Stupid Questions May 2015

Gondolinian

This thread is for asking any questions that might seem obvious, tangential, silly or what-have-you. Don't be shy, everyone has holes in their knowledge, though the fewer and the smaller we can make them, the better.

Please be respectful of other people's admitting ignorance and don't mock them for it, as they're doing a noble thing.

To any future monthly posters of SQ threads, please remember to add the "stupid_questions" tag.

Please be respectful of other people's admitting ignorance and don't mock them for it, as they're doing a noble thing.

To any future monthly posters of SQ threads, please remember to add the "stupid_questions" tag.

Following on from this question, since cheap energy storage is a big obstacle to using wind/wave/solar energy, why is gravity-based energy storage not used more?

Many coasts have some cliffs, where we could build a reservoir on top of the cliff and pump up seawater to store energy. What is the fundamental problem with this? Efficiency of energy conversion when pumping? Cost of building? The space the reservoir would take (or the amount of water it could hold)?

Actually, this scheme is currently employed by utilities, albeit usually not with seawater. The technique is called pumped storage hydro. Pumped storage hydro accounts for the vast majority of grid energy storage world-wide. Pumped storage hydro is used to by power companies to achieve various goals, e.g.:

flatten out load variations (as you suggested elsewhere in this thread)
provide "instant-on" reserve generation for voltage and frequency support
level out the fluctuating output of intermittent energy sources such as wind and solar (as you

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2Douglas_Knight11y

The operating cost for hydro power plants is very low, so the relevant cost is the initial building. If you dam a river, it just takes one wall, while if you want to create a swimming pool, it takes four. Actually, five, and the floor may be the biggest problem. If you dam a river, you already know that it isn't easy for the water to flow through the ground, because it isn't taking that route. Whereas pumping it onto dry ground probably won't work.

2Lumifer11y

Cost. Wind/wave/solar energy is more expensive than fossil-fuel or nuclear energy to start with, and adding not-too-efficient storage mechanisms to even out the supply does not help it at all. Really, the answer to most questions of this kind is "cost". It is the default and usually correct answer.