Dynamic Wave Energy Converter (WEC) models utilize a wide variety of fundamental hydrodynamic theories. When incorporating novel hydrodynamic theories into numerical models, there are distinct impacts on WEC rigid body motions, cable dynamics, and final power production. This paper focuses on developing an understanding of the influence several refined hydrodynamic theories have on WEC dynamics, including weakly nonlinear Froude-Krylov and hydrostatic forces, body-to-body interactions, and dynamic cable modelling. All theories have evolved from simpler approaches and are of importance to a wide array of WEC archetypes. This study quantifies the impact these theories have on modelling accuracy through a WEC case study. Theoretical differences are first explored in a regular sea state. Subsequently, numerical validation efforts are performed against field data following wave reconstruction techniques. Comparisons of significance are WEC motion and cable tension. It is shown that weakly n... [more]

Biodiesel is a clean, renewable, liquid fuel that can be used in existing diesel engines without modification as pure or blend. Transesterification (the primary process for biodiesel generation) via heterogeneous catalysis using low-cost waste feedstocks for catalyst synthesis improves the economics of biodiesel production. Heterogeneous catalysts are preferred for the industrial generation of biodiesel due to their robustness and low costs due to the easy separation and relatively higher reusability. Calcium oxides found in abundance in nature, e.g., in seashells and eggshells, are promising candidates for the synthesis of heterogeneous catalysts. However, process improvements are required to design productive calcium oxide-based catalysts at an industrial scale. The current work presents an overview of the biodiesel production advancements using calcium oxide-based catalysts (e.g., pure, supported, and mixed with metal oxides). The review discusses different factors involved in the s... [more]

The number of aircraft flights worldwide has increased steadily since the introduction of air transportation to the public. Accordingly, environmental issues caused by the exhaust gases of aircraft engines have emerged. In particular, international organizations have crafted emission regulations since gases exhausted during takeoff and landing have been identified as the direct cause of air pollution near airports. Nitrogen oxides (NOx) produced at high combustion temperatures and carbon monoxide (CO) due to incomplete combustion affect the performance of the combustion chamber. Therefore, annular combustors comprising two annular zones have been developed to reduce the emissions of these two substances, which occur under different conditions. Parameters that should be considered when modifying a conventional single annular (SAC) to a double annular combustor (DAC) are discussed herein. In this paper, an optimization algorithm for obtaining the main design parameters of the DAC is pres... [more]

The integration of distributed power plants that rely on renewable energy sources (RESs) is a major challenge for system operators (SOs) due to the variable nature of the input energy (e.g., wind and solar irradiation) to these power sources. A key solution to such a challenge is to coordinate and combine the power generation of these sources such that their behavior is closer to a conventional and dispatchable power station, taking into account the limitations imposed by the battery storage system (BESS), so it is seen as a hybrid power plant (HPP) from the SOs’ viewpoint. This paper develops a model of HPP that encompasses two generation technologies, wind and photovoltaic farms, which are assisted by a BESS. The paper proposes a comprehensive control method that can smooth the HPP output with minimized energy rejection whilst enabling the HPP to provide synthetic inertia and primary frequency response, which are grid-code compliant. The proposed control method is validated through v... [more]

The commercial and financial attributes of oil have significantly changed the evolution characteristics of prices and returns of the international crude oil market. Using monthly data from April 2003 to October 2020, this paper identifies dynamic characteristics of oil’s commercial and financial attributes based on the structural vector autoregressive model (SVAR) and further analyzes their market effects with different attributes. The result shows that there are situations of commercial and financial attributes dominating, and dual attributes co-dominating for oil. Furthermore, their durations account for 51%, 23%, and 26% respectively, of the full sample. Besides, the reactions of crude oil price or return to the different properties of oil are heterogeneous. Specifically, the dual attributes of oil play the most important role in the price evolution of the international crude oil market, which is 80.851. There are significant differences among the impact of different attributes of o... [more]

The sustainable environment has been a desired situation around the world for the last few decades. Environmental contaminations can be a consequence of various economic activities. Different socio-economic factors influence the environment positively or negatively. Many previous studies have resulted in the efficient allocation of inputs as an environment-friendly component. This paper investigates the effects of energy efficiency on ecological footprint in the ASEAN region using balanced panel data from 2001 to 2019. First, this paper technically derives the energy efficiency, using the stochastic frontier analysis (SFA) of the translog production type of single output and multiple inputs. Findings of the SFA show that the Philippines and Singapore have the highest energy efficiency (94%) and Laos has the lowest energy efficiency (85%) in the ASEAN region. The estimated average efficiency score of the ASEAN region was around 90%, ranging from 85% to 96%, indicating that there is stil... [more]

