Let's ignore the electrical power it provides for gadgets and connectivity as well as the extra weight it adds, and focus instead on the basic "energy harvest/ride boost" functions. I am sure the design is quite clever and ingenious from an engineering perspective, but I fear it has that "something for (almost) nothing" veneer, which is very misleading and actually counterproductive. Why?
First, the amount of power you can recover via regenerative braking from a bicycle is quite modest. The kinetic energy (energy of motion) of a bicycle is fairly low (remember, KE = ½ mv2); and most of the energy you put into moving a bike is actually lost due to air resistance. Therefore, it can't be recovered when braking, since it has been dissipated in frictional loss with the air (and some more is dissipated via the bike's mechanical losses, which are quite small). Aggravating the unrecoverable drag-loss factor, keep in mind that the air resistance loss goes up with the square of velocity.
Second, even if there was reasonable amount of energy of motion available, any half-way decent cyclist doesn't use the brakes very often; again, there will be little opportunity to get it back via regeneration.
Finally, it is a very inefficient use of input energy. Either you'll have to pedal harder to maintain your target speed, while your "excess" goes to charge the battery; or you'll have to ride more slowly while the difference goes to the battery.
But what you are really doing is using grown and digested food–eaten by a person and converted to muscle power–to generate electricity. That's a very inefficient process when you look at the total energy chain from growing and transporting the food, to converting muscle power to electrical power.
Wait a minute: wasn't a major advance and marker of modern civilization that we transformed "work" and motive power from being based on muscle effort–both human and animal–to being based on various types of engines? If I read this MIT thing right, we are going back to this inefficient, exhausting way to extract energy and provide power that resulted in a subsistence existence for most people. And we're patting ourselves on the back for doing it, as well. That's progress to be lauded? I don't think so. Or is Fred Flintstone's "car" their next planned advance?♦
Bill's review sounds right.
Perhaps if the electricity generated is enough for the bike's headlight (as in the good old times)the bike will be "green" enough.
And most of all - if one bikes now and then instead of driving would make the biggest difference. Even riding the most basic bike.
Biking in the rain in Vancouver
Of course there is one seemingly limitless source of energy not discussed - all the calories stored in people's fat!
So while the energy model is very inefficient, it is at the same time very plentiful.
Most of the US would greatly benefit from going back to some "old" ways.
EE and Cat3 bike racer
The fact is that Bill Schweber is exactly right. When traveling on my bike I seldom brake, and usually don't brake to a stop when I do brake. The really big question is just how much effort does this system add. One more concern is that I see no other brake system on the bike, so that alone makes it TOTALLY FOOLISH to even consider taking it into a city traffic environment. I am fearless, but not stupid, OK?
Sorry-- there is an error by a factor of 2 in the energy and power in my previous post. (Yes, I forgot to divide by 2 in K=(mv^2)/2. It's funny how you notice these things 100 ms after you click SUBMIT.)
The energy is 1 kJ, the power 0.67 W. However, the conclusion is essentially unchanged.
Some of us are old enough to remember when all street bikes had "dynamos" to power the nightime lights by extracting power from the wheel. We well knew that this was not free energy (except perhaps when coasting downhill), but came from our legs. However, a generation ago supplying the extra 2 W by pedalling was considered far easier than dealing with replacing or recharging a battery. (In those days, the intent of bike lights was very different than the $500, 400+ lumen sport lights being promoted today.) I believe the real intent of the MIT device is to provide the same conveneince for the bike-mounted electronics, by eliminating the need to maintain batteries.
I'm a bit disappointed in Bill Schweber's statement that the kinetic energy of a bike is low, as he gives an eqwuation, but doesn't run the numbers. Since he gives the formula, let's do the calculation. I'll use the mks unit system. I'm a good-sized guy; together with a lightweight bike, I have a mass of about 100 kg. A road speed of 10 MPH is 4.47 m/s in mks units. Plugging in the numbers, we find the kinetic energy is some 2 kJ, hardly a small amount of energy.
The device appears to be intended for cyclists in urban/suburban environments, where some use of the brakes is inevitable, not for open-road racers, who avoid braking. Let's conservatively say that every 5 minutes (300 seconds) I extract just 20% of this energy in partial braking. Each time I brake, I will extract 0.2 x 2kJ = 400J. If I do this every 300 seconds, the power available is 1.33 W. For modern electronics, that is a very significant amount of power! In some urban environments, where frequent (often panic) deceleration is the norm, a much larger power would be realized.
The 1.3 watts is of course too small to support the original article's claim of a meaningful burst of pedal-assist power when needed. However, in a hilly city (think San Francisco or Seattle) there are large amounts of energy that must be absorbed by braking on the steep downhills. It seems plausable that enough of this could be stored to provide a small but noticable assist on the uphills.
When I looked at the article, it seems that the unit should need about 500-600mW of power (assuming 300mW GPS, 150mW Bluetooth), and not motive power for the bike itself. I doubt that regenerative braking is sufficient to sustain this, so there is probably something in the hub that harvests by oscillation or rotation.
There are two bigger points, however. First, the functions performed are not related to the bike per se, but to the "good citizen" concepts of monitoring air quality and route popularity. The work goes to nebulous gains, verging on government nosing through your activities -- Danes now have a "black box" for bicycles! Second, it was necessary to introduce this in Copenhagen, because the U.S. is not bicycle oriented, highlighting the limited scope of any "green improvement".
Just to voice the question, were our taxes used so MIT could take this to Europe?
There may be no such thing as a free lunch but speaking of human powered vehicles, there was a court case in Ontario (successful I think) allowing bicycle couriers to claim lunch as a business expense!
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