As a major country with huge volumes of energy production, consumption and importation, China needs to formulate strategic plans with specific technical routes and practical measures for the energy security purpose in the views of present, mid-term and long-term. The “energy independence” proposed in this article is a strategic mission. It pursues an implementation of domestic produced energy accounted for at least 90% of energy consumption through the strategic and scientific planning. However, with the significant improvements in economy, technology and military force of the state, it may be no longer necessary to maintain the balance between energy production and consumption to pursue self-supply and self-control in energy security.

Human beings were born around 6 million years ago, building homes around the world, and initiating the era of energy utilization ^[1,2,3]. Energy, water and grain have been treated as the key materials for the survival of human beings since the application of fire for the first time. As the natural resources to power human society, energy can be classified into two categories: conventional fossil fuels and non-fossil fuels (i.e., the new energy). New energy refers to the renewable clean energy explored and used by new technologies to substitute the conventional energy. Primary forms of new energy include solar, hydraulic, wind, hydrogen, geothermal, ocean, biomass, nuclear energy, etc.^[4] New energy is significantly different from the traditional carbon-bearing fuels, like coal, oil and natural gas, in theoretical technologies, utilization costs, environmental impacts and management modes^[4].

The progress of science & technology, together with social development are the two contributors for energy development and transition. In fact, energy independence can be treated as the foundation for the safety and prosperity of a nation. The U.S. government initially proposed a strategy of “energy independence” in 1973^[5]. It focused on shale oil/gas and other unconventional resources, and relied on precursor strategies and relevant financial and tax supports to fully launch a commercialization of shale oil and gas exploitation. Through continuous efforts in the past five decades, it is expected to achieve the “energy independence” goal in 2022. The U.S. has exported a volume of 1085×10⁸ m³ natural gas in 2018, and is expected to be a net exporter for the crude oil in 2022. It is predicted that the U.S. will export fossil fuels of 3.1×10⁸ tons of oil equivalent in 2030, including 1700×10⁸ m³ natural gas, 1.1×10⁸ t crude oil and 1.0×10⁸ t coal^[6].

Overviewing the global situation of energy development and transition, this paper proposes five patterns in the current phase based on the relationship between energy supply and demand. It is predicted that the carbon-free new energy with intelligent management will be prevalent in the future. Currently, China is faced with many challenges in the energy issues, including the huge demand, the unclean pattern and unsafe supply. The specific situation on resources structure and basic conditions have determined that it is impossible to duplicate the development mode of the U.S. to solve the energy problem once and for all. Instead, China can learn effectively the successful experiences from the U.S. to formulate its own energy strategies. For the medium- to long-term perspective, it is necessary to focus on new energy revolution to initialize the long march road of “energy independence”. New energy revolution is the inevitable road and strategic selection for China. Under such circumstances, a “three steps” path should be considered: (1) to solve the energy security problem by promoting supplies of fossil fuels and new energy, (2) to fulfill the self-supply goal by counting on overseas and domestic production, (3) to achieve the “energy independence” mission by raising the new energy proportion and accomplishing the energy intelligentization. In this way, energy structure can be systematically changed from the pattern of “one major (coal) and three minors (crude oil, natural gas and new energy)” to “three equal shares” of coal, petroleum and new energy. The ultimate goal for the energy structure change is to achieve the “one major one minor” pattern characterized by the dominance of new energy with supplement of fossil fuels. In other words, only if the share of new energy accounts for the majority in energy consumption, the dream of “energy independence” could be a reality.

Chronologically, the first transition of energy types from woods to coal has accomplished during the period from 1600s to mid-1800s, and the second one of coal-to-petroleum has been achieved from mid-1800s to mid-1900s. Since then, the world has entered the third major transitional period from hydrocarbon to new energy^[4]. Moreover, energy utilization shows a trend of decarbonization from high carbon-contained types to low carbons, and even non-carbon energy. It also reflects a conversion from solid forms (i.e., woods and coal) to liquid (i.e., oil), and to gaseous (i.e., natural gas) resources.

Currently, each of the four energy types (i.e., coal, oil, natural gas and new energy) approximately accounts for a quarter in the global production and consumption structure. In 2018, the total global energy production was 138×10⁸ tons of oil equivalent, of which coal, oil, gas and new energy account for 28%, 32%, 24% and 16%, respectively. The structure of energy consumption is roughly similar to that of energy production, and the tendency of decarbonization has been promoted continuously.

In the future, the share of new energy will increasingly expand in global scale. Certainly, energy transition makes the conventional fossil fuels ultimately be replaced by renewable new energy. In 2018, the global consumed new energy was 21×10⁸ tons of oil equivalent, accounting for 15.3% of total energy consumption, with a year-on-year growth of 5.7%. Recently, global new energy mainly consumes hydraulic and nuclear powers. Meanwhile, solar and wind powers increased fast, and geothermal and biomass energy increased mildly. In addition, nuclear power declined during the course.

The U.S. is self-sufficient in energy supply, and characterized by the high volumes of annual consumption. It has abundant reserves and enjoys a steady energy demand to the social scale. Recently, it has launched an unconventional practice petroleum industry, and benefits from the fast increase in shale oil and gas production. In 2018, the U.S. energy supply and demand were 21.1×10⁸ and 23.0×10⁸ tons of oil equivalent, respectively, with a dependence rate of 8.3%. The U.S. government has supported the increase of domestic energy production for 50 years, since the “energy independence” goal firstly initiated by the President Nixon in 1973. It is predicted that the U.S. will achieve the goal in 2022 relying on the “shale revolution”. Notably, the U.S. has played a leading role in exploiting shale oil and gas worldwide, reshaping the global energy grids, influencing the political and economic structures of the entire world.

