Been tracking them for a long time. They've been at "pilot" stage since at least 2011. Personally I don't think that any form of alternative energy storage has

Been tracking them for a long time. They've been at "pilot" stage since at least 2011. Personally I don't think that any form of alternative energy storage has much chance against Li-ion, which has experienced unbelievable declines in cost (driven mostly by cell phones and electric cars). A bunch of extremely well funded compressed air storage companies have already run aground against this problem: Lightsail (Thiel & Gates backed), SustainX, etc. I'd be skeptical unless they can somehow actually prove economics against Li-ion, but these media pieces always seem to skirt that question.