This article presents the operation of vacuum solar collectors connected to a warm water storage. The layout of the test facility is shown. Simulation of the installation is performed with the help of differential equations that describe the solar collectors and the storage. Thus, the temperatures in the collector loop (at the collector and storage inlets and outlets) and the temperatures in the storage are determined. The developed computer programme calculates the temperatures of the complete system as well as the temperatures in the collector loop and in the storage. A comparison is made between the calculated and experimental data, showing a good concurrence between the two curves. (C) 2004 Elsevier Ltd. All rights reserved.