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Comment by Schroedingersat | Hacker News Reader

The system you described has a capacity of 35L (that's how much it can pour through both pipes and still be ready to cycle) and a cyclable capacity of 20L. Only someone deliberately trying to misconstrue the role of seasonal storage would characterise it as 5L. You also carefully ignored the upstream turbines which aren't two way.

> But that metaphorical battery fills itself very slowly. It's not cyclic capacity and thus isn't nearly as useful.

It's seasonal storage. The fastest it can empty or fill is a week. A renewable grid doesn't ever require it to run at max power until it is empty and then fill at max power until it is full. That's a failure mode of a grid with large centralised production that has major unplanned outages like nuclear plants.

Is a load balancing or grid forming battery more useful? Yes. Can snowy 2 form a buffer for 350GWh of energy consumption in any realistic scenario? Also yes.

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> You also carefully ignored the upstream turbines which aren't two way.

What about them? Those aren't pumped hydro storage plants, they're just normal dams. There's no pump: you can't supply them with electricity to pump water back into the reservoir.

Cyclable capacity is the only type of capacity anyone cares about. Again imagine I sell someone a battery claiming it has 10 GWh of capacity. they drain 10 KWh, and then they try to charge it back up but it stops at only 3 KWh. They call tech support and I say "well, sir, the battery only has 3 KWh of cyclable capacity." I guarantee you >99% of people would think they were cheated. Saying that the battery has a capacity of 10 KWh is highly misleading; it's only true in a pedantic sense.

The whole point of Australia's storage plans is to even out solar energy's daily output. The plan is to pump the water into the upper reservoir during the day, and release it at night. The requires cyclical storage. The trickle of water that precipitation puts into the upper reservoir is negligible.

> The whole point of Australia's storage plans is to even out solar energy's daily output.

...which it can do by curtailing or releasing the dispatchable energy in tumut 2 if tumut 3 needs to adjust

also the 'trickle' is an entire watershed, not surface precipitation

In all practical senses, over the time scales for which seasonal storage is required, snowy 2 adds 240-350GWh of load shifting. Your sleight of hand doesn't work I already know where the ball is.

A solar heavy grid mostly depends on cyclic storage, not seasonal storage. The non-cyclical storage potential is acceptable for the kind of storage that isn't needed.

Looping back to my battery analogy. The extra 7 Kwh of non-cyclical storage could come in hand if you needed to use it for an extended period of time if the power goes out. But it's not useful if you need to use it every day. Australia, California, and plenty of other energy markets need cyclical storage that is used every day/night cycle to smooth out the duck curve[1].

If you had clarified that most of Snowy 2's storage capacity is not suitable for cyclical storage from the outset, this whole tangent could have been averted. Cyclical storage is the kind of storage that it's in demand, so it's important not to present non-cyclical storage that has a very limited recharge rate as equivalent to a lithium battery.

1. https://en.wikipedia.org/wiki/Duck_curve

Nice backpedal, blaming other for your not reading or knowing anything about what you are attacking. What part of 2GW, 240-350GWh says diurnal to you, can you not divide?

The part where I'm responding to a commenter talking about a storage system that "turns non-disparchable [sic] power into dispatchable." Cyclical storage could effectively turn solar power into dispatchable power. If you have enough storage to store half the solar energy you generate and release it at night you've effectively turned solar energy into a dispatchable source. Seasonal storage does not do this. So it's pretty clear that this [1] comment is talking about cyclical power.

1. https://news.ycombinator.com/item?id=33636358

The word is diurnal storage, and it provides this for the same 2 GW it provides week long storage for.

It can diurnally cycle around 7% of australia's electricity production, it can provide several days power (about 5) at times when the dams are slightly lower (ie. The only time it is needed) and has the capability to provide a week of power (at the same 7%) if circumstances are not par for the course. It can regenerate any water it needs to expel in such a situation in a few weeks using Tumut 2's regular output. Only in conditions of severe drought does its capacity stay down at the 240GWh range.

Anyone with the ability to use arithmetic and basic logic can infer this from the diagram you linked.

Also there is plenty of precedent for something called a battery where using the full nameplate capacity has a high cost and is not easily reversible. It's called a lead acid battery and was one of the most common chemistries for the better part of a century

> It can regenerate any water it needs to expel in such a situation in a few weeks using Tumut 2's regular output.

