1. Operations and maintenance:
Operational support is provided 24/7, 365 days a year, including responding to unexpected events and turbine faults, weather monitoring, turbine condition monitoring plus customer and supplier interaction.
Maintenance includes scheduled and unscheduled activities and requires regular transfer of personnel to the wind turbines and onshore and offshore substation.
Safe access to the turbines is a critical area for further focused innovation.
If required, specialist staff from the turbine manufacturer will carry out major repairs.
‘Availability’ is the measure of the percentage of time the wind turbine is ready to produce power if the wind is blowing. Modern onshore turbines have availability of around 98%.
‘Capacity factor’ is the measure of the energy (MWh) produced as a percentage of the theoretical maximum that could be produced if all wind turbines ran at full power in high winds all year. For modern offshore turbines capacity factor may be as high as 40-50%.
O&M activities aim to optimize the availability and capacity factor of a wind farm whilst keeping costs to an acceptable level.
Typically, wind turbines are under warranty for the first 5 years of their lives and manufacturers provide full O&M services during this period. After this, the wind farm owner may operate the wind farm itself, contract to a specialist services company or develop an intermediate arrangement.
Components: Operations. Maintenance.
Monitor the performance of the wind farm and plan maintenance schedules, plus manage customer and supplier interaction.
The onshore control room provides access via SCADA and other systems to detailed real-time and historical data for the wind turbines, substation, met station, offshore crew and vessels. Wind farms are monitored remotely using SCADA and condition monitoring systems as well as active inspections, including of subsea infrastructure.
Review of SCADA data and prognostic condition monitoring can help to time preventative maintenance before failure occurs.
Careful planning of routine and unscheduled activities with due consideration of weather conditions and availability of spares and specialist vessels is critical. Systems ensure that the operations duty manager knows where all personnel and vessels are located.
In addition to hardware-related activity, environmental monitoring to understand the effect of the wind farm on the local environment and wildlife is also carried out.
Each turbine has a refuge and emergency provisions in case crew are stranded on the turbine. In emergency, individual turbines or the whole wind farm can be shut down remotely to allow safe access by rescue services.
Provide routine observation, service and repair.
Scheduled maintenance routines improve turbine reliability and are essential for safe operation. Turbine maintenance includes visual inspection of blades and all other key components, hydraulic checking of key bolted joints, lubrication (including refilling of automatic lubrication systems), end-to-end checks on proper operation of the safety and emergency systems, replacement of consumable items (such as slip ring brushes) and cleaning.
Scheduled maintenance is best done in the summer when on average access is easier and revenue loss from the turbine being stopped is less. Unscheduled maintenance is likely to be in response to turbine faults or warnings flagged by review of operational data. Routinely, if an unscheduled visit is required, then consideration is given to carrying out routine activities at the same time.
Strict health and safety requirements dictate the size of vessel and maintenance crews.
Components: O&M port. Technician and equipment transfer. Offshore accommodation. Large component refurbishment, replacement and repair.
1.1.1 Operations and maintenance port:
The provision of facilities from which to operate and monitor the wind farm, plus local services and fuel for vessels.
Typically wind farm operators will look to use the nearest port that meets its specifications to minimize time lost due to bad weather. For wind farms more distant offshore, the use of offshore accommodation and other facilities (possibly shared with other wind farms) becomes more attractive.
Office space can be shared as long as it has a secure area.
Ideally the buildings are close to the quayside to minimize the time loading support vessels. Large replacement components (i.e gearboxes) are unlikely to be kept on site.
A large wind farm may employ up to 100 people, of which three quarters will be technicians.
The availability of skilled people is a concern for wind farm owners and operators. O&M facilities need 24/7 access, 365 days a year.
As well as the port facility, operators will use remote land based support, such as specific engineering advice and information and support, performance monitoring, and 24/7 control room monitoring.
Uninterrupted access requires the availability of a non-drying harbor. Each support vessel will need a 20m berth. A large wind farm may require the operation of around 7 vessels, depending on distance to shore. The port may need a range of different ramped and stepped access to facilitate simultaneous transfer to multiple vessels.
Components: Administration facilities and operations room. Lifting equipment, for example forklifts (600kg) and small cranes (1 ton) to move components from the harbor to the service vessel. Workshop, with provision for hot work (including welding, angle grinders), clamping equipment, workbench areas and tool storage. Stores, with small components that do not need specialist vessels to facilitate use. Wet and dry rooms, with space for PPE. Fuel bunker, which stores fuel for helicopters and vessels.
1.1.1 Technician and equipment transfer:
Provide access for technicians to the wind farm, either by vessel or helicopter.
Key requirements are robust vessels that can operate in adverse weather conditions. Many wind farm operators are opting to use 20m aluminum catamarans with capacity for 12 technicians.
Vessel speeds can be over 20 knots and are designed to transfer maintenance team members in comfort and safety to the wind farm ready to start work.
Helicopters provide access to turbines and offshore substations or accommodation including when weather conditions prevent access by boat. They can accommodate five technicians.
Typically wind farm operators will contract the helicopter operator for a number of days use a year.
Turbine access is an area with scope for innovation. Some service vessels have adapted bows to facilitate access to the turbine platform. New solutions could include personnel lifting systems that could transfer personnel in higher sea states and wave compensating systems.
Main vessel operators: North Sea Logistics, Windcat Workboats, MPI Workboats and Turbine Transfers.
Manufacturers: Alicat, Alnmaritec, Arklow Marine and South Boats.
Helicopter operators: Bond Air Services.
1.1.1 Offshore accommodation:
Provides accommodation for technicians on the wind farm site, thus reducing transit time significantly.
Offshore accommodation will become an attractive option for wind farms operators for sites further from shore. An offshore accommodation facility would require many of the systems currently employed to meet the needs of personnel working on offshore substations, i.e. generators, lighting, water supply and treatment, access facilities and welfare facilities.
1.1.2 Large component replacement:
Replace large components such as blades, gearboxes and generators in a timely and cost effective manner.
Design methodologies for offshore turbines facilitate easier large component repair or indeed replacement with less external intervention. On-board service cranes can in some cases lift substantial loads
Some components on turbines however need a jack-up barge to enable replacement, although smaller vessels than those used during turbine installation can be used. Exchange is carried out in one visit, followed by off-site repair.
Retrofit programs are carefully planned to ensure effective vessel utilization taking into account repair turnaround times.
The Crown Estate. “A Guide to an Offshore Wind Farm”. Provides technical and policy-related information on offshore wind turbines. This is the source used for all the information in this document.