This paper evaluates the viability of installing photovoltaic (PV) systems in existing commercial buildings in Dublin. Data collected from previously installed photovoltaic systems at the Dublin Institute of Technology was analysed in order to determine the potential solar resource available in Ireland. A 1.1 kWp photovoltaic system installed in Dublin can produce over 900 kWh of electricity in a given year depending on the available solar resource for that year. A feasibility study was conducted in Dublin city centre in order to evaluate the technical, financial and environmental aspects of integrating a PV system into an existing building. The intention is that the results from this work will help in demonstrating the benefits and challenges associated with installing PV systems in existing commercial buildings in Ireland.