Here's an idea. Vibrator storage. Like a guitar string. You set it vibrating and that's your storage. (Then you find ways to keep the vibrational energy from

Here's an idea. Vibrator storage. Like a guitar string. You set it vibrating and that's your storage. (Then you find ways to keep the vibrational energy from bleeding off. Vacuum, magnetic bearings...) I'm pretty sure it's a thing. Sortof a linear flywheel.