Sizing of photovoltaic (PV) generators is an important issue which might affect the PV system overall yield and performance ratio. The procedure is realized according to inverter specifications with the most important one being the operating voltage range. The parameter that is affected by this specification is the number of PV modules per string and a software tool was developed in order to study the effects of this parameter on the system performance. Moreover, the PV generator voltage is highly affected by the ambient temperature of a specific location. Thus, the optimum number of PV modules per string will differ in locations with different environmental conditions. The importance of PV string sizing is high, since improper string length can lead to significant deficiencies on the overall inverter performance. A study of the effects of PV string size on annual system energy production and yield has been conducted for several locations in Europe with significantly different weather as well as for locations with extreme climatic conditions such as high altitude and desert areas.