Thanks for the flash from the past. Flywheels for energy storage.I believe that they have potential in stationary installations. Power generating stations to smooth out supply makes sense.
TANSTAAFL rules. There are alternative fuels already available for mobile use. We have a company crew bus in Eastern Canada that has been running on methyl ester /diesel mix for over a year, works like a charm. Methyl esters are using rapeseed oil as a feedstock so infinitely renewable.Energy input costs to output is 1 to 3 so positive output.
Haven't looked in to it too much but apparently algal oil farms are in pre-production phase and could replace much of U.S. domestic petroleum requirements. Input to output in the 1 to 12 range.
I have asked for responses to the use of these fuels in marine engines, Cat and MTU, so far no response. Will advise.