AbstractYield analysis is a crucial task during project deployment of solar thermal power plants. Currently, many different modeling approaches and computer tools for yield analysis are used. Within the SolarPACES project guiSmo, aiming at the development of guidelines for the annual yield prediction of solar thermal power plants, relevant effects for the steady-state modeling of plant sub-systems have been identified [1].The target of the ongoing project phase is the development of general definitions for all relevant effects. Furthermore, suitable modeling approaches have to be identified and described unambiguously. For every effect, the impact on the predicted electricity yield is estimated in order to assess the significance of the considered effect. Since the most significant effects have to be considered in a subsequent uncertainty analysis, reasonable model and parameter uncertainties have to be defined, too. Finally, default model parameter for state-of-the-art components or subsystems will be edited.Beside the present status of the project, this paper presents investigations on the effects of the optical losses of the sub-system collector field on the annual yield. These effects are namely the peak optical efficiency, incidence angle modifier (IAM), shading and end losses. For each effect, a precise definition is presented and relevant modeling approaches are identified and their pros and cons are discussed. To investigate the influence of these effects, a reference solar thermal power plant with parabolic troughs is defined. The annual yield is simulated for this reference system investigating the identified modeling approaches and assessing their significance.