## 4 Discussion  
As shown in Section 3, when not considering the PV energy surplus exportation, an oversizing of the PV field would increase the total costs significantly, while the reduction in grid energy consumption is marginal. However, the possibility of exporting surplus energy to the grid allows for more flexibility in the energy and cost management. Despite the solar fraction, which limits the amount of PV energy used to attend the demand, the possibility of exporting the surplus energy makes it feasible to implement more PV panels, representing a significant reduction in the LCC, as verified by comparing Figure 18a,b. The cost breakdown of Action 3 and scenarios A, B, and C for both configurations (PV energy exportation considering a net metering approach, and no energy exportation) is shown in Figure 18a,b, as a function of the number of PV panels. The colored square points correspond to the investment cost of PVs, the grey triangle points are the electricity costs billed by the electricity provider (Endesa in this  
Figure 17: Effects on the LCC and PV system optimal values for the three different exportation prices (net billing, wholesale prices). case), and the colored circle points show the overall LCC (i.e., the summation of the PV investment, the charged grid electricity and the compensation of PV energy exportation). The zoomed areas indicate the optimum solutions for scenarios A, B, and C. The optimal number of PV panels to be installed for each scenario was 630, 497, and 434, if no PV energy exportation was considered, or 1617, 1533, and 1512 when exporting the PV energy surplus, respectively. Making a rough approximation of the area that would be occupied by these panels, we obtained 1040 m\({}^{2}\), 820 m\({}^{2}\), and 716 m\({}^{2}\) for every optimal solution of scenarios A, B, and C if no PV energy exportation is considered, or 2668 m\({}^{2}\), 2530 m\({}^{2}\), and 2495 m\({}^{2}\), considering the possibility of PV energy surplus exportation, respectively. Action 3 would require an initial investment, which will strongly depend on the assumptions described in Section 2.6. Figure 19 presents the effects of the PV energy surplus exportation to the grid on the investment costs and payback periods. In Scenario A, for example, it can be verified that despite the increase in the investments due to the PV system sizing (from 630 to 1617 panels), the payback period increases to less than one year and the LCC savings go from 26.5% to 53.2%. The above-mentioned scenarios are feasible to implement since the entire rooftop available area of the industrial units was around 24,200 m\({}^{2}\) (three units with 5000 m\({}^{2}\) each; three units with 3740 m\({}^{2}\), 2040 m\({}^{2}\), and 1830 m\({}^{2}\) respectively; one commercial unit with 570 m\({}^{2}\); one administration unit with 940 m\({}^{2}\)). The parking area corresponded to 25,830 m\({}^{2}\), representing an option to implement PV panel coverages (canopy). Depending on the cost of the PV panels, the investment cost and break-even point will vary significantly, so precautions must be taken while defining the PV costs above-mentioned. Figure 20a,b show the energy profiles including the energy demand, the PV production, and consumption from the grid and from the PV system, and the PV surplus energy for both options, with no PV surplus exportation and with PV exportation to the grid. Scenario A (Action 3) and the net metering configuration were taken as the reference for these graphics. Figure 18: (**a**) Breakdown of Action 3 including its three scenarios with no PV energy surplus exportation. (**b**) Breakdown of Action 3 including its three scenarios with PV energy surplus exportation. Figure 19: (**a**) Discounted Payback period for the three scenarios of Action 3 with no PV energy surplus exportation (**b**) Discounted Payback period for the three scenarios of Action 3 with PV energy surplus exportation.