Hard to build, not a lot of places near cities where this can be done large scale and mainly: you really cant store that much energy there, both getting the water and producing power from it later is not that efficient.
Pumped storage is not a solution except for some specific places in the world.
There are multiple options to store energy from day to night, including pumped storage. The really big challenge is to store energy from summer to winter. When you store energy to use it at night, you only need to store about 12 hours worth of energy consumption, when you store it for winter, you are talking about months of consumption.
It lets you play with combinations of solar, wind, batteries, and hydrogen storage, and optimize for a minimum cost system that can provide "synthetic baseload" for an entire year for a region given high cadence historical climate data.
When I apply that to the US, for example, the storage needed is typically maybe 6 hours of batteries and a week or so of hydrogen. To put that last number in perspective: there is a salt formation in Delta, Utah that could supply enough hydrogen storage capacity to power the entire US for 30 hours.
Storong from summer to winter doesn't sound practical to me. Better just to overprovision generation (and do some strong load shifting away from low-generation periods for non-essential energy use)
It's extremely rare to need to store months of energy at grid scale.
Wind power works really well in winter as well as summer. In many places solar works sufficiently well in winter given the lower consumption levels due to lower air conditioning usage.
Extremely rare != never, though. So it's useful to have a very low capital cost "black swan" backup system. The name of the game here is extremely low capital cost, even at the price of terrible efficiency (which is ok since this system will almost never be running.) Hydrogen stored underground and burned in turbines could do it.
Can you show a single example - anywhere in the world - where this is done at grid scale?
> So it's useful to have a very low capital cost "black swan" backup system. The name of the game here is extremely low capital cost, even at the price of terrible efficiency
I've seen grid scale generators leased as a month-scale solution, so I suppose that counts. That seems more useful than any unproven scheme.
This is true in a lot of places. However, in the places that I am most familiar with, energy consumption is MUCH higher in the winter due to heating . . .
This may be where the international HVDC lines come in (that a sibling comment of yours mentioned), I suppose.
I don't think any country in the north would rely on imported energy for winter survival. I think pretty much every country even in EU counts that critical enough to warrant domestic capacity.
Which is why essentially every country in Europe relies on Russia for gas supplies?
I suspect most of Northern Europe would be happier importing energy from Southern Europe or even North Africa than relying on Russia as they currently do.
There are already some DC lines out there. I remember reading about one run starting in South Africa that runs north and it approached some multiple of the wave length of regular AC which would create too much radition (like an antena does).
It requires a naturally occurring basin to work, so there's not a huge number of suitable locations. The capital cost is huge, it's very disruptive of the land, and up till now very little storage market.
The UK basically has two, Dinorwig and Cruachan, and they're used for managing the demand peaks.
> why pumped storage is actually not going to work, or why we don't have more of it already
(1) Requires a lot of land. (2) It needs a height difference, at the required scale prohibitively expensive to make an artificial one. (3) Requires lots of water.
Something I've heard that's non-obvious is that pumped hydro doesn't work well unless the altitude change happens over a small-ish horizontal distance. It's no good to have a thousand feet of height difference if it happens over a hundred miles. (I'm not sure if this can be mitigated by making the pipes bigger to reduce drag, but I guess there must be a point beyond which it isn't really practical.)
PHES has been underestimated in the past because people looked only at existing waterways. Allowing PHES to be built off rivers radically expands its potential, to be orders of magnitude larger than necessary. There is still some geographical constraint, but transmission helps with that.
Pumped storage is not a solution except for some specific places in the world.