Commonly accepted power curves of wind energy converters are essential for an effective comparison and for a reliable energy output prediction. Power curve measurements therefore have to be performed according to some specific standards. Recommendations have been drawn up which are rigorous and represent a good base for a higher precision in power performance determination and energy output prediction. A well founded interpretation and evaluation of a power curve, however, presumes additionally a detailed knowledge about the possible error and uncertainty sources which can affect power curve measurements. This knowledge is also necessary for an estimation of the total uncertainty of the energy output prediction. This work concentrates on mostly physical effects which cannot easily be standardised and therefore have to be treated carefully and it elucidates some sources of error which appeared to be important.
EXPERIMENTAL DETERMINATION OF THE POWASER PERFORMANCE OF A WEC IS ESSENTIAL FOR THE PREDICTION OF ANNUAL ENERGY OUTPUT AND AVAILABILITY, FOR EXAMINATION OF POWER CONTROL BEHAVIOUR AND NOT AT LEAST FOR COMPARISON OF DIFFERENT WECS.
COMMONLY ACCEPTED GUIDELINES FOR POWER PERFORMANCE MEASUREMENTS ARE THEREFORE NECESSARY TO MEET THIS OBJECTIVE. THE RECOMMENDATIONS OF THE INTERNATIONAL ENERGY AGENCY (IEA) FOR POWER PERFORMANCE TESTING DEVELOPED IN 1982 ARE A SUITABLE TOOL FOR THOSE NEEDS. BUT THERE ARE SOME MORE INFLUENCES OF VARIOUS KINDS AFFECTING THE ACCURACY OF THE POWER CURVE LIKE ICING OF ROTOR BLADES, RAIN, CONTAMINATION OF BLADES, ANEMOMETER OVERSPEEDING, SCALE EFFECTS, DATA EVALUATION AND CORRECTION METHODS. DURING MEASUREMENTS TAKEN AT THE DFVLR TEST SITE "ULRICH HUTTER" SOME OF THEM APPEARED TO AFFECT THE POWER CURVE CONSIDERABLY.
THIS STUDY WILL INVESTIGATE THOSE INFLUENCES AND THEIR EFFECT ON A WEC POWER CURVE TO GIVE MORE DETAILED RECOMMENDATIONS ON HOW TO ESTIMATE OR AVOID ERRORS RAISING OUT OF THEM. AS ADDITIONAL TASK IN THIS PROGRAMME AN INVESTIGATION HAS BEEN AGREED ON HOW TO CONTROL THE BOUNDARY FLOW AROUND A PROFILE BY VORTEX GENERATORS. FOR THE EXPERIMENTAL PROGRAMME THE 25 M DIAMETER DEBRA-25 WEC OF THE GERMAN AEROSPACE RESEARCH ESTABLISHMENT (DFVLR) WAS USED. FIRSTLY THE FLOW BEHAVIOUR ALONG THE BLADE LENGTH WAS MADE VISIBLE BY WOOL FIBRES TO ESTABLISH THE AREAS OF SEPARATED FLOW. IN A SECOND STEP VORTEX GENERATORS WAS APPLIED AT LOCATIONS OF FLOW SEPARATION TO STUDY THEIR EFFECT ON THE FLOW BEHAVIOUR. BECAUSE OF THE OBVIOUSLY POSITIVE INFLUENCE ON THE STREAM VORTEX, GENERATORS WERE MOUNTED ON THE ROTOR BLADES IN THE WHOLE RANGE OF OBSERVED FLOW SEPARATION. PRESENTLY POWER MEASUREMENTS ON THE BASIS OF 30-S- AND 10-MIN-AVERAGES ARE IN PROCESS TO DETERMINE THE EFFECT OF THE VORTEX GENERATORS.