Building a Solar Charging Bike Trailer

The Solar Powered Bike

So now I have an electric bike that I love touring on (see Magic Pie page), I realised that I love riding through remote areas and camping out. How could I do this with an electric bike? There’s no power-points in the bush. Previous electric bike tours involved recharging at night at where ever we were staying. Well, build a trailer with solar panels to recharge as I ride of course!

First step, get a trailer. Ultimately I’d like to get a two-wheel trailer that is a sealed box (to house all my gear securely). But that requires a bit of time and designing / researching. So I decided on a single wheel bob-style trailer for the in-between time. This one I got from e-bay because it was only $200 ($300 cheaper than a bob trailer) and only a 2kg heavier. And I will not care as much about mashing it up to fit the solar panels etc.

Comfort in the Saddle

One thing that I can highly recommend is the Cane Creek Thudbuster seat-post. A more comfort-providing seat post you never will find. It’s maybe not for all, but if you want comfort in saddle while you tour or if you have a bad back / bum etc, these babies make every ride a plush ride.

The Solar Panels

Now to the solar panels. I’ve just ordered them from china. I wanted the maximum wattage I could get (because you can never have too much power). I also needed the output of the panels to be over 42v so that charging the 36v battery is possible. After much research, I settled on a 3 panel set up, each panel rated at 12v (12*3 = 36v). Each panel actually produces around 17v, so 3*17 = 51v, plenty to charge my batteries (simply wire the panels in series, not parallel to add each panel voltage together).

You can get cheap single 200w, 12v panels (for around $300), but I need the higher voltage output. I found these camping kits that are three panels that fold up. They produce 180w. The problem with this is their cost ($700!) and that they are 20kgs! The trailer is rated to carry 35kgs. My rig is already quite heavy and these panels would weigh almost as much as the bike/motor/battery itself.

The solution came in the form of these flexible 60w panels I found through Alibaba.com. They are only 2.5kg each, so 3*2.5kgs = 7.5kgs total a much more appropriate weight. Total power 3*60w = 180w.

The size of each panel is 85cm*55cm. The three panels together makes 85cm wide (across the trailer) and 165cm long. This means the panels will be a little wider on the road than the bike and overhang the back of the trailer by about half a meter.

If the panels only produce around 75% of their rated output, that gives me 130w. If you get 5-6 hours average sun each day = 6*130 = 780 watt-hours. The Magic Pie averages 8.5 watt-hours per km, so 780w / 8.5 = 91km of charge per day. That’s the theory anyway. Plan is to carry 2-3 batteries each one providing 500watt-hours (or around 60kms of riding) so around 180km of spare power. That gives a little lee-way for rainy or cloudy days.

30/09/11

The regulator arrived today! I bought a Morningstar TS 45 battery charger / regulator, the same one as the Electric Bike World Tour uses on his 90w solar charge trailer. The beauty of these is you can program them to charge any voltage up to around 60V. They are supper efficient and a bit of an industry standard. They are a little bulkier though with their large heat sink fins.

I got the older PWM version for only $170. I really wanted the newer MPPT version, but the difference in price (the MPPT is around $400) wasn’t worth it for the few extra watts gained in this small set up.

2/3/12

I got the first version of the trailer up and running just before x-mass 2011, but then went on a bike tour and havn’t had time to work on it since. As you can see in the picture the trailer is quite long and it does tend to ‘wag’ the bike if you are to aggressive with your pedeling. I used 3mm aluminium angle to make the fram for the panels.

I think I will take the third panel off the trailer and mount in over the rear basket. This will shorten the trailer and improve the ride quality.