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Energy is important for human survival and development. In September 2020, the Chinese government announced that “China aims to have their CO
2 emissions peak before 2030 and achieve carbon neutrality before 2060.” As China’s reformation and opening-up proceeds into its fifth decade, this new vision for its future is in line with that of the world’s major economies in terms of the need to reach net zero emissions globally by the mid-21st-century [
1]. However, coal-fueled thermal power generation is currently dominant and accounts for more than 70% of the total amount of power generated in China, making it the world’s largest energy consumer and carbon emitter. Based on the country’s domestic resources, namely the abundance of coal and scarcity of oil and gas, it would be difficult to fundamentally change this coal-based energy structure in the short term. In 2021, the global total energy sector was responsible for 36.3 Gt of CO
2 emissions, including approximately 12 Gt from China, which thus accounts for one-third of the total global emissions [
2]. The demand for efficiency, energy savings, and emissions reduction in the power generation industry has become increasingly prominent. The need has arisen to enhance ways in which to use coal cleanly and efficiently, reduce the consumption thereof, and replace coal with other forms of energy. In addition, carbon emissions need to be lowered by promoting the adoption of alternative power generation technologies that are more energy efficient. This would require transformation away from coal power and the exploration of clean, efficient, flexible, and safe forms of energy as the main future development directions [
3].
Solid Oxide Fuel Cells (SOFCs) provide a clean and efficient way to generate electricity from carbon-rich fuels, such as reformate, natural gas, biomass, propane, and alcohols, with a theoretical electrical efficiency of over 70% (lower heating value, LHV) and are not limited by the demand scale [
4,
5]. This technology converts the chemical energy of the fuel directly into electricity through an electrochemical reaction at high temperatures without combustion and the limitations of the Carnot cycle. At the same time, SOFCs are ideal for reducing CO
2 emissions because the fuel and oxidant (air) streams can be kept separate by design, thereby facilitating high levels of carbon capture without substantial additional cost. Compared with the traditional centralized power generation and grid unified transmission models, SOFC systems for distributed power generation can be established directly at the end-user side, effectively reducing the complexity and instability of the transmission process, significantly reducing power losses, and improving system efficiency in many ways [
6,
7]. This new type of distributed power generation technology is being vigorously developed and promoted in the world’s major developed countries [
8–
10]. Several hundreds of 100 kW-class SOFC systems for distributed power generation have been sold in the US and Japan. Typical SOFC systems for distributed power generation and their applications are shown in Fig.1, including different external environments and scenarios.
(1) Power plants
To achieve carbon neutrality, it is important to reduce the carbon dioxide (CO2) emissions per unit of heat generated from coal-fired power and heat through technological innovation.
A transmission end-power generation efficiency of more than 60% (LHV) can be expected in a 100 MW-class integrated coal gasification fuel cell system (IGFC), which is positioned as a future replacement for large-scale thermal power plants. This will enable carbon dioxide (CO
2) emissions from thermal power stations to be reduced by approximately 30%, even when coal is used as fuel [
11].
IGFC is a new type of power generation technology that combines coal gasification technology with fuel cells. IGFC could realize a technological leap from power generation based on a pure thermal cycle to power generation from a combined electrochemical and thermal cycle. This is a fundamental change in coal power technology [
12,
13].
(2) Data centers
SOFC systems for distributed power generation can serve as the basic power supply for data centers because of their stable and reliable power output. On-site energy generation could reduce dependence on the traditional power grid, improve the energy and economic efficiency of powering facilities, and lower the environmental impact. At the same time, these systems could also be used to provide backup power for an organization’s core server room, even during critical grid outages.
(3) Commercial buildings
Numerous advanced energy-efficient technologies have been developed to lower the energy consumption of buildings. In this regard, a distributed combined heat and power (CHP) system based on fuel cells presents a new solution. A fuel-cell CHP system uses the thermal energy from the exhaust gas of the fuel-cell stack to heat the hot water loop in a building or even to operate a small gas turbine, thereby increasing the overall efficiency of the system [
14]. This means that the fuel cell supplies the building with both thermal and electrical energy (heat and power). Because both forms of energy generated by the fuel cell are utilized, the overall system efficiency could be as high as 90% [
15,
16]. SOFCs are the most useful type of fuel cell for CHP systems, as they operate at high temperatures (600–1000 °C) and can use a variety of readily available fuels, such as natural gas or biogas, through external or internal reforming [
17,
18].
(4) Remote areas
Currently, a few remote areas in China are not connected to the grid, and they could benefit from SOFC systems for distributed power generation. These systems can be driven by a variety of fuels, including coal-bed methane, biomass, and various carbon-based liquid fuels, which make SOFC systems highly suitable for supplying power in these isolated areas.
