a Instituto de Energía Solar, Universidad Politécnica de M

s a draw uces th local st re pres grid is to the forecast of photovoltaic generation is a major drawback for the wide-Over the last years the amount of photovoltaic power installed worldwide has been increasing steadily [1]. This growth responds to various reasons, among which stand out the increasing aware-ness of global warmth caused by greenhouse emissions, the inevi-table exhaustion of traditional energy sources in the following decades (fossil fuels) and the need for countries to assure energy l as other y and, mo can play an important role in the solution of the aforemen problems. The growth ratio of the PV installed capacity in every year, so that the cumulative capacity shows an exponential behaviour [1]. It is noteworthy that this trend has been maintained also in recent years when some countries, particularly in Europe, started to cut down on subsidies and feed-in-tariffs. As a conse-quence of this growth the effect of photovoltaic power connected to public utilities begins to be noticeable for the overall system. For example, in Spain and Germany the share of electricit