By Terry Boston and Scott Baker Energy Storage Balancing the 21st century power grid. HILE MANY PEOPLE THINK OF NATURAL gas as the "go-to" fuel of the decade and near future, it is remarkable how much renewable energy is being installed. In 2013, approximately 44% of all new electric generation capacity (on a nameplate megawatt basis) W Digital Object Identifier 10.1109/MELE.2015.2447991 Date of publication: 1 September 2015 52 I E E E E l e c t r i f i cati o n M agaz ine / SEPTEMBER 2015 installed in the United States came from solar and wind. In 2014, that amount increased to 53% [1] (see Figure 1). While renewables still are a relatively small percentage of the total installed capacity in the United States, clearly a strong renewables build is underway. This steady trajectory should continue until another disruption changes its course, either increasing (e.g., carbon regulations) or decreasing (e.g., loss of tax subsidies) the rate of installation. 2325-5987/15©2015IEEE