*3.3. Zhongshan Station Load Data*

The load of Zhongshan Station can be divided into: (1) The first type of load is the internal heating system. Once the heating system is not working properly, it will affect the normal life of all the staff of Zhongshan Station and the lives of all personnel will be threatened. Thus, such loads cannot be cut <sup>o</sup>ff. (2) The second type of load is electricity for scientific research equipment. There is a lot of scientific research equipment installed in Zhongshan Station to monitor the climate, biochemistry, crustal changes, and movement of Antarctica in real time and obtain valuable on-site observation data. A power outage of equipment may lead to the discontinuity of observations and the lack of integrity of data. Thus, we need to ensure the continuous supply of electricity of scientific research equipment. (3) The third type of load is electricity for daily use. Such loads include electricity for lighting, recreational activities, electronics, etc., where necessary, such loads may be considered for power outages.

### **4. Analysis of Energy Storage System**

At present, most of the wind–solar hybrid power generation systems use secondary batteries that can be repeatedly charged and discharged as energy storage systems, and the electrical energy can be converted into chemical energy for storage. When using electrical energy, the stored chemical energy of batteries can be turned into electrical energy. When we choose a suitable energy storage device, the capacity of the energy storage device and its charge and discharge performance are mainly considered. The battery with high conversion e fficiency and low loss is suitable for the design of the standalone renewable energy system. In addition, the maintenance cost and life of the battery should be also key factors in the design. Commonly used batteries include lead–acid batteries, nickel–hydrogen batteries, nickel–cadmium batteries, lithium–ion batteries and sodium–sulfur batteries [20]. The key performance comparisons of each battery are presented in Table 5.


**Table 5.** Key performance comparisons of each battery.

It can be seen from Table 5 that the operating temperature ranges of lead–acid battery and lithium–ion battery are more suitable than other batteries for the requirements of this system. Compared with lead–acid batteries, lithium–ion batteries have certain safety hazards and lithium–ion batteries cost more than lead–acid batteries. Thus, the lead–acid battery is selected to design energy storage system.

A lead–acid battery consists of an electrolyte, positive and negative electrodes. *Pb* is used as the negative active material of lead–acid batteries, *PbO*2 can be the positive active material, and the electrolyte is diluted *H*2*SO*4. The energy conversion principle of lead-acid batteries can be expressed by the following chemical reaction equations.

$$P\_bO\_2 + H\_2SO\_4 + P\_b \stackrel{Discharge}{\rightarrow} P\_bSO\_4 + 2H\_2O \tag{7}$$

$$P\_bSO\_4 + 2H\_2O \stackrel{Ch\,\text{arg}\,\varepsilon}{\rightarrow} P\_bO\_2 + H\_2SO\_4 + P\_b\tag{8}$$

Equations (7) and (8) can describe the discharge and charging process of the lead–acid battery, respectively. In the process of discharge, *Pb* on the negative electrode is oxidized to become *PbSO*4, and *PbO*2 on the positive electrode is reduced to form *PbSO*4. Diluted *H*2*SO*4 in the surrounding area as an electrolyte participates in chemical reactions, forming *PbSO*4 while producing *H*2*O*.

In the process of charge, *PbSO*4 on the negative electrode is reduced to form *Pb* and *PbSO*4 on the positive electrode is oxidized to become *PbO*2. The concentration of *H*2*SO*4 in the surrounding area gradually recovers. The charging process of the lead–acid battery is not finished until *PbSO*4 of the positive and negative electrodes is completely reduced to *Pb* and *PbO*2.

In the process of charge and discharge of lead–acid batteries, the terminal voltage can be expressed as the following equations.

$$
\Delta I = E + \Delta \varphi\_+ + \Delta \varphi\_- + IR \tag{9}
$$

$$
\mathcal{U} = E - \Delta \varphi\_+ - \Delta \varphi\_- - IR \tag{10}
$$

Equations (9) and (10) represent the change in terminal voltage during the charging and discharging processes, respectively. *U* is the terminal voltage of the lead–acid battery (V); *E* is the electromotive force of batteries; Δφ+ is the overpotential of positive electrode (V); Δφ*-* is the overpotential of negative electrode (V); *I* is the charge or discharge current (A); *R* is the internal resistance of the battery (Ͳ).

The life of the battery directly determines the time when the power supply system runs stably. This lead–acid batteries used in this power system were developed by Taiyuan University of Technology. Based on the principles of battery array combination, the battery of 2 V, 3 KAh is extended and the battery pack of 60 V, 45 KAh is used as the energy storage device of the power system.

### *4.1. Study on Low-Temperature Characteristics of Battery*

The activity of the electrolyte of the lead–acid battery is easily affected by low temperatures, resulting in a decrease in battery capacity. The power supply system operating in Antarctica requires a long-term constant temperature treatment of energy storage system. Reasonable storage temperature needs to be determined, so as to reduce the energy consumption caused by maintaining the constant temperature as much as possible. Thus, a study on battery characteristics at low temperatures was designed and implemented.

In order to study the low-temperature characteristics of lead–acid batteries, a battery capacity calibration experiment was designed. A low-temperature test chamber (MDF-86V340E, Zhongkeduling, Hefei, Anhui, China) was used to provide stable low-temperature environments from −50 ◦C to 0 ◦C. The key specifications of the low-temperature test chamber are presented in Table 6.


**Table 6.** Key specifications of the low-temperature test chamber.

The ideal capacity of the battery to be tested is 2 V, 3 KAh under a normal temperature environment. The battery was discharged at a constant current of 15 A at different ambient temperatures from −50 ◦C to 0 ◦C. In addition, the battery capacity at different ambient temperatures can be obtained. The battery voltages were measured by an oscilloscope (MSO70404C, Tektronix, Beaverton, OR, USA). The discharge cut-off voltage was set as 1.6 V. The interval for the experimental temperature change was set to 10 ◦C. We obtained the correlation between battery capacity and voltage at −50 ◦C, −40 ◦C, −30 ◦C, −20 ◦C, −10 ◦C and 0 ◦C. At each ambient temperature, the battery continued to discharge at a constant current until the cutoff voltage was reached. During the experiment, the low-temperature test chamber could maintain the temperature. We took the average values of the voltage to minimize the statistical error and uncertainty. As the temperature decreased, the battery capacity also decreased. The standstill battery capacities were 98.42%, 98.11%, 97.62%, 96.77%, 95.83% and 94.12% at 0 ◦C, −10 ◦C, −20 ◦C, −30 ◦C, −40 ◦C, −50 ◦C, respectively. The discharge capacity of the battery was weakening due to low temperatures. Therefore, the storage temperature of the battery needs to be kept above 0 ◦C to avoid the low-temperature loss of the battery capacity.