Russia is a main energy exporter with extremely huge volume of hydrocarbon reserves and high productivity. It is characterized by its low annual consumption and high annual production. In fact, Russia barely develops new energy industry due to the rich preserves in hydrocarbons. In 2018, Russia supplied a volume of 14.5×10⁸ tons of oil equivalent products, and consumed only 7.2×10⁸ tons of oil equivalent, exporting a half of total produced petroleum.

The U.K. partially relies on the import business to balance the energy needs. It has gradually depleted fossil fuels, but has an enormous potential on renewable energy. The balance between supply and demand is basically maintained. In fact, the U.K. has played a leading role in proposing a low-carbon economy, introducing a carbon budget, and commercializing carbon capture and storage^[7]. In 2018, the state’s gross energy production was 1.27×10⁸ tons of oil equivalent, and the consumption was 1.87×10⁸ tons of oil equivalent, with a 33% dependence on import.

As a major energy importer, Japan is characterized by the high energy consumption and extremely low self-supply rate. The extremely low fossil fuel preserves make Japan entirely rely on importation. In 2018, there was a huge gap between energy supply (1.4×10⁸ tons of oil equivalent) and demand (4.5×10⁸ tons of oil equivalent) with an import rate reaching 70%. Meanwhile, the Japanese government has deeply cut nuclear power proportion, and simultaneously switched to the hydrogen after the Fukushima Daiichi Nuclear Disaster. By prompting the hydrogen industry, Japan may fulfill its “energy independence” around 2050.

China is enjoying the high economic growth and the fast increase on energy demand. Its energy supply partially counts on importation. The fossil fuel preserves are rich in coal, but insufficient in oil and gas. This resources structure leads to a very high dependence on oil and gas importation. Therefore, hydrocarbons are the most sensitive weakness for energy security. In 2018, China grossly produced 26.4×10⁸ tons of oil equivalent of energy, but consumed 32.7×10⁸ tons of oil equivalent of energy. There is a 19% proportion on the gross energy dependence, in which the importing rates for crude oil and natural gas are reaching 71% and 43%, respectively.

1.3.1. The consumption of fossil fuels exceeds the environmental carrying capacity in the local regions of the world

With the increasing emission of carbon dioxide and other greenhouse gases, global warming has accelerated in recent decades. In 2018, concentration of carbon dioxide in atmosphere peaked at 407.3×10^-6, the highest value in the past 800 000 years^[8,9,10]. At the same time, the concentration of other greenhouse gases, namely methane and nitric oxide, also reached historical high values of 1857.3×10^-9 and 330.9× 10^-9[10], respectively.

Currently, the earth is struggling with the environmental crisis induced by climate change^[11]. For example, coral bleaching events can be seen as reflections for seawater warming and die-off of corals^[12]. High temperature of permafrost results in the release of carbon dioxide and methane to the atmosphere to accelerate global warming^[13,14]. The temperature is continuing to rise in the Arctic area affected by global warming, exceeding the global average^[9], and ice sheets in Greenland melted at a great speed. It is predicated that if all these ice sheets melted, the sea level may rise by 7.2 m^[15,16,17].

1.3.2. The fourth industrial revolution further boosts the transition to the new energy

Currently, the world has entered into the sixth scientific- technological revolution. The past two scientific revolutions and three technological revolutions guided and pushed the world into the fourth industrial revolution stage, as well as the energy history has entered the third transition period to the new energy (Fig. 1). Every reformation of such revolution introduced innovative ways for energy utilization. With the progresses in mechanics and thermodynamics in the 1760s, the first industrial revolution specified the application of steam engines to promote the replacement of manual workers by machines, and disclosed the utilization of coal as a power source for steam engines. The second industrial revolution occurred in the 1870s, characterized by application of electromagnetics in power. The electricity became a new energy to power machines, and marked a new era of electrification. Subsequently, the invention of internal-combustion engine fueled by gasoline promoted the development of petroleum exploration and petrochemical industries. Accompanied by invention of binary computer languages, the third industrial revolution occurred in the 1950s, resulting in a close combination of mathematics with communication. This caused a connection of energy exploration, utilization and sharing. With the progresses of biological and computing sciences, the next generation quantum computers will lead to the fourth industrial revolution. New materials and techniques will emerge in large numbers, such as graphene, gene technologies, quantum intelligence, controlled nuclear fusion, and clean energy. The energy utilization will get more integrated and intelligent, entering the time of intelligent new energy.

Reviewing the history of energy development, each industrialization has been accompanied by the decarbonization of energy. In addition, utilization ways of energy also changed from direct combustion to multiple conversion, bringing a chance for energy transition. Eventually, the fossil fuels will be ultimately replaced by the new energy^[4], and the energy utilization will enter the era of clean and intelligence.

Since the first commercial oil well successful drilled in Pennsylvania in 1859, the theoretical and technical development of petroleum industry can be divided into three stages (Fig. 2): (1) The early stage was characterized by the anticline theories, and the proposal of the rotary drilling technologies. (2) The conventional development stages was guided by the theories of trapped reservoirs, forming a series of rotary drilling, jet drilling, and automatic drilling technologies. (3) The conventional-unconventional stage focuses on the continuous sweet spots of unconventional petroleum geology, making the hydraulic fracturing and platform operations prevalent. The large-scale and high-efficiency exploitation of unconventional resources have been successfully achieved, especially in the U.S. and China.

Recently, the global oil price has fluctuated around medium to low levels. Oil companies have been forced to conduct theoretical and technical innovations to reduce cost and improve production efficiency. Under such circumstances, a series of theories has been introduced to promote the petroleum industry, including unconventional petroleum geology, carbonate petroleum geology, conventional-unconventional systematic accumulation, and in-source oil and gas (Fig. 2). In contrast, the use of new energy, including wind, solar, geothermal and biomass, has increased significantly since 2000. In 2018, the new energy consumption (i.e., non-fossil fuels) accounted for 15.3% in primary energy consumption^[18].