But it regenerates this very slowly. It'd take over a month to recharge. Again, you can't compare a pumped storage reservoir with a precipitation-based reservoir (aka a dam). With the former you put energy in and energy is stored. With the latter you just have to wait for the rains to fall. This is not useful for cyclical, or as you insist we word it, diurnal storage. Anyone with a solid grasp of logic can see that, too.

> Also there is plenty of precedent for something called a battery where using the full nameplate capacity has a high cost and is not easily reversible. It's called a lead acid battery and was one of the most common chemistries for the better part of a century

Lead acid batteries only last ~300 cycles so you'd have to replace them every year if used for cyclical storage. This is why lithium based battery chemistries are used.

> But it regenerates this very slowly. It'd take over a month to recharge. Again, you can't compare a pumped storage reservoir with a precipitation-based reservoir (aka a dam). With the former you put energy in and energy is stored. With the latter you just have to wait for the rains to fall. This is not useful for cyclical, or as you insist we word it, diurnal storage. Anyone with a solid grasp of logic can see that, too.

The refill comes from tumut 2. And again, it's a 2GW storage that provides diurnal, five day, and seasonal. Do try to comprehend basic concepts like 'water that goes through a dam goes to the lower reservoir'.

> Lead acid batteries only last ~300 cycles so you'd have to replace them every year if used for cyclical storage. This is why lithium based battery chemistries are used.

This doesn't matter. It's called a battery and you can't typically use nameplate capacity. It's exactly the thing you keep acting outraged about. It's also probably the thing most associated with the word battery other than single use cells.

> The refill comes from tumut 2. And again, it's a 2GW storage that provides diurnal, five day, and seasonal. Do try to comprehend basic concepts like 'water that goes through a dam goes to the lower reservoir'

And for the fourth time, this water is from precipitation. You can't supply electricity to it and pump more water. It's not storage in the sense that you can supply it with a GWh of electricity and later tap the energy you put into it. You're literally saying every single dam is a "pumped storage" facility even if there's no way to pump water into the upper reservoir. Do try to comprehend the difference between pumped storage and a dam.

> This doesn't matter. It's called a battery and you can't typically use nameplate capacity. It's exactly the thing you keep acting outraged about. It's also probably the thing most associated with the word battery other than single use cells.

If you're not running them at full depth of discharge then you're cutting down your usable storage capacity. If you're running 1 GWh of batteries but you're only going to 50% depth of discharge to extend longevity then you've really only provisioned 500 MWh of storage.

> If you're not running them at full depth of discharge then you're cutting down your usable storage capacity. If you're running 1 GWh of batteries but you're only going to 50% depth of discharge to extend longevity then you've really only provisioned 500 MWh of storage.

But they're sold and advertised based on the emount of energy they can dispense when full. Once you use that much energy you can never store that much again. And everyone is fine with this. Snowy 2 is less limited than this.

> And for the fourth time, this water is from precipitation. You can't supply electricity to it and pump more water. It's not storage in the sense that you can supply it with a GWh of electricity and later tap the energy you put into it. You're literally saying every single dam is a "pumped storage" facility even if there's no way to pump water into the upper reservoir. Do try to comprehend the difference between pumped storage and a dam.

Every single dam is storage. It's why so many were built in the nuclear boom. The 40GWh can be cycled any time, the 240GW can be cycled at any point it is needed in any real scenario (ie. When water levels are not at max and tumut 3 is also using its storage in the same direction). The rest is recharged by curtailing normal hydroelectric flow later (by putting renewable energy into the grid) on seasonal timescales. The system needs to dispense a certain amount of water anyway so the full 350 is available cosistently on a seasonal basis. You may have a point if you were asserting calling it 350 rather than 240 was a bit misleading without further context and caveats (ie. Only once or twice a year and only for that 'week long renewable drought' so beloved of stans of generation technologies that go offline for weeks unexpectedly like coal), but you weren't. Instead you were yelling that it was 40.

Ergo bad faith.

> But they're sold and advertised based on the emount [sic] of energy they can dispense when full.

Right, but renewables need storage that we can charge and discharge daily, not seasonal storage. We're back to the 10 KWh battery that can only be charged to 3 kwh on demand.

> Every single dam is storage. It's why so many were built in the nuclear boom.

