Massachusetts topped energy efficiency rankings  produced by the American Council for an Energy Efficient Economy (ACEEE) for the second year in a row . Massachusetts has been a consistent high performer according to ACEEE’s methodology; in the six years the organization has published its state energy efficiency scorecard , Massachusetts has scored among the top ten each year.
ACEEE attributes Massachusetts’s success to its continued implementation of the Green Communities Act of 2008 (GCA) . Further, Massachusetts Governor Deval Patrick recently signed  into law Senate Bill 2395 , a piece of legislation expanding upon GCA. The law extends contracts between utilities and renewable energy firms and increases the cap on net metering.
In constructing scores, ACEEE considers a variety of state energy efficiency policies and weights them according to their potential energy savings. ACEEE updated its methodology this year, changing how some policies were scored to “better reflect potential energy savings, economic realities and changing policy landscapes.” Despite changes that increased the stringency of scoring, Massachusetts remained highly competitive along with California, Oregon, New York, and Vermont.
For more information:
ACEEE: State Energy Efficiency Policy Database 
C2ES: Energy Sector State Policy Maps