Okay, here is the $64,000,000,000 question:
What is the TOTAL cost in BTU vs. BTU output realized? And what is the
TOTAL acreage dedicated to producing the vegetable matter required? 
(Assuming total replacement of fossil diesel)
The last figures I saw (some years ago) on bio fuels still put them in
the same category as running a generator with an electric motor that
was powered by the generator:  Net loss in the system.
(And then you get into the mess they have in the UK of the government
collecting a fuel tax on the left over fish and chips oil)