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Comment by jh | Hacker News Reader

It takes about 1 Mega Joule of energy to bring 2500kg car to a stop from 60 mph. The model s with a 100kwh battery can store 360MJ and weights about 2500kg with passengers.

Is it wrong that I get uncomfortable with the idea of a spinning mass able to charge a model s that fits within the artists rendering of the charging station?

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Yes, because a flywheel is a very efficient device for producing flying shrapnel. It's already storing kinetic energy, it's simply a matter of letting all that kinetic energy loose. Energy storage flywheels have injured people in the past and even led to some flywheel energy storage startups going out of business[0]. However, with proper safety standards we can prevent many disasters. [0]http://www.sandiegouniontribune.com/business/sdut-quantum-en...

Would putting a vertical axis flywheel in a deep basement containment be a good start? Cap with rebar & concrete, or steel like a liquid storage tank - depends on wheel material and failure modes?

By the time you're considering building a concrete bunker, it's clearly better to give up on flywheels and stick with chemical batteries. A bunker will cost a lot more to construct than a few Powerwalls.

Just one Powerwall costs more than the cost of burying an underground gas tank, and you'd need 10 of them to store enough power to charge one Tesla 100 kWh car. That's $35,000 in batteries alone without the cost of installing them. $35,000 is much more than it would cost to put down an underground concrete foundation to drop a flywheel into. House-size basement foundations can cost 1/8th that.

Also consider the relative availability of battery chemicals vs steel and concrete. We already have the infrastructure set up to efficiently produce huge quantities of those building materials.

You probably meant “No [it’s not wrong for you to get uncomfortable], because...”

most gas stations store their volatile energy sources underground anyway, so the same for flywheels would make sense

A full gasoline tank is pretty safe. But not if you place it next to a detonator in the form of a massive, spinning fly-wheel... If nothing else you might vaporizer the gasoline up into an improvised fuel-air explosive... Maybe even superheat the gasoline first (due to high energy, little oxygen).

Not saying it can't be done, just saying setting up a flywheel right next to your volatile chemicals might not be a good idea..

It is odd; if these are targeting rural areas, surely they could just move the flywheels away from the charging station and connect them by cable. Maybe the cost of a cable capable of supporting that current is prohibitive?

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