Remote areas are characterized by complex terrain and extreme conditions resulting from the natural environment in which cables are vulnerable and prone to damage. This leads to power outages that could last for at least two weeks before the power supply is restored. Integrating SOFC systems for distributed power generation into the electricity grid offers opportunities to address various current challenges [
19–
21].
Remote areas could make use of biomass to power SOFC systems. Many methods are available for the conversion of biomass, including fermentation by biological methods [
22], direct pyrolysis, and reforming with air, oxygen, or steam at high temperatures [
23,
24]. Among these methods, biomass gasification, particularly high-temperature steam gasification, which produces bio-syngas with a high calorific value, has attracted the most attention because of its high efficiency and low environmental impact. Bio-syngas is generally composed of H
2, CO, CO
2, CH
4, and other gas components and can be used directly for power generation using SOFCs [
25–
27].
(5) Border posts and monitoring stations
According to the US Office of Energy and Efficiency Conversion, distributed fuel cells have great potential for military applications. In China, many military border posts have been established at high altitudes or on isolated islands, where SOFC systems could more effectively serve the basic electricity (heating) requirements of the servicemen. Therefore, establishing a suitable energy supply system and equipment is important for national security.
Border posts often have various types of monitoring stations, which require 24 h of silent operation, with high reliability, high stability, and a long service life. Solar energy or wind energy would not be able to meet the requirements of these monitoring stations because the weather conditions are typically volatile, whereas an internal combustion engine is noisy and cannot operate silently. Energy storage batteries are also unable to continue to provide backup indefinitely because of their limited storage capacity. SOFCs could therefore be the best power option for border posts and monitoring stations because of the wide range of fuel sources they accept and their high fuel efficiency and heat recovery [
28]. Simultaneously, long-term storage of solar or wind power can be easily realized using the reverse SOFC process— a solid oxide electrolysis cell (SOEC) [
29].
In China, the next decade is expected to be an important opportunity window in which to successfully achieve the goal of carbon neutrality. Furthermore, the energy sector, as the main battlefield, is facing historic opportunities and challenges, with arduous and monumental tasks but with extremely broad prospects. China is ambitiously building a clean, low-carbon, safe, and efficient energy system at this stage.
However, traditional power systems cannot be transformed and upgraded to new power systems overnight. Fuel cell technology, as a new, disruptive, and highly complex advanced power generation technology, also involves multidisciplinary intersections and is extremely difficult to develop. Only by conducting continuous research and experimentation and by strengthening multidisciplinary collaborative research, does it become possible to identify and solve problems with scientific experiments. Therefore, the following suggested practices could be helpful:
(1) Strengthening targeted policy guidance and support. Considering China’s vast territory, the development of high-efficiency SOFC systems for distributed power generation technology is of practical significance for supplying energy to remote areas. These systems are also strategically significant on the national defense front, in line with major national needs. In urban areas, a distributed combined heat and power supply system based on SOFC technology could rely on the mature gas pipeline network to keep construction costs low. Coupled with renewable energy sources such as wind and solar PV and energy storage, a safe, stable, clean, and efficient independent micro-energy network with high promotion and application value, could be built. Central and local governments should introduce relevant policy incentives, mobilize the enthusiasm of large state-owned energy enterprises, and encourage enterprises to increase product research and independently develop innovative SOFC systems for distributed power generation.
(2) Increasing key core technology R&D efforts. SOFC cells and power stacks are the core technologies of SOFC systems for distributed power generation and are already being commercially operated in developed countries and regions such as Japan, the US, and Europe. China should integrate resources, focus on the problems causing bottlenecks, the development of SOFC core materials, key components, and other “Chinese core” technologies with independent intellectual property rights, and improve the core technology level of key links. A supporting scientific research project system should be established by the National Science and Technology Department to increase technical and applied research in SOFC-related fields and train more engineers and technicians with the aim of accumulating professional knowledge and expertise in the development of this field.
(3) Promoting pilot operations and the commercial application of distributed SOFC technology. In China, the development of PEMFCs is relatively mature, and only the upstream and downstream industries of SOFC technology have been opened up. Policies to further encourage demonstration operation and commercial application are recommended, as is the establishment of pilot SOFC systems for distributed power generation and the support of field demonstration operation of SOFC-based distributed power generation systems to open the last mile from industry to demonstration application. Policies that encourage and support a collaborative effort among industry, academia, research, application, finance, and the government would enhance SOFC-related standard construction and management to ensure that the complete industrial chain for SOFCs is constructed; finally, the healthy, coordinated, and orderly development of SOFC technology along a scientific, sustainable, and market-oriented path can be ensured.
The development of a new power system represented by SOFC systems for distributed power generation must be carried out in earnest while comprehensively deepening the new development concept and implementing a new strategy for energy security. A variety of research avenues would have to be explored to develop SOFC technology with the ultimate aim of achieving carbon neutrality.
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