It seems easy, but this is a daunting engineering task. Harbor Freight has a little ornamental multi blade windmill that can barely overcome friction. Small motors are designed for high speed with the voltage applied proportional to speed. So, for a low speed application you would prefer a 180V motor. Lighting this little cabin would blow every other project off the table. While others see this as a technical problem to solve, I have another view.
Form vs. Substance......... This is like a big budget movie that flops at the box office because it doesn't have a good story line. I can say this because I volunteer as a judge at science fairs. Use the windmill and cabin as a backdrop. A project doesn't have to work to be great. I am more interested in the initial tests that were done that only generated a couple volts. Run those again and plot the voltage vs current by changing the load resistance. Find where the maximum power was generated and what happened to the speed. Power developed will be about the same no matter what motor is used. What effect will diameter have, what rpm do you get, and what will be the blade speed at the tip. You can take two identical motors and drive one as a generator from the other. Calculate the power going into the motor and that developed by the generator to estimate generator efficiency. Assume both efficiencies are equal. How could you measure the real efficiency? If you had a large supply of these generators that only generated a couple volts, could you charge smaller batteries and use them to fun your lamp for 2 hours. What are average ind conditions in your area? Lighting a lamp may look impressive but we are more interested in the thought process and how the student has researched the material. This isn't about lighting a lamp but the challenges in wind generation. From my judging handbook:
"Other projects will seem too sophisticated to be the work of a student of the age you are interviewing. That hunch merits further questioning, but not a conclusion. Some students are extremely bright. Others have helpful parents who will spend hours ensuring that their children have all the resources and contacts they need. You must distinguish between the students who used resources with comprehension and the student who just used them. Although child prodigies do exist, it is unlikely that ten of them will be placed side-by-side in the section you are judging. Your task is to make sure the real scholars are recognized. When you come to a project that obviously is the work of the student and yet original, simple, well conceived, clearly displayed and well understood, you have a winner!"
