**6. Conclusions**

The presented results indicate that general outcomes of the analysis for both 1 min and 10 min aggregation are similar. However where the requirements for the parameters are forced to be fulfilled during 100% of the observation time, the 1 min aggregation makes the observability of the object more restricted. This allows us to formulate general conclusion that the results of power quality assessment using the 1 min aggregation can be dependent on cooperation of the observed object with the power systems, the used regulation and integration systems, as well as the condition of the power system at the connection point. Furthermore, the obtained results show some potential in using variations of observed power quality parameters in the development of power quality analysis when a 1 min aggregation is used. It was shown that the voltage variation parameters including minimal and maximal values or standard deviations better express the variability of the observed parameters when 1 min aggregation is used. It was also shown that the assessment of power quality parameters at the connection point of a PV power plant, when the cloud effect or variable operating condition of the low voltage network are considered, is characterized by slightly higher values in the variation of the observed power quality parameters when a 1 min aggregation interval is applied than in case of 10 min aggregation. This allows us to conclude that using 1 min aggregation increases the sensitivity of power quality assessment that might be desirable in future when power grids with a high concentration of distributed energy resources, microgrids or grids working in the islanding condition are considered.

**Author Contributions:** Conceptualization, M.J. and T.S.; methodology, M.J., T.S. and P.K.; software, J.S., M.J. and T.S.; validation, T.S., J.R. and Z.L.; formal analysis, M.J. and T.S.; investigation, M.J., T.S. and P.K.; resources, M.J., T.S., P.K., P.J., D.B., M.R., J.S.; writing—M.J. and T.S.; writing—review and editing, M.J., T.S., E.J., D.K.; visualization, M.J., E.J.; supervision, T.S.; project administration, T.S.; funding acquisition, M.J. and T.S.

**Funding:** This research was funded by Polish Ministry of Science and Higher Education under the grants for young researchers 049M/0004/19 as well as under the project "Developing a platform for aggregating generation and regulatory potential of dispersed renewable energy sources, power retention devices and selected categories of controllable load" supported by European Union Operational Program Smart Growth 2014-2020, Priority Axis I: Supporting R&D carried out by enterprises, Measure 1.2: Sectoral R&D Programs, POIR.01.02.00-00-0221/16, performed by TAURON Ekoenergia Ltd. under Polish Sectoral Program PBSE coordinated by The National Centre of Research and Development in Poland.

**Acknowledgments:** This work uses weather condition data provided by the Center of Energy Technology in Swidnica, Poland. ´

**Conflicts of Interest:** The authors declare no conflict of interest.
