## 3 Results and Discussion
### Exploitation of Electricity Surplus at a National Level Without Investment  
Based on the methodology described in Section 2.2, we first determine the amount of aluminium production over the years, limiting the usage of electricity surplus at a national level to the assumed consumption of the large aluminium smelter. Based on the average amount of electricity required to smelt a tonne of aluminium (\(E_{AL}\) = 14 MWh), we determined the amount of aluminium produced. The quantity of aluminium remains unaffected by price fluctuations, so in Figure 7, we show the aluminium production that can be expected for each year. In line with the rise in electricity surplus over the years, we also observe higher aluminium production, with growth slowing down towards the end of the projected decade due to the limitation of maximum electricity surplus consumption.  
The estimation of economic viability depends on the prices of electricity surplus and aluminium, as well as aluminium production costs. Initially, we conducted a sensitivity analysis using the higher electricity surplus price, the average aluminium price, and the average aluminium production costs listed in Table 3 as base values. These values were then varied in steps of 10% \(\pm\)20% to assess the impact of price fluctuations on the NPV. The results of the sensitivity analysis are shown in Figure 8. It can be observed that aluminium prices have the greatest impact on the NPV, followed by aluminium production costs, while electricity prices have the least impact.  
\begin{table}
\begin{tabular}{l l} \hline \hline
**Term** & **Value/Unit** \\ \hline Lower price of electricity surplus & 10 EUR/MWh \\ Higher price of electricity surplus & 20 EUR/MWh \\ Low price of aluminium & 1750 EUR/t \\ Average price of aluminium & 2075 EUR/t \\ High price of aluminium & 2400 EUR/t \\ Low price of aluminium production costs & 1020 EUR/t \\ Average price of aluminium production costs & 1200 EUR/t \\ High price of aluminium production costs & 1380 EUR/t \\ \hline \hline \end{tabular}
\end{table}
Table 3: Prices of electricity surplus, aluminium, and production costs used for economic calculations.  
Figure 7: Aluminium production estimation based on the prospects of national electricity production surplus.  
To further determine the impacts of the different combinations of prices and production costs, we designed eight scenarios based on the prices set out in Table 3. The scenarios used to evaluate the economic viability are outlined as follows:  
1. Lower price of el. surplus + high price of alum.+ average alum. production costs;
2. Higher price of el. surplus + high price of alum. + average alum. production costs;
3. Lower price of el. surplus + average price of alum. + average alum. production costs;
4. Higher price of el. surplus + average price of alum. + average alum. production costs;
5. Lower price of el. surplus + low price of alum. + average alum. production costs;
6. Higher price of el. surplus + low price of alum. + average alum. production costs;
7. Lower price of el. surplus + high price of alum. + low alum. production costs;
8. Higher price of el. surplus + low price of alum. + high alum. production costs.  
For each scenario, we calculated the NPV according to the methodology described in Section 2.2 over a period of 10 years and show the results in Figure 9. The NPV starts to increase in the second year and increases at an accelerating rate, in line with the projected aluminium production shown in Figure 7. Over the whole period, projected savings range from approximately EUR 1 million in the less favourable Scenario 8, to around EUR 17 million in Scenario 7.  
Figure 8: NPV sensitivity to changes in aluminium and electricity prices, as well as aluminium production costs, over 10 years.  
Figure 9: NPV over a 10-year period based on aluminium and electricity prices, as well as aluminium production costs in the given scenarios.