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This section details the results on the confidence bounds of the installed capacities for the disaggregated renewable sources together with the fossil generation and energy storage. In addition, the confidence bounds for the accumulated CO2 emissions are shown. These results are obtained by applying the standard Vensim multivariate MCMC sensitivity analysis as applied to the policy scenarios discussed in Section 6.3 and for varying, the average consumption for nightly tourist stays. A total of 200 simulations were conducted, with the program randomly selecting values from the sensitivity ranges of the parameters shown in Table 6.5. The switches¹⁴ used for model implementation in the Vensim software for the EV expansion were also activated.

14 Switches are implementation within the Vensim software for turning on and off policy/specific implementations within the model using a binary (1) on and (0) off concept.

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Table 6.5 Important variables for the policy sensitivity analysis

The results displayed in the following graphs shows the confidence bounds as coloured bands using the percentiles of 50%, 75%, 95% and 100%. For example, a 75% confidence bound (green) indicates that 75% of all sensitivity runs fall within the top and bottom green bands (to include the 50% yellow band), 90% within the blue bands and 100% within the grey bands. The resulting range of possible outcomes for the capacity installations of the different technologies and the accumulated CO2

emissions of the system under the given ranges of these policies are shown in the following graph, Figure 6.31.

Figure 6.31 displays the range of outcomes in MW for the installed capacities of the disaggregated renewables capacity of the system. The base-load renewables such as geothermal and run-of-river hydro have the largest (possible) installed capacities outcomes. Geothermal is bounded within a higher range than the run-of-river hydro. The other renewables such as biomass, wind and micro/mini generation (solar) are bounded within lower ranges of installed capacities.

195 Figure 6.31 Sensitivity of the installed disaggregated renewables capacity

This implies that the base-load renewables will be more prominent in the long-term than the more intermittent renewables (the limits to their installations can be restricted by the availability of the

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respective heat and water resources within the island). Although biomass is not an intermittent renewable source it is observed that it struggles to compete with the more familiar (learning-by-doing) and cost-effective base-load renewables in the long term.

Figure 6.32 shows the range of possible outcomes of the aggregated renewables capacity by 2050.

This graph is the accumulated reflection (summation) of Figure 6.31 as all of the individual renewable sources are combined to show the confidence bounds of the total amount of possible renewables to 2050 under these scenarios. The figure shows that the confidence bounds are aligned with an increasing trajectory. This observation implies that in the long run under any combinations of the various policies of Section 6.3 there will be increased renewables capacity.

Figure 6.32 Sensitivity of the installed aggregated renewables capacity with various policies

Figure 6.33 displays the range of possible outcomes of the installed energy storage capacity by 2050. From this figure, we can conclude that energy storage will be tightly bounded by 2050 under these various policies. The observations stem from the fact that energy storage within this system is driven by a singular policy, as detailed in Sections 6.3 and 6.4.2. However, variations to this policy to embrace the effects of renewables will lead to larger ranges of outcomes as shown in Appendix B2 for the detailed sensitivity analysis of the model.

197 Figure 6.33 Sensitivity of the installed energy storage capacity with various policies

The following figure, Figure 6.34, captures the range of possible outcomes for the installed fossil generation and shows that, in the long term, there will be a decreased amount of capacity installed from fossil generation. This observation implies that in the long-run, any combinations of the

Figure 6.34 Sensitivity of the installed fossil generation capacity with various policies

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various policies of Section 6.3 (considering the results from the “relax all policies” and “all policies high” simulation runs of Section 6.4.2) will lead to a decreased amount of fossil generation capacity by 2050. Also observed is the wide range of installed fossil generation by 2050 which implies that the policies applied to the system for larger removal of fossil generation should be closely aligned to the lower part of the range of possible outcomes (driven by the renewables policy) shown in Figure 6.34.

Figure 6.35 gives the range of possible outcomes for the accumulated CO2 emissions until 2050.

This range of possible outcomes is bounded over a very large range and is guided by the large range of possible outcomes of the installed fossil generation within the system.

Figure 6.35 Sensitivity of the accumulated CO2 emissions with various policies

This observation reinforces the fact that the correct policies must be adhered to in order to minimise the environmental effects of CO2 emissions from the system. Policies that keep the installed fossil generation lower, in the long run, will thereby keep the accumulated CO2 emissions lower and prove to be the best choices for a low-carbon evolving isolated electricity system.

199 These confidence bounds for the policy scenarios gives a view of the wide ranging possible outcomes that each of the key variables examined can experience in the long term. The next section details the key investment and environmental implications for the island system as observed from the analysis and results of this and the previous sections.