Fossil fuels still have abundant preserves and great potentials, and are able to power the world over 100 years. In 2018, the reserve/production ratios of coal, crude oil and natural gas were 132, 50 and 51, respectively. The resource potential has been enhanced after the unconventional revolution. However, fossil fuels are facing with many challenges, such as unclean, high development costs and uneconomic operation. It is certain that the fossil fuels will be replaced by the new energy without the depletion of fossil resources.

The U.S. government proposed the energy independence strategy in 1973, focusing on unconventional oil and gas resources such as shale gas. It is expected to be achieved in 2022 owing to the prolonged joint forces of technical development, financial supports and legal protection in the past five decades.

Up to 2030, the United States may export energy up to 3.1×10⁸ tons of oil equivalent^[19]. The American strategic thinking and experiences based on long-term efforts and continuous solving of key problems may provide valuable guidance for China.

The key strategic point is to propose advanced planning. In terms of the “energy independence”, the U.S. has implemented three key measures, namely advanced science and technology development, re-organization of the Energy Department, together with implementation of the Crude Oil Windfall Profits Tax Act. In 1976, the Energy Department of the U.S. initialized the Unconventional Gas Research Project (UGRP) with its affiliating Eastern Gas Shales Project (EGSP). Till the end of 2005, the project has been in operation for 28 years. According to the Act for Reconstruction of the Energy Department in 1976, the Natural Gas Research Institute was established with capital investment over $50×10⁸. In addition, preferential tax credit policies have been implemented with reduction rate of $1.083/10⁶ ft³ (approximately 0.26 RMB/m³), while the natural gas price was $1.75/10⁶ ft³ only in 1989. China should follow a similar way to determine the global trend of energy development, systematically analyze the underground conditions, and formulate the energy independence strategy accordingly.

At the time of foundation of People’s Republic of China in 1949, the total energy production was 0.2×10⁸ t of standard coal only, which included 0.3×10⁸ t raw coal production, 12.0×10⁴ t crude oil, 0.1×10⁸ m³ natural gas and 43.0×10⁸ kW·h electric power generation. In 2018, by contrast, the nation’s energy production reached 26×10⁸ tons of oil equivalent, including 36.8×10⁸ t raw coal, 1.9×10⁸ t crude oil, 1 602.7×10⁸ m³ and 71 117.7×10⁸ kW·h electric power generation.

In the past 70 years, China has realized a full-scale innovation in respect to energetic theories and technologies, including the continental oil geology, marine gas accumulation, unconventional petroleum geology, and the development of oil and gas in micro-nanopores. China has become a major country in energy technological development and utilization, owing to the fast development of new energy including solar, wind, hydraulic and nuclear power. Currently, China is the largest energy production, consumption and importation country worldwide, exceeding the U.S.

In terms of the energy consumption structure, globally the oil and gas is dominant accounting for 57.5%, while it is coal in China representing 58.4%. If referring to the proportion of coal in total primary energy consumption, it was 37% in the world in 1965 which is expected to be reached in China around 2050. It indicates China is approximately 85 years behind the world in energy structure evolution.

Although fossil fuels will be still playing important roles in stabilizing supply and servicing the society in the near future, they are not capable to solely support the “energy independence” objectives. Thus, the development of new energy, and combination with fossil fuels are necessary for China.

2.3.1. Depending on cleaning coal, stabilizing oil and gas production and vigorously developing new energy to achieve “energy independence”

The different energy conditions determine that China may not be able to copy the U.S. mode to balance energy demand and supply solely depending on unconventional oil and gas. It is different that the surface and underground conditions for the development of unconventional oil and gas between China and the U.S. Environmental concern halts coal to be the primary energy over long period. Furthermore, China is unlikely to develop large-scale oil and gas production limited by its hydrocarbon resource conditions. The technological development and the industrial revolution offer China the historical opportunity to achieve the “energy independence” by cleaning coal, stabilizing oil and gas production, and vigorously developing new energy.

It is necessary to promote energy production and consumption revolution to accelerate energy transition through national key strategic planning. Underground coal gasification can improve clean utilization of coal. For stabilizing oil production and increasing gas production, it is necessary to increase domestic production and to expand international operation through “One Belt and One Road Initiative”. In addition, hydrate production tests should be implemented to increase natural gas supply. To vigorously develop the new energy, hydrogen revolution should be in acceleratory combination with oil and gas infrastructures. As for new energy technological revolution, more attention should be paid on the revolutionary technologies including energy-storage battery, nanomaterials, graphene, magnetically confined fusion to facilitate the transition of energy utilization towards carbon free, inter-connection, big data and intelligent.

2.3.2. The ecological environment issues leading clean energy to an inevitable choice

The combustion emissions of high carbon fossil fuels, such as coal and oil, are the main sources of air pollution, and also the primary reason for the formation of smog in most cities of China^[20,21]. With the increasing importance of environmental protection and the “Beauty China” purpose, the indexes of PM10, PM2.5, sulfur dioxide and nitrogen oxide in pollutant decreased by 35%-45%, and the content of atmospheric ozone increased from 140 μg/m³ to 150 μg/m³ from 2013 to 2018. The development of clean energy has become an inevitable requirement for ecological and environmental protection. In 2019, by vigorously implementation of coal-to-gas transition and other measures in Beijing and surrounding areas, the air quality index of PM2.5 concentrations decreased rapidly from 89.5 μg/m³ in 2013 to 42.0 μg/m³ in 2019.

