[dvirsky]

> Use all the excess solar/wind to create fuel for the natural gas plants

I don't know what the efficiency of the process described in TFA, but from Wikipedia I see that Electricity->Gas->Electricity has an efficiency of 30-40%. There are other alternatives like pumped hydro stations that are way more efficient.

[Schroedingersat]

There are not enough sites for pumped hydro.

Chemical energy is dense, easy to store, and you need methane for stuff like fertilizer.

Solar energy is basically free ($30/MWh and falling rapidly). The solutions we'lp use are the ones which scale and the ones which are cheapest for storage as it will be much more expensive than the energy.

For storing for a day, that's probably sodium batteries as the cost per MWh through is lowest.

For storing for a year, you want to minimize cost per MWh stored. Right now this looks like methane, maybe hydrogen or for heating, thermochemical batteries.

[ncmncm]

> There are not enough sites...

This is always claimed, and is always false. Please do not repeat falsehoods.

Existing hydro generation needs a watershed. Pumped hydro does not. All it needs is a disused hilltop and earthen dike, and not always the dike.

It doesn't always need the hill: underground cavities work to pump water up out of, and to drain into.

Batteries will always be the most expensive alternative. They will be used in limited amounts, mainly for very short-term (overnight) storage.

[Schroedingersat]

> It doesn't always need the hill: underground cavities work to pump water up out of, and to drain into.

Do you have any good numbers on real world projects? I'm very happy to be wrong here, but all the numbers I can find are either lies from nuclear shills or using existing watersheds. Most also only focus on the cost per kW which is higher than batteries and not the relevant metric (as batteries can drain in a few minutes) for season-long storage.

Also a quick back of the envelope seems to suggest emptying and filling lake Baikal could store as much energy as about a billion tonnes of chemical storage. This seems like a reasonable upper bound which would indicate pumped hydro is about an order of magnitude short of solving the problem. Current battery production is nowhere near (total cumulative seems to be about a megatonne chemical equivalent even if it is more than doubling annually it'll take over a decade to catch up), but this is expected because batteries are optimal for short term.

Overall by gut feel it seems a more feasible to make and store ten cubic kilometers of chemical fuel worldwide than move 200,000km^3 of water around.

[ncmncm]

Most current pumped hydro uses existing dams because duh. But nobody is building those anymore, for reasons you note. Existing hydro power dams were expensive because they needed to be deep to store years of water, and concrete because deep water has high pressure. They destroy ecosystems because that is where the water comes from.

Dedicated pumped hydro storage is typically quite shallow, with an earthen dike (if needed at all), and the only place with high pressure is at the bottom end of a penstock. It does not need to store years of water; just a day's worth is useful.

[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]

A day's worth puts it in the power limited regime where $100/kWh 4C batteries are already close to viable, and can use the 50x higher power per $ and higher efficiency for minute by minute arbitrage to offset costs. Do you have sources for real projects that can beat $60/kWh capacity and $600/kW power (what you'd be competing with by the time construction finished)? Moreover it also needs to beat hydrogen or methane storage (electricity->chemical-electricity) which (sans capex for tanks because I can't find good numbers, but I think it adds about 20%) is about $100/MWh out and $1000/kW using current technology including energy and projected to fall to somewhere around $40 and $500 in realistic timescales.

To make it impossible to mine more fossil fuels even for a mixture of slave-driving sociopaths unrestrained by law and theocrats actively seeking apocalypse we need to be able to use a MWh at night in mid winter that was produced at 2pm in summer for less than around $40 and then do it another billion times without hitting some resource limit. Hydrogen with storage is shockingly close, and if synthetic ammonia/methane or metal hydride get over the line, noone will look at fossil fuels again.

You seem to be telling me that pumped hydro is already there, but I can't find a decent source agreeing with you (or any numbers dealing with this use case for that matter).

[ncmncm]

What I am saying about pumped hydro is that it is deeply mature technology, with no surprises in store. All the equipment is essentially unchanged for decades, except for control-system electronics. All that is new is reservoirs not fed by watersheds.

