A solar cell module is discussed. The method also includes setting a field weakening constituent for the required operating point for the motor field voltage component as a function of a difference between a required operating point and an available value of the motor torque voltage component and as a function of a difference between actual and required motor torque current components. A method of broaching a work piece having an inner and an outer diameter includes machining the outer diameter and then applying circumferentially-distributed radial force to the inner diameter or the outer diameter to thereby center the work piece with respect to a broach tool. The derivatives can be used to treat a variety of pharmaceutical and cosmetic conditions. The gradient layer is formed by at least two elements of which one is silver and forms a matrix for the second element or forms an alloy therewith, or of which one is tin and the other is phosphorus or of which one is indium and the other is tin. The magnet temperature is able to be determined particularly simply and accurately if a phase voltage and the rotational speed of the electrical machine are measured, and the magnet temperature is determined from this.