2.3.3. The crude oil demand peak offering China the opportunity for energy structures transition

The crude oil consumption in the majority of the developed countries has double humps. Oil Crises in 1973 and 1979 hit the economy of developed countries heavily, thereby affecting the oil consumption, and facilitated the formation of the first consumption peak (Fig. 3). Due to different compositions of primary energy consumption and resource characteristics in most developed countries, their second consumption peak occurred at slightly different times. For example, in Japan and the U.S., the second consumption peaked in 1996 and 2005, respectively. In China, the crude oil consumption is still growing. Under the benchmark scenario, increased policy scenario and temperature control scenario^[22], the consumption is expected to reach the peak in 2025 or 2040. In China, the energy requirements, especially the peak time of crude oil consumption, will be an important opportunity time for transition of energy structures.

2.3.4. Technology innovations for new energy development providing necessary technical supports for “energy independence”.

With the technology development, the new energy has become popular and low-price, being used in large-scale. The future energy, such as hydrogen energy, energy-storage battery, nanomaterials, graphene, and magnetically confined fusion may be beyond our imagination. High efficiency water electrolysis in the field of hydrogen energy, magnetically confined fusion in the field of nuclear energy, new materials, graphene, nano- battery and other technologies in energy storage domain are driving energy utilization towards intelligence, interconnection and big data. Mature new technologies may provide necessary technical supports for “energy independence”. Technology explosion and technology iteration will promote the rapid development of new energy industry, and the era of new energy may come sooner than expected.

At present, the energy development in China is facing four challenges: the huge consumption, the unclean structure, the insecure supply and the unrealistic duplication of American model. Such circumstances determine the “energy independence” strategy in China is long-term and systematic, and cannot be achieved overnight.

China is the largest country in the world in terms of population and car ownership, and is the second largest economic entity in the world. The population base and economic volumes have determined that the energy consumption in China ranks the first in the world. Up to the end of 2019, the population of mainland China has exceed 14×10⁸, ranking the first in the world^[24], increasing 467×10⁴ than the end of 2018, with natural population growth rate of 3.34‰. On the other hand, the total number of motor vehicles was 3.48×10⁸ at the end of 2019, of which there are 2.6×10⁸ cars, with year-on-year growth rate of 8.8%. The number of cities in China holding over 100×10⁴ cars is 66, and the number over 200×10⁴ cars is 30^[25]. As the second largest economy in the world, China has gross domestic product (GDP) of approximate $14.36×10¹² U.S. dollars in 2019, with a growth rate of 6.1%^[26].

China is rich in coal but lack oil and gas resources relatively, which determines the specific resource compositions, production and consumption ratios. By the end of 2018, the proved recoverable coal reserve in China was 1388×10⁸ t, accounting for 13.2% of the total coal reserves in the world. The proved oil recoverable reserve was 35×10⁸ t, only 1.5% of the total oil reserve in the world. The proved recoverable natural gas reserve was 6.1×10¹² m³, only 3.1% of the total gas reserve globally.

In 2018, coal accounted for 58.4% of primary energy consumption in China, whereas the crude oil, natural gas and new energy were 19.6%, 7.4% and 14.7%, respectively. This leaded to a similar consumption structure as “one major and three minors”, that is, dominated by coal, and small-proportioned in crude oil, natural gas and new energy consumption. Globally the consumption structure is characterized as an equal consumption of coal, crude oil, natural gas and new energy, yet the energy structure in China is rich in coal but insufficient in oil and gas, which may restrict seriously the construction of beautiful China. The unclean energy structure, dominated by coal, in China needs to change towards the low-carbon.

In 2018, the primary energy consumption in China was 32×10⁸ tons of oil equivalent, with a shortage of 6×10⁸ tons of oil equivalent mainly in oil and gas, with an external dependence of 19%. Since 2010, the domestic oil production has been fluctuating around 2×10⁸ t, far from sufficient to satisfy consumption demands and the external dependence had increased dramatically from 55% in 2010 to 71% in 2018, exceeding the 70% limit for national energy security in China. The natural gas consumption increased from 1089×10⁸ m³ in 2010 to 2830×10⁸ m³ in 2018, with a growth rate of 160%^[18]. The dependences on imported natural gas had increased from 11% to 43% accordingly. Generally, the energy consumption pattern in China is characterized by stabilized oil consumption and ever-increasing natural gas consumption.

By 2030, the domestic crude oil production in China is expected to be (1.6-1.8)×10⁸ t, whereas oil consumption is expected to be (6.5-7.0)×10⁸ t. The two figures for natural gas are (1 800-2 200)×10⁸ m³ and (5 500-6 500)×10⁸ m³, respectively. Both crude oil and natural gas have external dependence over 70%. The gap between domestic supply and demand will be enlarged with the decreasing domestic supplying capacities, which will further manifest the shortage of oil and gas damaging the energy supply security. Due to the huge demand for considerable energy, but through relatively singular import channels, China’s energy supply security is extremely vulnerable.

The U.S. possesses the favorable geological conditions for unconventional oil and gas development such as the large distributed marine basins, shallow burial depth and flat surface landform. By contrast, the unconventional oil and gas have lower maturity in China and are usually reserved in the terrestrial basins with relatively little resources. At present, the resource and technical conditions are not available to establish (3-5)×10⁸ t annual production capacity. The unconventional gas resources in China are mainly composed of terrestrial tight gas, coalbed methane and marine shale gas. Marine shale gas is distributed predominantly in the Sichuan Basin and ohter surrounding areas, with complex surface landforms and various burial depths. Consequently, there is no resource basis to form unconventional gas reservoirs with annual production capacities of hundreds of billion cubic meters. In 2018, in the U.S., shale gas production was 6072×10⁸ m³, tight oil and shale oil production was 3.1×10⁸ t which seems to be too ambitious for China to achieve now.

