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    Shouwei ZHOU, Qingping LI, Xin LV, Qiang FU, Junlong ZHU
    Frontiers in Energy, 2020, 14(3): 433-442.

    As a new clean energy resource in the 21st century, natural gas hydrate is considered as one of the most promising strategic resources in the future. This paper, based on the research progress in exploitation of natural gas hydrate (NGH) in China and the world, systematically reviewed and discussed the key issues in development of natural gas hydrate. From an exploitation point of view, it is recommended that the concepts of diagenetic hydrate and non-diagenetic hydrate be introduced. The main factors to be considered are whether diagenesis, stability of rock skeleton structure, particle size and cementation mode, thus NGHs are divided into 6 levels and used unused exploitation methods according to different types. The study of the description and quantitative characterization of abundance in hydrate enrichment zone, and looking for gas hydrate dessert areas with commercial exploitation value should be enhanced. The concept of dynamic permeability and characterization of the permeability of NGH by time-varying equations should be established. The ‘Three-gas co-production’ (natural gas hydrate, shallow gas, and conventional gas) may be an effective way to achieve early commercial exploitation. Although great progress has been made in the exploitation of natural gas hydrate, there still exist enormous challenges in basic theory research, production methods, and equipment and operation modes. Only through hard and persistent exploration and innovation can natural gas hydrate be truly commercially developed on a large scale and contribute to sustainable energy supply.

    Weiliang WANG, Zheng LI, Junfu LYU, Hai ZHANG, Guangxi YUE, Weidou NI
    Frontiers in Energy, 2019, 13(3): 417-426.

    As the main power source of China, coal-fired power industry has achieved a great progress in installed capacity, manufacturing technologies, thermal efficiency, as well as pollutant control during the past century. With the fast development of renewable energies, coal-fired power industry is experiencing a strategic transformation. To specify the development of coal-fired power industry, its development history is reviewed and the technical progresses on aspects of thermal efficiency, pollutants control and peaking shaving capacity are discussed. It is concluded that the role of China’s coal-fired power source would be transformed from the dominant position to a base position in power source structure. Considering the sustainable development of coal-fired power industry in energy conservation, emission control, and utilization of renewable energies, it is suggested that the national average thermal efficiency should be improved by continual up-gradation of units by using advanced technologies and eliminating outdated capacity. Moreover, the emission standard of air pollutants should not be stricter any more in coal-fired power industry. Furthermore, the huge amount of combined heat and power (CHP) coal-fired units should be operated in a decoupled way, so as to release more than 350 GW regulation capacity for the grid to accept more renewable energy power.

    Haizhu WANG, Gensheng LI, Zhonghou SHEN, Zhenguo HE, Qingling LIU, Bin ZHU, Youwen WANG, Meng WANG
    Frontiers in Energy, 2019, 13(1): 1-8.

    With the rapid development of global economy, an increasing amount of attention has been paid to the emission of greenhouse gases, especially CO2. In recent years, dominated by the governments around the world, several significant projects of CO2 sequestration have been conducted. However, due to the huge investment and poor economic effects, the sustainability of those projects is not satisfactory. Supercritical CO2 (SC-CO2) has prominent advantages in well drilling, fracturing, displacement, storage, plug and scale removal within tubing and casing, which could bring considerable economic benefits along with CO2 sequestration. In this paper, based on physicochemical properties of SC-CO2 fluid, a detailed analysis of technical advantages of SC-CO2 applied in oil and gas development is illustrated. Furthermore, the implementation processes of SC-CO2 are also proposed. For the first time, a recycling process is presented in which oil and gas are extracted and the CO2 generated could be restored underground, thus an integrated technology system is formed. Considering the recent interests in the development of enhancing hydrocarbon recoveries and CO2 sequestration, this approach provides a promising technique that can achieve these two goals simultaneously.

    Shilie WENG, Chenghong GU, Yiwu WENG
    Frontiers in Energy, 2018, 12(4): 481-483.
    Jing LIU, Zhixiong GUO
    Frontiers in Energy, 2018, 12(2): 195-197.
    Ya-Ling HE, Ruzhu WANG, Anthony Paul ROSKILLY, Peiwen LI
    Frontiers in Energy, 2017, 11(4): 411-413.
    Frontiers in Energy, 2017, 11(2): 105-106.
    Muyiwa S. ADARAMOLA
    Frontiers in Energy, 2016, 10(4): 375-381.

    Globally, solar energy is expected to play a significant role in the changing face of energy economies in the near future. However, the variability of this resource has been the main barrier for solar energy development in most locations around the world. This paper investigated the distribution and variability of solar radiation using the a 10-year (2006 to 2015) data collected at Sørås meteorological station located at latitude 59° 39′ N and longitude 10° 47′E, about 93.3 m above sea level (about 30 km from Oslo), in south-eastern part of Norway. It is found that on annual basis, the total number of days with a global solar radiation of less than 1 kWh/(m2·d) is 120 days while the total number of days with an expected global solar radiation greater than 3 kWh/(m2·d) is 156 days (42.74%) per year. The potential energy output from a horizontally placed solar collector in these 156 days is approximately 75% of the estimated annual energy output. In addition, it is found that the inter-annual coefficient of variation of the global solar radiation is 4.28%, while that of diffuse radiation is 4.96%.

    Boyuan HAO,Zhe TIAN,Yan DING,Peng PENG
    Frontiers in Energy, 2016, 10(3): 249-259.

    Energy-saving awareness of heat users and heating enterprises can be stimulated by implementing heat metering for public buildings and by establishing scientific and reasonable policies for heat prices in China. In this paper, a two-part heat price for public buildings in Tianjin is introduced, which divides the heat price into a basic part and a metering part. According to the statistical analysis of information collected from two pilot heating enterprises, the specific heat load for public buildings in Tianjin is calculated, and three candidate schemes of heat price are proposed. A simulation of heat cost is also conducted, and the benefits for both heat users and heating enterprises are balanced. Finally, the two-part heat price for public buildings in Tianjin is determined: the basic heat price is recommended to be 20 CNY/m2, and the metering heat price is recommended to be 76.10 CNY/GJ. Such a price could be implemented in the initial stage of heat metering for public buildings in Tianjin.

    Frontiers in Energy, 2016, 10(2): 125-135.

    This paper investigates a new operation strategy for photovoltaic (PV) systems, which improves the overall reliability of the system as a result of the improvement in the reliability of the critical components. First, a mathematical model is proposed using the fault tree analysis (FTA) to estimate the reliability of the PV systems in order to find the suitable maintenance strategies. The implementations demonstrate that it is essential to employ smart maintenance plans and monitor the identified most critical components of PV systems. Then, an innovative analytical method based on the Markov process is presented to model smart operation plans in PV systems. The impact of smart operation strategy on the PV systems is then evaluated. The objective of this paper is to develop plans for improving the reliability of PV systems. A series of case studies have been conducted to demonstrate the importance of smart operation strategies for PV systems as well as the applicability and feasibility of the proposed method.