Electrofender

A rear horizontal bicycle fender with an integrated solar panel. Since the fender is horizontal, it can be made quite large without adding much air resistance to crosswinds or to the forward motion of the bicycle. The power from the solar panel will be intermittent so it should be stored in a battery where it can be used either for lighting or for powering the bicycle up hills.

The fender with solar panel should be larger than the typical rear fender; the electrofender will be about 70 cm long and 26 cm wide with the solar panel on the rear 44 cm. A good commercial solar panel that size will have a power output of about 9 W and a mass of 0.76 kg; the fender will have a mass of 0.14 kg, so the total mass is about 0.9 kg. Since much of the time the solar panel part of the electrofender will be in partial shade, the solar panel should have bypass diodes on each of the cells so that at least some power is produced at most times. Assuming that there is an average of six usable hours of sunlight per day and that the panel is on average half shaded, this works out to 9 W * 6 hours * 1 / 2 = 27 Whr / day or 27 Whrs * 3600 J / Whr = 97200 J, after battery and motor losses, about 50,000J; enough for 1000 seconds of 50 W assist per day.

A good 9 W solar panel costs about 130 $ US, with bypass diodes for each cell it would probably cost about 150 $ US. The rear fender costs 15 $ US, so the total cost with an extra 25 $ US labor and parts to integrate em, would be ( 150 + 15 + 25 ) $ US = 190 $ US. With this cyclists can go up hills without getting tired in order to pedal at gratuitous speed the rest of the time.