In order to evaluate the energy arriving at the focus of a solar concentrator named DEFRAC (from its Spanish acronym, Device for the Study of Concentrated Radiative Fluxes) a calorimetric study was carried out. We studied the heat transfer in the receiving plate of a calorimeter; the distribution of temperatures during the transient and steady states were obtained both theoretically and experimentally. We show that the calorimeter is close to ambient temperature which validates the use of the cold water calorimetry technique. Since the heat losses are reduced it is possible to increase the exactitude and precision during the thermal evaluation. Based on an energy balance, the solar energy absorbed by the receiver of the DEFRAC and the global heat losses to the environment are quantified. (c) 2008 Elsevier Ltd. All rights reserved.