10089_001.pdf - Load set calculation - ECN

Load set calculation DOWEC 6MW H. Efdé
5 Design variations.
By altering Phatas IV input files and/or executables by ECN and Stentec, design variations are
created. These are compared with the baseline DOWEC turbine. Not the whole load set is used, but
just the load cases that have caused the highest loads. The following load cases are chosen to
calculate the design variations: 012, 018, 024, 1B-5Vo, E50025, E50335, EcdVrb, Eog50-12,
GrEog1Voc.
5.1 Cost of energy.
To clarify the results, the cost of energy per design is calculated according ref. [9], chapter 5.
The cost of a wind turbine can be broken down in cost per component. Important design (and cost)
drivers of a component are the extreme and fatigue loads it has to withstand. A further break down is
achieved by weighing the several loads. By comparing load changes with the baseline configuration
an estimation can be made about the change in cost of the wind turbine.
Table 12: Influence of parameters on wind turbine cost.
cost of
component contribution
wind
cost to wind
turbine
contribution turbine cost
component (%) design driver load parameter (%) (%)
blade 6
extreme flat moment Myb[1]-p[01] 25 1.5
fatigue edge moment 1Hz-Mxb[2]-p[01] 25 1.5
gearbox 5
average torque Mxn mean 75 3.75
tower 16
extreme tilt moment foot Myt[01] 30 4.8
fatigue tilt moment top 1Hz-Myt[02] 20 3.2
If the change in annual yield is known as well, the cost of energy can be calculated by dividing the
wind turbine cost by the yield:
Influence of design variation on cost of energy = (change in wind turbine cost)
(change in annual yield)
It must be noted that these variations are one dimensional and therefore very crude. For example a
tip speed variation would be more effective with a blade design adapted to that speed. But in this
case the only change is the tip speed.
The results should not be judged for their values, but used as a guideline to further develop the 6MW
DOWEC.
5.2 Structural pitch.
By changing the position and rotation of the girders in the blades, the stiffness properties are
changed. The changed behaviour of the blades should result in smaller tip deflection and a decrease
of fatigue and extreme loads. 4 redesigns (ref [10]) are calculated :
• tr+5-5, girders 0.5 o rotated, at tip girder suction side 0.5m to aft and girder pressure side
0.5 m forward.
• tt+5, girders 0.5 o rotated, at tip girder suction side and girder pressure side 0.5 m aft.
R45.04/01.03/03 Stentec, 3-1-03 page 15