## 5 Conclusions  
This study has addressed the comparison of economic performance of lead-acid and Li-ion batteries in standalone renewable energy systems. For five real case studies, their energy supply has been simulated with a 100% PV system and with another PV-diesel hybrid. The economic optimum in terms of NPC have been sought and sensitivity analyses have been carried out on various parameters.  
The results show that for each case, the use of a lead-acid or Li-ion battery results in different dimensions of the economic optimum system. Battery capacity, PV generator power and fuel consumption (in hybrid systems) are affected. As these changes also affect the NPC of the system, the economic studies must consider them.  
Regarding the economic comparison, of the ten systems studied (five PV and five hybrids), in three of them the absolute optimum is obtained with Li-ion batteries and in seven with lead-acid batteries. In two of the latter, the differences in NPC are less than or equal to 2%. The differences in system NPC range from \(-16\%\) to \(+22\%\) in PV systems and from \(-\)7.2% to +5.9% in hybrid systems. On the one hand, the result of the comparison as a whole is virtually a tie. On the other hand, the five case studies produce different results. Furthermore, the results of each case keep similarities between both systems, PV and hybrid, although attenuated by the presence in the latter of a dispatchable generation (the diesel genset), i.e., currently, both lead-acid and Li-ion batteries compete for economic profitability in standalone renewable energy systems. The best choice depends on each case. Possible changes in the acquisition price can cause one or the other type to displace the other in terms of profitability, in a generalized way.  
The economic performance of Li-ion batteries, compared to lead-acid ones, is relatively better in hybrid systems than in PV. Greater solar irradiation favors Li-ion batteries in PV systems, but harms them in hybrid systems. In these, it would be favored by lower inflation in fuel prices. Finally, a 21% reduction in the price of Li-ion batteries would make them the economically optimal option in all hybrid cases and if 36% is reached in all PV cases studied.  
The limitations of the present study derive from the number of cases studied and their nearby locations. Sensitivity analysis to the magnitude of solar irradiation can be useful in this regard, but other effects of change of location are lacking, such as different temperature data.  
More studies are needed to advance in the identification and quantification of the characteristics of each case that influence the economic performance of both types of battery. Models should also be studied to in depth determine the maximum lifetime of Li-ion batteries in standalone renewable energy systems, beyond the design life indicated by the manufacturers.  
Conceptualization, J.C.; methodology, J.C. and C.E.-M.; software, R.D.-L.; validation, L.V. and R.D.-L.; formal analysis, L.V.; investigation, J.C. and C.E.-M.; resources, J.C. and C.E.-M.; data curation, C.E.-M.; writing--original draft preparation, J.C. and R.D.-L.; writing--review and editing, J.C.; visualization, C.E.-M.; supervision, J.C.; project