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Utility-scale power storage can use other technologies, such as pumped-storage hydroelectric generation. Basically they pump water uphill as a means of storing energy.


Pumped storage is not realistic. It’s a cute nice to have on the side but cannot ever possibly scale enough to meet even double digit percentage of our need. To be quick about it let’s take some data from [1].

Hydroelectric power generates 6.1% of all US power today. All those huge dams you see everywhere with their giant lakes you can see from space that did massive destruction to ecosystems across this country? Those generate a measly 6.1%. (Blows my mind I didn’t even know it was that low.)

Even if you turned every hydro dam in the US today into a pumped storage facility it would be barely a curiosity on our energy needs.

And you sure as heck aren’t going to 10-fold increase the number and size of dams and lakes we have in this country. Nobody will stand for that.

We all seem to keep doing these wishful mental gymnastics to try avoid nuclear power, but the numbers just never add up.

1. https://en.m.wikipedia.org/wiki/Hydroelectric_power_in_the_U...

What you're not taking into account is that hydroelectric power production facilities are currently sized only for the gravity-driven amount of water that reaches their reservoirs. Without making the reservoirs any larger, or adding any additional dams, you can simply add lots more turbines and pumps to the existing reservoirs and get a lot more power production out of them.

Consider that the vast majority of the pumping would be to even out the daily power cycle (the "duck curve"), whereas reservoirs are sized to hold years' worth of water. The amount of water pumped back uphill during the peak solar output of the day would be a negligible amount of water to the overall reservoir, and then you'd run it down through additional turbines in the evening to produce power.

Following up on this, here's some math.

As you may know, Lake Mead (the reservoir for the Hoover Dam) is currently running very low owing to various water shortage issues. If you've flown into Las Vegas recently this is very obvious. It's currently at only about 40% of its capacity, which is a shortage of about 210^13 L. The Hoover Dam's hydraulic head is 180m at peak height, but let's call it an average of 160m for our purposes below. Using the equations here: https://www.engineeringtoolbox.com/hydropower-d_1359.html

For the total amount of energy available if we were to use solar to pump the reservoir up to full during each day and then generate power at night:

PE = (1 kg/L) (210^13 L) (9.81 m/s^2) * (160m) = 3.14 * 10^16 J = 8.72 * 10^12 watt-hours (this should be knocked down a little bit for efficiency losses; cursory Googling shows that turbines are roughly 90% efficient at turning PE into electricity). Contrast this figure with the annual total electrical usage of the entire US of 4 * 10^15 watt-hours. Divide by 365 and you get 1.1 * 10^13 watt-hours.

So, if you fully pumped just Lake Mead up to its full capacity and then ran it back down its current level each day, you could store most of the energy used by the entire country in a day. Just in that one reservoir. Obviously you'd need to add a lot more pumps and turbines to do so, like orders of magnitude more, but the point is that you wouldn't actually need any additional land to do so. If you're willing to fill up and then empty Lake Mead each day, you can easily do more than the power requirement of the entire country.

So anyway, that's a long way of saying, yes, pumped storage is entirely realistic. Add in all the additional extra capacity in other existing reservoirs across the US and you can easily store many days' worth of power in reserve, just using pumped water.

That's an awesome thought :) but as you say, now we need to also get a few hundred GW of generating capacity out of the Hoover Dam and then we'd have something. Hoover Dam is about 2GW nameplate capacity IIRC, so if we could now somehow dig out 199 equivalently sized new turbine halls underground around the dam we would have a real tourist attraction. That might look something like 398 Manapuori power stations. We would also need to install however much solar is required to both provide enough renewable power during the day to offset fossil sources, and have excess to pump enough water to store energy in our Extreme Hoover Dam project to power the country during the evening post-solar peak hours and through the night.

Is there a good study that explains how pumped hydro and solar can actually work to make a significant dent in our gas/coal power?

Some more spitballing:

Demand ranges between 400-650GW over a summer day (over 700GW in heat wave). If we look at EIA data for a summer week we see Hydro produces about ~50 GWh at peak, ~21GW at a low point, over a day. And we see fossil sources producing about ~270GW at minimum to ~460GW maximum over a day. Solar producing nothing at night up to 22GW then unfortunately falling away too early to contribute during the peak demand period (see the duck curve).

So the argument for pumped storage here seems to be that we can somehow get that 21GW to 50GWh production up to some meaningful number. Lets assume we can convert every dam in the country into pumped storage (obviously not but let's assume). Now as discussed need to increase the production capacity of hydro a lot. Let's say we can quadruple the generating capacity of every hydro dam in the country and turn them all into pumped storage. 200GW would be meaningful (not a full solution but nearly half way to a solution).

How? Sounds incredibly unlikely to me. Especially given not all dams are well suited to pumped storage anyway. You build new tunnels and pumping systems to get the water from downstream lakes back up. You add three more generating halls for every one, probably buried alongside the dam, how much is that going to cost? A lot. How long is it going to take? A lot longer. We need something that we can production line produce at this point.

Now if we wave a wand and somehow do that though, we could produce a maximum 200GW with our hypothetical hydro/storage set up. But we now also need to build however much solar is also necessary to reach our green 200GW target and pump that water back up during the peak solar period so the hydro can run through the non sunny part of the day giving us some 200GW of continuous Solar+Pumped Hydro base generation. That would have to be somewhere in the vicinity of what? I'm spitballing but maybe like 400GW of solar we need to install? How much do we add on for that cost? So we've quadrupled our dam's generating capacity at some incredible expense and built on top about 13x the amount of solar we currently have installed.

And we still have to keep fossil around to generate 70GW at night and 260GW during the day.

I just don't see how we get pumped hydro beyond anything more than a curiosity at this point. (That doesn't mean I think it shouldn't be pursued where it's feasible and the business case stacks up.)

You seem to know what you are talking about based on your comment history, however this statement needs some backup to be accepted at face value:

> All those huge dams you see everywhere with their giant lakes you can see from space that did massive destruction to ecosystems across this country?

"dams are big" x6

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