4.2.1. Energy Input Level Effect

We computed the aggregated energy input level effect of each sector by summing the energy input level effect of each sector over 30 provinces. Figure 3 shows that the aggregated energy input level effects of 22 sectors in China contributed to a coal reduction of 1281 Mtce, and the top three sectors were electricity and hot water production and supply (Electricity), metallurgy, and the chemical industry, contributing 71% of that 1281 Mtce coal reduction. The reason lies in the dramatic improvements in the energy efficiencies of these sectors [31,32].

Unfortunately, the other nine sectors had a total rise in coal consumption of 243 Mtce, due to the energy input level effect (Figure 3). Growth in the sectors of coal mining and coking products stand out the most (Figure 3). With the reduction of easy-to-mine and high-quality coal resources, the increasing difficulty in coal mining and the enlarging need of coal refinement promoted unit energy consumption in coal mining [33,34]. As coal and electricity were the main energy types consumed in coal mining, according to matrix **C** in Equation (13), the unit energy consumption change majorly affected the coal consumption. The installation of environmental protection equipment and the instigation of long-term low-load operation in coking products led to an increase of the unit of energy consumption in this sector [35,36]. For example, wastewater facilities were installed for environment protection, and the unit energy consumption of coking products rose [36]. For the coking facilities, a lower processing amount (a lower load rate) results in a higher allocated unit energy consumption [36]. Coal was the main material for coking. Therefore, the increased unit energy consumption mainly led to coal growth.

Concerning oil consumption, the energy input level effects of 24 sectors acted as drivers to reduce oil by 166 Mtce, with the top sector being transport and storage, which had a reduction of 83 Mtce (Figure 3). The energy input level effect of petroleum refining causing oil use to grow by 23 Mtce cannot be ignored, as this amount was significantly higher than those of the next highest sectors (Figure 3). The increasing share of high-sulfur crude oil and low-load operation owing to excess capacity, induced a unit energy consumption growth in petroleum refining [37,38]. High-sulfur crude oil not only increased the processing difficulty of refineries, but also expanded the scale of environmental protection facilities, such as desulfurization [39]. As a result, the unit energy consumption of refineries increased, which led to oil growth, because oil was the main raw material of refineries. In addition, the energy input level effect on natural gas use change was quite small (Figure 3).

**Figure 3.** Energy input level effect by sector.

Subsequently, we ranked the disaggregated energy input level effects of 31 sectors of 30 provinces; the top ten and the bottom ten are listed in Figure 4. The coking products of Shanxi had the most energy growth among the 930 contributors (31 sectors × 30 provinces), at 58 Mtce (Figure 4). From the bottom ten, we were surprised to find that the energy input level effect of electricity was positive

at 47 and 20 Mtce in Inner Mongolia and Shanxi, respectively, even though the local governments announced an update of equipment at the power stations during the study period [40]. The problems of these sectors lie in the fact that the low-load operation of power generation units, as well as the poor equipment managemen<sup>t</sup> levels in Inner Mongolia and Shanxi, resulted in the ineffectiveness of the power generating units with large capacities and a high parameter [41–43]. The other contributors of the bottom ten were mainly related to coking products, coal mining, and petroleum refining, as expected (Figure 4).

**Figure 4.** Top ten and bottom ten contributors for energy saving related to energy input level effect. SD: Shandong; JL: Jilin; IM: Inner Mongolia; HB: Hebei; LN: Liaoning; HN: Henan; GD: Guangdong; ZJ: Zhejiang; JX: Jiangxi; SX: Shanxi; SH: Shanghai; XJ: Xinjiang.

Accordingly, further energy efficiency improvement in electricity, the chemical industry, metallurgy, coal mining, coking products, transport and storage, and petroleum refining would dramatically reduce energy use. However, the fact is that, by 2017, when these sectors encountered excess capacity, some of the technologies of sectors such as electricity, the chemical industry, metallurgy, and coking products were already close to or at the advanced level in the world [31,32]. That being the case, what counts is not replacing the equipment frequently, but promoting an energy saving approach under a low-load operation, and phasing out inferior production capacities. As for other sectors, such as coal mining and petroleum refining, both the lag in technology and the over-capacity should be addressed.
