When it comes to "power-assist" for the bicycle, even in the range of 300 watts...
A viable option to batteries - for could be: ... surprise, surprise: compressed natural gas (or propane) ! And as for the emissions, CNG (compressed natural gas) could actually be less polluting, overall, than batteries charged with grid power, given the line-losses and inefficiency. The key would be the direct conversion of heat to electricity in a small fuel cell. Here is an actual model of a FC bike made by Gore and Aprilla in 2005. It failed miserably and for good reason. The design was beyond-stupid: brain dead, you might say. It was way overpowered, way, way overpriced, and used unavailable hydrogen instead of CNG. Three strikes and your out, even if your name is Gore. Here is a table of energy density: CNG 3,100 Wh/l 12,100 Wh/kg NiMH Battery 280 Wh/l 100 Wh/kg Li-Ion Battery 200 Wh/l 150 Wh/kg Lead-Acid Battery 40 Wh/l 25 Wh/kg Propane 26 Wh/l 13,900 Wh/kg As you can see- compared to the best battery, CNG has about a 60,000:1 advantage !! Time to revisit this concept, but 1) Forget H2 2) Forget the Gore Fuel-cell, go with SOFC 3) Mistubishi has been running SOFC fuel cells on CNG for the past 15 years. This is not new
