Commissioning & Handover
Turning a field of installed machinery into a generating asset - energisation, turbine commissioning, first power, performance testing and the formal handover into operations. It is the end of the project and the first day of a twenty-five year maintenance job.
Last updated 2026-08-24
Typical duration
Commissioning runs in a rolling wave behind installation and continues for months after the last turbine is set; taking over is a contract date, but the reliability and performance runs behind it can extend into the following season.
What is Commissioning & Handover?
Commissioning is where an offshore wind farm stops being a construction site and becomes a power station. Every turbine that reached mechanical completion is a machine that is bolted together correctly and can be safely entered; it is not yet something that generates. Commissioning takes it the rest of the way: energising the supply to the tower, proving the auxiliary systems, checking the safety chain, verifying the protection settings, exercising the yaw and pitch systems, releasing the rotor, running the machine up, synchronising it to the grid and then watching it carefully for long enough to believe it. Multiply that by the number of turbines, do it from a boat, in a queue behind the installation vessel, with a weather window governing every transfer, and the scale of the exercise becomes clear.
It does not happen at the end. Commissioning overlaps installation heavily, because the alternative - waiting until the last turbine is set before starting - would waste an entire season and delay the revenue that pays for everything. So the offshore substation is energised early, array strings are brought alive one at a time as they are terminated and tested, and turbines are commissioned in batches behind the installation campaign. Early machines start generating while later ones are still being lifted, which is excellent for the project economics and demanding for everyone managing the interface, because part of the field is now a live high-voltage installation while the rest is still a construction site. The permit-to-work regime and the boundary between construction control and operational control become the most important documents on the project.
The end point is a formal handover: the contractor demonstrates that the asset performs as promised, the owner takes it over, the warranty period starts and a long operations and maintenance phase begins. That phase is where most of the wind farm's life is spent and where most of its total cost is eventually incurred. It runs from an onshore base with a quay, a warehouse and a control room, using crew transfer vessels for day trips and service operation vessels with motion-compensated gangways for the far offshore sites where technicians live aboard for weeks. What gets handed over - the as-built records, the data, the spares, the trained people and the honesty of the punch list - determines how well that phase goes. Availability figures are made or lost in the first two winters, and they are heavily influenced by decisions taken during commissioning.
Compare the methods at a glance
When and why is Commissioning & Handover used?
Commissioning starts as soon as there is anything to commission and continues in a rolling wave behind the installation campaign until the last machine is proven, which usually means it extends well past the end of the offshore construction season. It matters more than its position at the end of the sequence suggests, for two reasons. The first is commercial: every day a completed turbine sits uncommissioned is a day of lost generation on an asset that has already been paid for, so the pressure to accept machines quickly is intense and constant. The second is technical: this is the last point at which the project team, the turbine supplier and the installation contractors are all still present, still contracted and still motivated to fix things. Any defect not found and closed now becomes an operational problem to be solved by boat, in a weather window, by a small team with a lift capacity measured in what fits through the tower hatch. The purpose of a rigorous commissioning and handover process is to move problems back across that line while they are still somebody else's to fix.
Types of Commissioning & Handover
Explore each method in depth - benefits, limitations, plant and quality control on its own page.
Pre-commissioning and mechanical completion
The bridge between installation and commissioning: confirming that the machine is complete, correctly assembled, safely accessible and free of construction debris. Bolt tensioning records are audited, fluids and filters checked, cabling verified, safety systems and rescue arrangements proven and the tower dried and sealed. It generates the punch list that everything downstream is measured against, and it is the last comfortable moment to admit that something is not finished.
Energisation and cold commissioning
Bringing supply to the machine and proving everything that can be proved before the rotor turns under load. Protection settings are verified, control and communications links to the onshore control room are established, auxiliary systems and heaters are run, the safety chain and emergency stops are tested and the yaw and pitch systems are exercised. It is the stage where high-voltage discipline replaces construction discipline, and where the permit regime has to be understood by everyone stepping off the boat.
Hot commissioning and first power
The rotor is released, the machine is run up, checked through its operating range and synchronised to the grid for the first time. Vibration, temperatures, noise, pitch response and control behaviour are all observed against what the turbine supplier expects. First power on the first machine is a project milestone that gets photographed; first power on the fortieth is a routine step in a production process, and the discipline needs to be identical for both.
