EVALUATION OF A HYBRID SOLAR / GAS COMBINED HEAT AND POWER SMALL SYSTEM Jorge Facão and Armando C. Oliveira Faculty of Engineering, University of Porto Dept. Mechanical Engineering and Industrial Management Rua Dr. Roberto Frias, 4200-465 Porto PORTUGAL Tel. 225081763 E-mail: jfacao@fe.up.pt ABSTRACT The use of solar thermal collectors for electricity production is a way to contribute to the Portuguese objective of reaching 39% of electricity production from renewable energy sources, until 2010. This is also in accordance with the objectives of the European Union and the Kyoto Protocol. The system in analysis is powered by solar energy and supplemented by a natural gas boiler, specially for periods when solar radiation is low. Use of the system would result in significant savings in primary energy consumption and a reduction in CO2 emissions to the environment. The solar collectors are of the heat pipe type. In this work, the behaviour of a combined heat and power cycle producing 6 kW of electricity was simulated. The heat rejected in the cycle condenser is used for space heating/cooling in buildings. Several refrigerants have been considered for the cycle and methanol presented the best performance. The contribution of solar energy (solar fraction) was evaluated for the climatic data of Lisbon (Portugal). The energy and economic potential of the system is compared to the conventional alternative.