PPM technology rests on a simple but effective engineering device: the flywheel. The rotating flywheel is a store of kinetic energy that is used to power the vehicle. A typical PPM flywheel is made from steel laminates, 1m in diameter and 500kg mass, rotating at a maximum speed of 2,500rpm - simple, reliable and easily maintainable.

The flywheel allows the direct capture of brake energy (when slowing down or descending gradients) and its re-use for acceleration. Since the short-term power demand for acceleration is provided by the energy stored in the flywheel, there is no need a large engine or heavy-duty electrical supply along the whole length of the route.

The PPM concept allows maximum variability in the way the flywheel is 'charged':

• For zero emission operation with closely-spaced stops, the flywheel can be charged (in approx. 30 seconds) from an intermittent electrical supply at the stations only. The flywheel stores sufficient energy for the vehicle to reach the next stop in normal operation, and a battery is also provided for emergency use.
• For low-emission, high fuel efficiency and quiet self-powered operation, an on board LPG-fuelled automotive engine is used.
• Alternative possibilities include diesel- or hydrogen-fuelled internal combustion engines, or hydrogen fuel cells, while the intermittent electric version can be powered from solar cells or other renewable sources of electricity.

PPM Technology Allows:

• A two-litre engine to transport fifty passengers.
• Zero-emission street tramways without any electrification.
• Variable vehicle size, boarding height, power source, appearance, interior layout...
• The best environmental performance of any comparable mode of transport (see chart below).

For details of how PPM technology can improve local transport, go to the Community Transport page.

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