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.

> Is it just economics?

It's ~75% economics, 25% learning curve.

For hydrogen, you need an electrolyzer, a hydrogen fuel cell (or turbine), and storage. The electrolyzer is the main capital cost, and it is only running for a fraction of the day (either whenever there is curtailed solar/wind, up to 40% of the time you have your own captive plant). It needs to be sized for peak usage. The storage optimum depends on whether or not there is a nearby salt dome, but if not it is extremely expensive per kWh, and so days and days of storage are untenable (going directly to CH4 changes some of this). Existing fuel cells and H2 turbines have not yet walked down the learning curve in the same way that an NGCC plant has for CH4, but those are running 24/7 so the amortization is not as bad.

With a salt dome and captive PV plant, you end up with (optimistically) system capital cost that roughly doubles the PV capital cost (using US pricing). That means your amortized $/kWh rate is about 2x the PV rate. Since PV and NGCC are roughly the same $/kWh at the plant, it makes H2 extremely uncompetitive unless there is a carbon price or H2 subsidy. At $3/kg hydrogen, it's almost just barely within reach assuming everything works well. If the cost of electrolysis came down, or if H2 were easy to ship globally from high insolation regions, that would substantially help the problem.