"Breeze farmer" : an open-source bike-wheel wind turbine Brown, Stefan; Epp, Steve; Rabets, Yegor
Geopolitical and environmental concerns means the demand for alternative energies will continue to rise, but the largest inhibiting factor right now is cost as compared to cheap oil. To avoid environmental catastrophe, inexpensive solutions need to become available: distributed power generation, from a ubiquitous energy source such as wind, has the potential to fill this gap. However, the average household wind is typically slow for most of the year, so turbines need to be efficient and low-friction to take advantage of these slow winds. Since most mechanical friction results from the complexities of the hub and shaft assembly, where power is typically generated in most turbines, a key design feature would be to make the hub as simple as possible so that it spins freely like a bicycle wheel. This outer-rim induction is the basis for our project Breeze Farmer, an open-source home wind turbine that is designed to be assembled cheaply out of parts like a used bicycle wheel. Wind blades are first mounted onto the wheel, which itself can be mounted onto a rotating frame so that the wheel is always perpendicular to the wind. The induction required to convert mechanical to electrical energy takes place around the rim of the wheel, where a number of magnets are mounted. As these pass by inductor coils mounted onto a stator wheel frame mounted right behind, alternating current is produced. This induction will slow down the wheel, but since this drag is purely electromagnetic and not mechanical, it should be at a theoretical minimum. The current is fed into a circuit which converts it to DC, which can then be used to charge a 12V battery. This is but one possible application for the current produced. The Breeze Farmer prototype was constructed and tested in the Engineering Physics Project Lab. It was sponsored by Bernhard Zender of the same lab, who came up with the project idea. Breeze Farmer is based on the design of the far more expensive Honeywell Wind Turbine, but aims to be a cheap do-it-yourself endeavor. The prototyping project consisted of several different configurations of magnets, inductors, blade material and shape, and other variables in order to derive the most efficient setup for maximal power generation with a minimal start speed. These metrics were probed using very basic measurements of wind speed, rotational speed, load, and rectified power. After developing a Breeze Farmer prototype, it has been found that, with a reasonable number of magnets and many coils, the electrical power generated is rather small. Large factor of this is power losses in eddy currents in our aluminum stator rim, and losses in the coil conductors.
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