By definition in Australia, an electric bike cannot exceed 250w of rated output, and must be operated by a pedelec system (not a throttle), with a speed limitation of 25km/h. Any bike fitted with more powerful motors cannot be legally ridden on the road. Understand the Victorian law further.
There are 2 different types of motors available to turn your bike into an electric bike. The HUB Motor (in the wheel), and the MID-DRIVE Motor (drives the front chainring). See more information about the different electric bike motors.