Half a croissant, on a plate, with a sign in front of it saying '50c'
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Photovoltaic rear fender.
  [vote for,

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.

doomsayer, Apr 26 2001

Powerbike http://www.zapworld.com/powerbike.htm
Electrically assisted bicycle. [doomsayer, Apr 26 2001, last modified Oct 17 2004]

Rear horizontal bicycle fender http://www.adventur...d/backscratcher.htm
To ride in mudsville. [doomsayer, Apr 26 2001, last modified Oct 17 2004]

Solar panel http://www.realgood...&sd=1006&ts=1011513
Portable MSX Modules. [doomsayer, Apr 26 2001, last modified Oct 17 2004]

Aerodynamics of Cycling http://www.explorat.../aerodynamics1.html
Has a javascript cycling power calculator about halfway down the page. [doomsayer, Apr 26 2001, last modified Oct 17 2004]

Photovoltaic Frequently Asked Questions http://www.ttcorp.com/upvg/faq1.htm#01
Says that cell efficiency decreases by 12.5% at 50C. [doomsayer, Apr 26 2001, last modified Oct 17 2004]


       UB: [doomsayer] isn't talking about the very fancy, very high-tech, very expensive specialty vehicles used in the Solar Challenge, but rather a practical, inexpensive add-on to a normal bicycle that ordinary people might actually use. You'll never see a Solar Challenge vehicle on a city street.   

       Let me also commend [doomsayer] for actually posting quantitative analysis! The Halfbakery needs more of this and less rampant speculation.   

       50W doesn't seem like very much power to me, though. I imagine it would be a convenient boost, but not enough that you wouldn't also pedal. Of course, the motor and whatnot needed to use this power would add weight, complexity and cost to the package.
egnor, Apr 26 2001

       I may have missed this point with my limited vision, but there's a mobility scooter on the market with a large solar panel designed to charge the batteries as an option, while the scooter is left deliberately parked outdoors for long enough [days or part thereof as booster].

       Bikes could be designed to do this too but the weight of the batteries is not a problem for a slow mobility scooter as it would be for a dual-purpose bike.
[I use a non-solar mobility scooter most days.]
rayfo, May 05 2001

       50 watts is a whole lot of power for a cyclist. Record breaking athletes peak above 400 watts, but us mortals can only sustain 200watts. Gently cruising along is nearer to 100watts. I think the foot pound calculations ignore the gearing factor. When you are riding uphill in a very low gear, 1 foot of pedal movement will progress you less than 1foot along the ground. Personally if I wanted to electrify my bike with solar power, Id rather keep the solar panels on my house roof, and electrolyse water, for use in a fuel cell. On a long tour, solar panels could be good for powering radios and computers. Id like to see a solar panel combined with e-paper to provide a usable digital map. That would solve a real problem of having to carry a pannier full of maps to navigate any distance at large scale.
MichaelW, Feb 04 2002

       Why just the rear fender? Just the other day I was carrying a "wide load" on the back luggage - hit a guy on the leg as I squeezed between him and a car! :S (I'll never be a trucker!)   

       Could also be put on the front, maybe need to angle the back corners to stop your knees hitting it on corners...   

       (Question: are dry cell batteries damaged by the bumps encountered on rough roads? I was using one for about 3 months and it's died...)
agulesin, May 23 2003

       Angle matters. Mud on it. If gonna, make a 'sun/rain' cover above rider - flush to sun. Working on recumbent with partial top-only top of legs/over headtorso section. Wee bit nose, taper rear - stow gear. Just using regenerative braking/from coasting downhill would provide assist. Looking into simply mod of hub light generator tweaked.
dinosnider, Oct 02 2003

       Dude..just peddle it man.
clafever, Jan 21 2004


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