Generate power from passing cars.
Though the initial press release reasonably touted this as a way to get power to street lights in remote, off-grid locations, the idea was seized on by people with no comprehension of energy conservation as a “free” way to generate power.
The “best” proposal combines not only capturing the passing cars’ energy in pneumatic storage tanks but also powering the cars themselves with air pressure. The logical next step is to eliminate the cars altogether and build a perpetual motion machine.
Note that there are some legitimate situations where you could produce net energy this way – basically, you can extract a bit of a car’s kinetic energy just before the car was going to brake anyway. Even if you did come out ahead in purely energy terms, though, it’s pretty unlikely that replacing the output of large, efficient, highly regulated power plants by that of poorly maintained, gasoline-burning internal combustion engines will benefit the environment.
A related plan harnesses dancers’ energy to power a nightclub. Well, to power a small part of a nightclub, anyway.