Six states got 10 percent or more of their power from wind, solar and geothermal power in 2011. That's double the number from just a year ago. Not bad for a down year.

CleanEdge released its State Clean Energy Index on Wednesday, tallying up the state of green energy and technology across the 50 states of the union as of the end of 2011. Among the milestones, the Portland, Ore.-based research firm marked a doubling in the number of states that have 10 percent or more of their utility power coming from renewable sources, not including hydropower.

The list included South Dakota at 22.3 percent, Iowa at 18.8 percent, North Dakota at 14.7 percent, Minnesota at 12.7 percent, California at 11.2 percent and Wyoming at 10.1 percent. Last year’s top-three states were North Dakota, Iowa and California.

By the way, CleanEdge’s six-state figure doesn’t match the U.S. Energy Information Administration’s 2011 tally of nine states with 10 percent or more renewable generation. That’s because CleanEdge excluded biomass -- a big contributor for the forested states of Maine, Minnesota and Idaho that made EIA's list, said Ron Pernick, CleanEdge’s co-founder and managing director.

CleanEdge's figure also measures in-state generation, Pernick said. While California gets above the 10-percent mark by importing solar, wind and geothermal power from neighboring states like Nevada and Arizona, plains states are generally net exporters of wind power, he noted.

“Some people say that renewables are a rounding error. This shows that is not the case,” he said. “Coal plants are being shuttered; new ones are not being permitted. We’re seeing a future mix of natural gas and renewables.”

Up-and-coming states like Idaho and Nevada (at 9 percent) and Oregon (at 8 percent) are pushing at the border of inclusion in the 10-percent club, Pernick said. What’s needed is better regulations for interstate power transmission, to allow wind power growth in the Midwest, or solar power growth in the Southwest, to continue to increase without constraints, he said.

Renewable energy per capita was just one of many figures that went into CleanEdge’s index, which also tracks overall investment trends, patents, regulatory and policy issues and other factors to come up with its top 10 states list. That list put California on top, based on generation and its commanding lead for venture capital investment, followed by Oregon, Massachusetts, Washington, Colorado, New York, Illinois, New Mexico, Vermont, and Minnesota.

In other statistics:

-       CleanEdge found 2 million hybrids registered in the U.S. as of last year, but only 50,000 all-electric vehicles -- not surprising, given Chevy Volt and Nissan Leaf sales figures.

-       State-level renewable portfolio standards are becoming a key factor in the country's most energy-intensive regions. The 29 states (and Washington, D.C.) that have RPS requirements make up nearly two-thirds of the countr's total power generation, the report found.

-       Patents granted for clean energy surpassed 1,000 for the first time last year. The USPTO's fast-track program for green tech IP may have helped this along.

-       California’s dominance in green VC continues unabated. The Golden State saw more clean energy venture capital invested than the other 49 states (and D.C.) combined, CleanEdge found.

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