# Simulation and Optimisation of Utility-Scale PV-Wind Systems with Pumped Hydro Storage
## 3 Computational Results and Discussion
### Optimisation of an LSS System (System with Load Consumption)
#### 3.2.5 Optimisation Results
Simulation of the LSS Optimal System without PHS  
The optimal solution without a PHS (Table 4, first results column) is a hybrid PV-wind system in which all net renewable generation is injected (sold) to the AC grid, and all net load is purchased by the grid because there is no energy storage. Each case is simulated in 15 min time steps during the 25 years of the system lifetime. As an example of the visualisation of the simulation, a simulation of two consecutive days (for example, year 12, 9 March to 10 March) is shown in Figure 17. The unmet load is always 0 when the grid \begin{table}
\begin{tabular}{l c c c} \hline \hline \multirow{2}{*}{**Project Type**} & \multirow{2}{*}{**LSS—Optimal System without PHS**} & \multirow{2}{*}{**LSS—A (Buy for Arbitrage)—Optimal with PHS**} & \multirow{2}{*}{**LSS—B (No Buy for Arbitrage)—Optimal with PHS**} \\ \cline{2-2}  & & & **Arbitrage)—Optimal with PHS** & \\ \hline \(P_{PV\_N\_AC}\) (MWac) & 3 & 3 & 3 \\ \(P_{WT\_N}\times N_{WT}\) (MW) & 0.5 \(\times\) 8 = 4 & 0.5 \(\times\) 8 = 4 \\ \(P_{P\_N}=P_{HT\_N}\) (MW) & 0 & 0.5 & 0.5 \\ \(V_{UR\_max}\) (dam\({}^{3}\)) & 0 & 5.4 & 5.4 \\ Storage duration (h) & - & 2 & 2 \\ \(P_{Pr\_{pruch\_load\_stp}}\), first year (EUR/kWh) & - & 0.15 & 0.15 \\ \(P_{\%}\) (\%) & - & 60 & 80 \\ \(P_{Pr\_{pruch\_ssl\_Low\_stp}}\), first year (EUR/kWh) & - & 0.048 & 0.048 \\ \(P_{Pr\_{pruch\_ssl\_High\_stp}}\), first year (EUR/kWh) & - & 0.097 & 0.097 \\ PV energy (GWh/yr, average) & 5.14 & 5.14 & 5.14 \\ WT energy (GWh/yr, average) & 9.103 & 9.103 & 9.103 \\ Pump energy (GWh/yr, average) & - & 0.241 & 0.224 \\ Pump run hours/starts per year (average) & - & 556/467 & 567/478 \\ Hydro turbine energy (GWh/yr, average) & - & 0.21 & 0.206 \\ Turbine run hours/starts per year (average) & - & 404/307 & 385/280 \\ E sold (GWh/yr, average) & 7.367 & 7.478 & 7.441 \\ E purchased (GWh/yr, average) & 0.992 & 0.996 & 0.964 \\ UL (\%) & 0 & 0 & 0 \\ CAPEX (M EUR) & 7.765 & 8.4 & 8.4 \\ NPC (EUR) & 3.91 & 4.15 & 4.19 \\ LCOE (EUR/kWh) & 0.0464 & 0.0492 & 0.0497 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Results of the different optimisations with the LSS system. Figure 16: Evolution of the NPC of the best system found for each generation of the GA.  
limit is 2 MW, i.e., it is always higher than the load. Net generation is denoted as the excess energy injected into the AC grid with a maximum grid power limit of 2 MW. The net load was obtained from the AC grid. Figure 18 shows the annual energy consumption of the optimal project. We can observe the effect of the increase in the load over the years, the variation in the irradiation and wind speed, and the power decay of the PV and wind turbines. As a consequence of the increase in load consumption over the years, there is a trend towards an increase in the energy purchased and a reduction in the energy sold over the years. Simulation of the LSS Optimal System with PHS, Type A Project  
LSS optimal systems with PHS are similar for Type A and Type B projects, as shown in Table 4. The PHS is not competitive with the costs considered, and therefore, it includes the minimum pump turbine (0.5 MW) with the minimum reservoir duration (2 h). The simulation for the same two days as the optimal system for project Type A is shown in Figure 19. The upper part shows the electricity price in year 12 (purchased in red and sold in green, which are the same in this study) and the optimal set points. All these price values are the real values of year 12, that is, the values of the first year to which the cumulative inflation of the 12 years have been added (14.48%, Figure 13). The optimal value for \(Pr_{E\_{purch/sell\_High\_stp}}\) (first year) is 0.097 EUR/kWh; however, in year 12, it is 0.097 \(\times\) (1 + 14.48/100) = 0.111 EUR/kWh; the value of the optimal \(Pr_{E\_{purch/sell\_Low\_stp}}\) for year 12 is 0.055 EUR/kWh, and the optimal \(Pr_{E\_{purch\_load\_stp}}\) for year 12 is 0.172 EUR/kWh. Figure 17: Simulation of two consecutive days, March 9 and 10, year 12. LSS optimal system without PHS.