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Abstract The concept of a cTES (for cold Thermal Energy Storage) is experimentally investigated in this paper. It aims at demonstrating its technical relevancy, for arid regions, in improving the efficiency of a dry cooled turbine's condenser. Gain is realized by postponing total or part of the daily heat exhausted from the condenser and shifting the release of the remaining heat during the night-time when the ambient temperatures are lower. The global system consists in a 13 m3 dual-media water/rock thermocline TES connected to a 110 kW heat source and a 100 kW dry cooler. Experiments have been first conducted to validate the thermal storage behavior in well-controlled operations. Then, the thermal storage has been connected in parallel with the dry cooler to highlight the global behavior of the “dry cooler / cTES” cooling system under different operation's conditions. Results confirm that the cTES is able to compensate the performances loss of the dry cooler during daytime in case of high ambient temperature and to evacuate heat and to store cold during nigh-time. The control of the cTES is simple, characterized by continuous and smooth transitions from one mode to another and without discontinuities in performances and operations.

Abstract In arid areas, dry cooling technology is a preferable alternate of wet cooling mainly owing to the scarcity of abundant water supply. However, the supercritical CO2 power cycle still offers considerable thermal performance even at higher ambient temperature using dry cooling. The novelty of this work is the exhaustive designing of dry cooler for supercritical CO2 cycles (recompression and partial cooling) in concentrating solar power application. Prior to the design of tower, a preliminary analysis is conducted in achieving the optimum main compressor inlet temperature (33 °C-recompression and 40 °C-partial cooling) at which the cycle delivers the maximal efficiency. The comparison is performed at same higher and lower pressure and for the partial cooling, the intermediate pressure is optimized. At relatively higher compressor inlet temperatures (above 50 °C), the partial cooling achieves higher efficiency while at lower temperatures (30–49 °C), the recompression shows superior performance. An iterative nodal method is used for the air-cooled finned tube heat exchanger units that takes account of the dramatic variation in thermodynamic properties of CO2 with the bulk temperature. Kroger’s detailed methodology of designing dry cooler is adapted with the implementation of nodal approach for CO2 property variation. A dry cooling tower with 52.45 m height is essential for the recompression cycle, whereas the partial cooling requires two towers of the height of 35.4 m and 38.7 m. A thermal assessment is carried out on the dry cooler under various cycle fluid inlet temperatures and ambient temperatures. During hot and humid ambient conditions, lower compressor inlet temperatures (up to 53.1 °C) are obtained with the recompression cycle compared to partial cooling (up to 64.5 °C). In extreme climate condition of 50 °C air temperature, the recompression cycle provides superior thermal efficiency (46.5% against 45.5%). For future commercialization of dry cooled sCO2 power plant, the recompression cycle is preferred due to its superior performance and lower capital cost for cooling tower design and solar field. The work demonstrates the impact of dry cooling tower design strategy in the context of cycle thermal assessment under various working condition.

Abstract Comprehensive information about the concentrations, distribution, and modes of occurrence of elements in coal are important from the environmental and economic point of view. Although a great number of previous studies have investigated the geology of coalbed methane in the Qinshui Basin, only a few studies focused on the inorganic constituents in coal. More specifically, the mode of occurrences of valuable element Li in the No. 3 Coal is still unclear, although Li was found enriched. In this study, we present mineral characteristics, as well as multi-element data on the Permian No. 3 Coal from the Sucun and Gaohe Mines, Changzhi City, southern Qinshui Basin. The studied coals are characterized by low- to medium-ash yield (Ad = 5.72%- 28.18%, 12.34% on average), low volatile matter yield (Vdaf = 8.49–15.17%, 10.96% on average), suggesting a low volatile bituminous coal to semi-anthracite. NH4-illite and kaolinite are the main minerals in the coals detected by XRD, and trace amount of minerals calcite, dolomite, quartz, pyrite and diaspore can also be found. The major elements of the studied No. 3 coals are dominated by SiO2 and Al2O3, ranging 2.49–16.45 wt% and 2.13–12.9 wt% (on a whole-coal basis), respectively. Li is enriched in the No. 3 coals (5

The paper presents a novel approach to reveal loads having the biggest impact on damping of small-disturbed oscillations in power systems. The technique is based on a quasi-optimisation procedure with the cost function reflecting shifts of selected eigenvalues along the real axis when all unknown load parameters are varied within their constraints. The cost function takes into consideration a variety of power system operating conditions. All points of the cost function steepest descent trajectory, obtained in the space of unknown load parameters, correspond locally to biggest shifts of eigenvalues. Participation factors of load parameters are computed along the steepest descent trajectory, and they give ranks of load importance. Small ranks indicate loads which have no influence on damping of selected modes. Big ranks reveal loads whose parameters cause the biggest change in damping under the most unfavourable combination of unknown parameters. Parameters with biggest ranks should be measured first of all to avoid mistakes in evaluation of damping properties and power system stability margins.

