# Solutions to Increase PV Hosting Capacity and Provision of Services from Flexible Energy Resources
## 5 Conclusions  
In this paper solutions for increasing PV hosting capacity and distribution network connected flexible energy resources improved utilization for local (DSO) and system-wide (TSO) services were studied by PSCAD simulations during very low load situations. The focus was on the potential momentary mutual effects and simultaneous interaction between different functions. Based on the simulation results, it can be concluded that  
* PV hosting capacity in LV network can be increased with lower OLTC setting value. * Feasible and coordinated _QU-, PU-,_ and _Pf-_droop settings (with dead-zones) of PVs and BESSs are essential in maximizing the provision of their flexibility services. * During an over-frequency event without BESS, the best frequency support can be achieved by using _PU-_control blocking logic on PVs. * PV hosting capacity can be increased to some extent by remote LV voltage measurement from PV connection point to MV/LV substation connected BESS. * With BESS at the PV connection point however, the PV hosting capacity during steady-state operation can be maximized by simultaneously charging BESS in order to avoid local over-voltages. * During larger frequency deviations frequency adaptive _PU-_droops can enable larger PV and BESS power system frequency support as well as maximize smaller LV network connected demand (loads) participation in frequency control. * Actual implementation logic (e.g., _PU-_blocking or change of active _PU-_droop with frequency adaptive _PU-_droops) affects the PV and BESS frequency support contribution and the extent of PV curtailment (Table 10). In general, it can be stated that the dead-zones in BESS and PV unit _QU-, PU-,_ and _Pf-_droops are required in order to enable multi-use of active (_P_) and/or reactive (_Q_) power for different purposes. In the future, new adaptive management schemes to enable maximum availability of all types and sizes of flexibilities for different local and system level services are needed. New management and DER control methods must be also compatible with other flexibility service options and platforms like flexibility markets. Therefore, in the near future flexible _QU-, PU-,_ and _Pf-_droop functions for DER units are required. Flexible droop functions could also enable local operation optimization at DSO level by updating droop functions setting values and activation limits in a seasonal/monthly/weekly/daily/hourly manner. The adaptation of these droops to the changing network situations, however, should be increasingly done in the future based on the available local and/or remote measurements information. Therefore, in Section 4 new real-time adaptive management schemes for DER units' _PU-_droops, HV/MV substation transformer's OLTC setting value (dependent on the _P_Q-flow through the transformer), and DER units' _QU-_droops (dependent on OLTC setting value) were also proposed. It was shown by simulations that with BESS at the PV connection point the PV hosting capacity during steady-state operation and very low load situation can be maximized by simultaneously \begin{table}
\begin{tabular}{c c c c} \hline \hline
**DER Units(s)** & **Without _PU-_Blocking** & **With _PU-_Blocking** &
\begin{tabular}{c} **Frequency Adaptive _PU-_Droops** \\ **(Without _PU-_Blocking)** \\ \end{tabular} \\ \hline
**PV (only)** & Over-frequency support & Better over-frequency &
\begin{tabular}{c} No difference depending on the \\ _PU-_droop settings and over-voltage \\ limits in the logic (during \\ under-frequencies) \\ Smaller PV curtailment + smaller \\ BESS contribution with lower \\ over-voltage limit on the _PU-_droop_ \\ and implementation logic \\ (during under-frequencies) \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Summary about effect of functionalities implementation logic during simulated very low load situations. charging BESS. In reality this is only possible if State-of-Charge (SOC) of the BESS is at a suitable level.