North American Clean Energy, Nov/Dec 2016, by Jim Petersen.
http://www.nacleanenergy.com/articles/24810/advanced-storage-battery-technology-providing-a-foundation-for-the-new-energy-paradigm

"The burgeoning energy storage market is being driven by improved energy efficiency, the declining cost of solar equipment, and higher capacity energy storage made possible by improved battery technology, such as lithium ion. This creates a huge benefit to consumers of electric power, especially with federal incentives covering up to 30 percent of the total system cost."