Abstract Hydrogen sulphide is likely to become more common in produced hydrocarbon fluids, as the exploitation of deep reservoirs increases and unconventional resources get recovered significantly, such as heavy oils or bitumen. Hydrogen sulphide presence in produced oil and gas results in operational, environmental and treatment problems. Therefore, understanding the origin and the amount of hydrogen sulphide in petroleum reservoirs has great importance for petroleum engineers. Three natural processes are set forth to explain the generation of H 2 S in reservoirs: bacterial sulphate reduction, thermal cracking and thermochemical sulphate reduction (TSR). It is the TSR that leads to the largest amount of H 2 S. This phenomenon involves hydrocarbon oxidation and sulphate reduction and produces as by-products, hydrogen sulphide, carbon dioxide, carbonate minerals and heavy organo-sulphur compounds. The reaction mechanisms of TSR, as well as its kinetics, are not yet fully understood. In this paper, we checked the thermodynamic feasibility of TSR, at temperatures prevailing in the reservoirs where TSR is encountered. Firstly, we calculated the Gibbs energy of the reactions proposed by Worden and Smalley (Worden R.H. and Smalley P.C., 1996, H 2 S producing reactions in deep carbonate gas reservoirs: Khuff Formation, Abu Dhabi, Chem. Geol., 133, p. 157–171). We concluded that they are thermodynamically possible from 25 °C, confirming thermodynamic data published by Anisimov (Anisimov L., 1978, Conditions of abiogenic reduction of sulfates in oil and gas bearing basins, Geochem. Int., 15, p. 63) and Yue and co-workers (Yue C., Li S., Ding K., Zhong N., 2003, Study of thermodynamics and kinetics of CH4–CaSO 4 and H 2 S–Fe 2 O 3 systems, Chinese J. chem. Eng., 11, (6), p.696–700., Yue C., Li S., Ding K., Zhong N., 2006, Thermodynamics and kinetics of reaction between C1–C3 hydrocarbons and calcium sulfate in deep carbonate reservoirs, Geochem. J., 40, 87–94). Secondly, we used a non-stoichiometric approach without any pre-requisite chemical scheme this time. We calculated the Gibbs Energy of chemical systems composed by hydrocarbons, sulphur, anhydrite and water. The minimization of the Gibbs Energy lead to find the most probable chemical systems at steady state. Our theoretical results are consistent with the chemical schemes set forth for TSR by Orr (Orr W., 1977, Changes in Sulfur Content and Isotopic Ratios of Sulfur during Petroleum Maturation — study of Big Horn Basin Paleozoic Oils, in R. Campo and J. Goni Eds, Advances in onorganic geochemistry, Madrid Spain, Enadimsa, p. 571–595), by Worden and Smalley (Worden R.H. and Smalley P.C., 1996, H 2 S producing reactions in deep carbonate gas reservoirs: Khuff Formation, Abu Dhabi, Chem. Geol., 133, p. 157–171) and by Machel (Machel H.G., 2001, Bacterial and thermochemical sulfate reduction in diagenetic settings — old and new insights, Sedimentary Geology, 140, p. 143–175). Moreover, they are in concordance with some in-situ observations: anhydrite and hydrocarbon consumption with simultaneous formation of calcite, hydrogen sulphide and water. Our results showed as well that the larger the number of the carbon atoms in the reactant hydrocarbons, the more irreversible the reaction is.

In order to help keep readers up to date in the field, each issue of Progress in Photovoltaics will contain a list of recently published journal articles most relevant to its aims and scope. This list is drawn from an extremely wide range of journals, including IEEE Transactions on Electron Devices, Journal of Applied Physics, Applied Physics Letters, Progress in Photovoltaics and Solar Energy Materials and Solar Cells. To assist the reader, the list is separated into broad categories, but please note that these classifications are by no means strict. Also note that inclusion in the list is not an endorsement of a paper's quality. If you have any suggestions, please email Santosh Shrestha at s.shrestha@unsw.edu.au.

It has long been known that the use of finely textured transparent conducting oxide layers substantially improves the performance of thin film amorphous silicon (a-Si:H) solar cells. Major efforts to understand the nature of this effect and to fully capture its potential have been made by researchers using advanced modeling techniques. In this work, modeling the oblique angle optical performance and use of an effective medium approximation to simulate microrough interfaces suggests that effective interface grading makes a significant contribution to optical enhancement.

Short-term voltage stability is an increasing concern in today's power systems due to the growing penetration of induction motors. This paper proposes a systematic method for optimal placement of dynamic VAR support against short-term voltage instability. The problem is formulated as a multi-objective optimization model minimizing two conflicting objectives: 1) the total investment cost and 2) the expected unacceptable short-term voltage performance subject to a set of probable contingencies. STATCOM is employed for its stronger dynamic VAR support capability. Indices for quantifying the short-term voltage stability and the related risk level are proposed for problem modeling. Candidate buses are selected based on the concept of trajectory sensitivity. Load dynamics are fully considered using a composite load model containing induction motor and other typical components. A relatively new and superior multi-objective evolutionary algorithm called MOEA/D is introduced and employed to find the Pareto optimal solutions of the model. The proposed method is verified on the New England 39-bus system using industry-grade models and simulation tool.

Abstract In this paper, we examine the time-varying causal relationship between green bonds and other assets including US conventional bonds, WilderHill clean energy (equity) index, and CO2 emission allowances price during the period spanning from 30 July 2014 to 10 February 2020. We apply the novel time-varying Granger causality test (Shi et al. 2018) based on the recursive evolving algorithm introduced by Phillips et al. (2015a, 2015b) for controlling financial bubbles to detect real–time causality, detecting possible changes in the causal direction and dating financial turbulences, The study based on this algorithm reveals a significant causality running from the US 10-year Treasury bond index to green bonds starting from the end of the year 2016 until the end of the sample period. Besides, we find that the link CO2 emission allowances price causing green bonds is significant from the beginning of the sample period to the end of the year 2015. Furthermore, by using the recursive-evolving causality algorithm of the Shi et al. (2018) test, we find that the causality running from the clean energy index to green bonds is very limited to the year 2019. On the other hand, there is no significant causality running from green bonds to all considered assets, indicating no predictive power for this asset in its proper domain, which is not yet examined in the literature.