## 5 Conclusions and Future Developments Proposals  
After the detailed analysis of the results of the simulations of the developed model shown in Section 4, it is possible to take stock of the work that has been carried out. Looking ahead to a future in which renewables will be increasingly relevant in the energy mix, two strategies have been implemented to ensure they are able to help (or substitute) conventional generators in keeping the power system stable. In particular, Power Reserve Control and the Extended OPPT Method have been tested in this work, respectively, aiming at allowing photovoltaic modules and variable-speed wind turbines to participate in primary frequency control. Indeed, the challenge of using non-programmable renewable generators to provide the services that nowadays are delivered by fossil-fueled plants will become increasingly central, as the renewable presence increases to a more significant level. In this sense, the results obtained in this work, especially when both controls coexist, are encouraging. Indeed, even if the Power Reserve Control introduces a very small increase in the RoCoF in the very few instants after a strong and sudden perturbation, the frequency nadir is reduced with respect to the case in which the frequency is not supported by renewables, especially in a future scenario in which they are massively present in the power system. The tradeoff between RoCoF increases and the nadir reduces in a given power system depending on its characteristics and, particularly, on the settings of the respective relays. The model and the results rely on some simplifications, which generalize them but at the same time are lacking in detail. For this reason, there is an open field for future developments of the present work in some areas. One of the possible fields of improvement is the modeling of the photovoltaic system, in particular for what concerns shading conditions and inequalities in sun resource distribution among the modules. Indeed, this would allow for a deeper study of the capability of photovoltaic systems in supporting the system's frequency in more realistic situations. Another possible improvement regards the modeling of the load. Indeed, it could be very interesting to better characterize its active power demand profile in case of a small island to cause the study to be even more realistic. The last and more challenging proposal for future developments would be to model a small system node by node as the one studied in an overall way with the LFC approach in this work. This will completely fit it to a specific practical situation and ensure it is able to catch some details that are invisible with a general approach. At the same time, the adaptation to a very specific context removes one of the biggest advantages of the LFC approach, which is the generality and versatility of the developed model. Nevertheless, since the results obtained are promising, such improvements are interesting and can add cues to go deeper in the knowledge of this field. Figure 26: Simulation 7 for different scenarios frequency trend. **Author Contributions:** Conceptualization, S.M. ; methodology, S.M. ; software, L.R. ; validation, L.R. and S.M. ; formal analysis, L.R. and S.M. ; investigation, L.R. and S.M. ; resources, L.R. and S.M. ; data curation, L.R. ; writing--original draft preparation, L.R. ; writing--review and editing, S.M. ; visualization, L.R. ; supervision, S.M. ; project administration, S.M. ; funding acquisition, S.M. All authors have read and agreed to the published version of the manuscript. **Funding:** This research was funded by the Spanish national research agency Agencia Estatal de Investigacion, grant number PID2019-108966 RB-I00/AEI/10.13039/501100011033. **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** Not applicable. **Conflicts of Interest:** The authors declare no conflict of interest.