Buildings are responsible for a significant share of global energy consumption, subsequently, it is essential to reduce their energy usage. Numerous buildings with relatively poor energy performance had been constructed before the implementation of energy regulations. Building retrofitting is the main solution to address this issue. This study examines the energy efficiency of a school in Le Grand-Bornand, French Alps. In pursuit of this objective, innovative indicators, that complement the classic ones, are applied. The indicators in this research consider the environmental energy resources surrounding the building, notably the solar energy, which can be harnessed both passively as solar gains and actively through photovoltaic panels. Performance indicators are computed using building energy simulation software (DesignBuilder with EnergyPlus, following) for three different retrofitting strategies for the building’s envelope and HVAC system. The findings underline the potential of harvesting solar energy to meet the energy demand.