Due to the strong wind energy business in Denmark, the EWEA conference has been held a few times in Copenhagen. I attended one of those events, and there were a bunch of nice surprises I remember from that trip: the beauty of the city, changing of the guards at Amalienborg palace, and the strong leadership shown in a round table discussion by the European commissioner for Climate Action at the time, Connie Hedegaard.
I also remember the brochure of this blade manufacturing leader claiming in a big size font that ´size matters´. The minute I started unfolding to extend the brochure of their +60 metre length blade -a real scale sample was sitting at the parking lot-, I suspected that there was some pun intended in the leaflet title.
Jokes aside, size does matter in the wind energy business. The capability of a turbine to capture wind power is proportional to the swept area, and as a consequence, twice the blade length yields four times energy production below rated power. Not really rocket science, right? So, why not increasing blade length extensively? Well, because clients do not exactly demand bigger turbines, but turbines that produce cheaper energy considering OPEX, CAPEX and finance costs, the well-known LCOE. Thus, LCOE is not only affected by the swept area over rated power ratio, but also by logistics constraints, and average wind speed and turbulence intensity among others.
Although it is certainly true that bigger does not always entail lower LCOE, it shows a strong dependence on rotor size. As a consequence, several turbine manufacturers are recently joining the 4 MW club, including Nordex Acciona, Vestas, Siemens Gamesa, GE and Enercon.
It is our experience that around 20% of the rotors in existing wind farms show a significant amount of aerodynamic imbalance. For a significant amount, we mean that it not only increases fatigue loads, but it also leads to decreased performance in the below rated power region of the power curve. So, it affects energy production under the wind conditions in which turbines operate most frequently.
Removing rotor imbalance never paid off that much before!
P.S.: I took this picture from the rear door of a turbine prototype over a smaller turbine wind farm. This turbine -not shown in the picture- was for the time being a great commercial success due to lower LCOE greatly caused by larger rotor size for its class.