**8. Conclusions**

In this study, the standalone renewable energy system used in Zhongshan Station was proposed to achieve long-term stable operation. The meteorological data of Zhongshan Station obtained from a manned weather station in 2015 was comprehensively analyzed. Based on the atmospheric conditions and load data of Zhongshan Station, the physical model, operation principle and mathematical modeling of the proposed power system were designed in this study. The low-temperature performance and characteristics of energy storage system were tested and evaluated. The characteristics of battery and SOC estimation method were also present. To prevent the battery from low-temperature loss of the battery capacity, a temperature control strategy was adopted to keep the storage temperature of the battery above 0 ◦C. Energy managemen<sup>t</sup> strategy of the power system was proposed, including a MPPT control strategy for wind turbine and PV array and a power supply strategy. The whole power system is broadly composed of a power generator (wind turbines and PV array), an uploading circuit, a three-phase rectifier bridge, an interleaved Buck circuit, a DC/DC conversion circuit, a switch circuit, a power supply circuit, an amplifier, a driver circuit, a voltage and current monitoring, a load, battery units and a control system. The simulation calculation of power generation of the standalone renewable energy system was presented in this study. Zhongshan Station's estimated annual carbon dioxide emissions were 5.3 t in the year of simulation, which can reduce carbon emissions by 611.1 t in one year and 3666.6 t of carbon dioxide during the first six years of operation. Based on the cost savings estimation of other stations, the use of the standalone renewable energy system was estimated to save approximately 1.43 million US dollars in one year. The results of simulation calculation reveal that the proposed power system can satisfy the power demands of Zhongshan Station in normal operation.

In this study, the proposed power system does not realize completely environmentally friendly operation during its lifecycle because of use of lead–acid batteries and a small amount of fuel. In future work, a more environmentally friendly energy storage system needs to be designed and adopted, such as pumped energy storage, flywheel energy storage, etc. More renewable energy harvesting systems can be used to collect wave energy, temperature and salinity di fference energy in Polar Regions. The power generator and the energy storage system need slightly adjusted to achieve 100% environmentally friendly power generation. More works on using advanced sizing methods will be realized to choose power of the photovoltaic array, wind turbine and battery capacity more reasonable.

**Author Contributions:** Conceptualization, G.Z.; methodology, Y.D.; 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.

**Funding:** This research was funded by the National Key Research and Development Program of China, gran<sup>t</sup> number 2016YFC1400303, 2016YFC1402702.

**Acknowledgments:** The authors would like to thank the Chinese National Antarctica Research Expeditions for supporting our work in Antarctica. Comments from the anonymous reviewers and the editor are also gratefully appreciated.

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