[cupofpython]

95% stored energy by what measurement? See my other comment. It is not accessible to everyone, nor can it be made accessible to everyone, and the current storage capacity is a marginal fraction of what we actually use. It's a short term load balancing tool that operates within a small energy window.

[kenhwang]

95%+ by total energy stored/provided.

There's little to no water use in the storage or discharge of pumped hydro, water goes from one reservoir into another. The limiting factor is how much water can be pumped/discharged, not how much water is available in storage (which tends to be significantly more than the amount pumped around). So there's little reason why they wouldn't currently be fully utilized.

It's true that it requires specific geography (water and a place to put water), but it turns out population centers tend to be developed near water sources, already store water for the sake of storing water, and water can feasibly be stored in large quantities underground as well. Which means there's practically many viable large capacity sites near the places that use electricity.

[cupofpython]

the 95% is misleading. it is barely storing or providing energy but it is a passthrough akin to plugging your phone into the charger 24/7 and saying your phone battery is providing 95% of the energy just because the wall outlet charges the battery first then the battery powers the phone (not an exact metaphor). If you unplug your phone and the phone dies 10 minutes later, you wouldnt say your phone has a good energy storage solution.

Pumped storage is great at what it does, no denying that. And what it does is allow energy production to remain near average while demand varies, and consequently allows energy production levels to be adjusted a bit slower. You aren't addressing the raw numbers though. It serves best as a compliment to a continuous energy production system. As an actual battery/storage solution, it is weak. So it will not be the solution used to store a massive amount of energy generated over a short period of time in order to be used over a longer period of time.

I agree they should be fully utilized, but I am trying to explain that if you fully utilize pumped storage you are still going to have an incomplete energy storage problem. Of course the water levels dont get near max or min capacity - it is designed to take out exactly what you put in as soon as possible or else there is too much risk. The raw storage capacity is small to medium sized - about 10 hours at max discharge (and max discharge might not be enough to keep up with demand entirely on its own).

Basically, the more energy you need to draw the faster you need to drain it and the more energy you want to store, the more massive your reservoir needs to be.

These things cannot be made 100 to 1000 times bigger, nor is there capacity to make 100 to 1000 times more of them. We are better off having them vs not having them but it isnt enough, and if we find a better solution it may become obsolete

[kenhwang]

The reservoirs we already have are rated in the thousands of MW. There is no storage problem, we already have large enough reservoirs where we can practically store years of energy indefinitely; especially now in drought conditions where reservoirs are regularly well below historical levels. So if there's ever a need to store solar energy from summer for use in winter, pumped hydro is the only energy storage solution that works.

They also don't have issue with storing energy quickly, they can all store energy at a significantly faster rate than they can discharge. We can run pumps as quickly as possible and install as many as you'd like, but the discharge has to be controlled (thus limited) because releasing massive amounts of water at once. So their main use case today is storing massive amounts of energy generated in a short amount of time and releasing slowly across a long period of time.

What the grid actually needs is faster discharge than charging, because that more accurately matches summer energy use patterns. This is what chemical batteries excel at which pumped hydro cannot easily do.

So it's unlikely we'll be able to make them 100-1000x bigger, but they're already 100-1000x bigger than other battery solutions. We should be able to make 100x more of them because the reservoirs already exist and very few of them currently are used as both power sources and energy storage, we simply need to add pumping capability to them in most cases.

[cupofpython]

Agreed on charge vs discharge comments.

We seem to disagree on the storage numbers. Genuinely curious if my math is wrong on this. I did research a bit more about recent advancements in pumped storage since my first comment and found that my original numbers were almost an order of magnitude smaller than what would likely be built today since I had referenced older tech. So admittedly, pumped storage is much more feasible than my original attitude suggested - which is great because id love for it to be all we need. However, I'm still not sold on it's ability to act as sufficient storage, and I do not see in any way how it could possibly keep things running for multiple days, let alone years of energy as you suggest.

There is a reason we only talk about pumped storage in terms of its discharge rate rather than its storage. We dont really use it for storage. We use it to store the difference between peak and average energy demand, not the total actual demand. You keep the generators running near average all the time, fill the reservoir during the demand valleys and drain the reservoir during demand peaks. Discharge effects ability to actually reach the peak demand, while storage effects how long you can sustain the demand. My point is even if we could discharge as fast as we need to, the reservoirs would empty in less than a day if we needed to rely upon them while energy production was down.

There is a new project (snowy 2.0) in Australia that will have a notable storage capacity of 350,000 MWh .

Current energy usage in the US is over 10 TWh per day. 350,000 MWh = 350 GWh = .35 TWh. So we would need 28 of this brand new top-end pumped hydro stations to hold 1 days worth of US energy demand in reserve. It's ballpark feasible, but lets keep in mind that this plant is costing Australia ~$5-10 billion and is working with two dams that already exist. Very much still in short-term load balancing territory.

This would also lock up 500,000 liters of water per 10kWh. 1 days worth of storage for US: 10TWh / 10kWh = 1 x 10^9; then x 500,000 liters = 5 x 10^14 liters of water = 100 cubic kilometers* (26 trillion gallons). Storing 1 years worth of energy would be 100 km^3 * 365 = 36,500 km^3; which is 3 times the size of Lake Superior (12,000 km^3). I still dont see this as an energy storage solution. MAYBE if use seawater and find a cost-effective way to build facilities into the coastline?

*(1 x 10^12 liter = 1 km^3)

Also to keep in mind that all of this is assuming CURRENT demand, which excludes the incoming energy demand increase for electric vehicle adoption. that's about 2-4 kWh per gallon of gasoline. US uses about 369 million gallons of gasoline on vehicles per day. We can add almost another 1 TWh for that, and then still whatever is necessary for increased usage in general.