ROMO Wind has requested ECN to evaluate its iSpin Guardian approach, which is an approach for wind farm performance monitoring. ROMO Wind’s aim is to make wind farm performance more transparent and for this approach to be used in warranty contracts between wind turbine manufacturers and wind farm owners. It is de?ned in six steps:
1. Determine the power curve of one reference wind turbine according to IEC 61400-12-1.
2. Determine the Nacelle Transfer Function (NTF) for this wind turbine according to IEC
61400-12-2.
3. Determine the nacelle power curve for this wind turbine according to IEC 61400-12-2.
4. Determine the 360° power curve for this wind turbine.
5. Determine the 360° power curve for all wind turbines in the wind farm.
6. Determine the average wind farm Annual Energy Production based on a pre-described Rayleigh wind speed distribution. All turbines that operate according to speci?cations should have an AEP within 2 % to 3 % of this average.
Currently, often use is made of the traditional, standardized methodology to evaluate the performance of wind turbines in a wind farm based on the IEC 61400-12-1 standard. Although proven technology, it is clear that this methodology has its limitations. Because the wind energy industry is getting more mature and therefore more demanding, new and innovative means appear, to overcome identi?ed limitations. In ECN’s view the iSpin Guardian approach is such a new and innovative method to assess the performance of all turbines in a wind farm. ECN has seen promising case studies that would enable wind farm operators to use the iSpin Guardian approach in the ?rst place to identify the status quo of the power performance for the turbine of the wind farm. This already is very valuable in itself.
Next, and more importantly, ECN has investigated to what extent the iSpin Guardian approach
can be used in warranty contracts between wind turbine manufacturers and wind farm operators. Such contracts are best made based on standards. Therefore it is noted that the iSpin technology, which is the basis of the iSpin Guardian approach, is incorporated in the IEC 61400-12-2 standard. The obvious potential bene?t for the operator is that he has more means to validate the power performance of the (individual wind turbines in the) wind farm. On the other hand the potential advantage for the wind turbine manufacturer is that he can provide more attractive warranty conditions providing an advantage over competitors.
The most critical aspect of the iSpin Guardian approach, in ECN’s view, is the 360° iSpin based power curve, i.e. that the Nacelle Transfer Funcon is stable when applied in wake conditions. This is the most crucial and potentially most advantageous aspect of the approach. In the cases ROMO Wind presented to ECN, it was indeed shown that the 360° iSpin based power curve provided the same power curve as the iSpin power curve obtained in the undisturbed sector, i.e. according to IEC 61400-12-2. Of course the limitations of the speci?c cases are acknowledged here.
In order for the iSpin Guardian approach to be adopted in warranty contracts, international and industry acceptance of particularly the aspect of NTF stability in wake conditions is necessary. Industry acceptance can be achieved if this aspect is incorporated in internationally acknowledged recommended practices and/or guidelines as for instance in the framework of IEA Wind, MEASNET and/or IEC. For this, various independent studies should demonstrate under what particular wake conditions (near wake, far wake, multiple wake) the NTF is stable, and preferably why and under what terrain conditions: ?at terrain, complex terrain, o?shore.
Despite these necessary steps for warranty contract adoption, based on the presented cases ECN believes that the iSpin Guardian approach, as it is at this moment, already is a valuable tool for wind farm operators. The approach is well-suited for monitoring the relative performance of the turbines in a wind farm, which can be used to identify potential performance issues.