For a library of ebikes and specs: https://www.electricavenuescooters.com/store/blix-aveny/
Here's one: https://espinbikes.com/product/espin-sport-white/
This one is already towing stuff: http://www.frugalhappy.org/blog/2016/6/20/carfree-experiment-our-new-fleet but its sold out
This link includes laws by country and region (state).
Looks like some places the limit is 700w and some places the limit is a top speed of 20mph on flat ground with a 170lb rider. The 700w limit seems a bit arbitrary, and the top speed limit is no problem in terms of torque because a slow bike with lots of torque is perfect for pulling a bike trailer.
EU 168/2013 regulation prohibits pedal assistance above 25 kph (15.5mph)
"mid-drive" motors offer best torque.
Some "Top Torque Mid-Drive Motors": http://sandiegoflyrides.com/differences-top-mid-drive-electric-bike-motors/
Huge amount of torque at 90Nm and long-ass range on the battery. Under $3000.
Best explanation: https://support.electricscooterparts.com/support/discussions/topics/1000081497
HPC Electric Bicycle Powered by the Sun! High Efficient Solar Panel Powers Electric Bicycle. This shows
a 1000w bike that has the battery taken out, and is powered directly by the sun, AND is towing a lightweight bike camper with someone in it!
Where to buy such a thing: (controller/inverter included with a steady voltage rating of your choice) http://www.hi-powercycles.com/portable-solar-chargers/
Question on that: would these chargers word with any ebike or only with special connectors for their bikes? Cause their ebikes are expensive and go over the "750w" that California and USA Federal declared the legal limit before you need to classify it as a moped or street legal scooter...
How to make an electric bike for under $500! Fast & Cheap eBike tutorial!
Where a Bosch Performance Line Speed motor offers top speed with a heavier motor for commuting, the Yamaha PWseries motor provides a lighter unit that can be fitted with double chainrings to offer more gear options for trail riding. Knowing the differences between the most popular mid-drive motors on the market will help you make a more intelligent decision when choosing your new eBike.