Many people who have ever spent much time on a bike have considered the idea that the same system could be used to generate electricity. As far back as 1914, Popular Mechanics was writing articles about bikes adapted to generate power. Today, several companies offer kits that adapt or just connect to a bicycle that allow it to be used as a small scale generator. It would seem like the perfect convergence of efficiency, self-reliance, and simple solutions. Unfortunately, not so fast…Generating power by bike may not be such a great idea after all. The first issue is that humans really aren’t terribly strong. A healthy adult can put out about 100 watts of energy for a reasonable amount of time. That might drive a few light bulbs, but you’re not going to run an air conditioner or charge your new Nission Leaf with that. But if you’re going to ride to exercise anyway, why not capture that energy even if it’s just a small part of your daily usage? Well, because you may not be generating what you think you are.
As we’ve looked at before, one of the real bugbears of generating any type of energy or work is loss in conversion. Every step you take to transform or convert energy from one type to another typically has a pretty big loss. Bike powered generators are no different. First of all, the human body is not a terribly efficient converter itself. We use food to power movement. Transforming the stored chemical energy in our diet to power movement already has huge losses. Once we do start pumping our legs though, we still have to power the bike, converting muscle based movement to mechanical rotation, that rotation then has drive a generator, and then finally, we typically have to store the electricity somehow to allow for future use.
A recent article in Low Tech Magazine does some back of the envelope calculations and arrives at the conclusion that just looking at the losses that occur in the bike itself and the generator, roughly 2/3 of the energy you produce by pedalling is wasted. In looking at the energy and materials needed just to build the kit that converts your bike into a home generating station, the authors finds that you would be unlikely to ever even generate enough power to replace what was used to build the kit in the first place. Not so good. But this is not to say that there is no place for human powered work and specifically pedal power.
The article’s author goes on to explore ways to solve the massive loss built into a bike converted to generation. His first point is that your typical bike is well designed to drive you around, not to spin a generator. Custom built pedal machines designed specifically to drive a generator can remove most of the major mechanical inefficiencies in a standard bicycle. But as we’ve seen, anytime you convert energy, you have losses, so he points to one of the best improvements, take the electricity completely out of the equation.
Pedal Powered Machines work by using the pedalling force to directly drive work instead of generating electricity that is then used to perform work. Think of the foot powered sewing machine or potter’s wheel as two of the few versions of this technique that really survive today. Human powered machines go as far back as anitquity. But pedal powered machines really didn’t come into being until the 1870’s when the invention of the bicycle spurred other uses for the highly efficient foot powered design. (Ironically, it was only the arrival of the fossil fuel powered industrial age that allowed for more advanced steel manufacturing that made pedal powered machines possible.) The combination of using the most powerful muscles in the legs, with a compact design, with the ability to properly gear the movement made pedal power vastly superior to other human powered devices for most applications. The late 19th and early 20th centuries saw an explosion in pedal powered devices for home and industrial use that only died out as fossil fuels and electricity slowly became cheap and ubiquitous.
Other than a few niche and novelty attempts to bring back pedal powered machines like the Fender Blender, not much has been made of the advantages of pedal powered machines in the industrialized world in recent times. But there are those for whom the unique combination of efficiency, low-cost/simple design, and freedom from industrial energy has real advantages. Groups like Maya Pedal and others have developed pedal powered machines that are cheap, effective, and perform critical work in a developing world environment. Most of these machines are designed for basic farming tasks, water pumping, light weight industrial or manufacturing work and the like. The combination of greatly amplifying the body’s strength without being dependent on unavailable, unreliable, or unsustainable power sources make these machines ideal solutions for the tasks at hand.
So while mini devices to charge your iPod while you ride may be handy ways to harness your legs, think before you build that home generator system and instead look at making a pedal powered washing machine instead.