I built a single coil SSG a few years back. It took a long time to charge a car battery. There is a solid state version that would be more compact and easier to work with. I'll let you how it works out.
Here's a few pics of the first one.
[attachment=1:3d71m8ab]M2 rotor motion.JPG[/attachment:3d71m8ab]
[attachment=0:3d71m8ab]RE spikes 7.JPG[/attachment:3d71m8ab]