power-assisted cycles: A bicycle or tricycle which has an additional power source other than human power. This is normally achieved by the installation of a small petrol engine or electric motor. The electric motor obtains its power from on-board batteries and/or a photo-voltaic (PV) solar panel.
The pedelec specification under European Union law
Electrically-assisted cycles are usually classified as either pedelecs or e-bikes. Under European Union regulations adopted in the UK in June 2003, only power-assisted cycles meeting the pedelec classification are considered to be pedal cycles; e-bikes are now treated as motorcycles and require a license.
To meet the pedelec specification, motor power output must be inversely related to speed, and the power must cut out completely whenever the rider stops pedalling. Control of the motor by pedalling is often the key difference between a pedelec and and e-bike.
Pedelecs must also have a powered-assisted maximum speed limited to 25 km/h. Earlier UK regulations also require that the motor has an average power output limited to 200 W (250 W for an tricycles and tandems) and weight limited to 40 kg (60 kg for tricycles and tandems).
For models sold before June 2003, e-bikes conforming to the speed, weight and power limits may also be considered pedal cycles.
References
Croydon Cycling Campaign: Electric-Assist Cycles page describes pros and cons, and provides details and references for status under UK and European Union law.