To meet the global greenhouse gas emissions reduction target of 50% by 2050, based on 1990 levels, the UK government is committed to 80% reduction of their emissions over the same period. To achieve this target, the use of renewable technologies needs to be expanded. The UK has signed up to the EU Renewable Energy Directive, which sets the UK a target of 15% of its energy to be generated by renewable sources by 2020. Halcrow, UK has recently refurbished a 5-storey office building in London with the aim being to investigate interventions to reduce their carbon emissions. This building has been taken as a case study to assess the viability of using solar photovoltaic (PV) in refurbished non domestic buildings. Energy assessment has been performed. PVSyst software and other tools have been used to assess the incorporation of solar energy systems in the building. Although this research shows that the solar PV can provide a carbon saving, the cost benefit analysis presented in this paper suggests that this option is unlikely to provide an acceptable return on investment, given the very long payback period.