There are actually dozens of shallow reservoirs behind earthen dams way high up in California's Sierra Nevada mountain range, many almost a century old, constructed with bulldozers that used pulleys instead of hydraulics, hauled up there on fantastically bad cart-track roads. The reservoirs feed penstocks down to Pelton wheels thousands of feet below. For storage, they just attached pumps to the penstocks to push water back up.

[weq]

And destroy the earth. Hydro is not green energy, its an energy tradeoff. nuclear is much greeener then hydro. with nuclear, its only a possibility of screwing the environment. with damns, its garenteed.

[ncmncm]

Nobody is building hydro dams anymore, because there is noplace left to build them. Many are being razed, instead, to try to restore fisheries.

But pumped hydro is a completely different proposition.

Meanwhile, each dollar diverted to nukes from building out solar+wind+storage brings climate catastrophe nearer. The immediate cause for catastrophe will be global thermonuclear war triggered by ... more subtle ... effects of the change.

[peterashford]

How are you seeing hydro "destroying the earth?". New Zealand has a lot of hydro and we don't appear to be destroyed, as of yet

[Schroedingersat]

Hydro makes major changes to the local ecosystem and kills a lot of wildlife that can't breathe water. Although p\enty of things can live in a dam they're not what was there before. It also makes major changes downstram

People like to equivocate this with making entire countries uninhabitable or ongoing destruction.

It also requires vast quantities of concrete (and thus has high one time emissions)

We should still avoid it where we can now that we know better.

[philwelch]

> Hydro makes major changes to the local ecosystem and kills a lot of wildlife that can't breathe water.

It’s not that great for river fish, either.

[ncmncm]

This is not true at all.

Hydro power dams use up a watershed, but those are not being built for storage systems. Pumped hydro storage does not consume a watershed or harm wildlife or fisheries. Pumped hydro does not need concrete for construction.

Please do not repeat this falsehood.

[Schroedingersat]

Please show me a funded or built project (or even a plausible proposal or projection from past and current projects) in the global north that has a lower cost per capacity than Fengning Pumped Storage Station that has the following properties:

- Is at a site of a type that is available with over 100x the capacity of fenging (ie. a hill with a dirt berm would count if there are 4000GWh of hills that could be plausibly used somewhere). If it does this it will help, but is still several orders of magnitude shy of replacing fossil fuels.

- Fulfils your criteria about not destroying an ecosystem.

- Is not built on top of a past project unless there are enough of whatever the past project is to fulfll criterion 1 (ie. a quarry or mine is fine if there are many similar mines or a handful of immense ones) or the cost of repeating the project elsewhere is included.

- Can empty its reserves in 2 months

- Doesn't take up a prohibitive amount of surface area (is at least 20kWh/m^2 or at most 10x the size of a solar array to fill it).

- Has an operating cost under $30/MWh of stored and produced energy

Otherwise pumped hydro does not meaningfully exist as it cannot beat batteries (the thing that is a long way from being good enough to replace fuels) or must destroy a watershed or other ecosystem.

[ncmncm]

There is no need for batteries to "replace fuels". Batteries are useful in places, but fuels, soon sythetic fuels, will continue to be used, particularly for shipping and aviation. There is no need for pumped hydro to "beat batteries". Both will be used.

There is no shortage of land to use for elevated reservoirs, and (again) no implied threat to watersheds in building them. There is no need for "at least 20 kWh/m^2". Reservoirs have many uses that all add value. They may store energy and water, provide recreation, habitat, irrigation, and a site for solar, all at once. There is no need for them to store 2 months' power. There is very little economy of scale: a dozen reservoirs are as good as one. Construction cost is not proportional to capacity. At worst, it goes as the square root, to build the perimeter dike.

Extraction rate is a question of how big and how many Pelton wheels attached to generation equipment you care to install.

And, as always, immediate and local cost will dictate choice. There is no need for universal numbers or a single answer for everybody.

[dvirsky]

Nuclear can't store solar energy, I'm only talking about giant scale energy store, not generation itself. I'm all for nuclear FWIW.