If you thought the efficiency data for electric motorcycles was sketchy, you ain’t seen nothing yet.
Best guess, consistently driven at or below 20 MPH, an e-bike might appear to be about ten times more efficient than the best electric car. But even with that, in my situation, it’s not a cost-effective way to avoid carbon emissions.
Note: The artwork in this post is from various free text-to-picture AI sites. So far, the only thing I’m learning about such sites is that you can waste a considerable amount of time on them.
E-bikes, electric power only, call it … 40 miles per KWH.
First, you have to be careful. A lot of folks will cite e-bike electricity consumption, for propulsion via a mix of electricity and muscle power. What I want is an estimate of miles per KWH for electrically-powered transportation only. These are my calculations from various sources:
- 30 miles/KWH (electric only, this reference).
- 50 miles/KWH (electric only, brand new, this reference).
- 20 – 60 miles/KWH, depending (per this reference).
- 67 miles/KWH (pedal-assisted, from this reference).
- 87 miles per KWH (pedal-assisted, from this reference).
I don’t think I’m going to pin it down much better than that, for three reasons.
First, there’s no such thing as a standard test cycle for e-bikes. As noted in the just-prior post, without that, you really have no good idea what any stated mileage figure represents.
Second, efficiency is inversely related to air speed. Below, you can see that moving a bicycle at 10 MPH required about one-third the energy of moving it at 20 MPH. (I believe the graph below is a theoretical estimate of power required at the drive wheel, and so does not include various losses such as losses incurred in charging and discharging the battery, losses within the motor and motor controller, and losses within the rest of the bicycle drive train).
Source: Adapted from Electric Bikes: Survey and Energy Efficiency Analysis EFFICIENCY VERMONT, DSS TECH DEMO REPORT: 000-053, Tom McCarran, Nicole Carpenter, Efficiency Vermont, March 8, 2018
Third, most claims of e-bike efficiency that are well in excess of 40 miles per KWH are based on a mix of electrical and human power. People who cite such numbers appear to believe that the human-supplied energy is free, or at least free of fossil fuel inputs. But that’s nonsense. If I fuel my bicycle by eating the standard American diet, I get about 63 MPGe. That’s nowhere near as good as a Prius Prime running in electric mode. See Post #1785, My car gets better mileage than my bicycle.
If I had to pick a number, to represent ebike efficiency, without aid of human muscles, I’d pick somewhere around 40 miles per KWH. Or about ten times as far as a KWH will take you in an efficient EV.
Two caveats.
First, the bike-versus-car comparison is not an apples-to-apples comparison. The figure for the car is the EPA drive cycle, a mix of city and highway driving. The figure for the bike is (presumably) some course with an average speed below 20 MPH or so.
That said, for reasons that I don’t quite fathom, it looks like you get only modest efficiency gains from driving an EV very slowly. Based on this one analysis (below), it looks like driving at 15 MPH is only about one-third more efficient than driving at 50 MPH.
Source: Geotab.
Second, e-bike batteries don’t last very long. Near as I can tell, you should expect a useful life similar to batteries for electric lawn mowers — three to five years. And, likely, for mostly the same reason, that “normal” treatment of the battery, in this use, amounts to life-shortening abuse. Charging to 100%, discharging to zero, high current draws, temperature extremes, rapid re-charging. These are all normal for an e-bike battery, and they can drastically shorten lithium-ion battery life.
This matters not just for the average cost per mile, but, as discussed in Post #1776, on electric lawn mowers, a) there is no good solution to recycling lithium-ion batteries in the U.S. as of yet, and b) those batteries embody considerable energy in their manufacture. I doubt you could trash them fast enough to turn e-biking into a net environmental negative, but the short expected battery life detracts from the overall environmental picture.
That said, an e-bike is still just a bicycle.
I bike a lot, and I am acutely aware of the drawbacks. Aside from limited capability to carry loads, and not being useful in all weather, bikes have some significant advantages and drawbacks as a form of suburban transport.
Safety: By my calculation, bicycling on an urban road network is every bit as dangerous as it looks, as you pass bicyclists in the road (see Post #1853). It’s hard to arrive at good statistics on this, because you have to combine accident statistics from one source, with “estimated annual miles” from other sources. The last time I looked at it, my best guess was that it’s more than 10 times riskier than driving a car, in terms of deaths per 100,000 miles.
Health benefits: The overall risk from bicycling has to factor in the benefits of the exercise. As a fat guy (who thus has a hard time finding feasible ways to get intense cardio exercise), reduction in all-causes mortality from the the exercise of bicycling exceeds the likelihood of being smashed flat by a passing F150. (Again, by my rough calculation). In other words, on net, bicycling reduces my risk of dying.
How much that health benefit would degrade, if I switched from a standard bike to an e-bike, I couldn’t say. All I know for sure is that an e-bike gives me all the risk of bicycling, with (plausibly) less health benefit.
Trails and sidewalks are at your disposal. Out here in the ‘burbs, nobody walks anywhere. Or close to it. And, under Virginia law, as an adult, I may ride on the sidewalk when, in my opinion, it is not safe to ride in the road. The upshot is that the sidewalks — where they exist — form a sort of private, unused road network for bicyclists. I don’t have to care how congested traffic is, because I’m not riding in traffic, I’m riding on the sidewalk or path beside traffic.
But not arterials and interstates. The flip side of that is that sometimes, you just can’t get there from here, on a bicycle. Or the bike-feasible path is so roundabout that it amounts to the same thing. This is particularly true once you get out of the congested suburbs. Frequently, in Virginia, the only route between two rural towns is a two-lane 55 MPH country road with unpaved shoulders. Not exactly suicide-by-bicycle, but close enough for me.
Conclusion: Efficient, but still costly per ton C02 avoided.
I’ve been pondering my transportation options, for something other than than a new car. Maybe an old used car? E-bike? Motorcycle? Scooter? This post was part of that series.
I looked at electric motorcycles in the just-prior post, and concluded that, viewed purely in terms of environmental benefit, I’d be paying more than $9K per ton of C02 emissions avoided. That’s mainly because the device is expensive, has a relatively short service life, and because my existing alternative is already quite efficient.
With an e-bike, I don’t need any more accuracy than I got from this quick review. No matter how you slice it, the energy required to operate an e-bike is trivial. Certainly, at 40 miles per KWH, transportation by e-bike would be below rounding error in my overall annual carbon footprint. At Virginia’s generating mix, 1200 miles on an e-bike would generate the same C02 release as burning one gallon of gasoline.
That said, an e-bike is not an all-purpose vehicle. It would only work for those trips that would fit comfortably with the limits of range, weather, and capacity. And that limited utility has a surprising impact on cost per ton of C02 avoided.
The upshot is that adding an e-bike, to our current transportation fleet, would be an expensive way to avoid C02 emissions. With the (seemingly reasonable) assumptions above, an e-bike would cost about $2700 per ton of C02 emissions avoided. That’s still more than an order-of-magnitude higher than the return to, say, improving insulation in the home.
I think my conclusion is the following: I might consider an e-bike for health reasons, when I can no longer ride a regular bike. I might buy one just to have a brand new shiny toy. But I wouldn’t buy it as an investment in C02 emissions avoidance. For me, there are cheaper ways to avoid C02 emissions.
