This paper presents the complete design of a photovoltaic installation that may be either used for internal electric consumption or for sale using the premium subsidy awarded by the Spanish Government. Electric optimization strategies are detailed in the project, as well as the sizing of the photovoltaic installation and economic and financial issues related to it. The project optimizes the electricity demand, improving reactive power and studying the convenience of hourly discrimination fees in addition to the design of the photovoltaic installation. A specific computer application for the automated calculation of all relevant parameters of the installation-physical, electrical, economical as well as ecological-has been developed to make the process of calculating photovoltaic installations easier and to reduce the design development time. Moreover, the budget of the photovoltaic installation is included, as well as its corresponding financial ratios and payback periods. Finally, the conclusions reached in the technical and economic design of the installation are shown. (c) 2005 Elsevier Ltd. All rights reserved.