**2. Evaluation Index System for Site Selection of HRSs**

HRSs construction and planning are affected by many factors. Although few people directly study the influencing factors of HRSs location planning, potential influencing factors can be found from other aspects. On the basis of the existing literature and research, and our expert consulting and workshop discussion, we further subdivided influence factors of HRSs planning. The influencing factors selected in the study are divided into three categories: economic, technical, and social factors. Under each factor, there are three specific sub-factors, as shown in Table 1.


**Table 1.** Factors affecting HRSs planning in China.

EC: expert consultation.

#### *2.1. Factors Affecting HRSs Planning*


HRSs planning and construction are generally approved and managed by national governmental departments; the construction party needs to submit a series of qualification documents before construction and operation qualification can be obtained [5]. Fixed HRSs also need to apply for planning and construction permits, but skid-mounted stations do not need this procedure [59]. Therefore, the construction scale is also a factor affecting HRSs planning. The larger the construction scale is, the more complicated the approval procedure is, and the corresponding cost would far exceed the infrastructure construction cost [50].

(2) Investment strength U12

The main difficulty affecting HRS development is the high construction cost. Although local governments pay increasing attention to the construction of HRSs, and planning and supporting policies are issued one after another, the high construction cost requires investors to have certain financial strength. All HRSs in China are in the form of external high-pressure hydrogen storage. The initial cost of constructing an HRS larger than 200 kg in China exceeds CNY 10 million [5]. In addition, if debugging, engineering-design, and management costs, and other factors are taken into account, the superposition of these factors directly leads to almost all completed HRSs in China hardly being profitable [13].

(3) Operational costs U13

The cost of operation and maintenance is an important part of the life-cycle cost of a HRS [51]. On the one hand, the construction and development of HRSs in China is still in the initial stage. Compared with the mature operation and maintenance technologies of HRSs in the United States and Japan, China lacks maintenance experience, resulting in relatively high maintenance costs of HRSs [59]. Besides the initial equipment investment of HRSs construction, the amount of the continuous daily fault-free hydrogenation of hydrogenation power consumption, and the cost of employing personnel should also be considered as influencing factors of operating HRSs costs [49]. In other words, operation and maintenance costs are an important factor to be considered in the planning and construction of HRSs.


Hydrogen production from natural gas, coal gasification, industrial byproducts, oil refineries, and water electrolysis are the main sources of industrial hydrogen [13,16,50]. However, because of technical barriers, China still relies on imports for key components in most hydrogen production facilities [15]. Expensive equipment makes it difficult to reduce the cost, and the incomplete domestic hydrogen production technology is the main factor affecting the construction of HRSs.

(2) Hydrogen storage technology U22

Mature hydrogen storage technology and unbreakable key links are key factors affecting the construction of HRSs in China [13,16]. Hydrogen can be stored in three ways: high-pressure gaseous hydrogen storage, low-temperature liquid hydrogen storage, and metal alloy hydrogen storage [51]. High-pressure gaseous hydrogen storage and lowtemperature liquid hydrogen storage are widely used at present. Low-temperature liquid hydrogen storage has a high density, but it is difficult to liquefy hydrogen, which leads to high cost and the requirement for container heat insulation [51,60]. The advantages and disadvantages of different hydrogen storage technologies are compared in Table 2, which reflects the immature hydrogen storage technology in China [60].

(3) Transportation technology U23

There are three common hydrogen transport modes: tube trailers, pipeline, and liquid trucks [5]. China mainly uses long-tube trailer transport, and its long tube trailer transport equipment industry is mature. According to transport industry standard JT/T 617.1-2018 Dangerous Goods Road Transport Rules of the People's Republic of China, long-tube trailers are used for transport, and transport and storage pressure is 20 MPa. Due to cost limitations, this method is suitable for short-distance hydrogen transportation—the economic transportation radius is about 200 km. Low-pressure pipeline transportation is suitable for large-scale point-to-point transportation [54]. Due to the existence of hydrogen embrittlement between hydrogen and some metals, pipe materials have special requirements, so the investment cost is high [53]. In China, large-scale low-pressure pipeline transportation does not exist. The cost of a hydrogen pipeline is more than twice that of a natural-gas pipeline, and hydrogen density is much less than that of natural gas, resulting in a higher transportation cost of hydrogen than that of natural gas. Liquid hydrogen tank transport is widely used in other countries, but it is only used in the aerospace and military fields in China, and is not yet commercialized [5]. To sum up, the current mainstream hydrogen transportation technology needs to be improved, and hydrogen transportation technology is the main factor affecting the construction of HRSs in China [59]. Table 3 summarizes and analyzes current mainstream modes of transportation.

**Table 2.** Advantages and disadvantages of hydrogen storage technologies [60].


**Table 3.** Comparison of scale, cost, and energy consumption of three modes of hydrogen transport [59].


2.1.3. Social Factors U3

(1) The population density U31

HRSs built in urban areas are located in densely populated areas, and are far more dangerous than conventional gas stations are because of the energy produced by hydrogen explosions. Hydrogen as an energy source is widely used in transportation, and safety is greatly important, which is one of the reasons why the hydrogen industry is developing relatively slowly [25,55] In June 2019, the explosion of a hydrogenation station in Sanvika, Norway, also impacted China's hydrogen and fuel-cell vehicle industry, with negative market sentiment [55].

(2) Environmental factors U32

Hydrogen is lighter than natural gas, has a wider explosive limit, spreads faster, and is likely to cause more dangerous accidents [45]. High-pressure hydrogen embrittlement is common, and high pressure demands more stringent safety spaces in the surrounding environment [51]. Hydrogenation station construction must consider whether there are dangerous sources or crowded places around, such as schools and hospitals [5,52]. Therefore, in the process of the expert evaluation of built hydrogenation stations in China, the surrounding environment of all hydrogenation stations is first objectively evaluated by experts.
