Abstract This work aims at describing a simulation model that studies the influence of the cell string layout on the performance of solar panels taking into account the environmental conditions. Several solar cell string configurations in the photovoltaic modules are simulated using a simulation program for integrated circuits, looking for a mitigation of the effects of shading and/or non-uniform illumination of the solar panel. The simulation model is validated using data provided by Solarus, 1 as well as results obtained experimentally in Sweden concerning outdoor tests or using a lab solar simulator with similar collectors. The model is simple and flexible enough to be easily matched to various string layout configurations and, unlike several maximum power point tracking procedures, it allows the correct assessment of the maximum power in situations presenting multiple maxima in the power versus voltage stationary characteristic of the solar panel. The simulated and experimental average electrical efficiency in December in Gavle (Sweden) for flat collectors manufactured by Solarus with strings of 38 solar cells connected in series is around 20%. Modifications in the solar modules currently manufactured in Solarus are proposed, together with the identification of the contexts in which they represent a reasonable added value. Examples of module configurations with overlapped bypass diodes show an increase of almost 100% in the short circuit current. The methodology used in this work for the design of the solar cell configuration is a valid contribution to the analysis of stationary roof/ground grid-tied or off-grid small installations and it represents undoubtedly an important tool for the enterprises in the manufacturing process.