In case of sites with lower than expected wind speeds, an increase in rotor area will improve the energy yield. As larger blades are typically not an economically feasible option due to the high cost, an extended blade tip can be a solution. Such extensions are usually limited to 3-5% of the length of the original blade.
Sample Layout for a 34m long 1.5MW blade
Limitations of blade extensions: The loads will increase and have to be re-calculated.
It is not easy to do a proper adjustment of the extension piece when retrofitting the blades on the turbine. Only a few 0.1 off will result in a loss of performance.