Suppose solar energy is the best we can come up with for the foreseeable future, besides nuclear. Storing excess energy might not require a maximum efficiency if the tradeoff was clean storage. Would simply pumping water up hill and then using it to generate electricity on the way back down be feasible?
Incidentally, there was an article in my local paper the other day about such a facility near my hometown, see here (sorry, only German link)
It was originally completed in 1969 to store energy in times of low consumption (at night) and to level high demands for energy (mostly at noon when the people were cooking). But by now, it’s almost solely used for storing energy produced by natural means like wind or solar energy and has immensely grown in importance, just like the other such facilities in Germany. I remember that the article mentioned that it runs with an efficiency of 75 %, so only 25 % of the naturally produced energy is wasted by the process.
Sure, the basic principle is solid. When renewables are producing more power than is required by the grid, there needs to be a way to store and then release this energy.
Pumped storage is not only feasible, it is already a thing (as others have mentioned) and has been in use for over a century.
Other means are being explored as well. and that’s not an exhaustive list.
The big issue is ensuring energy delivery when intermittent renewables don’t work and your storage has been exhausted. That’s why nuclear has to remain on the table for the time being.
In fact, I bicycled right by this pumped storage facility just a few years ago on a tour. I’m not sure if the utility owned lookout spot is meant for observing lake Michigan or observing the stored energy operation, but it gave great views of both.
Banks Lake has been used as a power storage reservoir for quite a while.
Now the world holds seven wonders
That the travellers always tell
Some gardens and some towers,
I guess you know them well
But now the greatest wonder
Is in Uncle Sam’s fair land
It’s the big Columbia River
And the big Grand Coulee Dam
Beyond the pumped-storage, there are all sorts of storage mechanisms proposed.
The 5 Most Promising Long-Duration Storage Technologies Left Standing | Greentech Media
What if we invented a device that used electrochemical reactions to store the energy? We’re probably have to experiment with different metals and chemicals, but I bet we could figure it out
Batteries are great of course, and are already being used widely for grid storage. But right now, they’re only cost effective for short-term use. This will destroy the market for peaker plants (thankfully), but doesn’t solve the problem days/weeks/months. We need cheaper storage for that.
Of course, the cheapest storage is to not need it in the first place. Industry dependent on cheap power can reduce their demand (and output) at times of low production. It’s almost certainly cheaper to just turn off your aluminum smelter when there’s low production, as compared to using expensive storage to keep it running.
Some industries can basically use their output stock as storage. Desalinated water is one. You don’t even need a mountain for that. Just run your desalinator when power is plentiful, and use stored water when it’s not. You can smooth power consumption quite a bit this way.
Some of this will require rethinking of how plants are built. For example, there’s a company looking to create very cheap solar-based hydrogen using electrolysis. The trouble is that existing electrolyzers are very expensive, so it’s capital-inefficient to not run them 100% of the time. But what if they can be made much more cheaply at the expense of power inefficiency? Then, you can run them on very cheap peak solar power, and then turn them off at night. And solar is getting to be very, very cheap.
Grid storage will absolutely play a part, but so will reducing the need in the first place.
We could also store the energy into a second sun (sure somewhat smaller, but that’s ok it only needs to work when the OG sun is unavailable). With enough mirrors we can make this happen.
Eh, they already built one in Knoxville but they turned it into the Wigsphere.
From @wguy123 's link:
That makes no sense whatsoever. Why let water down in one reservoir, just to pump it up in a different reservoir? If you’re going to have hydropower in the mix anyway, then it makes much more sense to just turn off the hydro turbines when generation outstrips demand.
For example, Candlewood Lake in Connecticut was created 97 years ago for this purpose.
The primary use of Banks Lake is to feed the extensive Columbia Basin Project, a huge irrigation network. They have to pump it up high enough to feed all the canals. A secondary benefit is they can generate electricity with it when needed.
I heartily recommend touring Grand Coulee Dam if in the area. I’ve toured quite a few dams, and that is the most interesting of all.
2 min YT video of solar concentrator plant
northern Chile … superheats a couple of tons of salt on top of a tower (which turns into a liquid (the salt, not the tower 
)) … and it remains superheated all night, so you can harvest solar (vapor driven generators) even without sun.
The Washington Post had an article (gift link) the other day on how molten salt or heated sand could be used to store heat, and therefore energy. Excess energy from wind turbines or solar cells is used to heat sand to over a thousand degrees. The heat can be used to warm buildings.
Slightly off topic but I wonder if solar energy panels could be used on open pasture land to provide shade for cattle.
The main problem with mixing solar panels with cattle is that cows tend to use the supports as scratching posts. Since cows weigh 800 lbs or more, you need to make the supports really strong to avoid them being knocked over. But yes, it’s done:
https://www.agproud.com/articles/57002-agrivoltaics-and-grazing-dairy-cattle-under-solar-panels
Agrivoltaics, which is a combination of farming and solar panels, applies to more than just cow pastures:
One twist on pumped storage is the “gravity battery”. In both cases you are simply raising a large mass with excess energy, then, when needed, letting it fall and harvesting that energy.
For indoor climate control, accumulating cooling capacity by freezing water during off-peak times (when electricity is cheaper) is already a thing:
This might not work so well with solar, since peak insolation tends to coincide with peak cooling demand.