Energy storage if you want to rely solely on renewable energy sources is THE KEY to making that even remotely feasible.
Current solar and wind renewables are NOT predictable nor reliable for sustained power generation. With Coal, Natural Gas, Nuclear and Hydro you can generate power on demand, no matter what the environment is doing. Well, Hydro in the west is getting dicey with the drought - but even that is far more stable than wind/sun which can vary wildly week to week, day to day or even hour to hour.
That's why technology like this is so exciting. If you can look at the average production of a renewable over a month, then within a year the peak month, then look at the worst months, then have enough storage to cover a percentage of a peak month based off the hedge of the worst month then you are getting to a point where a solar farm isn't just an opportunistic source of power based on how much the sun is shining, but a reliable energy source that can be counted on whether the sun is shining or not.
Same for wind farms.
Energy storage is crucial if we seriously want to transition to renewables and hence the investment from Goldman Sachs.
If this company is even remotely successful in actually delivering then $250M is a pittance to what they will receive back in the long term.
There are also a lot of unused/abandoned underground structures - from various wells that are now dry of the resource they were originally drilled for to mines that are no longer productive. The problem has been sealing them from seepage so you don't loose your stored air - this article was light on details but that seems to be this companies claim to fame. They seem to have found economical ways to deal with those issues - enough to convince the boffins at Goldman Sachs they are worthy of investment. I guarantee you Goldman is not just tossing out money willy-nilley without performing some significant due diligence!