**1. Introduction**

The rapid changes of sea ice condition in Arctic and Antarctica in recent decades have been considered one of the most impactful phenomena on Earth [1–3]. There are more and more researches and observations organized by China in Antarctica every year. Up to now, China has four Antarctic research stations, namely the Great Wall Station (62◦12 59" S, 58◦57 52" W), the Zho2033ngshan Station (69◦22 24" S, 76◦22 40" E), the Kunlun Station (80◦25 01" S, 77◦06 58" E) and the Taishan Station (73◦51" S, 76◦58 E). The Great Wall Station and Zhongshan Station are both perennial research stations, which have the ability to accommodate dozens of expedition members and researchers to spend the whole year in Antarctica. Zhongshan Station was established in an area of Larsemann Hills on East Antarctica on 26 February 1989 as a Chinese observation base of high altitude physics, glaciers, atmosphere, ocean, biological ecology, geology, geomagnetism etc. Zhongshan Station is also the base camp for the Chinese National Antarctica Inland Research Base. Zhongshan Station can accommodate about 25 wintering personnel and 600 summer personnel. The current energy supply of Zhongshan Station mainly depends on fuel. The ecological environment in Antarctica is very fragile, and the

fuel produces a lot of harmful gases. Although treated by Zhongshan Station, it cannot achieve zero pollution. The fossil fuels used by Zhongshan Station were transported by the Chinese observatory ship Xuelong every year. As the demand of research and observations increases in Antarctica, the amount of fuel consumption increases accordingly. Therefore, new demands for power supply in Antarctica for green, sustainable and less costly energy sources such as wind, solar, ocean were created.

When humans do research in Antarctica, the impact of human activities on the natural environment of the polar region should be minimized as much as possible. Based on the special meteorological condition of Antarctica, some demands need to be proposed during designing and building the power system used in Zhongshan Station, East Antarctica. The use of fossil fuels is limited due to the inevitable pollution. There are abundant resources of wind, solar, and ocean energy in Antarctica, which can be considered a grea<sup>t</sup> advantage in the development of environmentally friendly power generation. Some works and research have reported on small standalone hybrid wind–solar systems which are isolated from the grid for observing systems deployed in the field in the Arctic Ocean and Antarctica [4]. The design of the hybrid wind–solar system was adopted because of the fluctuations of the solar and wind energy resources in polar regions. Some researches of hybrid wind–solar systems have reported. A report by Reference [5] indicates that the best fit of the wind turbine and photovoltaic (PV) array to a given load can be determined by the least square method. Some methods of modeling, designing and evaluating of hybrid renewable energy systems were also developed [6]. A hybrid solar–wind–battery system was used in the isolated site of Potou in the northern coast of Senegal to realize the minimization of the annualized cost and loss of power supply probability [7]. Based on a methodology of optimal sizing of a hybrid PV/wind system, this hybrid power system was installed on Corsica and can meet the desired system reliability requirements [8]. In some harsh environments in Iraq, the design of hybrid systems can be considered renewable resources of power generation and the simulation results illustrate that it is possible to use the solar and wind energy to generate enough power for remote areas [9]. Renewable energy such as wind energy and solar energy have been used in Antarctica. Mawson Station of Australia has built two 300 KW wind turbines to provide continuous power since 2003. On Ross Island in Antarctica, a wind farm has been used to realize 100% of the energy supply of Scott Base of New Zealand and part of the power requirements of McMurdo Station of United States of America. For Princess Elisabeth Station of Belgium, 300 m<sup>2</sup> solar panels have been installed and can generate 49 MWh [10]. Syowa Station of Japan has built 55 KW of solar panels to produce an annual output of 44,000 KW h for accommodating up to 110 people in the summer and 28 people in the winter [11].

