Analysis of a micro-cogeneration system using hybrid solar/gas collectors

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 by 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, especially 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 and hybrid: they act as a boiler economizer, as boiler exhaust gases circulate below the absorber plate, increasing the energy input and collector efficiency. The behaviour of a combined heat and power cycle producing 6 kW of electricity was simulated. The heat rejected in the cycle condenser can be used for space/water heating or cooling of 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), for two applications: a pool complex and an office building. The energy and economic potential of the system was compared to the conventional alternative.