Performance testing and taking over
Proving the asset does what the contract says: power performance measured against the guaranteed curve, availability demonstrated over a defined reliability period, noise and grid compliance verified, and the control system shown to respond correctly to grid instructions. Successful completion triggers the taking-over certificate, the start of the warranty and the transfer of the asset to the operations team. It is a contractual event supported by data, which is why the data has to be trustworthy from day one.
Best suited for
- Converting installed machinery into a proven, contractually accepted generating asset
- Surfacing systematic defects while the installation vessels and suppliers are still on site and still contracted
- Establishing the data baseline that the operations phase will rely on for the life of the wind farm
- Transferring knowledge, spares and trained people so the operator can run the asset rather than learn it
Commissioning & Handover: step by step
- 1
Step 1: Close out mechanical completion, machine by machine
Each turbine is walked down against the supplier's checklist before commissioning will accept it. Bolt tensioning records are audited rather than assumed, fluids and lubrication checked, filters fitted, cabling and terminations verified, lightning protection continuity confirmed, the service lift and climb assist proven, and the tower cleared of the debris that construction leaves behind. Drainage and sealing are checked, because a tower that takes water in year one is a corrosion problem for the next twenty-five. What comes out is a punch list, and its honesty is the single best predictor of how the operational phase will go. A punch list that says a machine is complete when it is not simply moves the work to a team who will have to reach it by boat.
- 2
Step 2: Energise the export route and back-energise the array
Power comes from the grid outwards. With the onshore substation and grid connection ready, the export cable and offshore substation are energised, then each array string is brought alive in turn as its cables are terminated and tested. Every energisation is a controlled operation with isolation verified, protection proven and a permit regime that all parties have signed up to. This is the moment the site changes character: part of the wind farm is now a live high-voltage system while turbines nearby are still being installed, so the boundary between construction control and operational control has to be drawn on a drawing, briefed to every crew and enforced without exception. Confusion about who controls what is the root of most electrical incidents on projects like these.
- 3
Step 3: Cold commission the turbine
With supply available, the machine is commissioned without generating. Auxiliary systems, heaters, dehumidifiers, lighting and small power are proven, the control system is brought up and its communications to the onshore control room established, protection settings are loaded and verified, and the safety chain is tested - emergency stops, overspeed protection, vibration monitoring, rotor lock arrangements and the interlocks that keep technicians alive. Yaw and pitch systems are exercised through their range and their responses compared against expectations. Sensors are calibrated and their signals confirmed at the control room, because a machine that generates perfectly while reporting rubbish is a machine that cannot be operated or proven.
- 4
Step 4: Release the rotor, run up and take first power
The rotor lock comes off and the machine is run for the first time, brought up gradually while temperatures, vibration, pitch behaviour and control response are watched by people who know what the turbine supplier expects them to look like. Any anomaly is investigated before it is normalised. When behaviour is satisfactory the machine is synchronised to the grid and exports for the first time, then run through its operating range and observed under real conditions. The first machine on a project takes days and teaches the team what to look for. By the tenth the sequence is routine, and the risk shifts from unfamiliarity to complacency - which is precisely why the checklist stays the same for every machine, however many have gone before.
- 5
Step 5: Close out defects while the vessels are still there
Commissioning finds things, and the window in which they can be fixed cheaply is short. Some defects need a heavy-lift vessel and can only be dealt with while the installation campaign is still on site, which is why early commissioning of early machines is worth so much - it surfaces systematic problems while there is still a means of correcting them. Others need a specialist, a spare or a supplier engineer, and getting those offshore takes planning. Defects are tracked centrally rather than in each technician's notebook, categorised by whether they block generation, block takeover or can be lived with, and the ones that repeat across machines are escalated as fleet issues instead of being fixed forty times over.
- 6
Step 6: Prove performance and availability
Contractual proof comes from measurement, not opinion. Power performance is tested against the guaranteed curve using measured wind data from met masts or remote sensing equipment, over a period long enough to cover a useful range of conditions. Availability is demonstrated over a defined reliability run, with the control system data providing the evidence of how much of the time each machine was able to generate. Grid compliance is verified against the connection agreement - the wind farm has to respond correctly to instructions and behave properly during disturbances. All of it depends on the monitoring data being complete and trustworthy from the start, so gaps in the record during commissioning are not an administrative nuisance, they are a hole in the evidence that takeover depends on.
