If you ignore efficiency then you stop making a profit pretty quickly. You can solely focus all you want on cost; sooner or later efficiency will make you pay.

Goldman wouldn't be making that kind of an investment if they didn't have a handle on both parts of the equation. Indeed efficiency (dealing with losses from seepage) have been the nut that hasn't been cracked with compressed air storage; these guys seem to have an economical (efficient) way to deal with that problem. If true, then they really are worthy of Goldman's investment.