[Schroedingersat]

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.

[Manuel_D]

> 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.

[Schroedingersat]

> 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.

[Manuel_D]

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

[Schroedingersat]

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?

[Manuel_D]

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

[Schroedingersat]

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