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Comment by colechristensen | Hacker News Reader

You don't need battery storage if you've got hydro.

You need solar. Make hydro the backup, fill reservoirs as your reserve and sell extra energy when they're nearly full.

I can see this makes sense especially for medium term storage. A lot full of batteries is great for the next ten seconds, next ten minutes, even to some extent the next ten hours, but it surely doesn't make much sense to store ten days of electricity that way compared to just keeping the water behind a dam. We know that many of the world's large dams are capturing snow melt or other seasonal flows, running them only when solar or wind can't provide the power you need lets you make more effective use of the same resource.

Except for very short term peaks (less than 15 minutes-ish) it doesn't make any sense at all to use hydro to charge batteries. You've got a dam, you might as well let water through later than incur the losses of a round trip to batteries and back to the grid.

Except that in many cases there's people living downstream doing agriculture using that water for irrigation. There's just this tiny dispute about that in the nile delta between Egypt and Ethiopia

https://en.wikipedia.org/wiki/Grand_Ethiopian_Renaissance_Da...

There are two types of hydro - run of river, and ones with large lake storage. You need the ones with large lake storage, rather that the ones with a lake to build a head.

Pumped hydro storage only holds about 8-12 hours of power. To be economically viable to build you need to cycle it daily.

It uses enormous amounts of land and capital to build, and is ongoingly dangerous in a unique way. If LiFePO4 can do 4 hours at full output already, and be placed anywhere using volume manufacturing to expand, then batteries are straight up better.

Pumped hydro is an expensive dead end.

I'm not talking about pumped hydro.

The you're talking about a geographical limited, extremely finite resource with a substantial ecological footprint.

Yes... countries with extensive existing hydro using less of it by displacing it with solar, ultimately enabling the dismantling of some of the dams.

In NZ we're discussing pumped hydro in Lake Onslow which will provides months of backup for the country

Each way you move the energy costs you 50% in efficiency. Which is why pumped hydro has to have a 4x different in the price of energy in vs energy out to make it economically viable. That's why PG&E almost never uses their pumped storage. Only on days where the mid day price of power is very low does it make sense. And keep in mind that California is the ideal place for pumped storage. I seriously doubt that NZ has a 3x duck curve in its energy demand.

It's nowhere close to 50%. Round-trip (so that's after both ways) efficiency is about 70-80% for a pumped storage scheme. Buy 10MW to pump the water, and get back 7-8MW when you release it. Contrast that with a reality here in the UK where the gas dominated spot price this morning when I woke up was about £180 per MWh, yet yesterday afternoon solar and wind had it down to £25 per MWh, so you could buy 100MWh of energy for £2500 but sell it less than a day later and make 400% on your investment in under 24 hours despite the efficiency loss. Very silly to insist this can't be profitable.

For the cost and expense of building a pumped hydro plant though, you could just deploy batteries which will do the same thing for a much lower capital and management investment and vastly simplified engineering. And a higher round-trip efficiency.

LiFePO4 works to demand shift on a daily cycle just fine and scales better to solar input (where you need much higher power handling so you can charge it on limited sunlight - a pumped hydro system is limited to charging at about half its discharge rate).

I think that's the point about the lake Onslow project - its MASSIVE. So yes, expensive, but months of backup for the whole country would not be cheap even with batteries

It seems a long time ago now since I first proposed the possibility of pumped storage at Lake Onslow. But just confirming - having the equivalent amount of energy (4-5 TWh) in batteries would be impossibly expensive. Also, the batteries would need to be replaced from time to time.

Hey! Thanks for responding to my comment. And welcome to HN!

The 1000 MW installed pump/generating capacity of the proposed Lake Onslow Scheme is not unusual by world standards. However, its energy storage capacity (up to 5 TWh) would appear to make it the world's largest pumped storage scheme by energy storage measure. The unusual ratio between energy storage and installed capacity comes about from New Zealand's special hydro generation situation. Hydro is the dominant mode of power generation but national hydro storage capacity is relatively limited. This makes hydro electricity output vulnerable to extended dry periods. Developed to 5 TWh of storage, the large Lake Onslow Scheme would more that double New Zealand's total hydro storage capacity. The scheme would thus provide dry period insurance as well carrying out the usual short-term pumping and generating operations. It would be an open-cycle system. The lower reservoir is the Clutha River, which is New Zealand's largest river by discharge measure.

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