The complex geological conditions in China may not support the large-scale and rapid increase in unconventional oil and gas production, and consequently, the energy consumption demands are not easy to be satisfied immediately. At present, the scale of new energy development is insufficient to make up for the rising consumption gap. The huge requirement for energy consumption determines that China cannot simply duplicate the American model. China has huge energy demand, but the domestic oil and gas resources are relatively low. In addition, new technologies for energy development have not made great breakthrough in scale yet. Therefore, China appears to face great challenges to achieve the “energy independence” strategy in the short and medium term.

The “energy independence” strategy of China refers to the orderly realization of the basic balance between oil and gas production containing both domestic and overseas with mining right, and the consumption capacity, i.e. the independent production basically equal to consumption demand, through a series of efforts including energy strategy making, scientific and technological investigation, policy guidance and scientific planning. The strategy aims to ensure that domestic production can basically meet the requirements for consumption during crisis events. Orderly realization means that the current production mode, dominated by domestic and supplemented by the overseas mining right production, needs to orderly transfer to a full-scale domestic mode that is the domestic energy production along could satisfy the consumption demand if necessary.

Landmarks for “energy independence” in China include: (1) Domestic production accounts for more than 90% of consumption, and clean energy production accounts for more than 70% of consumption. (2) Energy supply can realize the long- term security and independence and self-control. The “energy independence” in China is expected to satisfy the following two scenarios: (1) Under normal circumstances, domestic energy production and overseas oil and gas mining right production can basically meet the domestic energy consumption demands and realize long-term security of energy supply. To be more specific, domestic production need to meet no less than 90% of consumption demands, whereas strategic reserve can satisfy urgent demands for 3 to 6 months during extremely emergent events. (2) In emergency, domestic energy production and strategic reserve can basically meet the domestic energy consumption demand in order to ensure the independence and self-control of energy supply under short-term extreme conditions.

China's “energy independence” strategy corresponds to the goal of building a strong socialist modernization country and serves the construction of a socialist modern country. What is needed is to control the maximum consumption, and guarantee the energy supply. It is also necessary to promote the development of green and clean energy, and accelerate the establishment of a new consumption pattern, in which coal, oil and gas, and new energy account for 40%, 30% and 30%, respectively, of the total energy consumption. The balance between energy production and consumption is desperate to be realized by increasing domestic and overseas oil and gas mining right production. In addition, the energy structure should be optimized by dramatic increase of new energy production and consumption. The “energy independence” is expected to be realized when the energy consumption is composed primarily of new energy (70%) and secondarily of fossil fuels (30%).

The innovation of energy technology, untilization of clean coal, stabilization of petroleum consumption, increase in natural gas consumption and development of new energy are fundamental requirements to realize the “energy independence” strategy in China. It is essential to coordinate the development of three major fields including coal, oil and gas and new energy.

4.2.1. Accelerating the clean utilization of coal, enhancing the scale of coal chemical industry and promoting the centralized utilization of coal

Underground coal gasification is an effective way for clean utilization of coal. It changes the traditional mode for coal mining and utilization fundamentally. This technique can effectively reduce negative environmental impact of coal mining and application. China is striving for the successful gasification and utilization of onshore coal resources buried between 1 000-3 000 m underground. In this way, production capacities of methane, hydrogen and other relevant gases are expected to reach (272-332)×10¹² m^3[4].

Coal chemical engineering, such as surface coal-oil conversion, is another way for clean utilization of coal. The scales of coal chemical industry can be enlarge with the combination of coal chemical industry and petrochemical industry. Byproducts generated in coal chemical industry such as hydrogen and CO₂ could be supplied to refineries or oilfields for refining or oil flooding. With the construction of the commercial chain composed of coal chemical plant, petrochemical plant, and oil and gas field, it is expected to realize efficient and clean utilization of coal and CO₂ storage. In 2018, the production capacity of oil, olefin and glycol from coal chemical industry in China reached 1138×10⁴ t, 112×10⁴ t, and 363×10⁴ t, respectively^[27]. Centralized utilization of coal is helpful to improve coal combustion efficiency and reduce pollution emission. As the largest coal-fired thermal power generation country in the world^[18], China has an annual thermal power generation capacity of 4 732×10¹² kW·h, accounting for 47% of the thermal power generated in the world. Low load operations of low-power commercial boilers would induce the flue gas temperatures failed to meet the technical requirements of denitrification devices and, eventually, resulting in the emission of nitrogen oxide exceeding the standard. The efficient and clean utilization of coal can be realized by promoting the full load centralized utilization of coal-fired boilers.

4.2.2. Relying on both conventional and unconventional hydrocarbon resources, and promoting offshore and overseas oil and gas development in oil and gas industry; enhancing integrated development of hydrogen energy industry and petroleum industry

The development of onshore ultra-deep and unconventional oil and gas needs to be enhanced. Ultra-deep oil and gas resources have been discovered in three major petroliferous basins in China, including Tarim, Sichuan and Junggar Basins. The depth of successfully developed marine and continental oil-gas reservoirs in Tarim Basin exceeds 8000 m, and the average depth of oil-bearing reservoirs in the Shunbei Oil Field reaches up to 7632 m. The geological resources of the Ordovician system from Tabei to Tazhong are up to 60×10⁸ tons of oil equivalent. With accumulative proven reserve of 26.5×10⁸ tons of oil equivalent at the end of 2018, a major oil and gas production region with capacity of 1005× 10⁴ t has been established. A “deep oil and gas revolution” is occurring in China. The “unconventional oil and gas revolution” of China has stepped into a significant stage with strategic breakthrough. The sustainable growth in reserves and production of unconventional oil and gas is the realistic way to ensure energy security in China. In 2018, China has a total unconventional oil and gas production of 6365×10⁴ tons of oil equivalent, accounting for 22% of the total oil and gas production.

