Seriously, having built a pedal driven custom made hand wound permanent magnet alternator myself, I can state with pretty good certainty that you'd do extremely well to put 100 watts into the utility system after you acount for losses.  50 watts or less would be more realistic.  A flywheel of any kind will not change that number appreciably.

By the way, the economics of your scheme don't work any better than the physics.  A typical grid tie inverter, by itself without the installation or the permits or the other bits and baubles will generally cost a couple grand at least.  Cheapie MSW inverters CANNOT hook up to the grid without very bad things happening.

Good luck and have fun!