Search

This paper is the second in a two-part series on the concavity-convexity of the distribution system security region (DSSR). In Part I, the concave-convex characteristics and mechanism of DSSR are revealed by observing many case grids. In Part II (this paper), the concave-convex principle of DSSR is revealed through mathematical deduction. Firstly, the relevant concepts of sub-regions are proposed, and a DSSR model based on the union of sub-regions is developed. Secondly, the concave-convex principle of DSSR is proposed. The proposed criteria show that the security region of a distribution system with a single load transfer path for each feeder is convex, while that with multiple load transfer paths for some feeders can be concave or convex. Thirdly, the proposed criteria are deduced mathematically. Fourthly, based on the criteria, a method is proposed to judge whether a DSSR is concave or convex. Fifthly, the proposed criteria and method are verified through several cases, and the DSSR concavity-convexity of real distribution systems in China is also analyzed. Finally, the applications of DSSR concavity-convexity are illustrated. This work lays a mathematical foundation for the research of the topological properties of DSSR and is also useful for the application of DSSR. • The DSSR mathematical model based on the union of sub-regions is developed. • Three criteria are proposed and proved, revealing the concave-convex principle of DSSR. • A judgment method for DSSR concavity-convexity is proposed based on these criteria. • The DSSR concavity-convexity of real distribution systems in China is analyzed. • The application values of DSSR concavity-convexity are demonstrated. [ABSTRACT FROM AUTHOR]

Over the recent decades, China’s building energy consumption has been growing rapidly. Also the fuel mix has been changing quickly with more natural gas & electricity and less coal being used. Meanwhile, the technologies used in building sector are improving in efficiency. In this paper, the impact of technical progress and the use of renewable energy in building sector are analyzed. The energy saving and emission reduction potential of building sector are also measured. China TIMES model is used to model the future energy consumption and carbon emissions in building sector. The modelling results indicate that building energy consumption is expected to grow to around 41.6EJ in the reference scenario in 2050. The energy saving potential in 2050 can be up to 4EJ due to the improvement of both building insulation (envelop) and energy use technologies. Renewable energy used in buildings can be a great contributor to the carbon mitigation in buildings. China’s building sector can reach a relatively low-carbon future with more low- and non-carbon fuels consumed. [ABSTRACT FROM AUTHOR]

Abstract: To find the key impact factors of CO2 emissions to realize the carbon intensity target, this paper examined the impact factors of population, economic level, technology level, urbanization level, industrialization level, service level, energy consumption structure and foreign trade degree on the energy-related CO2 emissions in Guangdong Province, China from 1980 to 2010 using an extended STIRPAT model. We employed ridge regression to fit the extended STIRPAT model. Empirical results indicate that factors such as population, urbanization level, GDP per capita, industrialization level and service level, can cause an increase in CO2 emissions. However, technology level, energy consumption structure and foreign trade degree can lead to a decrease in CO2 emissions. The estimated elastic coefficients suggest that population is the most important impact factor of CO2 emissions. Industrialization level, urbanization level, energy consumption structure, service level and GDP per capita are also significant impact factors, but the other factors such as technology level and foreign trade degree are less important impact factors. Some policy recommendations are also given on how to mitigate the growth of CO2 emissions. [Copyright &y& Elsevier]

Abstract: A new model used to design the shape and dimension of salt cavern gas storage is proposed in the paper. In the new model, the cavern is divided into two parts, namely the lower and upper structures, to design. The concepts of slope instability and pressure arch are introduced into the shape design of the lower and upper structures respectively. Calculating models are established according to the concepts. Field salt cavern gas storage in China is simulated as examples, and its shape and dimension are proposed. The effects of gas pressure, friction angle and cohesion of rock salt on the cavern stability are discussed. Moreover, the volume convergence, displacement, plastic volume rate, safety factor, and effective strain are compared with that of three other existing shapes salt caverns to validate the performance of newly proposed cavern. The results show that the max. gas pressure determines the shape and dimension of cavern lower structure, while the min. gas pressure decides that of cavern upper structure. With the increase of friction angle and cohesion of rock salt, the stability of salt cavern is increased. The newly proposed salt cavern gas storage has more notable advantages than the existing shapes of salt cavern in volume convergence, displacement, plastic volume rate, safety factor, and effective strain under the same conditions. [Copyright &y& Elsevier]

Abstract: In this paper, we present a process-based model to estimate the well-to-tank (WTT) costs of vehicle fuels (gasoline and diesel). The model breaks down the WTT process into four stages, i.e., crude oil sourcing (import and extraction), crude oil transportation, crude oil refining, and vehicle fuel transportation and distribution, which can provide high-resolution data for the WTT cost components. Using this model, we further develop an empirical study of China. The results obtained from the study indicate that the price of imported crude oil is the dominant factor affecting the WTT costs of vehicle fuels in China and that the cost of crude oil refining also has a relatively large influence. By comparing the costs with the prices of vehicle fuels under the volatile price of imported crude oil, we illustrate the unstable margin caused by China’s current pricing policy, which causes a distorted price signal and fiscal risks. The key findings derived from the empirical study reveal that the WTT cost is an essential guide for altering the vehicle fuel price with the aim of not only smoothing the impacts caused by the volatile price of crude oil price but also reflecting the correct oil price signal and reducing the fiscal risks. [Copyright &y& Elsevier]

