Many times while riding to The Gambia, we discussed how we’d get back to England. A Citroen 2CV or an electric hub motor with solar panel driving the tandem were the two options most talked about. In the end, we did neither and flew instead.
I’ve recently bought a Heinzmann electric motor retrofit kit for what turned out to be one of my failed projects. However, the motor’s still with me and so is my curiosity. So, what about electric bikes for touring? Are they realistic over distance?
The motor on bikes is normally housed in either the front or rear wheel, but there are variations. The Watt Bott is an electrically assisted trailer whose battery is charged by a 20 watt solar panel. There’s little information to be found on this trailer online, but Kristin Rule, a cellist, tours with one, along with her Yuba Mundo cargo bike.
Cargo bikes seem to be a popular choice for electric assist cycle touring. As do recumbents, some with interesting panel mounting.
The Solar Tour bike and trailer is a project developed by two mates in a garage. What they wanted to design was, “a bike we could ride all day if we liked, perhaps as much as 200 miles entirely powered by the sun and our muscles. We wondered whether off-the-shelf commercial technology had advanced enough for two guys to build our 200-mile-per-day dream vehicle affordably and without a million dollars or a 50-person university team. “
Find out if they were successful here
The guy at “my solar electric cargo bike” had to deprive his dog of its transport to make his electric assist long john.
But what about range? If you want to tour with a legal motor (250 watts in the UK for a two wheeler (Source), how big does your solar panel need to be to keep the battery charged for all day touring?
The Czech Solar Team took part in a 7300 km solar-powered ride from France to Kazakhstan in July 2013. The event is called the Sun Trip and is a race between 30 or so invited participants. The Czech team was powered by a Bionx 250 watt motor charged by a 500 watt panel measuring 250cm x 80cm.
This meant they had power all day, assuming half decent weather. But, despite the hefty panel, they didn’t win the race. That accolade went to Raf Van Hulle riding a Hase Pino tandem and pulling a home made trailer. He was probably the person we needed to talk to about our Pino conversion.
Raf is also the designer of the Solarwind trailer. There are 3 variations of this trailer, increasing in power as they increase in price, but all giving decent output.
The people at the Solar Bike Project point out that the weight of the vehicle will also be a determining factor in how much energy you need to put in versus the output you can expect in return.
“It was clear that putting solar panels on wheeled vehicles made more sense when applied to lighter vehicles. As the whole system scales down, the weight and therefore the power required decreases as the cube of the scaling factor, but the solar power decreases as the square. You win if the system gets smaller. Thus a vehicle half the size may have a quarter of the solar, but an eighth of the required power. Little toys about two inches long powered only by a small array of cells on top zip along quite nicely. Clearly, as the size is decreased, the ratio between operating power and solar panel power decreases, so you can charge for less time between runs, and even run all day without having to charge (when the ratio is 1). One can use this run/charge power ratio as a design goal. For instance, if you expect to charge four times as long as you run, then a 100W panel with a 400W motor is about right. Of course there are inefficiencies and variations in available sun that aren’t taken into account in this simple approach, but this has been the rule of thumb for the design of the cars from the beginning, and it seems to work.” (Source)
The AKT Solar Bike crossed Western Sahara to the Mauritanian border on a bike powered purely by a solar panel with no battery for storage to raise money for Oxfam. They used a 180 watt 24v motor powered by a 220 watt panel. Here’s the video…
And finally, here’s the trailer for the 2015 Sun Trip.
All in all, a great mix of transport solutions and another reason to chase the sun on your next cycle tour.