There are now more than 2 million solar installations in the United States, a milestone reached just three years after hitting the 1 million mark, an industry trade group said on May 9.

U.S. solar installations now produce enough electricity to power more than 12 million homes, the Solar Energy Industries Association said in a joint statement with energy research firm Wood Mackenzie.

The number of installations in the United States is forecast to double to 4 million in 2023, Wood Mackenzie said.

"We believe that the 2020s will be the decade that solar becomes the dominant new form of energy generation," SEIA CEO Abigail Ross-Hopper said in the statement.

Solar energy has boomed in the United States over the last decade thanks to rapidly falling prices on the technology, state mandates that require utilities to source large amounts of renewable energy and a federal tax credit worth 30% of the cost of a system. Solar is now a $17 billion industry, SEIA said.

Yet despite this growth, solar is still a small part of the U.S. energy mix compared with fossil fuels. This year solar, wind and other renewables excluding hydropower are expected to provide 11% of U.S. electricity generation, compared with 37% for natural gas and 24% for coal, according to the U.S. Energy Information Administration.

California accounted for 43% of the second million installations, but represented more than half the first million. Other states where solar has grown rapidly over the last three years include Texas, Utah, Florida, Rhode Island and Maryland, SEIA said.

By 2024, there will be one solar energy system installed per minute in the United States, Wood Mackenzie said.

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