CO2 doesn't vary much in concentration by how close you are to an emission source unless you are literally sucking air out of a tailpipe. You might get a 10-20% increase in the centre of a city instead of the countryside, hardly enough to make up for being somewhere with so much energy coming in that they frequently have to curtail it (which could then be used for this instead).

This isnt CCS which cheaply turns CO2 into an inert form of carbon, its an expensive process for turning CO2 into a very useful form.

They could route emissions through a system like this directly from smoke stacks, capturing the carbon before it even reaches the atmosphere

How much do we have an over generation problem in general though? I suppose the argument would be that solar is curtailed because they don't want to deal with the potential for overgeneration, but we already have a number of approaches for energy storage. Their pricing for generating at most a gallon a day is a price exceeding a battery system of LFP that could do a lot more than a gallon of gas. This is ignoring the rather significant potential of Sodium batteries.

So this doesn't look to be cheaper than battery systems, it looks to be way less efficient than battery systems. The biggest use case as energy storage in general seems to be if you want it to spend a few months (but not too many months, fuel degrades in the tank after all). The more narrow use case is to cater to scenarios where you absolutely need the energy density of gasoline, so boats and airplanes critically so, maybe some heavy equipment. I'll grant that, but if particularly sodium batteries will be an acceptable approach, it'll be better than this solution in that very wide variety of circumstances.