From AC HENDERSON
The flywheel energy store in your article on Oxford’s electric buses
seems to be very underrated to only store one kilowatt hour. A spin stressed
hoop of carbon fibre reinforced resin of a density of 2300 kilograms per
cubic metre and tensile strength of 1.5 times 1010 newtons per square metre
could store a maximum kinetic energy of 3.26 times 106 joules per kilogram
(Or 0.905 kilowatt hours per kilogram). This is 226 times more than that
used in the bus.
Even with a safety factor of 10 the energy to run the bus could be stored
in a device whose moving element had a mass of only 22.6 kilograms (comparable
to a heavy duty lead acid battery). With automatic pick-up points, either
overhead at bus stops or from embedded coils underneath in bus lanes, a
bus could operate more or less continuously with no performance penalty
compared with ordinary buses.
A. C. Henderson Braco, Falkirk