Breakthrough is necessary in deep-sea oil and gas exploration and the development and utilization of hydrates resources. Meanwhile, overseas oil and gas rights and interests need to be increased. China has abundant offshore hydrocarbon resources, with proved oil reserve of 64.7×10⁸ t and natural gas reserve of 6.7×10¹² m³. Currently, China has established five overseas cooperation zones in Asia-Pacific, Central Asia-Russia, Middle East, Africa and America, respectively. In 2018, overseas production was up to 2×10⁸ tons of oil equivalent, which was 3.7% higher than 2017. Regions along the Belt and Road Initiative should be considered as the key areas for joint development of hydrocarbon resources.

The development of hydrogen energy is of importance for China which includes the hydrogen generation from fossil fuels and the construction of comprehensive industrial chain system. Currently, hydrogen generated from fossil fuels thermochemical reforming is the major source of hydrogen energy in global scale. It has a market share over 96%^[28] and an average cost of $1.9/kg. China is the largest hydrogen producer in the world at present^[29]. Its annual hydrogen production reached 2100×10⁴ t in 2018, making up 30% of the global hydrogen production. China should accelerate commercialization of hydrogen energy production and facilitate the integration of oil and gas industry with hydrogen energy industry. Oil and gas companies need to take advantage of the existing natural gas pipeline network, gas stations and other infrastructures, to achieve the coordinated development of oil station, gas station, hydrogen station and power station, and ultimately promote the high-quality development of hydrogen industry.

4.2.3. Speeding up the low-cost and large-scale production of new energy, and making great breakthrough in new material and new technology

It is essential for China to accelerate low-cost and mass production of solar, wind, hydraulic, nuclear, geothermal, biomass and other new energy sources. In 2018, new energy consumption in China was 4.8×10⁸ tons of oil equivalent, increasing by 11.8% year-on-year. It made up 14.7% of total primary energy consumption in China and 22.7% of total new energy consumption in the world. Hydraulic energy consumption reached 2.7×10⁸ tons of oil equivalent, with a year-on-year growth of 3.2%. Nuclear energy consumption had a year-on-year growth of 18.7% and reached 0.7×10⁸ tons of oil equivalent. Wind energy consumption increased to 0.8×10⁸ tons of oil equivalent, with a year-on-year growth of 24.0%. Solar energy consumption reached 0.4×10⁸ tons of oil equivalent, increasing by 50.6% year-on-year. Biomass and other energy consumption was 0.2×10⁸ tons of oil equivalent. With increasing in investment, the production cost of new energy is now approaching the cost of fossil fuels.

It is needed to accelerate breakthrough in green hydrogen production technology to realize the large-scale development of hydrogen industry in China. In addition to hydrogen production from fossil fuels thermochemical reforming and chemical by-products, biomass hydrogen production and solar hydrogen production are the key technologies for hydrogen production. Hydrogen production from biomass reforming can be classified into two categories: hydrogen production using thermo-physicochemical principle and hydrogen conversion through biological pathway. Hydrogen generation using solar power may be the major approach in hydrogen industry in future due to its renewable and zero-carbon emission features.

The breakthroughs in new materials and innovative technologies in China rely significantly on revolutionary progresses in multiple fields, for example, green and high-efficiency hydrogen generation and low-cost fuel cell in hydrogen energy sector; fast reactor, magnetically confined fusion and micro power station technologies in nuclear power field; new perovskite and laminated power generation in solar power field; production of cyanobacterial ethanol in biomass field; liquid metal battery, nano-battery and super-capacitor in power storage field; high-performance 2D grapheme, dark scales and others in new material field. From the perspective of scientific and technological development, full-scale integration of big data, cloud computing, artificial intelligence, Internet of things, etc. will draw forth the revolution of intelligent energy management.

The energy structure should be optimized to achieve the ultimate goal of “energy independence” in China. Core strategic significance of “energy independence” can be summarized as follows: Firstly, it can guarantee the national energy supply security; secondly, it can promote development of industries related to new energy revolution; thirdly, promote management reform characterized by intelligent energy; fourthly, Achieve environmental protection objectives characterized by zero carbon energy. It was estimated that the energy consumption in China will peak at 4×10⁸ tons of oil equivalent in 2030. It is essential to find a suitable way of development on the basis of resource characteristics in China, to realize the sustainable development with low energy consumption.

For the implementation of “energy independence” strategy in China, intelligent energy management system is essential, as it is characterized as high efficiency. Intelligent energy is not a specific energy type. Instead, it refers to the sum of all energy types that could be interconnected and intelligently deployed with artificial intelligence, big data and information technology. Intelligent energy could promote complementarity of multiple energy resources, inter-connection of upper, middle and lower sectors, and interflow among production and consumption, through integration of power grid, oil and gas pipelines, coal distribution and other systems. In addition, it could enhance energy efficiency, minimize energy consumption, avoid energy waste and contributed to the establishment of an intelligent energy management system, which is characterized by coordination among various energy resources, intelligent complementary and high-efficiency energy utilization.

The “energy independence” strategy of China can not only rely on any singular energy. Instead, it relies on the utilization of clean coal, stabilization of petroleum consumption, increase in natural gas consumption and development of new energy. The complementation of multiple energy sources can be realized in three steps. With a clear awareness of the resource reserves in China, it is not necessary to blindly reduce coal consumption and over-emphasize the importance of oil and gas. The importance of new energy should be emphasized, and China must, but not only, rely on new energy to achieve “energy independence”. Hopefully, the roles of fossil fuels and new energy in energy consumption can be exchanged by 2100 and thereafter, new energy will become the major energy type in China. The expansion of new energy as a major energy type in the future is most likely resulted from the requirement for energy decarburization, low cost and environmental protection, rather than the exhaustion of fossil resources.

