# Optimizing Sustainable Energy Transitions in Small Isolated Grids Using Multi-Criteria Approaches
## 1 Introduction
### Research Organization and Major Contributions
By converting emission penalties into monetary values, it becomes possible to estimate the financial threshold at which a renewable energy scenario, in addition to being environmentally preferable, also becomes more profitable from an economic perspective. In addition to the optimized renewable scenario, two other reference scenarios have been analyzed to provide a comprehensive comparison. The first scenario reflects the diesel-based power generation system that operated on the island until around 2015, before the hybrid hydro-wind power plant reached near full capacity. This \"fully fossil-based\" scenario is particularly significant, as it closely mirrors the energy systems still prevalent in most isolated regions worldwide. As such, it serves as a critical benchmark for evaluating the performance and benefits of transitioning to renewable energy, offering a clear point of reference for both economic and environmental metrics. The second scenario examined is the current hybrid system, which combines renewable sources with diesel generation. This configuration underlines the importance of proper system sizing; without it, even hybrid systems can suffer from inefficiencies and reliability issues, ultimately failing to meet performance expectations. By carefully comparing these three scenarios--the original diesel-only system, the present hybrid renewable-dieselsystem, and the proposed fully renewable system--it becomes possible to quantify the key differences in terms of both economic costs and greenhouse gas emissions. The island's gradual transition, from a system entirely dependent on diesel to a hybrid and ultimately to a fully renewable configuration, exemplifies a significant move toward sustainability. Hybrid systems, in particular, offer a practical intermediate step by enhancing energy reliability and reducing dependence on fossil fuels, which can lead to both cost savings and substantial reductions in emissions. This progression is not only relevant for the island in question but also provides valuable insights for other islands and isolated territories, many of which continue to rely heavily on fossil fuel imports and face unique challenges such as high energy costs and logistical difficulties. By analyzing and contrasting these three distinct scenarios, this study delivers actionable knowledge that can inform energy planning in similar regions. The findings highlight the tangible environmental and economic advantages of transitioning to renewable energy sources, offering a practical roadmap for isolated communities seeking to improve their energy sustainability and significantly reduce their carbon footprint. Specifically, the first scenario analyses a system in which electricity generation relies almost entirely on fossil fuels, specifically diesel generator sets. This situation reflects the current reality for many islands and isolated regions. Consequently, this scenario represents a typical generation system for remote areas and regions with low energy demand over recent decades. It provides insight into the characteristics and operational behavior of such systems, highlighting that their GHG emission levels are unacceptable in the context of the ongoing fight against climate change. The second scenario, in turn, describes the current situation on the island, demonstrating that a strong commitment to decarbonization--merely through the deployment of renewable energy systems with high penetration rates--is not sufficient. Instead, this transition must be preceded by a comprehensive and rigorous analysis. As will be detailed throughout this document, the outcomes achieved do not align with the initial planning, primarily due to shortcomings in the design of the energy storage system, which exhibits insufficient storage capacity and limited pumping power. As a result, the expected levels of renewable energy coverage have not been attained, curtailment rates are higher than anticipated, and the reduction in emissions has fallen short of projections.