Thermosyphon solar collectors are popular in warm climates since their initial and operating costs are lower compared to forced-circulation units. Recently new types of thermosyphon collector with integrated storage, without any external tank, to meet law requirements about solar applications in restricted areas (e.g. old town of particular architectural significance) are put in the market. Such a collector is modelled in this paper using the software MATLAB Simulink. This model is able to describe the transient behavior of the natural circulation phenomenon and it requires a much lower computational effort compared to CFD codes. The present mathematical model has been validated using ad-hoc experimental tests and numerical simulations. The validated model has been run varying the tilt angle, the geometry and the working conditions to analyze the solar thermosyphon performance. It can predict the minimum inclination and solar radiation that is needed to promote the flow circulation. (C) 2018 Elsevier Ltd. All rights reserved.