Referring to the experience of the U.S. and China should make plans in advance in two aspects at the national level: (1) policy: the medium and long-term energy independence plans should be made and search supports from all aspects, including policies, laws, financial and tax. (2) Science and technology: making science and technology support plan for national “energy independence”, focusing on revolutionary technologies to solve the forward-looking major science and technology problems.

There are four major revolutions and one cooperation needed to be implemented in supplying, consumption, technology and system aspects: (1) Accelerate the commercial production of conventional and unconventional oil and gas^[30], underground shale oil upgrading and coal gasification, clean utilization of coal, and the low-cost production of solar, wind and other new energy resources. (2) Optimize energy consumption structure, enhance energy efficiencies, reduce consumption, and set up energy consumption ceiling and cordon. (3) Make breakthroughs in revolutionary technologies and coordinate comprehensively the development of 3 key strategic domains for coal, oil and gas and new energy. (4) Make high-quality top-level design of commercial structure, guide forward-looking basic research, support new energy talent reserve, and facilitate construction of advanced laboratories for new energy. (5) Strengthen international cooperation for oil and gas and new energy development, implement energy strategy in a global perspective, and accelerate technological innovation to promote energy production of overseas oil and gas mining rights.

The three-step roadmap is based on the basic situation of energy resources, and is according to the rational judgment on the overall situation of future energy development, as well as in close conjunction with the goal of building a great socialist country, to strives to achieve China’s “energy independence”.

At this stage, the “making energy clean, stabilizing oil and gas, and vigorously enhancing new energy” path will be implemented, and a bamboo ceiling of energy consumption will be set that is adapted to China's national conditions. The goal is to ensure the security of domestic energy supply and simultaneously protect the environment. The focus of this process is to “determine the direction, break the bottlenecks, develop strategies and ensure the energy security”. To be more specific, the main part depends on fossil resources to ensure energy supply, grasp the direction of the revolution of new energy technology, and break through the bottleneck of rapid development of new energy. It is clear that the future energy mainstay will rely on new energy sources in order to achieve the strategy of “energy independence” and ensure China's “security of energy supply” at this stage.

At this stage, the practical fields for the energy development include the clean utilization of traditional fossil energy, keeping growth of production, key breakthroughs of key technology in the hydrogen industry, the popularization of low-cost energy storage and new material technologies, and the establishing an efficient managing system for “smart energy”. Clean energy utilization should be integrated with current oil industry to form an industrial chain. We should speed up the recovery rates of oil and gas, and the breakthroughs of “water-control development” technology, and should strengthen industrial exploitation of shale oil and gas, hydrates and other unconventional oil and gas. At this stage, a breakthrough in the industrial chain of hydrogen production, transportation, storage, hydrogen addition and hydrogen use should be basically achieved, as well as the large-scale and low-cost utilization in the development, storage and new materials of solar, wind, water and nuclear energy. The Government will promote the integration of various energy applications, realize the intelligent allocation of production and consumption, significantly improve the energy utilization, and reduce energy consumption, and basically establish a “smart energy” management system.

According to the current energy development situation in China, primary energy consumption is expected to peak at 40×10⁸ tons of oil equivalent in around 2035. The energy supply situation is therefore becoming increasingly challenging (Fig. 4). The total coal consumption in this phase remains at about 20×10⁸ tons of oil equivalent, and will remain the mainstay of our country's energy consumption as its share of primary energy will decreases from the current 60% to 50% by 2035. Crude oil consumption will be remained generally stable and controlled at (6.0 to 6.5) ×10⁸ tons, with the share of primary energy reducing from 18% of the current to 15% by 2035. Total consumption of natural gas as a transition energy source from fossil to new energy sources will rise from 2.5×10⁸ tons oil equivalent in 2018 to 5.0×10⁸ tons oil equivalent, and its share of primary energy will rise from 8% to 13% by 2035. As the main force to meet the ever-increasing demands of energy, new energy may be put on a fast track with consumption increasing from 4.8×10⁸ tons of oil equivalent to 9.0×10⁸ tons of oil equivalent, and with shares in primary energy increasing from the present 15% to 22% in the year 2035.

At this stage, the implementation of reducing coal utilization, stabilizing oil and gas production, and increasing new energy usage will promote the replacement of coal by new energy. With improved efficient energy utilization, reduced the total energy consumption and the enhanced new energy supply capacity, coal, oil and gas and new energy sources will play an equal roles in China’s energy supply. The focus of work in this phase is to “adjust the structure, build hydrogen energy and strive for autonomy”, as well as to accelerate the adjustment of the primary energy consumption structure to make it reasonable, and to build a green “hydrogen energy China” society, and achieve “production autonomy” by relying on the “domestic production + overseas oil and gas mining rights” model.

The practical fields that should be focused on at this stage include the revolutionary breakthroughs in fossil energy, the full industrialization of hydrogen energy, the explosion of disruptive technologies and the full establishment of the “smart energy” system. The large-scale clean utilization of coal, underground shale oil in-situ recovery and underground coal gasification operations shall be conducted to achieve revolution and large-scale production. The “four-station” integrated layout of refueling, gas filling, hydrogenation and charging has been comprehensively completed. And China's “hydrogen industry” system has been built with reference to the petroleum industry model to forming a green “hydrogen energy China” society. Disruptive breakthroughs or large-scale use should be brought out in new material energy storage, controlled nuclear fusion and other areas. By using the “new energy + smart energy” model, and by focusing on diversification of energy types and intelligent energy interconnection, respectively, to fill the gap between fossil energy and total consumption will be filled and a balance between production and consumption will be achieve.

