Energy requirements in Greece have been continuously increasing in the past three decades. The share of renewable energy sources use has not kept up with the increase in energy demand. As a result more and more conventional energy sources are used and in this case lignite which is an indigenous source of energy and natural gas, imported from Russia. This energy picture leads towards a greater environmental impact due to the increase of pollutants to the atmosphere. It has been the objective of the European Union to satisfy 22.1% of its electric energy needs by the year 2010 with renewable energy sources. In the year of 1997 only 13.9% were satisfied with renewable energy. For Greece the corresponding figure was 8.6%. Renewable energy sources could cover a major part, if not all, of Thessaloniki's “Makedonia” airport needs, following the promising results of the recent renewable energy sources exploration in the region. The airport “Makedonia” is located a few kilometres south of the city of Thessaloniki on the coastline of Thessaloniki's bay. In this work an optimization model has been developed to determine the optimum share of renewable energy sources in various end-uses such as heating, cooling, and lighting. In this model the reliability and environmental parameters were taken into consideration. The renewable energy sources include solar energy, geothermal energy and biomass.