For a hybrid PV/wind system in Polar Regions, an energy storage system (ESS) plays an important role in storing excess energy and releasing the power as a reliable back-up to the power system for unpredictability and weather dependence of wind and solar energy. An integrated wind–PV hybrid system with a battery ESS was proposed and a power managemen<sup>t</sup> strategy of this system can realize rapid control of the outputs of wind and PV power for regulating the battery current [12]. In the design of an isolated renewable hybrid power system, a methodology of battery sizing was used to determine the sizing curve and the feasible design space [13]. Using solar, wind, fuel cell, and batteries as input sources may be able to meet the load demand and an energy managemen<sup>t</sup> strategy is proposed for a DC microgrid [14,15]. A case study of a stand-alone photovoltaic (PV) system was proposed and the environmental impact of batteries used in the renewable energy system was evaluated [16]. Due to the di fferent seasonal changes of power production and demand, the design of renewable energy system should involve the use of surplus energy [17]. A multi-energy system with seasonal storage was designed and optimized in terms of total annual costs and carbon dioxide emissions [18].

In this study, a new standalone renewable energy system of the Chinese Zhongshan Station in Antarctica was designed to realize an environmentally friendly energy supply and to obtain high power generation e fficiency. The physical model and mathematical model of the standalone renewable energy system were proposed [19]. Lead–acid batteries were selected as an energy storage system for the standalone hybrid windsolar system and a temperature control strategy was adopted to prevent the

battery from low-temperature loss of the battery capacity. Energy managemen<sup>t</sup> strategy of the power system was also proposed based on results of low-temperature characteristics of battery. The whole power system is broadly composed of 13 parts: (1) a power generator (wind turbines and PV array), (2) an uploading circuit, (3) a three-phase rectifier bridge, (4) an interleaved Buck circuit, (5) a DC/DC conversion circuit, (6) a switch circuit, (7) a power supply circuit, (8) an amplifier, (9) a driver circuit, (10) a voltage and current monitoring, (11) a load, (12) battery units, (13) a control system. A case study of the operational results of the standalone renewable energy system was examined to evaluate the technical feasibility and stability. Analysis of simulation operation results, emission reduction and costs and benefits of renewable energy applications in Antarctica were completed.

In these contexts, this paper focuses on exploring a standalone renewable energy system for Zhongshan Station. Section 2 describes the atmospheric conditions of the study area. Section 3 gives the results of the physical model, operation principle, and mathematical modeling of the power system. The results of the low-temperature characteristics of batteries are shown in Section 4. The energy managemen<sup>t</sup> strategy of hybrid wind–solar system is given in Section 5. Section 6 introduces the design of the whole power system. The results of a case study of the hybrid wind–solar power system in Zhongshan Station are presented in Section 7. The conclusions are in final section.

### **2. Atmospheric Conditions of Zhongshan Station, East Antarctica**

The meteorological data of Zhongshan Station were obtained from a manned weather station in 2015. Table 1 summarizes the various sensors used in the manned weather station. The weather station consists of a wind speed and wind direction detection sensor (Wind Monitor Model 05103-45, R.M.Young, Traverse City, MI, USA), a temperature and humidity sensor (HMP155A, Vaisala, Vantaa, Finland), an atmospheric pressure sensor (PTB110, Vaisala, Vantaa, Finland). The Wind Monitor sensor has a rugged and corrosion-resistant construction which is suitable for wind measuring applications in harsh environments. The four blade helicoid propeller of the wind speed sensor produces an AC sine wave voltage by rotation. The vane angle of the wind direction sensor is sensed by a precision potentiometer. The Wind Monitor sensor mounts on standard one-inch pipe. The temperature and humidity sensor has excellent stability and can withstand harsh environments. The temperature and humidity probe is protected with a sintered Teflon filter and a radiation shield, which can increase its lifetime by waterproofing, sandproofing and dustproofing. The atmospheric pressure sensor (PTB110) with the capacitive detection principle is a silicon capacitive absolute pressure sensor, which combines the outstanding elasticity characteristics and mechanical stability of single-crystal silicon.