The Renewable Energy Directive and the Electricity Market Directive, both parts of the Clean Energy for all Europeans Package (issued in 2019), provide supranational rules for renewable energy communities and citizen energy communities. Since national transpositions need to be completed within two years, Austria has already drafted corresponding legislation. This article aims at providing a detailed comparison of the European guidelines and the transposition into Austrian law. The comparison not only shows how, and to what extent, the European guidelines are transposed into Austrian law, but also helps to identify loopholes and barriers. The subsequent discussion of these issues as well as positive aspects of the Austrian transposition may be advantageous for legislators and policy makers worldwide in their process of designing a coherent regulatory framework. It is concluded that experts from different areas (i.e., project developers, scientists concerned with energy communities, ener... [more]

The building sector, as a major energy consumer with high direct and indirect CO2 emissions, plays a vital role in the fight against climate change. In order to make buildings more comfortable, functional, efficient and safe, building services are used. Therefore, building services are the key to decrease their contribution to climate change. Due to the lack of organized literature on this topic, this paper presents the first comprehensive assessment of trends in the literature on building services related to climate change, which was completed by conducting a bibliometric analysis of the existing literature on the topic. The ultimate goal is to provide a source where researchers and other interested parties can find this information in an organized manner. Results show that the most abundant and recent studies related to building services are based on improving energy efficiency by optimizing systems such as ventilation or lighting, the latter with the installation of LED lights. In a... [more]

This paper aims to assess the direct economic impact on the maritime sector from its inclusion in the European Union-Emission Trading System (EU-ETS). The Monitoring, Reporting and Verification (MRV) data are analysed for the estimation of carbon dioxide (CO2) emissions within the European Economic Area (EEA). The economic impact assessment model used is scenario-based, and includes different price incentives, geographical coverage and emission allowances allocation methods. According to our findings, in case the emission allowances are fully auctioned or partially free allocated on the basis of a uniform benchmark, the increased costs would be disproportional among the maritime segments. Such a scheme would penalise Roll-on/Roll-off (RoRo) and Roll-On/Roll-Off/Passenger (RoPax) segments due their high fuel consumption per transport work in relation to oil tankers and bulkers. The establishment of differentiated benchmarks per segment seems to be a prerequisite for the effective inclus... [more]

The negative impact of transport on climate has led to incentives to increase the amount of renewable fuels used in internal combustion engines (ICEs). Oxygenated, liquid biofuels are promising alternatives, as they exhibit similar combustion behaviour to gasoline. In this article, the effect of the different biofuels on engine efficiency, combustion propagation and emissions of a gasoline-optimised direct injected spark ignited (DISI) engine were evaluated through engine experiments. The experiments were performed without any engine hardware modifications. The investigated fuels are gasoline, four alcohols (methanol, ethanol, n-butanol and iso-butanol) and one ether (MTBE). All fuels were tested at two speed sweeps at low and mid load conditions, and a spark timing sweep at low load conditions. The oxygenated biofuels exhibit increased efficiencies, even at non-knock-limited conditions. At lower loads, the oxygenated fuels decrease CO, HC and NOx emissions. However, at mid load condit... [more]

Many photovoltaic (PV) parks suffer from a decrement in their generated power capability due to a phenomenon called potential induced degradation (PID). In this paper, a regenerative system using a high step-up DC−DC converter is proposed, for regenerating PV cells that have been degraded due to the PID effect. The same device also can be used for artificially creating PID on PV panels in order to study the effects of the PID under controlled conditions. The power converter offers multiple voltage levels at the output to adapt to various voltage ratings of PV parks. The device has plug-and-play features, ultra-low cost, small size and is simple in operation. Experimental tests are conducted in real PV panels and comparative results verify the operational principles of the proposed system. The artificial creation of the PID phenomenon and the regeneration of the PV cells are successfully proven experimentally.

Maintaining transient stability is crucial in power system operation. Transient stability is mainly affected by the generation amount of the study region, as well as the transmission topology. Several countermeasures can be taken for transient stability, but the usually used control means are generating unit tripping and generation curtailment. In terms of economic operation, one can say that the solution of generating unit tripping is more beneficial. To maintain the transient stability of the east coast region in the Korean power system, applying generation curtailment in the normal state is further needed, because the required tripping amount is too large for the case of only taking generator tripping, and this might cause a critical decrease in system frequency, possibly resulting in operation of the first stage of under frequency relay (UFR). This paper presents the application of battery energy storage systems (BESSs) to relieve the generation curtailment, using the characteristi... [more]

This paper proposes an original approach to investigate the influence of the geometry of Francis turbines draft tube on pressure fluctuations and energy losses in off-design conditions. It is based on Design of Experiments (DOE) of the draft tube geometry and steady/unsteady Computational Fluid Dynamics (CFD) simulations of the draft tube internal flow. The test case is a Francis turbine unit of specific speed Ns=120 m-kW which is required to operate continuously in off-design conditions, either with 45% (part-load) or 110% (full-load) of the design flow rate. Nine different draft tube geometries featuring a different set of geometrical parameters are first defined by an orthogonal array-based DOE approach. For each of them, unsteady and steady CFD simulations of the internal flow from guide vane to draft tube outlet are performed at part-load and full-load conditions, respectively. The influence of each geometrical parameter on both the flow instability and resulting pressure pulsatio... [more]

