# Optimizing Sustainable Energy Transitions in Small Isolated Grids Using Multi-Criteria Approaches
## 4 Results and Discussion
### Scenarios Pre- and Post-Full Operation of the Hydro-Wind Power Plant  
As outlined in the initial sections regarding the energy scenario of El Hierro island, at the beginning of the 21 st century, a project was initiated to install a renewable generation plant that was pioneering for its time and remains advanced today. This plant started its operation in 2014 but became fully operational close to the end of 2015. Until then, the island's energy system relied entirely on electricity generation using fossil fuels, specifically through the Llanos Blancos diesel plant. Consequently, to establish a maximum reference value for GHG emissions and a cost reference for a fossil fuel-based system, analyzing this scenario was considered important. Indeed, similar scenarios exist in many parts of the world due to various factors. These influences, which can favor the use of fossil fuel-based systems or their combinations with renewables, include those related to locations with significant isolation, cheap and continuous access to fossil fuels, low technological advancement in electrical systems, and a desire for high reliability of the generation system at reduced costs, among other possible reasons. First, a detailed analysis of the diesel generators' performance for 2023 will be made, which is summarized in Table 4. It is worth noting that there are 10 units of between 670 and 2000 kW, totaling a maximum power of 13.04 MW, which facilitates straightforward coverage of the entire demand and its regulation. In the year 2023, there was a total demand of 50.23 GWh, which means an average hourly demand of 5.75 MWh. These hourly demand values range between 3 MW and 8 MW approximately, with a maximum hourly demand value of 7.71 MW (Figure 3). In other words, the average capacity factor (CF) of diesel engines is 43.97%, while the peak CF is 59.13%. As for the economic data, the total system costs are almost 7 M EUR, of which variable costs (fuel costs) account for almost 95%, and the remaining slightly above 5% is for fixed O&M costs, whereas in relation to GHG emissions, these are around 40 kt. After presenting the results provided by the code for the scenario on El Hierro island prior to the hydro-wind power plant becoming operational, i.e., demand covered exclusively by diesel generation, the results of the current generation system have been evaluated. This system features the hybridization between renewable generation from the Gorona del Viento power plant and the Llanos Blancos diesel station. Specifically, it combines wind generation and reversible pumped storage with diesel generation. To further analyze the accuracy performance of the code, the simulation results shown by the code for the current island system are compared with the real values available on the REE website for the year 2023 [45]. The choice of the year 2023 is justified after the analysis of historical data, specifically since the beginning of the current century, given that the year had adverse environmental conditions from the point of view of generation, thus being conservative in the analysis carried out. To estimate solar and wind resources, NASA's POWER Data Access Viewer was used [67]. Hourly solar data comes from satellite observations combined with surface solar irradiance data from NASA's Global Energy and Water Exchange Project (GEWEX)/Surface Radiation Budget (SRB) Release 3 and NASA's CERES Fast Longwave And Shortwave Radiative project (FLASHFlux). Similarly, for the wind resource, its magnitude was obtained using the global wind data access viewer POWER developed by NASA [67]. This database is based on wind measurements from the Modern Era Retrospective-Analysis for Research and Applications (MERRA-2) assimilation model products from the Goddard Global Modeling and Assimilation Office (GMAO) and the near-real-time GEOS 5.12.4 products from the Advanced Processing Instrument Teams (FP-IT) of the GMAO.