Considering the rapid development of PV power generation, one of the greatest challenges to the integration of this solar resource into the electricity grid, is its intermittent nature and, therefore, the variability of the power produced. As a result, some transmission system operators have issued new grid codes to limit the maximum allowable ramp-rate and make it easier for them to react appropriately to harmful short-term power fluctuations. In order to comply with the established grid codes, there is a need to include some kind of energy storage systems, thereby increasing the cost of the renewable energy generation system. This paper presents a methodology to size the storage requirements of a centralised energy storage system connected at the distribution level, serving to smooth out the power variability of a PV fleet in either a grid sector or in the main grid in the case of stand-alone power islands. Then, a study is conducted of the storage requirement savings by taking advantage of the smoothing effect of geographical dispersion on PV power output using a centralised instead of a distributed energy storage system. The general validity of the model was confirmed through simulations carried out with real operational PV power output data taken every 1 s in the course of one year at five PV power plants located in the south of Navarre (Spain). (C) 2015 Elsevier Ltd. All rights reserved.