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Comment by Retric | Hacker News Reader

Hydro is 6% of US electricity supply and is already used as built in storage.

Pumped storage is vastly better than batteries. Also the variance between median days and calm days for wind is far less extreme than generally assumed. PV solar also provides power in cloudy weather.

Anyway the US can get to ~99.99% from ~30% oversupply and ~6 hours of grid storage which is vastly less than many people assume.

PS: Cloudy calm days over large areas are fairly rare. Heavy clouds are generally associated with weather and increased wind. EX: Hurricane incoming, solar down wind UP.

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California uses more pumped storage than is generally realized. Some of the reservoirs of the California Water Project are uphill from their water source, and thus have large pumps. These can also be run as generators. They pump water uphill at night when power is cheap, and generate power during the daytime peak. This generates some profit for the CWP. The reservoirs and pumps are needed anyway, so there's very little capital cost associated with doing this. Because big Water Project storage reservoirs are involved, the water levels don't change rapidly.

Purpose-built pumped storage plants, such as Helms near Fresno, tend to have much smaller reservoirs, about enough for a daily cycle, and they go from full to empty and back each day. This annoys some people. They're not recreational lakes. Efficiency is 60% - 80% round trip from electricity in to electricity out.

"Also the variance between median days and calm days for wind is far less extreme than generally assumed."

Actually, the variance is worse than assumed by enthusiasts. Here's today's output from wind, hour by hour, for the entire CAISO area, which is about 400 miles across and covers most of California.[1] Today was a bad day; about 10x variation between peak wind and minimum wind. 5:1 is typical; a good day is 2:1.

You can also see similar data for PJM, which covers the Northeastern US.[2] Today's wind variation is about 2:1.

There's a myth that, with enough transmission distance, fluctuations in wind will average out. The two largest power grids in the US aren't seeing that. Maybe for the whole planet, but not for any area one can reasonably interconnect.

[1] http://content.caiso.com/green/renewrpt/DailyRenewablesWatch... [2] https://dataviewer.pjm.com/dataviewer/pages/public/windpower...

At grid scale Peaks are unimportant, it's median and minimum numbers that matter. The grid needs to meet demand anything past that point is useless. Remember wind and solar don't use fuel they just need infrastructure. Hydro does use 'fuel' but can act as defacto storage by ramping up when there is a gap between supply and demand.

Also of note you can smooth out or shift solar by shifting power east-west without involving storage.

You could create much larger power grids, that smooth out these fluctuations, even if they don't eliminate them entirely.

Fairly sure you are citing this article:http://www.sciencedirect.com/science/article/pii/S0378775312...

And the actual numbers are considerably less optimistic than you report, and that paper was rather optimistic to begin with.

But I agree with the gist of it: storage worries are quite a bit overrated,and oversupply and transmission capacities are underrated. We can fix those easily enough, though

No, one of the major assumptions was existing hydro got converted to peaking power plants. A reasonable assumption that takes little land or capital and would payback if there where significant day to day demand and a regular oversupply of power. The other major assumption is significantly increased energy transmission which circles back into demand as transmission losses add up.

> Pumped storage is vastly better than batteries

Yes, except for those who live next to the reservoir (or actually, in the would-be reservoir). That could be people, or nature.

Raising or lowering two existing lakes by a few feet can provide lot's of pumped storage with minimal issues.

Or in the extreme case, consider Lake Erie is next to Lake Ontario. Pumping extra water back up for a few hours a day would have minimal issues as boat bilge water has already cross contaminated them.

Almost 700,000 gallons of water go untapped over Niagara Falls every second. There's no point in pumping water back up until you've harnessed that first.

They also do hydro so Niagara Falls is effectively just a large and expensive fountain with controlled discharge. As long as pumping up does not increase the rate of Niagra Falls the area works just fine as pumped storage.

PS: The water feature is even down for matinee. http://www.refinery29.com/2016/02/102431/new-york-niagara-fa...

> As long as pumping up does not increase the rate of Niagra Falls

But isn't that what it does? Unless you start to limit (more than before) the waterflow to the falls themselves, which probably would meet resistance from conservationists.

(I understand the Lewiston power plant already does have capability to pump water up.)

And, many places don't have such reservoir capacity at hand. Over here any new reservoir project meets fierece resistance, and it's rather the other way round: nature conservationists want to shut down existing hydroelectric capacity.

https://en.wikipedia.org/wiki/Robert_Moses_Niagara_Power_Pla... is just one of several hydro power projects in the area.

It's complex there are few environmental effects from blocking the falls as they are already one way and tend to kill fish that make the trip. However, there is a treaty that set's minimum flow levels and more water is diverted at night to a holding area which is then used for hydro in the day.

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

Anyway, the area already has plenty of pumped storage it's only by importing a lot of power that you would need to expand. But, at that point you can scale really far with few environmental costs.

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