"The system takes in energy in the form of electricity and turns it into separate streams of hot and cold air. The hot air heats up the salt, while the cold air cools the antifreeze, a bit like a refrigerator. The jet engine part: Flip a switch and the process reverses. Hot and cold air rush toward each other, creating powerful gusts that spin a turbine and spit out electricity when the grid needs it."
Salt can apparently store energy for days, so this would give energy companies that are dumping off electricity generated from wind farms and solar panels a place to hold it. According to Bloomberg's sources, California had to dump off over 300,000 megawatts of electricity (which could've powered "tens of thousands" of homes) already this year. That's a lot of wasted juice.
This isn't a full-on X experiment like Project Loon, however. It isn't fully funded yet, but Alphabet has built a proof of concept in a Silicon Valley warehouse and is working to find business partners for a commercial prototype that can connect to the electrical grid.
From here it's a lot of testing build materials that can be sourced cheaply, and making sure the thermodynamics are good to go.
Salt-based storage could be cheaper than things like lithium-ion batteries by quite a bit, but from the sounds of it, this is still a ways off from being ready for market. Largely because current gas and oil prices are low and investors don't see short-term pay-offs with alternative fuels. Good thing Alphabet isn't exactly hurting for money, then.