The XD137 is a wind turbine with a nominal power of 4 MW and a three bladed rotor with a diameter of 137 meters. The turbine design is derived from the XD115 offshore dedicated wind turbine generator. The turbine is designed according to IEC 61400-1 for a wind class IIA.
Supply chain management
Darwind uses the philosophy of horizontal integration what means all manufacturing is outsourced and we only assemble and test before sending the turbine to site. All design work however is done in house and in conjunction with strategic suppliers for components such as blades, bearings, hydraulic systems, towers and pitch system. In this sense we are a system integrator although the majority of the components are of exclusive design.
All intellectual property rights of the XD115 turbine are vested in XEMC Darwind B.V. (Netherlands). To date no license rights have been granted to third parties. To protect XEMC Darwind’s unique position over 20 patents are pending.
XEMC Wind turbine technologies
XEMC turbines are based upon the single bearing, direct drive, and permanent magnet principle.
Use is made of a single multiple row roller bearing on which the hub is mounted on one side and generator carrier and –rotor on the other side. The stator is mounted on the opposite side of the carrier which in turn is mounted on a compact casted nacelle frame. The advantage of this design is the relative big diameter the load path follows, contrary to the traditional designs with a main shaft. Hence considerable weight reduction is achieved.
Innovative design and new materials have resulted in an easy to install, large, lightweight turbines.
Our product platform is based on the direct drive principle, thereby dispensing of the need for gearboxes. Gearboxes pose a significant problem for offshore wind turbines because the torque of multi-megawatt wind turbines is enormous. In contrast, gearless turbines require less maintenance, are more reliable and therefore boast higher operating availability.
The rotor speed during power production is variable. The matching between the available aerodynamic torque and the produced electromechanical torque of the generator is determining the rotor speed. No use of a gearbox is made. The torque-speed curve is programmed in the frequency converter controller and the inverter is adapting the generator stator current in response to the measured generator power frequency.
Single main bearing & generator in one
The XEMC Darwind XD and XE platform is based on the single main bearing concept. The bearing has a large diameter that enables it to bear the enormous force of the rotor: there is no central shaft. The bearing component is integrated into the generator and is possible because the turbine uses direct-drive technology. This innovative design not only creates a compact and lightweight permanent magnet direct-drive generator; it also results in significant savings in logistics, foundation and support structure costs.
The tower and nacelle of the turbine are fully sealed to keep out the salty and moist sea air. This protects our valuable components, increases operational availability and saves a great deal of maintenance.
Coil driven generators make use of electrical excited magnets. XEMC’s Permanent Magnetic systems are lighter/compacter, more efficient and require less copper than Coil Driven generators. As no additional electricity is required to magnetise the rotor coils, there is no need for generator `brushes` to transfer this electricity. This increases both efficiency and reliability because the rotating part of the generator contains no electrical systems.
Full power conversion
The AC-DC-AC converter, located in the bottom tower section, allows the generator to operate with a variable speed while the power is fed into the grid with a constant frequency of 50 Hz (or 60 Hz for the countries where this applies). It furthermore assures an average constant power output for wind speeds above rated. The power factor at the grid side is controllable at standstill as well as in operating mode. Above rated wind speed, the blade pitch control maintains a more or less constant rotor speed between admitted boundaries.
Grid code flexibility / grid code compliance
XEMC wind turbines have a pitch-controlled variable speed rotor and a full power converter, capable of meeting the requirements of the most demanding grid codes, e.g. with respect to reactive power.
- On the 23rd of February 2012 XEMC Darwind signed a contract for the delivery and installation of 10 XD115 5MW wind turbines with Windkraft FiT GmbH, a joint venture between project developers Norderland GmbH and Strabag A.G. Value of the contract is Euro 75 million.
- The contract is a straightforward Turbine Supply Agreement with a payment schedule according to work progress and a down payment.
- This offshore project is called Albatros 1 and forms part of a larger and other concessions by the project developer.
- Reasons for choosing Darwind as the supplier can be summarised as follows:
- Project developer evaluated XD115 as ‘best value for money’
- Transparency of Darwind’s offer and openness of technical & commercial discussions i.e. negotiations
- Parent company XEMC Windpower, backed by the XEMC Group, signed-up for the liabilities associated with the contract
Albatros project financing
The Albatros project contract is to be seen as an exception to the rule where Windkraft FiT also took on the role of project financer. In this case Strabag had an additional incentive to choose for the XD115 as the wind turbine perfectly fits the envisaged concrete foundation developed by one of Strabag’s divisions, Strabag Offshore Wind GmbH.
Technical and financial risks associated with offshore wind are considerably higher than those associated with onshore wind. Nevertheless in both cases a project developer most often needs to turn to financing institutions to reach financial close. Financing institutions in general co-finance wind projects up to a maximum of 70%-80%. For obvious reasons reaching financial close for onshore projects takes considerably shorter than for offshore projects.
XEMC Darwind faces the hurdle that for its product portfolio there is little European track record available. However, this is overcome as:
- The XD115 has received its Provisional Type certificate and therefore in principle is bankable. In addition insurers are willing to insure the XD115 to LEG3 levels.
- From revenues generated by the operational XD115 in the Wieringermeer together with parent company guarantees, sufficient collateral and securities are provided. Certainly in cases of (smaller) onshore projects.
- Performance of the XD115 can be demonstrated to be as if it were a commercial seriesbuilt wind turbine.
- Technology used for the Darwind portfolio of products is the same as for the since 2006 already installed 1500 units of 2MW and 2.5MW XE Series in China (XEMC Windpower)
- Technological track record is therefore considerable and in Europe unequalled for DD PMG turbines.
- Contacted banks in the Netherlands have shown their interest in co-financing onshore wind projects incorporating a Darwind wind turbine.
- Via its parent company Darwind has direct access to Chinese banks showing an appetite to co-finance wind projects in the Western world.
- Once projects are realised and track record further established, bankability of Darwind turbines becomes more robust and bigger projects will be taken on.