An energy source is still needed at the input to this process. Creating fuel is a way of storing energy, creating fuel requires "winding in" Joules from somewhere else. There will be an EROI (a number of Joules in vs a number of Joules out) , applicable per gallon of fuel yielded.
How does that compare with hydrogen, for example?
If the process is similar to creation of human edible fuel, like "Solein", which is created by single cell bacteria fed by hydrogen in a bio reactor, then the input fuel is hydrogen, so the end to end EROI of Solein is a product of the EROI of (a) the conversion from electrical energy to hydrogen, and (b) the conversion from hydrogen to your biofuel.
Either way, the Joules input to creation of your fuel, if they can't be piped from solar, then they have to come from finite stores already on Earth, which means there has to be an environmental cost for creation of that fuel.
A further factor of interest is comparing how quickly Joules are transferred from input to storage. Hydrogen is fast, limited only by electolyser capacity. Usable hydrogen is generated in minutes and hours, rather than in terms of weeks, as it sounds from your description of your biofuel creation.