Scroby Sands analysed -- Offshore performance

Both the availability and production performance of the 60 MW Scroby Sands offshore wind farm in England was better than forecast last year, despite outages to replace 11 of the generators in the 30, Vestas 2 MW machines and the replacement of a number of gearbox bearings in the fleet. The wind plant, on a sandbank about 3.5 kilometres off the coast of Norfolk in eastern England, was planned to be available for operation 78.8% of the time last year, but reached a commercial availability, which allows for the loss of the external grid connection and time spent waiting for access, of 87%. The technical availability, which does not include any allowances for routine or other maintenance activities was 83.8%. The wind farm's owner, utility E.ON, indicates in an annual report on the wind farm's performance issued by the UK government, that the good availability was due to major work undertaken with the aim of improving reliability and availability.

The average wind speed at the site during the year was 8.6 m/s and power exports amounted to 145,201 MWh, giving a capacity factor of 27.6%. Capacity factors of individual turbines ranged from 14% to 36%. The long term capacity factor is estimated to be 30.1%. Problems with one of the three cables that connect the wind farm to the shore led to some restriction of the output during the year. The Scroby Sands annual report illustrates the importance of careful scheduling of maintenance activities: there were 116 days when access to the wind farm was not possible. The wind turbines are accessed using specially adapted "transfer vessels" and these cannot operate in wave heights of more than about 1.5 metres.