[throwaway2a02]

People have built solar bikes, as in regular ebikes with 2-300w panels attached that power the motor. That's more impressive if you ask me. Other than that, lots of people (myself included) have run old, indirect injection diesels on used veg oil. That was years ago when it was financially very advantageous.

If you ask me, these are more impressive/interesting technical feats, but with real world applicability and usefulness.

[AtlasBarfed]

That's what popped into my mind: the old waste fryer diesel fuel. A nice "gee whiz" science reporting that the MSM eats up, but not scalable in any way for any significant application.

[ineedasername]

Also not scalable because "waste" oil is, by & large, not usually wasted. Restaurants are often paid by collectors who repurpose it for a variety of applications, including biofuel. So the idea that massive quantities of fryer oil get wasted when it could be used is a myth.