I put a 750 watt “Golden” brand “brushless hub motor front wheel that I purchased through ebay on a “comfort” bike. The advantages over an off the shelf bike is that it used a motorcycle style accelerator grip and would do about 25mph on the flat without pedaling. I am not sure but I believe that most electric bikes that you can purchase are limited to about 15mph. It cost much less than an off the shelf bike.
I still have an electric scooter with a geared hub motor that has brushes. The scooter has a lower wattage motor but has much more torque than the bicycle did.
The controller for the brushless hub motor creates a rotating magnetic field that drags a bunch of permanent magnets mounted in the hub around with it. Unlike a motorcycle or car if you give it full throttle it actually does not give you as much torque and acceleration as when you advance the throttle so that the magnetic field is rotating just slightly faster than you are traveling. It takes a little getting used to. But the motors are efficient, and have a good top speed.
I am one of these people who take almost everything apart and the brushless motor is a simpler design than the geared hub motors. All it has in it are bearings stationary coils and rotating permanent magnets. I appreciate greatly the simplicity of the device. They can also be easily used as generators and controllers are available that use the hub motors for regenerative braking.
One has to be a little skeptical of the specifications on eBay, but you can still put together a bike that is much faster and more powerful than one you can buy, and cheaper also. It I not very difficult and complete kits are available. I would encourage you to put something together yourself... depending on how mechanically inclined you are.
Looking at the Golden Motors website, I can see that the motors looked refined since I purchased the kit that I installed. The hub motor kit that I purchased was a good quality item. If you look toward the bottom at the ebike DIY section you will see that they have an incredible amount of options for a reasonable price.
I don't know about the lunacycle kits you linked to. A hub motor based kit is much easier to install can be found to fit almost any bicycle. I also have put together a gasoline power bicycle which is what the lunacycle kits remind me of. It was more difficult to put together, and I had to find just the right bicycle to put it in. They simply will not work in any bike. But it was a kick in the pants. Mine was an 80cc two stroke bolted to inside of the frame and it was amazing to have impressive power on what was a basically a motorcycle that weighed only about 70 pounds. It had very little torque when starting out, but it would do about 40mph and when you hit the “power band” it was almost scary.
They used to have a bunch of forums devoted to both electric and gasoline powered bikes. There are lots of pictures and people willing to share what they have learned.
States vary on the max motor for an ebike (750W or 1,000W), but the max street speed is widely 20 mph.
With an LCD display, it is common that you can very easily reprogram the controller for “off-road” use - typically producing 24-28 mph (just change one setting). Almost nowhere in the States are speed limits enforced on ebikes like that operating on the street.
I have weak experience mechanically, but it was always something that I would have liked to get better at - because my father valued it, and had me tag along when he fixed things.
You point out that these simple electric motors have some advantages in efficiency and reliability (and almost no maintenance), but the gasoline engines pack the big punch (energy density in the fuel, total horsepower). As the batteries get better, electric will be competitive in more niches.
You might get around some of the recharging issues with electric vehicles, by using modular powerpacks that can be swapped out in a minute for a fully charged one. They are still not competitive with gasoline engines for range or cost though.
Battery technology is the long pole in the tent for electric vehicles - and they would change the equation for solar power systems as well. Many new battery technologies are coming out of the labs now, with a variety of improvements.
Graphene batteries will be a big jump in performance, and they are just starting to hit the market. They can make it possible for electric cars to have 500 mile ranges before recharging, and to recharge in minutes rather than hours. Also, you can get five times the power per pound of battery. They will be working their way into products over the next few years, but starting now.
Graphene cells for laptops have been unveiled this May. They will soon be bundled for ebikes (lots of current ebike batteries are bundles of standard laptop 18650 size LI-ion cells). I am actually planning to hold off until next summer to get a back up battery for my ebike, hoping for graphene options by then.
Lots of other new battery technologies have been demonstrated, that will be providing big cost/function improvements over the next 5-10 years.