I'd do one if I could find an easy way. Despite having a bicycle there are few places I dare ride with driving being risky round here. So something in the house that I can plug into the grid would be nice, if anything it would mean I could measure my output properly.
I hear you about the safety when you want a serious ride.
Here is what you need for the home made solution, look at the photos below:
1 old fashioned up-write spinner type bike, with seat that adjusts 2 ways, vertically and horizontally.
1 Micro-V groove belt used in exercise equipment, 8-10 v grooves. Get a long enough belt to sit on the wheel.
1 Used treadmill motor, around 120vdc, with flywheel and Micro-V groove pulley.
Not in photos-
TI switching regulator which goes from 100v to 9v in DC, 6v out.
Either Arduino of PIC board, with 2 channel 12 bit adc.
1 optical sensor on treadmill motor for true RPM feedback.
2 nice big 100v caps.
1 strong mosfet and huge 200-300 watt resistor 2-4 ohm.
Use the MCU board connected to a PC to log voltage and current for power consumption and control motor resistive level VS rpm.
The MCU PWMs the mosfet to control resistive braking setting.
I wont directly recommend feeding power back to the grid for safety reasons, but, there are boxes which can do this and your on your own if you are going to tie your project to the mains.
This design is fairly silent as the treadmill motor is designed to be non-cogging and the Mivro-V groove belt has no bumps or teeth in it.
The belt wont slip on the bike's polished flat steel wheel unless you get sweat on it. You just need to add a protective cover so your sweat wont come into contact with the bike's wheel.
This design, after friction and DC motor efficiency as a generator is only around 50-60% efficient. If you want better, the treadmill motor needs to be changed to a 3 phase neodymium permanent magnet low RPM generator.