After China's primary energy consumption peaks in 2035, there may be an overall downward trend overall, with primary energy consumption projected to fall to 36 ×10⁸ tons oil equivalent in 2050, providing development opportunities for new energy sources to accelerate their substitution of coal (Fig. 4). The dominance of coal as a primary energy source will be changed radically in this phase as total coal consumption decreases from 2.0 ×10⁸ tons oil equivalent in 2035 to 13 ×10⁸ tons oil equivalent in 2050, with its proportions in primary energy reduced from 50% to 36% in the year 2050. Crude oil consumption will continue being stable, with consumption of about 6.5 ×10⁸ tons in 2050, increasing from 15% to 18% of primary energy in 2035. Whereas the natural gas consumption will be generally stable, with consumption of 55 ×10⁸ tons oil equivalent in 2050, increasing from 13% to 15% of primary energy in 2050. In addition, the development of new energy will be accelerated with consumption increasing from 9.0×10⁸ tons of oil equivalent to 11×10⁸ tons of oil equivalent, and with shares in primary energy increasing from 22% to 31% in the year 2050. This will accelerate the replacement of coal consumption as another main type of consumption in addition to coal.

At this stage, the implementation of the “hydrogen society, new energy-led, disruptive technology realization” path will lead to a sustained reduction in domestic energy demand and a gradual stabilization. The consumption of coal, oil and gas and other fossil fuels will be reduced. On the other hand, new energy may become the dominator due to supports of production scale and low production cost. The goal is to achieve full domestic production of energy, new energy sources accounting for 70% and fossil energy for 30% of energy supply (one major and one minor structure), and to work towards “energy independence”. The focus of work at this stage is on “stabilizing the structure, new energy and striving for independence”, stabilizing the energy consumption structure of “one major and one minor structure”, striving to fully realize the dominance of new energy production and consumption, and relying on “new energy + smart energy” to achieve "energy independence" on the basis of "energy independence".

At this stage, the practical field needing to be focused on is the realization of low-cost and large-scale applications of multiple new energy types. Solar, wind, hydro, nuclear, geothermal, biomass and other new energy sources will achieve low-cost production, and large-scale utilization of particularly hydrogen, controllable nuclear fusion, new materials and other new energy sources of. By 2100, the historic transformation of the status of fossil energy and new energy production will be achieved, so that the new energy will become the main body of China's energy structure. And we will strive to form a pattern of 70% new energy and 30% fossil energy, so as to achieve a revolutionary transformation of the energy structure.

Primary energy consumption may be gradually reduced from the 36×10⁸ tons of oil equivalent in the year 2050 to approximately 30×10⁸ tons of oil equivalent at the end of the century. New energy may become the mainstay of our primary energy consumption (Fig. 4). During this period, total coal consumption will be reduced from 13×10⁸ tons of oil equivalent in the year 2050 to approximately 2×10⁸ tons of oil equivalent in the year of 2100, with the proportion in primary energy reduced from 37% in the year of 2050 to 7% in the year of 2100. At the same time, crude oil consumption will be reduced significantly to approximately 3×10⁸ t in the year of 2100 with its proportions in primary energy reduced from 18% to 10%. At the same time, consumption of natural gas will be reduced gradually to 4×10⁸ tons of oil equivalent in the year of 2100, with its proportion in primary energy proportions in primary energy reduced from 15% to 13%. With the accelerated development of new energy sources, consumption will rise from 11×10⁸ tons oil equivalent to 21×10⁸ tons oil equivalent, and will strive to increase the share of primary energy from 31% to 70% to form the main body of energy consumption in China.

China's energy development is characterized by large energy consumption, the resources rich in coal but insufficient in oil and gas, and with increasing dependence on import oil and gas. It determines that China's has large total energy consumption but unclean energy structure and insecure supply. Therefore, it is unrealistic to simply copy the U. S. “energy independence” model. China needs to establish an “energy independence” strategy meeting its basic national requirements according to its special energy circumstances.

China's energy development should implement the strategy with the principles of “clean coal, stable oil production, increasing gas production, vigorously develop new energy” and take advantage of the period of peak energy demands and opportunity to adjust the energy structure. In addition, it should promote the development of new energy production to a large-scale, low-cost and popularized status relying on science, technology, the talents and innovation. The strategic choice for China’s future energy development is to emphasis the “new energy revolution”, to gradually achieve China's “energy independence”.

A “three-step” strategy needs to be followed: (1) from 2020 to 2035, focusing on fossil energy and accelerating the development of new energy, and to achieve “supply security” relying on “clean coal and stabilize oil and increase gas production, and vigorously improve new energy”; (2) from 2035 to 2050, realizing the equal of fossil energy and new energy and achieving “independent production” relying on “domestic production + overseas oil and gas mining rights” model; (3) from 2050 to 2100, striving for the predominant role of new energy production, and achieving “energy independence” relying on “new energy + smart energy”.

The vigorous development of new energy is expected to solve the energy security problem, to get rid of energy import dependence, and to truly achieve national energy security and green development. When the new energy sources dominate, China is likely to basically achieve “energy independence”. The transition from traditional fossil to non-fossil new energy sources is an inevitable trend and an inevitable choice for energy development. The new energy replacement will probably arrive ahead of time before the fossil fuels are exhausted.

It should be emphasized that the “energy independence” of China presented here is a strategic proposition. The “energy independence” strategy should be led by national policies, and supported by energy science & technology and innovation. As the country's strength grows, it may not necessarily to complete the form of “energy independence” by a completely independent production, but it could also guarantee security of energy supply can still be ensured to achieve the goal of “autonomous and controlled” and “long-term security”.