There's an island in Spain which uses this model to produce most/all of its electricity

http://euanmearns.com/el-hierro-another-model-for-a-sustaina...

(pump water up with cheap wind energy, use the hydro when needed)

Cool!

The system has three basic components – an 11.5 MW wind farm, a 380,000- cubic-meter upper pumped hydro reservoir in a conveniently-located inactive volcanic crater at 709.5 meters elevation and a lower 150,000-cubic-meter reservoir at 56 meters elevation.

I especially like the inactive volcano part. Technology that tempts the gods.

already exists. It's called pumped storage hydroelectricity: https://en.wikipedia.org/wiki/Pumped-storage_hydroelectricit...

Here's one (built in 1977.. uses power from the grid), and can produce 3000MW (stores 24000MWH): http://thinkprogress.org/climate/2013/08/27/2524501/hydro-pu...

Many of them were built to make nuclear plants more efficient.. nuclear plants turbines are most efficient at full power.. so they would store the water during the night (when demand is low) and then use it the next day to handle peak demand.

So they were also made to start generating electricity quickly.. the one above takes 5-10minutes.. but there are others that respond within a minute. Much faster than starting a oil-fired generator.

These account for the vast majority (90%+) of stored capacity worldwide.

There's no reason they couldn't be used to store solar/wind energy.

There's a couple in Scotland, where I grew up. My school did a tour once. (The tour was uninspired and rather dull. The nuclear reactor tour was way more interesting.)

They're strictly limited as to how much they can store. Ben Cruachan (the one I visited) can generate 440MW for up to 22 hours before the reservoir empties. It's used for emergencies and buffer usage spikes; Ben Cruachan can spin up in two minutes from standby, or thirty seconds if they have some warning, and is used to provide power while the much slower reacting gas or coal plants rev up. I don't know how quickly it can pump water uphill, but it's probably a lot slower than it consumes it. Round-trip efficiency looks to be ~70%.

According to Wikipedia the UK uses about 40GW of electricity at peak, so you'd need a hundred Ben Cruachans to store enough to run the country for under a day.

Here's a picture of the upper reservoir: https://upload.wikimedia.org/wikipedia/commons/6/6d/Cruachan...

See the grey border around the water? Hydro power reservoirs are ecologically pretty bad --- freshwater life isn't equipped to deal with what are basically irregular tides, and so the shorelines are always completely barren.

But there are a limited number of sites that you can convert and whilst China can just have the army move people out at gun point.

This might be a bit controversial in western democracys I cant imagine the SNP being keen on having large numbers of glens flooded

Long but interesting read, with actual numbers and math: http://physics.ucsd.edu/do-the-math/2011/11/pump-up-the-stor...

Some hydroelectric power plants do that, but storage is finite and it's not amazingly efficient.

If you already have a dam, why would a day or two's worth of water be troublesome?