Average productivity in Denmark, measured in the number of kilowatt hours of output per square metre of rotor swept area, is 716 kWh/m2, compared with 589 kWh/m2 in Germany. Both Denmark's highest producing turbines are Vestas 200 kW turbines, thought both have larger than normal rotor spans. The Vestas machines are among the overwhelmingly large proportion of single units in Denmark -- 1111 in the study sample alone -- compared with turbines sited in clusters or wind farms.
"There is a significant proportion of smaller machines among those achieving the highest outputs," notes the analysis of Denmark. The same trend is also seen in Germany, although here it appears that older, smaller turbines occupy the best wind sites, pushing newer, and larger, turbines into areas of lower wind speeds, which accounts for the discrepancy. "A more detailed analysis of the German data does show an underlying trend of better performance with higher ratings," states the analysis.
The study also compares the output of machines from the eight top suppliers of wind turbines to the German market, with two Danish companies, Vestas and Bonus, coming out on top. Nordex turbines from Borsig Energy and Tacke turbines from Enron were among the poorest performers. An Enercon 200 kW machine, however, had the highest capacity of them all, 47%, topping a Vestas 200 kW machine in Denmark by one percentage point.
"Overall the picture that emerges from this analysis is of a healthy industry steadily improving the energy output of wind turbines by various means -- larger machines, higher outputs and higher and higher ratings," concludes the WindStats report.