The development of trigeneration systems is especially important in the buildings sector, where the thermal loads are imposed by the needs of heating, domestic hot water, and cooling. A strong seasonal character is indicated, since the demands depend totally on local climatic conditions and vary considerably throughout the year. Geographic locations were chosen so as to represent the climatic variety in Spain: Canary Islands, Mediterranean Coast, Atlantic Coast, and different locations in the interior of the Iberian Peninsula. The solution of a mixed integer linear programming model (MILP) that incorporated local economic/environmental conditions determined the optimal configuration of the different energy supply plants as well as the optimal operation modes throughout an entire representative year. From an economic point of view, the optimal configuration for all localities included cogeneration modules. From an environmental point of view, the optimal solution was strongly dependent on the origin of the electricity supplied by the grid. (C) 2010 Elsevier Ltd. All rights reserved.