MIT engineers make converting CO2 into useful products more practical

Perhaps someone with more knowledge can comment on why solutions like these can't be used to solve the energy storage problem. Is it just economics?

That is, renewables are now the cheapest form of energy by a significant margin, but they are unreliable with respect to timing, so a storage solution is necessary in order to provide electricity on cloudy days when the wind isn't blowing, at night, etc. Most of the research I've seen into solving the storage issue involves batteries or things like pumped hydro. If things like solar and wind were "overbuilt", could a solution like this be used to create hydrocarbons when there is excess electricity? Power prices already go negative in some places when it's particularly sunny/windy. If the excess energy at that time could be used to make gas that could then be utilized by gas plants, well then there is your net 0 storage solution.

I'm assuming solutions like this are uneconomic (and similarly with hydrogen plants, e.g. by using the excess renewable energy to generate green hydrogen by electrolysis for storage and later use), but I'd like to understand better why.

We need vast amounts of energy storage is the problem and that won't be cheap no matter how you look at it. 20 years ago I saw an annalists that suggested the US needs the equivalent of lake Superior to get enough hydro storage - that is that much water, plus the ability to drain it all in just one day (to where!), and then pump it back up the next. Pumped hydro where we can use it should be used, but there isn't any place we can put it left (and we want to take some of what we have out because it is an ecological disaster). Batteries work but are expensive. This would probably work as well, but again be very expensive.

Remember you are competing with something we can pump/dig out of the ground for nothing anytime you propose storage. Renewables when the wind is blowing or the sun is shining are very cheap, but as soon as you need storage the costs go way up.