Local particle deposition and solar irradiance data, from Photovoltaic Geographical Information System (PVGIS) in the Alentejo region (southern Portugal), are used for the development of a modified effective irradiance model featuring soiling. The model allows to calculate the optimum tilt angle for soiled PV systems, as the inclusion of soiling gives realistic results for different tilt angles to be used in the absence of cleaning; instead of using an optimum tilt angle solely based on irradiance. Consequently, the proposed model enables an increase of maximum energy production and the design of multiple tilt angle configurations to further maximize the annual energy yield, regarding a common fixed structure. The presented calculations include the seasonal soiling effect for the region, showing the applicability that this type of approach has for multiple tilt angle configurations. An economic analysis is also carried out to choose the best design, taking into account the trade-off between the increase in energy production and the costs of changing the tilt angle. The effective irradiance model for clean and soiled scenarios is also explored with the development of a method to infer when a PV installation should be cleaned for the desired efficiency. (C) 2018 Elsevier Ltd. All rights reserved.