Frequently changing regulation codes, photovoltaic (PV) technology progress and variations in economic parameters that determine a specific economic scenario make a prospective owner of photovoltaic grid-connected systems (PVGCS) on buildings require information concerning the profitability of their investment on these systems. Hence, an analysis of the main economic factors of PVGCS on buildings addressed to ascertain their influence on the latter profitability is demanded and welcome. Consequently, a sensitivity analysis of some profitability indices such as the net internal rate of return, the net present value, and the discounted payback time has been carried out. This sensitivity analysis is aimed at demonstrating the influence on these indices of possible changes in the factors that are involved in their estimation. Two scenarios have been considered that closely resemble two top PV geographical areas: Germany and Spain. The results obtained here provide clear evidence that factors such as initial investment subsidy, dividends of own capital, taxes, annual loan interest exert a relatively small and similar influence on the net internal rate of return, the net present value, and the discounted payback time. However, other factors such as the initial investment, the annual PV electricity yield, and the PV electricity
unitary price have a bigger influence on these profitability indices.