The purpose of this work consists in thermodynamic modeling of hybrid photovoltaic thermal (PV/T) solar systems, pursuing a modular strategy approach provided by Simulink/Matlab PV/T solar systems are a recently emerging solar technology that allows for the simultaneous conversion of solar energy into both electricity and heat This type of technology present some interesting advantages over the conventional "side-by-side" thermal and PV solar system, such as higher combined electrical/thermal energy outputs per unit area, and a more uniform and aesthetical pleasant roof area Despite the fact that early research on PV/T systems can be traced back to the seventies, only recently it has gained a renewed impetus In this work, parametric studies and annual transient simulations of PV/T systems are undertaken in Simulink/Matlab The obtained results show an average annual solar fraction of 67%, and a global overall efficiency of 24% (1 e 15% thermal and 9% electrical), for a typical four-person single-familiar residency in Lisbon, with p-Si cells, and a collector area of 6 m(2) A sensitivity analysis performed on the PV/T collector suggests that the most important variable that should be addressed to improve thermal performance is the photovoltaic (PV) module emittance Based on those results, some additional improvements are proposed, such as the use of vacuum, or a noble gas at low pressure, to allow for the removal of PV cells encapsulation without air oxidation and degradation, and thus reducing the PV module emittance Preliminary results show that this option allows for an 8% increase on optical thermal efficiency, and a substantial reduction of thermal losses, suggesting the possibility of working at higher fluid temperatures The higher working temperatures negative effect in electrical efficiency was negligible, due to compensation by improved optical properties The simulation results are compared with experimental data obtained from other authors and Perform reasonably well The Simulink modeling platform has been mainly used worldwide on simulation of control systems, digital signal processing and electric circuits, but there are very few examples of application to solar energy systems modeling This work uses the modular environment of Simulink/Matlab to model individual PV/T system components, and to assemble the entire installation layout The results show that the modular approach strategy provided by Matlab/Simulink environment is applicable to solar systems modeling, providing good code scalability, faster developing time, and simpler integration with external computational tools, when compared with traditional imperative-oriented programming languages (C) 2010 Elsevier Ltd All rights reserved