There is also endless debate about how much you actually get back with regen, some poopooing it at just 1-2%, and other regen proponents touting the 10-20% claims. The fact is both these extremes and everything in between are true. It depends entirely on your riding environment; how hilly is your terrain and how much stop and go you have to endure.
This can be easily seen in the cross-canada ebike stats. Riding from Calgary to Northern Ontario across the Canadian Prairies I rarely hit 1% regen. It's just all flat or rolling hills and pretty much no reason to brake. In fact, it surprised me that I got as much back as I did from just the couple times I would come to a stop for a drink or pit-stop and the likes. Then if you look at the numbers through the mountainous parts of BC I got nearly 18% regen down Manning Park and 12.6% over Roger's Pass.
However, what is missing from these stats and is most relevant to the discussion are the regen figures while riding around inside the cities, since that's where most people do their biking. Here, the numbers are more consistent and ranged from 8% to 14% (which I got from riding around the bike paths in Calgary, moving slow with lots of stopping and short steep hills).
This correlated pretty well with tests in Vancouver before leaving on the trip. In preparation for the VEVA talk I took a mountain bike outfitted with a 500 watt Golden hub motor and a regen motor controller set to a 20A current limit, and then rode it along what I considered a typical stretch of road in Vancouver, straight along Main Street from Terminal Avenue to Marine Drive:http://tinyurl.com/67psys
This route has a total span of just over 7km and has a net elevation gain and drop of 77 meters, or 250 feet, and the start and end point are at almost the exact same altitude. My procedure for riding and using the regen was as follows: I used the regen brake whenever I knew I needed to stop, such as approaching a stop sign or red light, and whenever going downhill steep enough that without the brake I would be coasting over 40 kph. I didn't consciously try to maximize the regen (such as by pedaling while ebraking) but at the same time I didn't engage in the momentum saving practices of a lot of regular cyclists (like cruising through stop signs, or gradually coasting to a an anticipated stop well in advance to save on pedal energy and brake pad wear).
The data was logged at 1 second intervals with a Cycle Analyst, and is plotted for both the north and south trips along with the calculated statistics. The pink line is the speed, blue line is my current draw from the battery (a 36V 8Ah NiCad), and you can see pretty clearly going to negative 10 amps or so before each stop, and then a prolonged region between -5 to -10 amps just at the end of the trip where I was going down a steeper part of the street and had to use the regen to keep the speed at 40 kph.
And similarly, on the return trip from Marine drive to Terminal.
In this case, I had better luck with the intersections and only had to stop for red lights 7 times rather than 10 times, and you can see that the % energy recaptured was slightly less (9.7% vs 11%). So, the analysis here is basically 10% regen on this route. I haven't summarized it in the graphs above, but of that regen energy 56% came from the stopping, while 44% was from governing the speed on the downhill. In both cases I used slightly under 10 Wh/km which is the typical figure we see for ebikes that travel in the 35-40 kph speed range.
So, although this is a just from a single run, you could easily conclude that we'd expect about 5% regen for city riding in mostly flat terrain, 10% regen for city riding with lots of moderate hills, and probably more like 12-14% regen if there are really steep hills.
Having since ridden all around Vancouver many times with the cross-canada regen ebike, it seems I'm almost always pegged somwhere bewteen 8 to 11% regen by the time I complete a return trip, but I probably use the regen more aggressively than I would otherwise use a mechanical brake, so this may skew the results somewhat. I would expect others with lighter bicycles would probably average more in the 6-10% territory here.