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Excuse me if the question is poorly worded or there already is a similar question, I searched but as a physics layman I do not know the proper terminology.

I was watching a Nova story just now and they mentioned that the major problem about renewable energy (solar and wind) is that there is no place to store the energy. Ie on a sunny day what do you do with the extra power generated to compensate for a cloudy day.

They mentioned how batteries are used but this is not an ideal solution for various reasons. I thought in my head could the extra power that is generated be used to pump water to a higher elevation and stored. Once power is needed again the water can be released to power water turbines to create hydro-electric power. (this is what I meant by water differential, if there is a proper term for this please feel free to correct my question.)

Now obviously this is not some brilliant idea or else someone would be doing it, so my question is why is this not practical?

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    $\begingroup$ Something like that en.m.wikipedia.org/wiki/Pumped-storage_hydroelectricity $\endgroup$ – Kalpak Gupta Jan 12 '17 at 2:50
  • $\begingroup$ Oh wow, I was not aware that this was being used. That article mentioned upto 80% of the energy can be stored. I knew this wasnt some brilliant idea of mine but I had no idea so many people did this. I was also interested in the link about pneumatic storage which was the second thing I thought of. Thank you for that link that was a very interesting read! $\endgroup$ – ed.hank Jan 12 '17 at 2:54
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Yes, it can be done and it is done. It is called pumped-storage hydroelectricity.

When there is a surplus in electric energy available (e.g. during the night, when people sleep and factories are not operating) this excess is used to pump water to higher altitudes. The energy stored in this way is then used to buffer during times of high consumption. More details here:

https://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity

It is obviously not available everywhere (there need to be mountains or similar), I assume they are pretty expensive to build and they are stationary, so you have to consider the loss transporting the electric energy to and from the plant. The German Wikipedia has a more detailed article, that lists the total efficiency of the plant at 70% to 80%. This includes the loss pumping the water and the inherent loss of the turbines.

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  • $\begingroup$ I just became aware of this, see my comment to the OP. They mentioned this is the most efficient way or one of the most. I was just curious what percentage efficiency do batteries (lithium or whatever tesla etc. use) and is there possibly a more efficient way than either of those? $\endgroup$ – ed.hank Jan 12 '17 at 2:57
  • $\begingroup$ Off the top of my head, it's slightly less efficient than most battery systems, but it can be very different in scale: it can store much more energy than is practicable with batteries, it can deliver it much faster (hundreds of MW), and despite huge capital costs it's rather cheaper than batteries in terms of £/MWh. $\endgroup$ – Flyto Jan 13 '17 at 8:07
  • $\begingroup$ @SimonW - gotcha! i see what you mean about scale and cost. Thank you very much for your input. $\endgroup$ – ed.hank Jan 13 '17 at 15:32

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