Which way a wind turbine turns might not seem to matter

IF THE HANDS of dial clocks swept over their faces the other way around, that would be the direction known as “clockwise”. And they would tell the hour just as faithfully. It is convenient to have all clock hands turn in the same direction, but it is an accident of history which direction that is. Similarly, it seems an arbitrary but efficient choice by wind-turbine makers that the blades of almost all of those devices turn clockwise. However, a study presented on May 4th to the General Assembly of the European Geosciences Union (held online, instead of in Vienna, as planned), suggests that in the northern hemisphere, where 96% of these turbines are found, universal clockwiseness may be bad.For a single turbine it does indeed not matter. But turbines are usually planted in groups. If, in such a group, one turbine is behind another then it does matter, according to Antonia Englberger of the German Aerospace Centre, in Oberpfaffenhofen, and her colleagues. They have built a computer model which simulates the flow of air over a turbine turning in either direction, and then calculates the effect this has on a second turbine, downwind of the first. By day, the team conclude, there is no difference. But at night the power output of the downwind device may be up to 23% higher if its upwind colleague is turning anticlockwise.