An investigation on the power requirements of ships at berth for implementing Offshore Power Supply (OPS) is presented. It is highlighted that this technology acts as a suitable measure for reducing air pollution in port areas. The study is conducted for Cartagena Port (Spain), analyzing the data port traffic in the period 2010–2016. Accurate predictions of energy consumption of auxiliary engines based on experimental data provided by Port Authority lead to obtain the hourly energy consumption for each kind of vessel. A Monte Carlo procedure is applied to the variability assessment of both the power and the energy demand. The renewable energy resources available at Cartagena area are considered. Solar, onshore and offshore wind resources are assessed for supplying the energy demand. The solar resource reveals as important, but not sufficient; therefore, wind resource deserves a special attention. In particular, FAST/Aerodyn/Hydrodyn codes are used for determining the wind power capacity. The benefits of OPS technology are demonstrated, following the trends observed in the literature. The impact on reduction of Green House Gases (GHG) and other pollutant gases is estimated and the Energy Efficiency Design Index (EEDI) is calculated. As a relevant result, more than 10,000 tons of CO2 per year could be reduced. The related policy implications of the presented purpose have been discussed.