Resumen: Distributed storage systems embedded in distribution power systems could complement renewable generation and improve their operation, reducing peak power levels and providing supply support to island zones in the cases of outages. This paper proposes a multi-objective optimisation, which takes advantage of the possibility of operating in an island mode. The optimisation considers the siting and sizing of storage systems placed on power distribution systems with radial topology. The objectives to be minimised are: the amount of energy storage, power losses and expected energy not supplied (EENS). Loads and generators are uncertainty variables, and a probabilistic power flow based on the point estimate method helps with assessing the electrical parameters. The optimisation uses the IEEE-34 and IEEE-123 test feeders. The Monte Carlo simulation benchmarks some results. The final results show that storage systems could reduce the peaks of power required from the central network and improve other electrical parameters. In addition, those systems with higher interruption probabilities or those working near their operation limits could benefit from storage systems. This point of view is different from other authors’. Here, storage energy systems and the island mode of operation are defined by a probabilistic point of view. The siting and sizing of storage energy systems is decided from data obtained on the probabilistic power flow and the universal generating function. Idioma: Inglés DOI: 10.1016/j.epsr.2017.10.013 Año: 2018 Publicado en: ELECTRIC POWER SYSTEMS RESEARCH 155 (2018), 225-235 ISSN: 0378-7796 Factor impacto JCR: 3.022 (2018) Categ. JCR: ENGINEERING, ELECTRICAL & ELECTRONIC rank: 92 / 265 = 0.347 (2018) - Q2 - T2 Factor impacto SCIMAGO: 1.037 - Energy Engineering and Power Technology (Q1) - Electrical and Electronic Engineering (Q1)