In the current work, the heat flux in nucleate pool boiling has been predicted using the macrolayer and latent heat evaporation model. The wall superheat (ΔT) and macrolayer thickness (δ) are the parameters considered for predicting the heat flux. The influence of operating parameters on instantaneous conduction heat flux and average heat flux across the macrolayer are investigated. A comparison of the findings of current model with Bhat’s decreasing macrolayer model revealed a close agreement under the nucleate pool boiling condition at high heat flux. It is suggested that conduction heat transfer strongly rely on macrolayer thickness and wall superheat. The wall superheat and macrolayer thickness is found to significantly contribute to conduction heat transfer. The predicted results closely agree with the findings of Bhat’s decreasing macrolayer model for higher values of wall superheat signifying the nucleate boiling. The predicted results of the proposed model and Bhat’s existing m... [more]

Induction contour hardening of gear wheels belongs to effective heat treatment technologies especially recommended for high-tech applications in machinery, automotive and aerospace industries. In comparison with long term, energy consuming conventional heat treatment (carburizing and consequent quenching), its main positive features are characterized by high total efficiency, short duration and relatively low energy consumption. However, modeling of the process is relatively complicated. The numerical model should contain both multi-physic and non-linear formulation of the problem. The paper concentrates on the modeling of rapid induction heating being the first stage of the contour induction hardening process which is the time consuming part of the computations. It is taken into consideration that critical temperatures and consequently the hardening temperature are dependent on the velocity of the induction heating. Numerical modeling of coupled non-linear electromagnetic and temperat... [more]

This paper addresses the modeling of convective and radiative heat transfer to achieve an acceptable level of indoor temperature. The results presented were obtained in a pilot project in which an energy-efficient house was built on a site located west of Algiers. The main objective was to perform a numerical simulation to investigate how the temperature of the heat-transfer fluid circulating in the floor heating system affected the temperature of the indoor air and also how surface radiosity affected the temperature profile of the indoor air. The study employed the finite element method integrated into the Comsol Multiphysics software. The model was validated using experimental data reported in the literature for the pilothouse at the same meteorological conditions. An error of about 2.32% was apparent between the experimental and theoretical results. Results showed that the increase of the heating transfer fluid temperature from 30 to 50 °C produced the same temperature of about 15.1... [more]

Since buildings are one of the major contributors to global warming, efforts should be intensified to make them more energy-efficient, particularly existing buildings. This research intends to analyze the energy savings from a suggested retrofitting program using energy simulation for typical existing residential buildings. For the assessment of the energy retrofitting program using computer simulation, the most commonly utilized residential building types were selected. The energy consumption of those selected residential buildings was assessed, and a baseline for evaluating energy retrofitting was established. Three levels of retrofitting programs were implemented. These levels were ordered by cost, with the first level being the least costly and the third level is the most expensive. The simulation models were created for two different types of buildings in three different climatic zones in Palestine. The findings suggest that water heating, space heating, space cooling, and electri... [more]

The issue concerns the initial stage of work on a method for performing a rapid assessment of the energy efficiency and illuminance of a street lighting installation. The proposed method is based on simultaneous measurement of illuminance from three lux meters placed on the roof of the vehicle. The data are acquired in road traffic, while the vehicle is driving. The proposed solution will allow in the future to quickly and reproducibly obtain data about the lighting parameters of the studied road section. The illumination values are localised using Global Navigation Satellite System (GNSS). Based on the collected measurement data, with the use of terrain maps, geographic information system (GIS) data and installation design documentation, it will be possible to determine in detail the parameters of energy efficiency indicators for a selected section of the street for the entire street according to the EN13201-5 standard. Preliminary tests were conducted on a section of about one kilome... [more]

Adsorption cooling can recover waste heat at low temperature levels, thereby saving energy and reducing greenhouse gas emissions. An air-cooled adsorption cooling system reduces water consumption and the technical problems associated with wet-cooling systems; however, it is difficult to maintain a constant recooling water temperature using such a system. To overcome this limitation, a variable mode adsorption chiller concept was introduced and investigated in this study. A prototype adsorption chiller was designed and tested experimentally and numerically using the lumped model. Experimental and numerical results showed good agreement and a similar trend. The adsorbent pairs investigated in this chiller consisted of silicoaluminophosphate (SAPO-34)/water. The experimental isotherm data were fitted to the Dubinin−Astakhov (D−A), Freundlich, Hill, and Sun and Chakraborty (S−C) models. The fitted data exhibited satisfactory agreement with the experimental data except with the Freundlich m... [more]

