just as there is not much petroleum stored today. Petroleum is extracted and delivered continuously and reliably. Myriad tropical solar farms will synthesize ammonia year-round, shipping anywhere needed on demand, so storage is needed only until the next shipment arrives.

And HVDC transmission lines will move power from where it is being produced to where it is not, over 1000s of km, at a wholly tolerable loss rate. Much of this will move power eastward from afternoon production and westward from morning production, but also generally fill in for local production and storage shortfalls everywhere.

So Finland can have ammonia shipped in continuously all winter long, just as they ship in petroleum and NG today. Transmission lines will compete for that business.

[Schroedingersat]

Further looking into HVDC, it seems to be about $500k/km. Over distances of 4000km, that's $2/Watt ($2.20 with losses) or about the cost of producing the electricity in the first place.

Better than fuels at present, but inherently fragile so not a complete solution. Also those are just claimed building costs not including operation (and assuming it lasts about as long as the pv), and the natural monopoly spawned always winds up being a massive tax money sink, so it's not clear that building thousands of hvdc lines is going to work out.

[LargoLasskhyfv]

What is inherently fragile in HVDC compared to conventional transmission?

AFAIU it is even less fragile because it's usually 'point-to-point', which means to integrate it into the grid you need very modern substations with the ability to 'transform' the DC into the AC of whichever pre-existing grid by means of mass cascaded https://en.wikipedia.org/wiki/Insulated-gate_bipolar_transis...

Which in turn makes the grid around these substations smart, the more, the smarter. Because you have much better ability to switch and regulate(diversion from same frequency in AC-grid due to dynamic load or failure) much faster.

Think of the difference between the large external 'power-brick' for older laptops vs. the small switching power-supplies for contemporary notebooks. Just in reverse.

[Schroedingersat]

> What is inherently fragile in HVDC compared to conventional transmission?

Nothing? The point is transmission is extremely fragile. To physical conditions (weather, accidents, faults). To market effects (massive price gouging during those failures due to lack of buffer). And to market failures (harmful monopolies always form around private utilities and neoliberals always privatize utilities).

Then if the oceans are involved, cost becomes a non-starter.

[LargoLasskhyfv]

> Then if the oceans are involved, cost becomes a non-starter.

That remains to be seen. Some people seem to think different.

https://electrek.co/2022/04/21/the-worlds-longest-subsea-cab...

&

https://xlinks.co/morocco-uk-power-project/ is just the latest of those ideas/projects. I think it was on HN too.

[Schroedingersat]

> We also have underground compressed air using existing deep cavities, and undersea compressed air. And underwater buoyancy, drawing floats down toward seafloor-mounted pulleys, using a winch and motor-generator on shore. Demand will not exceed our capacity to make cables and floats.

These are more technologies that compete with batteries, not fuels. And poorly at that. CAES in ideal sites might compete with batteries for a while yet, but the others do not. Even a single truck full of ammmonia can store the equivalent to tens of thousands of cubic metres worth of displacement storage. A cubic metre float in a 500m deep body of water can store 5MJ, or about the same as a battery you can lift with one hand and buy for a few hundred dollars.

> But the real answer is that there is nowhere even close to as great a need for long-term storage as you imagine, just as there is not much petroleum stored today. Petroleum is extracted and delivered continuously and reliably. Myriad tropical solar farms will synthesize ammonia year-round, shipping anywhere needed on demand, so storage is needed only until the next shipment arrives.

Moving energy 2000-4000km as not-electricity is strictly a harder problem than storing it for 6 months and is solved with a subset of the same solutions. The main upside is energy input is cheaper and there is less idle time. This is definitely part of the solution but comes under the same heading.

HVDC systems are a solution for most of the issues, but distant solar isn't completely uncorrelated. Also no country is going to stake their survival on a system with cascading failure modes that can be triggered by anything from war, to a heat wave, to a blizzard, to a cyclone, to a forest fire, to political games. Thus capacity for months of backup is still required.

All of this is moot anyway because your other comment led me to find sources stating green ammonia is already within 50% of cost parity with fossil fuels for the cheapest solar energy sources and ammonia fuel cells are now viable as well with the same technology. Between that and thermochemical storage, fission is obsolete immediately and fossil fuels only need one more price shock for the transition to start.

Also none of this supports your original assertion that pumped hydro meaningfully exists in a non-ecosystem-altering way.

[ncmncm]

All countries have "staked their survival" on exactly what you describe for most of a century. Nobody seems exercised about it.

You are always free to invent falsehoods about pumped hydro, as about anything else.

[Schroedingersat]

No they don't. Proposing international transmission from the equator over a hanful of many thousand km long lines in competition with your neighbors in all directions as a sole source of winter energy is far more fragile than a mixture of local fossil fuel reserves, nuclear, local production, and imports from any direction from immediate neighbors.

PVs solve net energy needs. Perovskites might even make them do so without needing strategic mineral reserves. But they don't really provide energy security, and keeping fossil fuel infrastructure working for 1 month in 30 is extremely costly.

> You are always free to invent falsehoods about pumped hydro, as about anything else.

Then show the real numbers. I did. Demonstrate it being viable as a significant portion of primary energy in a typical country as a new project.