**Table 1.** Sensor information of the manned weather station.

The data of wind speed, wind direction, air temperature, relative humidity and air pressure measured by the weather station in Zhongshan Station from 1 December 2014 to 1 November 2015 are shown in Figure 1. The height of the wind speed and direction with respect to the ground is 10 m. During this period the mean wind speed was 9.8 m/s. The maximum and minimum values of wind speed were 35.9 m/s and 0 m/s, respectively (Figure 1a). The wind near Zhongshan Station was dominated by strong easterly winds, but there were westerly winds with lower wind speeds in February and March (Figure 1b). Surface winds at Zhongshan Station are generally consistent with the observations before. Air temperature of Zhongshan Station is shown in Figure 1c. The average air temperature was −11.18 ◦C. The maximum and minimum values of air temperature were 8.30 ◦C and −39.9 ◦C, respectively. The lowest air temperature occurred on 8 July 2015 and the highest was on 20 December 2014. The results of air temperature distribution are similar to the previous observations. The average relative humidity was 59.6%. The maximum and minimum values of relative humidity were 96% and 26%, respectively. The highest relative humidity occurred on 25 October 2015 and the lowest was on 26 November 2015. As shown in Figure 1d, Zhongshan Station has low relative humidity and dry air. The average atmospheric pressure was 982.4 hPa. The maximum and minimum values of atmospheric pressure were 1013.3 hPa and 942.3 hPa, respectively. The lowest atmospheric pressure occurred on 11 April 2015 and the highest was on 18 July 2015 (Figure 1e). The short-term variations in wind speed, wind direction, air temperature, relative humidity and atmospheric pressure were considerable, which can prove the complexity of the weather conditions at Zhongshan Station.

**Figure 1.** Time series of hourly (**a**) wind speed, (**b**) wind direction, (**c**) air temperature, (**d**) relative humidity and (**e**) air pressure obtained by the manned weather station at Zhongshan Station, Antarctica.

The multi-year average meteorological data are presented in Figure 2. The monthly average wind speed, radiation, day length, and air temperature in Figure 2 were obtained from the Atmospheric science data center of NASA. The monthly average wind speed from NASA and observed wind speed are shown in Figure 2a. The trend of wind speed from NASA is consistent with the observed results. For the multi-year average wind speed, the maximum and minimum wind speeds were 9.88 m/s in June and 7.5 m/s in January, respectively. The maximum and minimum monthly-observed wind speeds were 10.9 m/s in December and 4.8 m/s in February, respectively. The annual average wind speed from NASA was 9 m/s, which was similar to the annual observed result (9.78 m/s). The monthly average radiation and day length at Zhongshan Station are shown in Figure 2b. The radiation and day length decreased from January, and reached the minimum values at the same time (June). Then the radiation and day length continued to increase until December. The monthly mean radiation in May, June and July were 0.05 KW <sup>h</sup>/m<sup>2</sup>/day, 0.00 KW <sup>h</sup>/m<sup>2</sup>/day, 0.01 KW <sup>h</sup>/m<sup>2</sup>/day, respectively. Additionally, the monthly mean day lengths were 4.05 h, 0 h and 1.23 h, respectively. This phenomenon can indicate that polar night occurs from late May to late July in this region. The monthly mean radiation in January, November, and December were 6.05 KW <sup>h</sup>/m<sup>2</sup>/day, 4.97 KW <sup>h</sup>/m<sup>2</sup>/day, 6.69 KW <sup>h</sup>/m<sup>2</sup>/day, respectively. The monthly mean day lengths in January, November, and December were 24 h, 20.8 h and 24 h, respectively, which polar day lasts from late November to early February of the following year at Zhongshan Station. As can be seen from Figure 2c, the monthly average air temperature at Zhongshan Station exhibited obvious seasonal characteristics. The average yearly air temperature was −19 ◦C. The maximum and minimum monthly mean air temperature was −7.13 ◦C in January and −27.3 ◦C in July.

**Figure 2.** The monthly meteorological data of Zhongshan Station. (**a**) wind speed, (**b**) solar radiation and day length, (**c**) air temperature.

The weather condition of Zhongshan Station can be summarized as strong easterly winds, lower relative humidity, lower barometric pressure and cold air. The operating temperature range of the standalone renewable energy system in this study should be −50–30 ◦C based on the analysis of meteorological data at Zhongshan Station. Other meteorological elements should be taken into account during the design of the power supply system. Thus, in this study, the characteristics of power system at low temperatures should be considered and studied for achieve a long-term operation of research station in Antarctica.