Pumped Thermal Energy Storages (PTES) are suitable for bridging temporary energy shortages, which may occur due to the utilization of renewable energy sources. A combined heat pump (HP)-Organic Rankine Cycle (ORC) system with suitable thermal storage offers a favorable way to store energy for small to medium sized applications. To address the aspect of flexibility, the part load behavior of a combined HP-ORC system, both having R1233zd(E) (Trans-1-chloro-3,3,3-trifluoropropene) as working fluid and being connected through a water filled sensible thermal energy storage, is investigated using a MATLAB code with integration of the fluid database REFPROP. The influence on the isentropic efficiency of the working machines and therefore the power to power efficiency (P2P) of the complete system is shown by variation of the mass flow and a temperature drop in the thermal storage. Further machine-specific parameters such as volumetric efficiency and internal leakage efficiency are also conside... [more]

The effect of partial shading in photovoltaic (PV) panels is one of the biggest problems regarding power losses in PV systems. When the irradiance pattern throughout a PV panel is inequal, some cells with the possibility of higher power production will produce less and start to deteriorate. The objective of this research work is to present, test and discuss different techniques to help mitigate partial shading in PV panels, observing and commenting the advantages and disadvantages for different PV technologies under different operating conditions. The motivation is to contribute with research, simulation, and experimental work. Several state-of-the-artsolutions to the problem will be presented: different topologies in the interconnection of the panels; different PV system architectures, and also introducing new solution hypotheses, such as different cell interconnections topologies. Alongside, benefits and limitations will be discussed. To obtain actual results, the simulation work was... [more]

A physics-based compact analytical model for studying the current−voltage characteristics of perovskite solar cells has been proposed by considering the external voltage-dependent carrier transport, exponential photon absorption, and bulk charge carrier recombination. The explicit analytical expressions for both the forward dark and photocurrents in perovskite solar cells are derived. The current in the external circuit is calculated considering the actual solar spectrum. The mathematical models are verified and useful physical parameters are extracted by comparing the model calculations with the published experimental results on various perovskite solar cells. The proposed model shows excellent agreement with the experimental results. The power conversion efficiency can be improved further by enhancing the carrier transport in the perovskite layer. The improvement in charge carrier transport enhances the fill factor and hence the power conversion efficiency.

Currently, international business and society are on the eve of large-scale changes. The study aims to develop a methodological approach to assess the energy flexibility of multinational corporations in the context of the structural transformation management of renewable energy production. The methodology of this study is based on a comprehensive approach, which includes the methodology of the United States Agency for International Development (USAID), diagnostics of the level of development and energy flexibility of multinational corporations, regression analysis and scenario modeling. In particular, scenario analysis of renewable energy development in countries of the Commonwealth of Independent States (CIS) and economic analysis of projects for the development of corporate renewable energy industry were carried out. The results showed that the Russian renewable energy business is flexible enough for changes; however, at the same time, changes are needed in the national legislation,... [more]

The residential sector has become the second largest energy consumer in China. Urban residential energy consumption (URE) in China is growing rapidly in the process of urbanization. This paper aims to reveal the spatiotemporal dynamic evolution and influencing mechanism of URE in China. The spatiotemporal heterogeneity of URE during 2007−2018 is explored through Kernel density estimation and inequality measures (i.e., Gini coefficient, Theil index, and mean logarithmic deviation). Then, with several advantages over traditional index decomposition analysis approaches, the Generalized Divisia Index Method (GDIM) decomposition is employed to investigate the impacts of eight driving factors on URE. Furthermore, the national and provincial decoupling relationships between URE and residential income increase are studied. It is found that different provinces’ URE present a significant agglomeration effect; the interprovincial inequality in URE increases and then decreases during the study per... [more]

The current research focuses on assessing the potential of municipal solid waste (MSW) conversion into biofuel using pyrolysis process. The MSW samples were taken from Zaatari Syrian Refugee Camp. The physical and chemical characteristics of MSW were studied using proximate and elemental analysis. The results showed that moisture content of MSW is 32.3%, volatile matter (VM) is 67.99%, fixed carbon (FC) content is 5.46%, and ash content is 24.33%. The chemical analysis was conducted using CHNS analyzer and found that the percentage of elements contents: 46% Carbon (C) content, 12% Hydrogen (H2), 2% Nitrogen (N2), 44% Oxygen (O2), and higher heat value (HHV) is 26.14 MJ/kg. The MSW pyrolysis was conducted using tubular fluidized bed reactor (FBR) under inert gas (Nitrogen) at 500 °C with 20 °C/min heating rate and using average particles size 5−10 mm. The products of MSW pyrolysis reaction were: pyrolytic liquid, solid char, and gaseous mixture. The pyrolytic oil and residual char were... [more]