While I'm an advocate of getting out and using your own two feet for transportation as much as possible, sometimes you just want a little more oomph around town. Which is where the old reliable, pedal-powered bicycle comes into play and has served admirably well, and super efficiently, for some time—in many cases the bike is the personal mobility vehicle par excellence. But what if you live in a hilly place or just want a little electric help on your daily two-wheeled commute? What ends up using more energy and what are the resultant carbon emissions, an electric-assist bicycle or electric scooter? A Vehicle for Around Town Trips and Short Commuting
Let's set some parameters: We're talking short range commuting here and comparatively lower speeds, so there's no need for a scooter the size of say, the Vectrix. Nor do you want to spend more for the bicycle than you would for the scooter, so some of the really high end electric bicycles—such as the $9000 Optibike—are out as well.
A top speed of about 30mph and range of 30 miles on a battery charge seems about right. Not too fast and not too far, but faster and farther than is easy to go every day by foot, or the average commuter probably wants to go day in and day out by pedal power alone.
For the sake of comparison then, let's use the Ecobike Elegance model for the electric-assist bike. For the electric scooter, the ZAP Zapino will serve as our benchmark. The Ecobike will set you back about $1600, the Zapino about $3500. While there are plenty of other options out there with better and worse specs, and prices to match, this seems pretty middle of the road.
Which brings us to the bike's batteries themselves and how they perform:
Electric Bicycles: 25 Miles at 20 MPH+
The EcoBike Elegance uses a 36V 10Ah battery which should last in pedal-assist mode for about 25 miles and a top speed of 20mph on its own (though if you pedal faster you can obviously go faster...). The battery system adds about 10 pounds to the weight of the bike, so the final weight comes out out to 52 pounds. In other words, if the battery goes dead you can still ride the bike.
Electric Scooter: 30 Miles at 30 MPH
The ZAP Zapino goes a bit faster and a bit farther on a battery charge than the Elegance: about 30mph and 30 miles per charge of its 60V 38 Ah batteries. There's an upgrade available to extend the range to 65 miles, but we'll leave that aside. The whole bike weighs in at 300 pounds (about 75 pounds heavier than a comparable gasoline-powered scooter like the Vespa S50), so if those batteries die, you better be awfully close to a power outlet.
What About Replacing the Batteries?
In both cases the batteries may need replacing within the useful life of the vehicle, though in neither case for a couple of years of average use; and while disposal and replacement is a factor which would need to be considered in a more detailed comparison of each vehicle, for the sake of this question, they are being left aside. Ditto the charge time for each bike: In both cases you can easily charge them every night from an ordinary household outlet.
What's the Emissions per Mile?
So which comes out ahead in terms of energy needed per mile of riding and what are the resulting carbon emissions? Without going into the calculations of each, this is how I looked at it: How much energy can each battery store, divided by how far can that battery take you, multiplied by the amount of emissions generated to charge the battery.
Where things get complicated is in determining the emissions. If you use a renewable energy source then you have essentially zero emissions in either case, though the amount of energy required does vary. But as we are far from having renewable energy predominate in the United States, I used a national average of 1.34 pounds of CO2 per kWh of electricity. Your state's electric mix may vary on either side of that, primarily depending on how much coal versus hydro or nuclear power your state uses.
Electric Bike Beats Electric Scooter on Emissions, Easily
When all the conversions are completed, from amp hours to kilowatt-hours, divided by average distance travelled per charge, and converted into pounds of CO2 using that average figure, the Ecobike Elagance emits about 0.02 pounds of CO2 per mile travelled; and the ZAP Zapfino emits 0.10 pounds of CO2 per mile. For sake of comparison with a gasoline-powered scooter, again the Vespa S50 (which gets a bit under 90 miles per gallon and can go about 200 miles per tank of fuel, pretty darn good really...), it emits about 0.25 pounds of CO2 per mile travelled.
Though in both cases the emissions created by charging the battery in the electric-assist bike and scooter are much better than the gasoline scooter—and either is a greener option based on emissions alone—all in all the electric-assist bike seems the best bargain. You can't go quite as fast or as far as the electric scooter under power, but it is much more energy efficient, and if that power runs out you can still keep peddling along.
Less Embedded Energy in Bicycle Than Scooter, Too
Though I didn't figure it directly into this comparison, according to calculations done by WattzOn, the bicycle comes out pretty far ahead of the scooter in terms of embedded energy. It takes about 1.5 times more energy to make the materials for a scooter, assemble them, and then dispose of them at the end of 10 years than it does to make a bicycle. So the bicycle beats the electric scooter here as well.
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