Instead of building a generator from scratch, electric motors, generators and alternators can be modified for wind or water use. Here is a breakdown of some advantages and disadvantages of each method. We are very interested in other people's experiments with alternators and generators, especially permanent magnet alternators. We offer some unique, interesting, and cheap books about alternators and generators, including information about rewinding them for slow speed operation. Check our products page for Alternator Secrets by Thomas Lindsay, and The LeJay Manual.
Alternators usually have a simpler design and a simpler commutator than generators.
There are 2 kinds of alternator, permanent magnet and electromagnetic. Alternators that use electricity to generate the field current are less efficient and more complicated. The advantage to them is they are somewhat easier to regulate. In general, car alternators rotate at too high a speed to be practical in wind or water power applications without significant modifications. Also, the brushes and slip rings wear out, requiring more maintenance.