To add some perspective. Riding my 40lb Opafiets @ 13 mph on flat ground requires about 70 watts. My max on my slightly hilly ride to a local café each morning is 92 watts.
During the entire time that I had power meter pedals on it I think my highest output was 190 watts climbing a fairly steep hill.
Even a 50 watt motor would provide 3/4 of my propulsion on flat ground and over half up smaller hills. 100 watts would provide 100% of my power for most of my daily riding and half for the most strenuous hill I climb.
Granted, these aren't road racing levels of power (my max is about 400 watts IIRC) but they are the levels of about 97% of the population and they are my levels for routine transportation or recreational riding (E.G., anything but racing or training).