Renewable growth predated the nuclear boom by a long margin: concrete and effective turbines made possible bid advances in hydropower around the 1930s and 1940s. This is when the Hoover dam, the Coulee dam, and most of the other big hydro power plants were built. The nuclear boom was in the 1960s and 70s.

> The 40GWh can be cycled any time

And again, this is the main form of storage we need to flatten out the duck curve.

> the 240GW can be cycled at any point it is needed

Yes, but then it takes a long time to refill. This is useful for seasonal storage, as you point out, but again flattening the daily fluctuation is what's really necessary. The bigger value is for the use case that's not in as much demand.

The point of storage is that you can capture the surplus energy of renewables. The idea is that if my grid consumes 100 GW of electricity and I produce 150 GW during the day I can capture that extra 50 GW. Dams can't do this. Yes, you can reduce a dam's production when renewables are at peak generation and let water levels rise. But that's not really storage. What happens when the renewables produce so much energy that it's saturating demand? You can't capture that surplus energy with just a dam, you need a bidirectional connection.

Pointing out that you're sidestepping the fact that only a much smaller portion of storage capacity can by cycled daily like a lithium battery is not at all bad faith.

> Right, but renewables need storage that we can charge and discharge daily, not seasonal storage

...which it can do for the full 2GW rated power without discharging water.

Every time load shifting or diurnal storage is mentioned, there are cries of 'but what abuurt the 3 day energy drought you need four days'

Now when presented with a system that is designed precisely for this use case you start whining.

Make up your mind.

> What happens when the renewables produce so much energy that it's saturating demand? You can't capture that surplus energy with just a dam, you need a bidirectional connection.

In addition to this you can use Tumut 2 as your output, then when there is surplus energy store it via snowy 2. This will take a few weeks, but it is a way to fill the entire 350GWh with curtailed renewable energy if that is what you really want. Some water is lost in a full emptying or when changing from diurnal capability to 5 day capability, but some water must go downstream anyway or blowering cannot work. The full 7 days can be cycled a few times a year, which is what it was built for.

Even without that, you've absorbed 2GW with your hydro curtailment and your 2GW storage facility is storing 2GW for a week exactly as advertised. Focusing on a technicality that doesn't come up is bad faith. You can't cycle 350GWh with 2GW in a day. Can you not divide?

> Every time load shifting or diurnal storage is mentioned, there are cries of 'but what abuurt the 3 day energy drought you need four days' Now when presented with a system that is designed precisely for this use case you start whining. Make up your mind.

You were the first one to bring up seasonal storage here [1]. Nobody was ever talking about seasonal storage until you brought it up. "but what abuurt the 3 day energy drought you need four days" this is all you talking, bud.

> In addition to this you can use Tumut 2 as your output, then when there is surplus energy store it via snowy 2. This will take a few weeks, but it is a way to fill the entire 350GWh with curtailed renewable energy if that is what you really want.

But it's not what we really want. What we really want is to capture the excess production of intermittent sources. Saying a dam is energy storage is like saying natural gas plants are energy storage. You can curtail their output when renewables are in production, sure: If you have 100 GW of demand and 50 GW of solar production during the day you can run your natural gas plants at 50 GW during the day and 100 GW at night. But what happens when solar grows to 200 GW? The objective is to use 100 GW and store 100 GW during the day and tap into the stored energy at night. Dams and natural gas don't let you do that.

1. https://news.ycombinator.com/item?id=33648855

> Nobody was ever talking about seasonal storage until you brought it up

It says 2000MW on the document you linked. It's not anyone else's fault if you can't be bothered comparing the numbers 2, 24 and 350.

> But it's not what we really want. What we really want is to capture the excess production of intermittent sources.

Think it through for even half a second. If Tumut 2 is operating at average, then the water it ejects over the course of days or weeks can be stored at any rate up to and including 2GW. In all practical scenarios (which do not include a week straight with nothing but draw followed by a week straight of nothing but charging) what you describe is exactly what snowy 2 does. In situations where the entire system doesn't need to produce net energy, diurnal draw cycles can feed water into Talbingo, and diurnal charge cycles can feed that water into Tantangara (and tantangara s higher so it can be a small jet energy draw). The water needs to be released anyway (but not in any particular week) for irrigation and to keep the river healthy so where is the problem?

If you lack the imagination or ability to apply logic necessary to see how three parts can fit together that's not on anyone else for not spoon feeding you the obvious conclusions available from the sources you cited.

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