Current US demand as of 20:30CST is ~560,000 Megawatt Hours. This facility can provide 8500megawatt hours over 100hours, or 85Megawatts/hr or about .015% of US electricity demand in an hour.
At a cost of around ~$150million, that means to have enough storage for 10% of US demand, you would need ~670 of these facilities, or about $100 Billion.
Not too bad tbh. But of course this facility has a storage capacity of zero until it actually get's built (if it gets built).