# Optimizing Sustainable Energy Transitions in Small Isolated Grids Using Multi-Criteria Approaches
## 3 Materials and Methods
### Definition of Scenarios
Renewables also use abundant natural resources like sunlight and wind, reducing reliance on limited and polluting fuels, and they prevent the release of other harmful pollutants such as SO\({}_{2}\), NOx, and particulate matter. However, it should be noted that renewable energy systems are not entirely free of emissions. Noting divergences in reported emissions for various generation technologies over their life cycles highlights that emission estimates can vary significantly between technologies. These variations are the result of several factors, such as geographic location, the scale of the facility, methods of construction and operation, and the particular technology employed. The location of a generation facility can influence emissions due to factors such as climate, availability of natural resources, local regulations, and existing infrastructure. Similarly, a plant's size or capacity plays a role, i.e., larger facilities tend to be more efficient; consequently, their emissions per unit of energy are generally lower than those of smaller plants, which tend to be less efficient. Emissions are also affected by the construction, operation, and maintenance practices of the plant; for instance, equipment efficiency and waste management approaches can vary widely. Even among systems using the same technology, such as solar PV or wind, different facility designs and configurations might lead to changing life cycle emissions due to differences in efficiency and material usage [61]. However, to provide a more general and manageable estimate of emissions from different generation technologies, average values are used. These average values are obtained from studies and analyses conducted by specialized organizations such as the United Nations Economic Commission for Europe (UNECE) [62] and the National Renewable Energy Laboratory (NREL) in the United States [63]. These organizations collect and analyze data from numerous bases and conditions, generating average values that serve as standard references for comparison of GHG emissions from different generation technologies. Thus, in Table 3, the quantities employed for estimating the life cycle emissions of the technolo \begin{table}
\begin{tabular}{l c c c} \hline \hline \multirow{2}{*}{**Production Type**} & **Investment Costs** & **O\&M** & **Lifetime** \\  & **(M EUR/MW)** & **(\%)** & **(Years)** \\ \hline Diesel power & 0.4 & 5 & 20 \\ generator 1  & 0.3 & 1.5 & 50 \\ Hydro turbination & 3 & 1.5 & 50 \\ Hydro storage 2  & 7.5 \(\times\) 10\({}^{-3}\) & 1.5 & 50 \\ Hydro pump & 0.6 & 2.5 & 30 \\ Solar Photovoltaic & 1.3 & 0.27 & 20 \\ \hline \hline \end{tabular}  
* O&M costs do not include fuel consumption, as it strongly depends on the use. 2 Investment cost of hydro storage is in M EUR/MWh of installed storage capacity.  
\end{table} 
Table 2: Sub-system costs for the El Hierro forecasts (based on [15; 18; 58; 59; 60]). gies used in the current work are shown. In the particular case of diesel generation, the emissions shown in the table are corroborated by the emission data provided in reports relating to energy audits carried out on the diesel installation itself on the island of El Hierro [46]. The remaining values are based on research papers and reports, with values widely spread in the scientific world [62; 63]. In the battle against global warming, there are two main options for penalizing GHG emissions: a carbon tax and a GHG emission allowance trading market [64; 65]. A carbon tax directly establishes a cost per ton of emissions. The resulting reduction in emissions depends on how much emitters change their behavior in response to the tax. Emission-trading systems (or cap-and-trade systems) set the total amount of GHG emissions that can be released. The government then issues a limited number of emission permits, either by giving them to emitters for free or through an auction. For each ton of emissions released, the emitter must hold one permit.