## 7 Conclusions  
In this study, we proposed a standalone hybrid wind-solar system for the polar regions. The operation of the observation system in the Arctic Ocean in 2016 and the meteorological environment of the deployment positions were analyzed. A new observation system and a power-supply system with a hybrid solar and wind charging circuit were designed to achieve long-term stable operation in the polar regions at a temperature range of \(-\)50-30 \({}^{\circ}\)C. We presented a comprehensive understanding of the low-temperature performance and characteristics of batteries, including battery capacity at different temperatures, and the charging characteristics of the lead-acid battery. Based on the low-temperature characteristics of the battery, a charging strategy adapted for the battery was proposed. We evaluated the low-temperature performances of the charging circuit to implement charging strategy. The detection and ADC circuits of the charging circuit have excellent stabilities in the range of \(-\)50-30 \({}^{\circ}\)C. The simulation calculation of power generation of the standalone hybrid wind-solar system was presented in this study. The results of the simulation calculation reveal that wind power had a relatively higher share of energy production than the PV. The observing system and the standalone hybrid wind-solar system were applied to the observation of ice-matter balance in Zhongshan Station, East Antarctica from February to July 2017. The power generation of the PV and wind turbine during the field experiment was calculated. The case study shows that the standalone hybrid wind-solar system can be proven to have high stability, and also indicates that our study on battery characteristics in low-temperature environments could greatly improve battery reliability. This paper demonstrates that the standalone hybrid solar-wind system is an ideal solution for automatic observation systems in the polar regions.  
In this study, the standalone hybrid solar-wind system does not emit any pollutants during its lifecycle. However, lead-acid batteries were used as energy-storage units for the power system. Although we designed a leak-proof container to place small batteries to avoid polluting the environment, more environmentally friendly energy storage unit needs to be adopted in future work. More renewable energy, such as wave energy, temperature-difference energy, and salinity-difference energy, in the polar region can be used to design power-supply systems with larger installed capacity.  
Figure 21: Power voltage of the observing system. Area between the red lines is the polar night.  
**Author Contributions:** conceptualization, G.Z.; methodology, G.Z.; software, G.Z.; validation, G.Z.; formal analysis, Y.D.; investigation, Y.C.; writing--original draft preparation, G.Z.; funding acquisition, Y.D., X.C., and Y.C.  
**Funding:** This research was funded by the National Natural Science Foundation of China, grant number 41606220, 41776199; the National Key Research and Development Program of China, grant number 2016 YFC1402702, 2016 YFC1400303; and the Natural Science Foundation of Shanxi, grant number 201701D121127.  
**Acknowledgments:** The authors would like to thank the Chinese National Arctic Research Expeditions and Chinese National Antarctica Research Expeditions for supporting the deployment of the observing and power-supply systems. Comments from the anonymous reviewers and the editor are also gratefully appreciated.  
**Conflicts of Interest:** The authors declare no conflict of interest.