Clever idea for bulk power storage

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raytaylor

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#2949972 2-Aug-2022 23:12

djtOtago:

I haven't seen any proposals to use solar to refill lake Onslow. Only the uses of excess energy from current energy sources when demand is low.

Which I read as, our current hydro lakes when there is plenty of water and not a lot of demand.

Maybe i need to do some more reading but every other pumped hydro scheme uses cheap electricity to recharge and then sells during a peak when they can sell it at a higher price.

Buy Low, Sell high - at least 20% higher to offset the inefficiencies.

Although in other parts of the world like the UK, they are using constant base loads like nuclear as a source of cheap off-peak supply for recharging.

Any other hydro scheme that wanted to spill water could indeed offer to generate at a super cheap price which the "OnslowCo" could then buy - effectively transferring the water energy via the electricity grid.

Rather than spilling the water down the spillway they would just spill it via their turbines.

The same system could be used to buy excess solar and wind energy for uphill pumping.

Edit: This of course does require water to be available coming down the clutha river for pumping up to lake onslow. I dont know much about the geography of the clutha river but I would hope a small lake is created at the bottom for daily cycling up/down hill while the river in general provides long term filling.

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Scott3

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#2949973 2-Aug-2022 23:39

raytaylor:

Scott3:

Building Onslow is cripplingly expensive, and with climate change we run the risk of say 2 or 3 consecutive dry years, where it would end up empty and useless regardless.

I thought onslow was pumped hydro - that is it absorbs excess solar during the day to pump the water from the lower reservoir to the top reservoir then releases it at night, placing less demand on hydro lakes which only refill from river inflows.

I worked out it would be about 4 months of average residential consumption at 5tw of storage.

So in a dry year I would assume there is more sunlight, so the daily recharge from solar would be fine, but the greater capacity of the lake would provide more long term security.

I don't see us as having much other option than going ahead with the onslow project.

Yes, Pumped hydro.

Absolutely could do some daily cycling, but that is not the reason we would pay $4b to build the project.

5.5 TWh (potentially as high as 12TWh at a higher cost), 1,200MW @ approx NZ$4b.

Enough energy to run flat out for 191 days continuously.

This project is epic. Currently the largest pumped storage capacity in the world is 40GWh, so we are talking about 137 times bigger. (however that one has more generation capacity at 3.6GW)

Lets compare to Horndale power reserve (Tesla Big battery in Victoria).

194 MWh & 150MW. Cost AUD172m (commissioned in 2017, upgraded in 2020)

Enough energy to run for 1.3 hours continuously.

If we just wanted 1,200MW of daily peaking capacity to get us through dinner time, we could just build 8 of the Horndale project, at cira NZ$1.52b, and save cira 2.5b. To boot, we could distribute that capacity around load centers, reducing peak loads on transmission lines etc.

Actually NZ's current hydro does a pretty good job at daily cycling as is, and for a much lower cost than the above could be configured to do more of the same, the big battery would never be viable here. In aussie it's role is largely to keep the lights on if some big bit of gear trips offline, allowing time for slowish start thermal power plants to fire up.

Onslow would largely be about dry years. Any daily cycling, seasonal assistance & additional reserves are largely (very welcome) side effects.

I lifted some graphs from a presentation I found online to show what the project (the presentation used a 8TWh capacity) would do to NZ's storage. Top graph is the current situation, bottom shows the addition of 8TWh more (full) storage.

https://cdn.auckland.ac.nz/assets/business/about/our-research/research-institutes-and-centres/energy-centre/summerschool/2021presentations/day2-m-taylor.pdf

Quite good slides above, well worth a look through.

My take on onslow:

Obscenely expensive. Would require about a $400/tonne carbon price to justify.
Takes a decade to build (plus a few years to fill), so we need to hit the go button at least a decade before we need it.
Probably the only realistic way to get to 100% renewable power. (but man could we save a lot of money if we settled for 98%, and kept Huntley and giant coal pile to bail us 1:25+ year return period dry year events.
Currently we wouldn't have the spare renewable capacity to fill it in a reasonable time, so would need to be paired with massive investment in renewable generation. (which I think we should be doing either way).
Electricity market needs to be completely shaken up, to reflect a goal of near 100% renewable power. (again regardless of on slow)

Scott3

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#2949974 2-Aug-2022 23:58

raytaylor:

Maybe i need to do some more reading but every other pumped hydro scheme uses cheap electricity to recharge and then sells during a peak when they can sell it at a higher price.

Buy Low, Sell high - at least 20% higher to offset the inefficiencies.
...

Onslow would be unlike any other pumped hydro.

As in my other comment, 170x the storage of the current worlds largest (yet only 1/3rd the generation capacity).

Absolutely (when fairly full) it would get cycled daily where market prices allowed a profit (spot price differential greater than efficiency losses in the round trip + the marginal cost of running). Might as well when you have the asset sitting their.

But mostly this about filling it up and keeping it fairly full, so in a dry year event it can run (generating power) for months on end, hence giving us the confidence to decommission all our remaining fossil fuelpower plants (in reality we would probiably keep few peckers to deal with rare events like transmission line failures).

Should note it is pretty rare hydro schemes to spill water when generation capacity is available. Other than rare gaming of the electricity market, the only reason to do that would be if the wholesale power price was near zero. Spillway's are largely to deal with flow in excess of of what can be generated. Either because a reason prevents generation (i.e. transmission line outage), or because the power station is already running flat out. On running flat out, there is a diminishing returns on adding more capacity, at some point the run hours per year will be so low that it is not worth building. Engineers and hydrologists do their best to pick the sweet spot.

mattwnz

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#2949976 3-Aug-2022 00:53

Rikkitic:

Another term for battery, though not entirely synonymous, is accumulator. It doesn't have to be electrical. Anything that accumulates energy qualifies.

From what I understand, hydro dams are like big batteries. I still don't know why we don't have more plans for hydro power here, although maybe we just don't need it yet. It also creates lakes. It isn't much different to a volcano eruption blocking a river and creating a new lake.

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