In this work we simulate structured-surface covers of photovoltaic modules with different patterns in order to compare the optical performance (fight trapping) of these patterns at different conditions. To achieve this, we use a new software application with an optical calculus engine. Although the primarily reflected light represents a small percentage of the total incoming energy at normal incidence and some part of that fraction will be lost due to Fresnel and absorption losses, there is a substantial increase of the final energy reaching the photocell, specially for large angles of light incidence. In particular, we analyze two different covers: an abrupt-shaped pattern of triangular form and a smoothed-shaped pattern of sinusoidal form in order to evaluate and compare their light transmission properties. We study both structures by varying their geometrical parameters, and also by considering different angles of the incoming light, and different absorption coefficients of the materials. We conclude that the use of these types of covers can improve the performance of regular photocells molding these structures in their encapsulation. (C) 2007 Elsevier B.V. All rights reserved.