- 7
Step 7: Hand over the documentation, the spares and the people
The physical handover is the easy part. What actually transfers is knowledge: as-built drawings and records for every structure, cable and machine, protection settings and test results, operating and maintenance manuals, software versions and access credentials, the position and details of every cable joint and protected section, and the inspection baselines that every future survey will be compared against. Spares are received into the warehouse and checked rather than assumed, special tools and lifting equipment are transferred with valid certification, and the operations technicians are trained on the specific machines they will maintain. The onshore base - quay, warehouse, control room and vessel arrangements - has to be running before takeover, not after it.
- 8
Step 8: Take over, start the warranty and begin operations
Taking over is a contractual event with a date, a certificate and consequences. Risk and control transfer to the owner and operator, the warranty period starts, and the defects liability arrangements define who fixes what and for how long. The remaining punch list transfers with an agreed programme and, usually, retained money against it. From that point the asset is in operations: a rolling programme of scheduled maintenance, blade and cable inspections, condition monitoring and unplanned repairs, delivered from crew transfer vessels or service operation vessels according to how far offshore the site sits. The first two winters teach the operator what the project team really handed over, and the quality of the commissioning records is what makes that education survivable.
Plant & equipment
- Crew transfer vessels for day access and service operation vessels with motion-compensated gangways for offshore living
- Helicopters for personnel transfer and rapid response on the more distant sites
- Onshore control room, monitoring and data systems linked to every turbine and to the substation
- High-voltage test equipment, secondary injection sets and commissioning instrumentation
- Met masts and remote sensing equipment for measuring the wind during performance testing
- Internal turbine service lifts, climb assist and rescue equipment for working at height
- Onshore operations base with quay, warehouse, spares holding and workshop
- Diagnostic and condition monitoring systems for drivetrains, blades, structures and cables
Quality control & testing
- A completed commissioning record for every individual turbine, held against its serial number
- Protection settings verified end to end from the turbine through the array to the export connection
- Monitoring and control system data continuity proven from first energisation, since availability cannot be demonstrated from a record with gaps
- Power performance measured against the guaranteed curve using verified wind measurement
- Alarms, trips, emergency stops and the safety chain individually proved rather than assumed
- Bolt tensioning and torque audits sampled across the fleet, not just recorded at installation
- High-voltage test records for the substation, array and export systems compared against factory baselines
- As-built documentation, spares and certification checked in on receipt rather than accepted on a list
Safety watchpoints
- The wind farm is a live high-voltage installation during commissioning, with construction still under way nearby - the control boundary must be explicit and enforced
- Permit-to-work and isolation discipline between the contractor and the operator, agreed and briefed before the first energisation
- Working at height inside turbines, with rescue arrangements proven for every position and every access route
- Stored energy in the rotor, drivetrain and pitch systems, controlled by rotor lock and isolation before any hub or drivetrain entry
- Transfer between vessel and turbine in a seaway, which remains the most frequent source of injury in offshore operations
- Small teams working in remote positions, requiring communications, tracking and a workable emergency response plan
- Weather and sea state limits governing every transfer and every decision to leave people offshore
- Fatigue management across long shifts, long transits and rotating crews, which quietly underlies most of the above
Common defects to hunt
- Turbines accepted with open punch items that become operational work reachable only by boat
- As-built documentation incomplete, inconsistent or missing, leaving the operator to rediscover the asset
- Gaps in monitoring data during commissioning, making contractual availability impossible to demonstrate
- Protection settings never verified end to end, so a real fault is not cleared where it should be
- Early drivetrain, bearing and blade issues that appear in the first winter and were visible in commissioning data nobody reviewed
- Water ingress, blocked drainage and corrosion inside towers, traced back to seals and hatches left incomplete
- Spares not physically on the shelf despite being listed, so the first failure becomes a long outage
- Access, lifting and rescue equipment transferred without valid certification, stopping work at the worst moment
How long does Commissioning & Handover take?
Typical duration: Commissioning runs in a rolling wave behind installation and continues for months after the last turbine is set; taking over is a contract date, but the reliability and performance runs behind it can extend into the following season..
Related processes
Previous in sequence
04 - Offshore Substation