Abstract: A dynamic evaporator model of air source heat pump (ASHP), considering the ratio of the latent heat to sensible heat of wet air, is presented to analyze the performance of ASHP under frosting. The performance parameters, such as the heating capacity, COP and the outlet temperature of compressor, are simulated with CYCLEPAD. Then a semi-empirical correlation that predicts frost accumulation on the air-side of fin-tube heat exchanger is developed with dimensionless analysis and also modified by a test conducted under cold-moist conditions in winter. In addition, eight influence factors are considered involving the ambient conditions and structures of heat exchanger, whose effects are analyzed as well. Among them, the equivalent diameter of air flow cross-section in fin-tube deq is especially proposed. Lastly, the relationships between the ratio, the performance parameters and the frost accumulation are discussed in this paper, followed by an evaluation of an optimal defrosting time interval to improve the ASHP’s energy efficiency and operational reliability at cold-moist conditions in central-south China. [Copyright &y& Elsevier]

Abstract: This paper uses nonparametric efficiency analysis technique to estimate the energy efficiency, potential emission reductions and marginal abatement costs of energy-related CO2 emissions in China. We employ a non-radial slacks-based data envelopment analysis (DEA) model for estimating the potential reductions and efficiency of CO2 emissions for China. The dual model of the slacks-based DEA model is then used to estimate the marginal abatement costs of CO2 emissions. An empirical study based on China’s panel data (2001–2010) is carried out and some policy implications are also discussed. [Copyright &y& Elsevier]

Abstract: Electricity is a special energy which is hard to store, so the electricity demand forecasting in China remains an important problem. This paper aims at developing an improved hybrid model for electricity demand in China, which takes the advantages of moving average procedure, combined method, hybrid model and adaptive particle swarm optimization algorithm, known as MA-C-WH. It is designed for making trend and seasonal adjustments which simultaneously presents the electricity demand forecasts. Four actual electricity demand time series in China power grids are selected to illustrate the proposed MA-C-WH model, and one existing seasonal autoregressive integrated moving average model (SARIMA) is selected to compare with the proposed model using the same data series. The results of popular forecasting precision indexes show that our proposed model is an effective forecasting technique for seasonal time series with nonlinear trend. [Copyright &y& Elsevier]

Abstract: This paper reports the investigation results on application of the solar assisted air source heat pump systems for hot water production in Hong Kong. A mathematical model of the system is developed to predict its operating performance under specified weather conditions. The optimum flow rate from the load water tank to the condenser is proposed considering both the appropriate outlet water temperature and system performance. The effect of various parameters, including circulation flow rate, solar collector area, tilt angle of solar collector array and initial water temperature in the preheating solar tank is investigated, and the results show that the system performance is governed strongly by the change of circulation flow rate, solar collector area and initial water temperature in the preheating solar tank. [Copyright &y& Elsevier]

Abstract: This paper presents a model to quantify the impact of electric power outages on GDP by using Cobb–Douglas production function to develop an economic relationship between the reliability of the electric power supply system and the cost of electric energy unserved. Our findings show that average costs for providing a stable power supply are much lower than disruption costs, which is supported by recurring to the data available of Shanghai. Estimated by using Shanghai’s macroeconomic data of 1990–2006, this relationship indicates that the impact of electricity service disruption on Shanghai’s GDP is about 48.18×108 CNY in 2006, matching an alternative “back-of-envelope” estimate of 50.91×108 CNY. The estimated costs per kWh unserved are 1.81–10.26 CNY in 1990–2006, mirroring the increasing importance of electricity in the period’s economic development. These results demonstrate the usefulness of our approach for quantifying the reliability benefits of investments in electricity infrastructure. [Copyright &y& Elsevier]

Abstract: This paper presents life-cycle-analysis (LCA) energy consumption (EC) and greenhouse gas (GHG) emissions of China’s current six biofuel pathways, which are: corn-derived ethanol (CE); cassava-derived ethanol (KE); sweet sorghum-derived ethanol (SE); soybean-derived bio-diesel (SB); jatropha fruit-derived bio-diesel (JB); and used cooking oil (UCO)-derived bio-diesel (UB). The tool utilized here is the WTW (Well-to-Wheels) module of Tsinghua-CA3EM model covering the entire lifecycle including: raw materials cultivation (or feedstock collection); fuel production; transportation and distribution; and application in automobile engines, compared with Conventional Petroleum-based gasoline and diesel Pathways (CPP). The results indicate: (1) the fossil energy inputs are about 1.0–1.5 times the energy contained in the fuel for the CE, SE and SB pathways, but 0.5–0.9 times for the KE, UB and JB pathways; (2) compared with CPP, the JB, KE and UB pathways can reduce both fossil fuel consumption and GHG emissions; the CE and SB pathways can only reduce fossil fuel consumption, but increase GHG emission; the SE pathway increases not only fossil fuel consumption but also GHG emission; and (3) the main factors inducing high EC and GHG emission levels include: high EC levels during the fuel production stage and high fertilizer application rates during the planting of raw feedstocks. Conclusions are that of the aforementioned biofuel pathways in China: (1) only the JB, KE and UB pathways have energy-saving merits as indicated by the LCA energy inputs and outputs; (2) compared with CPP, all but the SE pathway reduces fossil fuel consumption. However, the SB and CE pathway increase GHG emission; (3) all six displace petroleum by utilizing more coal; and (4) feedstock productivity levels must be increased, and there must be a reduction in fertilizer utilization and EC consumption during the cultivation and transportation stages in order to achieve the goals of energy balance and GHG emission reduction. [Copyright &y& Elsevier]