Building integrated photovoltaics (BIPV) presents a great opportunity for decreasing building energy demand and related CO2 emissions, specially in the refurbishment of old isolated high rise highly glazed office buildings. This article presents a simulation study of the impact of BIPV on a Spanish office building of the 60’s, aiming to serve as a reference for this type of buildings in the Mediterranean region. Upgrade of the envelope with BIPV is evaluated. The solutions for the glazing system include conventional solar control window and a transparent photovoltaic prototype window. On the opaque part, commercial BIPV is considered. A comprehensive model integrating the BIPV impact in walls in windows for the thermal, electrical and daylighting is presented. Dynamic simulations carried out with TRNSYS software allow to evaluate the impact on daylighting, energy demand and economics. The results show that transparent BIPV reduced the energy demand by 6.9% and the total energy balance by 21%. The opaque BIPV further improved these results achieving a 38.3% reduction in the energy balance. Moreover, transparent BIPV also reduces the hours with excessive daylighting, although at the cost of reduced daylighting autonomy. The economic analysis highlights the importance of electricity pricing schedules in the promotion of BIPV, comparing current tariff structure in Spain and the duck chart from California Independent Operator. Results show the capabilities of this technology and provides guidelines for investment cost and efficiency targets.