Quote:
Originally Posted by Eratosthenes
can you provide an example of "something" that doesn't store energy?
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No - but that's not my point.
Alex commented that the potential for flywheels
"to run around and do damage had not occurred to me", and I was just making the point that ALL energy storage systems have the potential for destruction if the stored energy is released in an uncontrolled fashion. It's the quantity of stored energy that matters, rather than the mode of storage (although some storage systems are inherently safer / more controllable than others.)
It's probably helpful to think about how much useful energy is stored in a couple of common storage scenarios:
AA NiMH Rechargeable Battery: 2500 mA.hr x 1.2 volts = 11 kJ approx
Typical 12 volt Car Battery: 40 A.hr x 12 volt = 1.7 MJ (or 160 AA batteries)
Tesla Powerwall Mk II (
"can power a two-bedroom home for a full day" according to the publicity material): 14 kW.hr = 50 MJ (equivalent to approx. 4700 AA rechargeable batteries or 30 car batteries)
Typical Car Fuel Tank: 60 litres @ 46.4 MJ/kg ~ 2100 MJ (approx. 200,000 x AA batteries, or 40 fully-charged Tesla Powerwalls - people tend to forget just how much energy we deal with every day when we drive around in our cars!)
Wivenhoe Pumped Storage Hydro Power Station: 2 x 250 MW x 10 hr = 18 TJ (1.6 billion AA batteries, or 350,000 Tesla Powerwalls, or 8,000 full car fuel tanks)
Typical Commercial Flywheel: 2 kW / 6 kW.hr / 100,000 rpm Flywheel UPS, e.g. as used in Telecomms UPS applications: 6 kW.hr = 22 MJ (2000 AA batteries, or 12 car batteries, or a bit less than half a Tesla Powerwall)