Geronimo Energy, one of Minnesota's most prominent renewable-energy developers, has been sold to a large British utility company for $100 million.

In conjunction with the deal completed Monday, National Grid is also paying $125 million for a 51% stake in a joint venture that owns wind and solar projects being developed by a Geronimo affiliate. The other 49% is owned by the Washington State Investment Board.

Edina-based Geronimo will continue to be headquartered in the Twin Cities, where it employs about 60 people, said Blake Nixon, the company's chief executive. Geronimo employees another 25 people in several field offices, and has done projects in 16 states. Nixon will continue to lead Geronimo.

The deal should bolster Geronimo's efforts to expand both on its traditional turf — the Midwest — and nationally, Nixon said.

"It clearly brings additional capital to grow the business, and a name brand that is well respected in the energy industry," he said.

National Grid is known in this country for its regulated electricity and natural gas utilities in the northeastern United States. But the company is trying to extend its nonregulated business through its National Grid Ventures arm, of which Geronimo is now a part.

The Geronimo deal marks National Grid's entry into U.S. wind- and solar-energy development. "Geronimo was acquired to be our platform in U.S. renewables," said Daniel Westerman, president of renewables and distributed energy for National Grid.

National Grid, based in London, is one of the world's largest investor-owned utilities with about $19 billion in sales last year, its business spread roughly evenly between Great Britain and the United States. The company serves about 20 million people in New York, Massachusetts and Rhode Island.

The Geronimo deal was originally announced in early March.

As a developer, Geronimo purchases land, wrangles government permits and finds buyers for a wind or solar farm's electricity. The company was founded in 2005 by Noel Rahn, a retired Twin Cities money manager, who built a wind farm on his own farm in southwestern Minnesota.

To run the wind project, Rahn selected Nixon, a former financial-industry colleague. Geronimo has grown with Nixon at the helm and Rahn as chairman. Rahn, Geronimo's largest shareholder, will now serve as a consultant. Nixon said he and several other employees have been significant Geronimo shareholders.

Geronimo has developed over 2,400 megawatts of wind and solar power, which includes several projects in Minnesota. A megawatt is 1 million watts, and 2,400 megawatts is the equivalent production capacity of three to four coal or nuclear power plants — though wind and solar farms can't operate constantly.

Those megawatts translate into about a dozen large wind and solar projects for utilities, including the Odell and Prairie Rose wind farms in Minnesota.

Geronimo is currently developing Blazing Star, a particularly large wind project in southern Minnesota for Minneapolis-based Xcel Energy. Xcel has worked with Geronimo on several projects.

Geronimo also developed the Aurora solar project in Minnesota, and has been a major force in Minnesota's Community Solar Garden program, accounting for over one third of its production capacity. The program accounts for the majority of solar energy produced in Minnesota.

Mike Hughlett • 612-673-7003

Correction: An earlier version of this story incorrectly stated the total power generation capacity of wind and solar energy projects that Geronimo Energy has completed. They can produce 2,400 megawatts.