In a power system analysis, it is useful to find the relation between power losses and generated power on a power system. It can be performed using loss coefficients. The main drawback of traditional loss coefficients is that they must be recalculated in case that change in conditions takes place in the power system. In this paper, a comparison is performed by using different estimation methods of loss coefficients. The first method is the traditional Kron method (KM); the second one is a proposed modification of the traditional incremental method (IM); finally, a heuristic estimation method, robust under different changes in conditions of power systems, is proposed. Additionally, the paper presents an application of power losses estimation in power systems with solar and wind energy. The stochastic behaviour of solar and wind energy is modelled using the probability distribution of solar irradiance and wind speed, respectively.