The method for estimation of I-V curves of photovoltaic (PV) panel by analytic expression is presented in the paper. The problem is defined in the form of an optimization problem. The optimization problem objective is based on data from I-V curves obtained by manufacturers' or measured I-V curves. In order to estimate PV panel parameters, the optimization problem is solved by using an evolutionary strategy. The proposed method is tested for different PV panel technologies using data sheets. In this method the I-V curve approximation with two linear and a sigmoid function is proposed. The method for estimating the knee of the I-V curve and maximum power point at any irradiance and temperature is proposed. (C) 2014 Elsevier Ltd. All rights reserved.