Grid-connected photovoltaic systems with energy storage

There are different interesting ways that can be followed in order to reduce costs of grid-connected photovoltaic systems, i.e., by maximizing their energy production in every operating conditions, minimizing electrical losses on the plant, utilizing grid-connected photovoltaic systems not only to generate electrical energy to be put into the power system but also to implement some other important auxiliary services normally implemented by properly conceived apparatus (electrical power quality control, load demand peak control,...), making easy the integration of different kind of renewable electrical energy resources (wind plant, fuel-cells,...). Recently, a great attention has been devoted to researches on efficient techniques able to continuously track the maximum power point (MPP) of the photovoltaic generator (PG), also in the presence of critical mismatching in solar irradiance conditions. In the paper, the use energy storage in grid-connected PV plants is introduced, discussed and tested by experimental measurements. Energy storage, operated by means of batteries installed in a distributed manner, can improve the energy production of a conventional grid-connected PV plants, especially in presence of mismatching conditions, so representing a valid alternative to other technical solutions, such as distributed active MPPTs, based on a number of DC/AC or DC-DC power electronic converters connected in cascade to each modular component of the PV generator.