I have found some small mistakes in KD 748 which I have corrected. So if someone wants to do something with this idea, please use the latest version.
Chapter 4 out of KD 748 describes how the optimum number of turns per coil and the optimum wire thickness can be found for a certain windmill rotor having a certain optimum cubic line. The formula for the optimum cubic line is given as formula 8.1 of report KD 35. As the question about the optimum number of turns per coil has been asked already many times on this forum, one should read this chapter 4 if one has designed a certain PM-generator for a certain windmill rotor.
In the calculation example I have neglected the voltage drop over the rectifier diodes to make the process simple but I think that this is allowed, especially for higher nominal battery voltages than 12 V. Formula 13 of KD 340 gives the DC voltage for star rectification if the voltage drop over the rectifier diodes is neglected. Formula 14 of KD 340 gives the DC voltage if the voltage drop over the rectifier diodes is taken into account. As the unloaded AC voltage at a certain rotational speed is proportional to the number of turns per coil, formula 13 gives a linear relation in between the number of turns per coil and the DC voltage.