Photovoltaic (PV) systems are usually not recommended in heritage buildings for preserving their values and aesthetic features. However, these buildings are widespread in Europe and their energy requirements, due to heating, cooling, and electrical energy, can be significantly reduced with PV modules and hybrid systems. Also, recent aesthetical and technological innovations focus on more compatible systems, thanks to low-rate reflection, mimetic appearance, compact shape, and geometric flexibility. The paper aims at checking the opportunities for PV integration in heritage buildings. The study is applied to the “Rustico Macchi”, an Italian heritage building that need a complete retrofit for hosting exhibitions and didactic activities. To do so, a dynamic building energy model (BES) is created considering the data from on-site tests. This model is tested adding various types of PV modules on roof, façade, or windows, and integration levels, checking, for each case, the reduction of non-renewable input primary energy and self-consumed electrical energy produced by PV. The results highlight that a balance between conservation and energy production is possible integrating advanced PV systems and considering the traditional principles of architectural restoration: heritage significance of the building and its settings, minimum intervention, reversibility, and technical compatibility.