Human survival depends on the continuous supply of energy whose demand has been steadily increasing. Sharp rises in fuel prices have had major repercussions on the economies of the countries with the greatest energy dependence, and make it imperative to change attitudes and practices in business and social circles. Today, the problem is how to meet energy needs without negatively affecting the environment, as well as ensuring the well-being of current and future generations (sustainable development). The promotion of alternative energy is one of the priorities of the energy and environmental policy of European Union, since it is a decisive factor in reducing greenhouse gases, thus enabling compliance with the Paris agreement. In this work the contribution of a photovoltaic systems installed for self-consumption in the headquarters of the parish council of São Bartolomeu de Messines, Algarve, Portugal is assessed. The results indicate that a system with an installed capacity of 6 kW, requiring an investment around 10 000 €, could achieve it’s economic pay-back in 6.7 years, contributing to reduce the building’s annual electricity bill by 60%.