Solar panels.Texas installed 22.6 megawatts of photovoltaics last year.Photo: Duke EnergyThe United States solar businesses boomed, as usual, in 2010, growing 67 percent to $6 billion, according to an annual report [PDF] released Thursday by an industry trade group.

That’s been the story for the past several years, but what’s notable is that solar is no longer just a California thing. The industry is expanding to the East. Back in 2004-2005, California accounted for a whopping 80 percent of the U.S. market. In 2010, that share fell to 30 percent, with 258.9 megawatts of the 878.3 megawatts of photovoltaic power installed that year, according to the report prepared by the Solar Energy Industries Association and GTM Research.

New Jersey is now the nation’s second solar state, with 16 percent of new photovoltaic installations in 2010. And while it is no surprise that sun-soaked states like Arizona, New Mexico and Nevada are also in the top 10, the list also includes states like Pennsylvania and North Carolina. Texas, the country’s No. 1 wind power state, made the top 10 with 22.6 megawatts of photovoltaics installed in 2010. The rest of the country collectively put 135.2 megawatts of solar on its roofs.

Back in 2007, only four states installed more than 10 megawatts of solar. Last year, 16 states did. The U.S. now is generating a total of 2.6 gigawatts from photovoltaic panels.

But the domestic market was a relative laggard as the solar boom continued overseas.

“U.S. demand growth was, however, outpaced by a global market boom driven primarily by the German and Italian markets,” the report noted. “Over 17 GW were installed globally in 2010, more than 13 percent growth over 2009. As a result, despite U.S. demand expansion, the U.S. market share of global installations fell from 6.5 percent in 2009 to 5 percent in 2010.”

That could change in the years ahead, though, as subsidies subside in Europe and solar companies look to the U.S. as the big growth market.

The report predicts the U.S. solar market will double in 2011, but warns that expiring federal subsidies make growth in 2012 and beyond uncertain.

At least one Chinese solar company is betting the solar boom will continue. On Thursday, JA Solar announced it will begin construction this year of a new factory that will have a capacity to manufacture 3,000 megawatts’ worth of photovoltaic cells a year, thanks in part to a government loan.