MUNICH/MADRID (Reuters) - German engineering group Siemens (>> Siemens AG) and Spanish renewable energy group Gamesa (>> Gamesa Corporacion Tecnologica SA) are in final negotiations on a deal to merge their wind power assets, two sources familiar with the situation told Reuters on Wednesday.

"They are all sitting together in Madrid at the moment," one of the sources said, adding that a deal was imminent and that the enterprise value of the joint venture would be close to 10 billion euros (7.76 billion pounds).

A Siemens-Gamesa joint venture would overtake Denmark's Vestas (>> Vestas Wind Systems A/S) to become the world's biggest wind farm manufacturer by market share, operating in the mature North American and European markets and fast-growing markets like India, Mexico and Brazil.

Siemens is dominant in the offshore wind market but relatively weak onshore and has struggled to make wind power profitable.

Gamesa is strong in emerging markets, notably Latin America, where it expanded when the Spanish government cut subsidies to clean energy producers in 2013.

A Siemens-Gamesa deal would be the latest in a string of mergers in the wind industry. Having weathered years of overcapacity and losses, it is now thriving as demand for carbon-free electricity increases.

Pooling R&D efforts and funding gives groups more options in an industry where products are developing and improving fast.

Gamesa had already partnered with France's Areva to build offshore wind turbines through their Adwen joint venture.

A Siemens-Gamesa joint venture would give Siemens a foot in the nascent huge French offshore market but could also raise competition issues in that market segment.

Gamesa expects double-digit sales growth through 2017, when it hopes to sell 3,500-3,800 MW of capacity, up from an estimated 3,100 MW in 2015.

Last year, 12.8 gigawatts of wind capacity was installed and grid-connected in the EU, a 6 percent increase on 2014, with growth especially strong in offshore, where installed capacity doubled to 3 GW, according to the European Wind Energy Association (EWEA).

More wind power was installed than any other form of power generation in 2015 and accounted for 44 percent of total 2015 power capacity installations, EWEA said.

Market leader Vestas started the consolidation trend late in 2013, when it teamed up with Japan's Mitsubishi Heavy Industries (>> Mitsubishi Heavy Industries Ltd) to build offshore wind turbines, a capital-intensive industry with long lead times that favours companies with strong balance sheets.

German turbine maker Nordex said in October it was buying the wind power business of Spain's Acciona (>> Acciona SA) for 785 million euros.

(Reporting by Alexander Huebner in Munich and Jose Elias Rodriguez in Madrid; Writing by Georgina Prodhan and Geert De Clercq; Editing by Maria Sheahan and Louise Heavens)

By Alexander Hübner and Jose Elías Rodríguez