* Has applied for permission to test 10 MW turbines
* Says has no immediate plans to develop the turbines
* Siemens plans 10 MW turbine for later this decade
By Shida Chayesteh
COPENHAGEN, July 11 (Reuters) - Denmark's Vestas is seeking a green light from the government to test the largest offshore wind turbine yet, papers submitted to local government show, in a bid to catch up with rival Siemens at the new frontier of wind energy.
Although Vestas said it had no immediate plans to develop them, the documents show it has applied for permission to set up test turbines of up to 10 megawatt (MW) in waters west of Jutland, the part of Denmark linked to continental Europe.
That is a quarter more powerful than the 8 MW turbine Vestas is testing now and which could power 7,500 homes a year.
Vestas is developing these turbines together with Japan's Mitsubishi Heavy Industries (MHI) as part of their MHI Vestas Offshore joint venture.
Vestas is the world's largest wind turbine maker based on its market share for windmills on land but it has fallen behind in the race for the fledgling offshore market.
The industry is developing larger and larger turbines that can be placed further offshore, where the wind potential is greater and prospects of public resistance are smaller.
"We will not make any comment now on the precise development plans for future wind turbines, but we are always looking to optimize our platforms," Chief Executive of the joint venture, Jens Tommerup, said in an email to Reuters, adding that the focus now was on the 8 MW turbine.
The documents submitted to the Ringkobing-Skjern commune, on the west coast of Jutland, relate to tests of the 8 MW turbine but show a request to be allowed to install 10 MW units.
Siemens, which plans to unveil a 10 MW offshore turbine by the end of the decade, extended its offshore lead over Vestas last year, with a European market share of 60 percent, data from the European Wind Energy Association showed.
But Vestas has a habit of surprising the industry with its investments. In 2011 it unveiled a 7 MW turbine when investors had expected a 6 MW unit, before announcing that the turbine would then run at 8 MW.
It's most powerful turbine in service has a capacity of 3.3 MW and stands at between 140-190 metres, depending on its location, with the capacity to power 3,300 homes.
The 8 MW turbine has a tip height of about 220 metres with 164-metre rotors that have a sweep area of more than 21,000 square metres, equal to three football pitches. Siemens' 6 MW offshore turbine has 154-metre rotors.
A 10 MW turbine would have a rotor diameter of up to 200 metres and an overall height of up to 250 metres, according to the documents.
Siemens was Europe's top offshore supplier last year, installing 1,249 wind turbines compared with just 574 turbines from Vestas.
Britain and Denmark are Europe's leading offshore wind markets, with installed capacities of 3.68 gigawatts (GW) and 1.27 GW respectively. In Denmark, 33-34 percent of electricity is provided by wind farms and the government wants to increase that to 50 percent by 2020. (Editing by Sabina Zawadzki and Mark Potter)