# Storing kinetic energy instead of potential energy - practically possible?

One of the big problems today considering energy is its storage (e.g. batteries are not that efficient, very expensive and polluting). Energy is classically mostly stored as some kind of potential (in a battery, a high-level water tank, ...).

Compare it with the equivalence between a condensator and a coil: a condensator holds a potential energy of $1/2CV^2$ and a coil holds a kinetic energy of $1/2LI^2$. We use batteries to store a voltage as a potential energy, but is there a way to store current (e.g. in a hypothetical superconductor that superconducts at regular temperatures)?

I could imagine one example where kinetic energy is actually "stored", i.e. thermal energy storage (as used e.g. in solar thermal electricity systems). But are there other ways to store kinetic energy, and in particular an electric current? Or is this inherently a less attractive option due to thermodynamics (i.e. due to thermalization the kinetic energy will get useless)?

The question may boil down to: is it inherently physically more attractive to store energy as potential energy, or are we till now just hold back by practical limits (such that in the future we may be able to store kinetic energy in an efficient way)?

*Some context: the reason why I came up with this question is that energy transportation is also a big issue. Energy is of course transported as a kinetic energy (a current through the grid); but if it would be possible to also store it kinetically, less conversion would be needed. Moreover, energy would be stored (in some kind of PEC storage loops) and transported by the electricity grid.*

• If we had room temperature superconductors, then they could be a good storage way. – jinawee Jun 5 '14 at 11:37

Yes, we can store energy as the kinetic energy of a flywheel. The problem is that we can never completely eliminate friction, so our energy leaks away over time.

But then we don't store energy as charge if we want long term storage, because we can never make resistance infinite and our charge gradually leaks away. Batteries store energy as chemical energy, and this is good for long term storage as we can slow chemical reactions to essentially zero.

It is possible to store a current in a superconducting loop, but maintaining the system in a superconducting state requires energy, and as soon as the system makes the transition to non-superconducting the current rapidly decays to heat.

• We have almost frictionless mechanical systems like the solar system. A practical approach to storing and using energy by changing planetary orbits would be interesting. – Fitzgerald Creen Jun 5 '14 at 11:53
• Storing energy in the Solar System seems like a cool idea, but it's going to be a devil of a job wiring it into the grid :-) – John Rennie Jun 5 '14 at 15:20

## protected by Community♦Aug 5 '14 at 0:34

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