Spanish construction and renewable energy giant ACS Group says it has sold a chunk of its wind energy business to a private equity firm for $850 million.

ACS, which announced last year it would put its operating renewable energy assets up for sale, completed a deal Friday with European private equity firm Bridgepoint for a portfolio of 11 wind farms in Spain's northwestern Castile and Leon region.

Bridgepoint described the portfolio as the largest independent platform of wind assets in Spain with 443 megawatts of installed capacity.

"This is a strong platform of wind operating plants in a strategic industry with attractive growth prospects," Bridgepoint Director Felipe Moreno said in a statement. "Wind is the leading technology within the growing global renewable energy sector and we believe that this business, with the right leadership, can become the leading player in the Spanish wind industry."

ACS, or Actividades de Construccion y Servicios S.A., announced in November it would dispose of its Spanish and international renewable energy portfolio.

At the time, its portfolio totaled about 1,757 megawatts, comprised of 1,056 megawatts of wind power in Spain, 352 megawatts of wind power installed outside Spain and 349 megawatts of concentrated solar power in southern Spain.

Last month ACS sold its 90 percent stakes in its Andasol 1 and 2 solar plants to the Deutsche Bank-controlled RREEF Pan-European Infrastructure Fund and to Antin Infrastructure Partners, which is partly owned by BNP Paribas.

Both solar plants use parabolic-trough technology and each has a capacity of 50 megawatts, the Norwegian online energy trade journal Recharge.com reported.

Meanwhile, ACS also sold its stakes in five wind farms with a total capacity of 95.5 megawatts to the Spanish utility Gas Natural Fenosa.

ACS, which is led by Madrid businessman and Real Madrid soccer club president Florentino Perez, is locked in a legal battle to gain a seat on the board of directors of Spanish utility giant Iberdrola.

ACS is Iberdrola's largest single shareholder at 20 percent, and the utility has been fighting to keep Perez's representative off the board on the grounds it is a direct competitor and aims to merely further its own interests and eventually take over the company, Recharge.com reported.

Analysts have speculated ACS is selling its renewable power assets to demonstrate it's not a direct competitor to Iberdrola.

Bridgepoint, the buyer for the Castile and Leon wind farms, said the wind sector in Spain is a good investment.

"Notwithstanding the financial crisis, the wind sector in Spain achieved (a compounded annual growth rate) of 15 percent since 2005, and in 2010 alone provided over 16 percent of total electricity generation in the country," it noted.

"This high growth is forecast to continue with government long-term energy planning envisaging an increase in wind capacity of nearly 15 gigawatts by 2020."

Bridgepoint, RREFF and Antin Infrastructure Partners are hardly the only private firms venturing into the European renewable energy market.

A subsidiary of the New York firm Blackstone this month announced it had completed a $1.7 billion financing for Meerwind, an 80-turbine wind farm about 30 miles off the German coast in the North Sea.

Blackstone also said it would provide $1.9 billion to construct the 64-turbine Nordlicher Grund wind farm about 60 miles off the German coast, with work to begin in 2013 and completion in 2016.