Until the end of September 2008, photovoltaic solar energy (PV) was conceived as a very attractive business in Spain, reason why many were invested in the PV sector. Since then, a number of legal amendments have been published, some of them with retroactive effect, causing a certain degree of instability in this sector. Therefore, in the present work we have analyzed the regulatory changes undergone by the Spanish PV sector and, in addition, we have studied the effect of these changes on a real plant. Some authors have analyzed the main regulatory changes suffered by the PV sector in Spain.