After four years, there is a new No. 1 in the American Council for an Energy-Efficient Economy’s (ACEEE’s) annual ranking of best states for energy efficiency.

Massachusetts overtook California, which slipped to No. 2 after holding the top spot for the first four editions of the ACEEE’s State Energy Efficiency Scorecard.

The Scorecard ranks states based on an array of metrics that recognize best practices and leadership in energy-efficiency policy and program implementation. The Scorecard benchmarks progress and provides a roadmap for states to advance energy efficiency in the residential, commercial, industrial, and transportation sectors.

“Through our Green Communities Act, we set aggressive goals and laid the foundation for greater investment in energy efficiency,” Massachusetts Gov. Deval Patrick said.

Rounding out the top 10 are New York, Oregon, Vermont, Washington, Rhode Island, Minnesota, Connecticut, and Maryland.

The six most improved states are Michigan, Illinois, Nebraska, Alabama, Maryland, and Tennessee.

“As a result of Gov. (Martin) O’Malley’s vision in establishing one of the nation’s most aggressive energy-efficiency goals, Marylanders have already saved over 700,000 MWh of electricity and over $91 million since 2009, and our peak-demand program has helped us avoid major blackouts during our record-setting summer heat wave,” Malcolm Woolf, director of the Maryland Energy Administration, said.

“Illinois is a purposeful leader in the area of sustainability, investing more than $600 million in energy-efficiency projects over the last four years alone,” Illinois Department of Commerce and Economic Opportunity Director Warren Ribley said. “By supporting aggressive policies, including the state’s energy-efficiency-portfolio standard and advanced building-industry training and education, we are creating jobs, building more sustainable communities, and securing our place in the new energy economy.”

The 10 states most in need of improvement (starting with last place) are North Dakota, Wyoming, Mississippi, Kansas, Oklahoma, South Carolina, West Virginia, Missouri, Alabama, and South Dakota.

According to the Scorecard:

• Budgets for electricity-efficiency programs totaled $4.5 billion in 2010, up from $3.4 billion in 2009. Combined with natural-gas-program budgets of about $1 billion, energy-efficiency budgets totaled $5.5 billion in 2010. Given increasing regulatory commitments to energy efficiency, the ACEEE expects this growth to continue over the next decade.

• Twenty-nine states—up from 20 in 2010 and 10 in 2009—have either adopted or made significant progress toward adopting the latest energy-saving building codes for homes and commercial properties.

• Twenty-four states have adopted an energy-efficiency-resource standard (EERS), which sets long-term energy-saving targets and drives utility-sector investments in energy-efficiency programs. States that adopted EERS in 2007 and 2008 are now realizing significant energy savings and moving up in the Scorecard rankings.

• States continue to improve policies to reduce financial, technical, and regulatory barriers to adoption and deployment of combined-heat-and-power (CHP) systems, which generate electricity and thermal energy in an integrated system. Tremendous potential remains for CHP, particularly in states with heavy industrial and manufacturing bases.

“Energy efficiency is America’s abundant, untapped energy resource, and the states continue to press forward to reap its economic and environmental benefits,” ACEEE Executive Director Steven Nadel said. “The message here is that energy efficiency is a pragmatic, bipartisan solution that political leaders from both sides of the aisle can support. As they have over the past decades, states continue to provide the leadership needed to forge an energy-efficient economy, which reduces energy costs, spurs job growth, and benefits the environment.”

For the complete Scorecard, click here.