The supply-cost curves of renewable-energy sources are an essential tool to synthesize and analyze large-scale energy-policy scenarios, both in the short and long terms. Here, we suggest and test a parametrization of such curves that allows their representation for modeling purposes with a minimal set of information. In essence, an economic potential is defined based on the mode of the marginal supply-cost curves; and, using this definition, a normalized log-normal distribution function is used to model these curves. The feasibility of this proposal is assessed with data from a GIS-based analysis of solar, wind and biomass technologies in Spain. The best agreement is achieved for solar energy. (C) 2009 Elsevier Ltd. All rights reserved.