RES installed the met mast at the site in the Irish Sea in August, shortly before the Dong Energy and Scottish Power Renewables project was completed.
Under the O&M deal, RES will maintain the entire structure and its instrumentation. It is located 14 kilometres off the UK's north west coast.
The company was awarded the contract to construct the mast in June 2013. It is designed as a performance management tool aimed at improving the efficiency of the wind project.
RES currently carries out met mast O&M services at several sites around the UK, including Forewind's 7.2GW Dogger Bank zone and the 4GW Hornsea zone, both in the North Sea.