I'm used to producing ethanol (low test brewing) and can be quite efficient if you are not brewinng for taste to brew from any starchy material, as long as it is consistant you can run a chain easily, the problem is although it is a renewable source as far as material goes, it is one hell of a CO2 producer both in the fermentation process and combustion (eta based on J/kg yield for equivelant energy release from Oil).
Distillation could be achieved by solar furnace or similar, reducing the need for High potency initial ferms, as distallation would technically be econmically Free (apart from the plant the manpower etc)
you would also have the problem of all those dead yeast cells, now unless the world desires an overwhelming urge for Marmite / Twiglets / MSG then you are going to have tonnes of autolysing yeast, I suppose you could possibly immobilise the yeast and ferment that way but that would be incredibly inneficient.
Spent Grist (whatever it's form) could be used in many forms, if there is remaining cellulose then it could be used in fibre production, if it is just protein slurry then rendered to bulk out energy rich foods in animal feed etc.
If we could engineer a yeast cell with a good cellulase production, as well as good general properties, this would be a good start, however I believe other than Airports or static fleets on fixed sites that ethanol will catch on, however a generally worthwhile idea it is.
Spend the money earmarked for solar tidal and Bio on a few decent Fission plants, then plough the money into fusion research (this goes for the UK too
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