According to GTM Research's Q2 2014 Grid Edge Executive Briefing, released this week, there are approximately 270 distributed energy storage projects (deployed and planned) across the United States. The number of projects is up from 120 at the end of 2013, and combined, the total is 212 megawatts. 
The chart below maps out the deployments, with concentrated pockets in Hawaii, California and the Northeast.
FIGURE: Planned and Deployed Distributed Storage, August 2014

Source: GTM Research Q2  2014 Grid Edge Executive Briefing
As covered previously, there are four factors driving the growth of distributed storage: demand charge reduction, the growth of PV, frequency regulation in select markets, and state-level incentives. Ravi Manghani, senior grid analyst at GTM Research, notes that California, where three out of these four factors are at play, has seen by far the most planned and deployed distributed storage projects, in terms of both project count and megawatts.
U.S. distributed storage projects range in size from 5 kilowatts to more than 5 megawatts, but the briefing notes that the majority of projects are rated less than 750 kilowatts.
GTM Research forecasts 720 megawatts of distributed storage to be deployed in the United States between 2014 and 2020.
For more on distributed storage, check out GTM Research's report Distributed Energy Storage 2014: Applications and Opportunities for Commercial Energy.
Grid Edge Executive Council members gain access to all of GTM Research's quarterly briefings. Learn more here.