Right now, the best solution in most cases is probably renewables and batteries. But this could be a useful solution for something like air travel, where batteries are currently too big and heavy to allow for a good zero-carbon approach.
Indeed, it's a losing game, not even zero sum. But it's suitable for some scenarios: absorb the renewable production peaks (broad daylight, wind blowing, massive output from solar panels and wind turbines), now you have a reserve for when production is lower than demand. Bonus, this reserve is not just a battery, you can fuel cars with it. Or fill a lake if you really have a lot. whatever.
But it can be better than that. If you had a zero sum technology that evened out fluctuations in other renewables then you're in the realms of CO2 reduction.
You also may have the possibility of more practical sequestration than CO2 though I can think of a few pitfalls with ethanol lakes, especially around Spring Break time.
Worse than zero sum.
>The reaction turns CO2 into ethanol, which could in turn be used to power generators and vehicles.
I am no scientist, my question is this: wouldn't it be a zero sum game at best? You are taking C02 out of the atmosphere, turning it into fuel, which then is used in C02 emitting engines.