What's the best way to store mechanical energy?

One way to store mechanical energy is to convert it into potential energy, such as raising a weight. Many grandfather clocks use this method, and it can store energy for an unlimited amount of time. In a similar way, you can store energy in compressed springs. This is much more compact and does not depend on gravity; however, the springs can degrade with time.

A ferromagnetic Bose-Einstein Condensate rotating at near c velocity within a carbon nanotube torus, contained by a strong magnetic field.

[edit, removed by me, as I am just repeating]

Compressed springs store mechanical energy. So do spring motors.

I feed MIlo. He lurks until I am lulled into a sense of false complacency; then he springs. Often he goes from the floor to the kitchen counter to the top of the refrigerator in two connected leaps. Here resting after the second leap. Kinetic energy?

Clockwork and other spring-based mechanisms are best for storing mechanical energy for long periods of time. Flywheels wind down, so you have to use their energy fairly quickly before the waste of friction saps all of the energy out uselessly, but springs hold energy practically indefinitely.

There are lots of creative ways to store energy. You can store compressed gas, for example. Maybe you can even store a vacuum.

There is probably a method involving magnets, where two magnets are held together, and they release energy when they are able to push apart.

There’s a really interesting power storage reservoir in Ludington on Lake Michigan.

They built an elevated lake (2.5 miles by 1 mile, 27 billion gallons!) next to Lake Michigan.

At night when demand is low, electric motors pump water up into the reservoir.

During the day, water falls back through the same motors, and they run backwards to produce electricity.

Consumers Energy – Ludington Pumped Storage

@jaytkay I should have remembered that, I’ve visited one of those lakes before (not in Michigan, but in South Carolina). Basically, they use the excess power from a nuclear power plant to pump water upstream into the lake, and they can drain water from the lake to release extra energy during the day.

Sling shot? 26.72 J of mech. energy Source

Pumped storage works for some electric power generation. That is, pump water into a storage reservoir during times of low demand for the base-load electric power, then allow the stored water to run through turbines during peak demand times to produce more power.

Would the way plant roots transport water be considered a mechanical system? They maintain a salt concentration gradient that increases as you move toward the plant. There are membranes that keep the salt from diffusing, so instead the water diffuses, moving from soil to plant along the roots If the cells in the membranes could be replaced with non-living materials then the salt gradient would be a way of storing mechanical energy..

Correction – the xylem, which carries water in plants, is made up of dead cells.
In most plants, the greater part of the energy for water transport comes from the pull of evaporation from the leaves, but the salt gradient in the roots is usually a part of the overall system.