When is Energy Storage Eligible for the 30 Percent ITC?

Near the end of 2015, the IRS quietly updated a little known rule on storage eligibility for the 30 percent Investment Tax Credit (ITC). The timing seemed odd, with the ITC about to expire, but the IRS must have been privy to what congress was about to do, in passing the Christmas Miracle of a five-year ITC extension at 30 percent.