This study aims to test the effects of changes in international crude oil prices on changes in crude oil and hydropower use from 1965 to 2016. We suggest a cointegration relationship between the consumption of coal, crude oil, and hydropower and the real crude oil price. The real price is weakly exogenous for the long-run relationship and has impacted energy consumption accordingly. The long-run crude oil price elasticity of oil use is 0.460. Our estimate suggests a positive oil price−oil use relationship in China, which is dramatically different from many previous studies but is consistent with a few past studies. The growth in external oil prices may lead to a long-run increase in hydropower use in China, with a long-run price elasticity of 0.242. The long-run crude oil price elasticity of coal use is −0.930. Hence, increased oil and hydropower use could make up the energy supply−demand gap left over by the decreased coal use. Strictly planned domestic fuel prices and rapidly growing... [more]

With an ever-increasing release of harmful greenhouse gases into the environment, there is an ongoing search for a renewable source of energy to replace the current means of producing energy. One promising source is from methanotrophic bacteria, which uses methane as its primary carbon source to produce valuable byproducts including lipids. These lipids could be used in the production of biofuels and other important industrial chemicals including plastics and surfactants. The use of methanotrophs would lower the amount of methane in the atmosphere from two sides, in the growth and cultivation of methanotrophs and in the replacement of conventional fossil fuels. The development of such a system requires a good understanding of the bacteria responsible and the steps of growth/culturing and extraction. An integrated system that uses every product of methanotrophic growth could impact multiple markets and help make this technique economically feasible as well as provide the groundwork for... [more]

Overdischarge often occurs during the use of battery packs, owing to cell inconsistency in the pack. In this study, the overdischarge behavior of 2.9 Ah cylindrical NCM811 [Li(Ni0.8Co0.1Mn0.1)O2] batteries in an adiabatic environment was investigated. A higher overdischarge rate resulted in a faster temperature increase in the batteries. Moreover, the following temperatures increased: Tu, at which the voltage decreased to 0 V; Ti, at which the current decreased to 0 A; and the maximum temperature during the battery overdischarge (Tm). The following times decreased: tu, when the voltage decreased from 3 to 0 V, and ti, when the current decreased to 0 A. The discharge capacity of the batteries was 3.06−3.14 Ah, and the maximum discharge depth of the batteries was 105.51−108.27%. Additionally, the characteristic overdischarge behavior of the batteries in a high-temperature environment (55 °C) was investigated. At high temperatures, the safety during overdischarging decreased, and the amou... [more]

A super high-head Francis turbine with a gross head of nearly 700 m was designed with computational fluid dynamics (CFD) simulation and laboratory tests. Reduced-scale (1:3.7) physical and numerical models of the real-scale prototype were created to investigate the hydraulic performance. According to the CFD analysis, a strong rotor−stator interaction (RSI) between guide vanes and runner blades is observed as a result of the high-speed tangential flow towards runner created by the super high water head as well as the small gaps between the radial blades. At the designed best efficiency point (BEP), there is no significant flow recirculation inside the flow passage and minor loss occurs at the trailing edge of the stay vanes and guide vanes. Maximum velocity is observed at runner inlets due to flow acceleration through the narrow passages between the guide vanes. The elbow-shaped draft tube gradually decreases the flow velocity to keep the kinetic energy loss at a minimum. The laborator... [more]

In the last years, an increasing number of countries has been affected by water shortage. Seawater desalination driven by solar energy, which is usually available in arid regions, might be a solution to satisfy the freshwater demand. In this study, the feasibility of a stand-alone multi-effect desalination (MED) plant driven by solar energy for an isolated community was studied. The system was made up of a solar field, a MED unit, and a thermal storage that mitigated solar energy fluctuations. Simulations with different top brine temperature and inclination and number of the solar panels were carried out in Matlab and Aspen Plus on an hourly basis by considering one typical meteorological year for ambient temperature and solar radiation. Two different sources of electrical energy were considered: A photovoltaic (PV) field and a diesel generator. The results were compared from an energetic and economic point of view, by considering the adoption of plastic as a material for MED heat exch... [more]

Recently, use of supercapacitors as energy storage systems has attracted considerable attention. However, the literature is scarce of information about the optimization of hybrid systems, using supercapacitors as the main energy storage system. In our study, we focused step-by-step on the engineering concept of a photo-rechargeable energy storage system based on silicon solar cells and supercapacitors. In the first step, based on commercially available elements, we designed a solar charger and simulated its work in idealized conditions. Secondly, we designed appropriate electronic connections and control systems, allowing for the charging−discharging process of the energy storage system. After constructing three type of demonstrators of solar energy charger, we tested it. The novel design allowed us to achieve total available energy from solar panel energy conversion up to 93%.

As one of the main businesses in Jeju-do in South Korea, specialized local products are grown in greenhouses. For greenhouse farming, it is preferable to use geothermal heat pump systems for energy conservation because of the stable temperature of the ground. In the same manner, heat pumps using underground air is recommended for greenhouse farming since underground air can easily be obtained from porous volcanic rocks in Jeju-do. However, direct usage of the underground air is not feasible for planting in the greenhouse or livestock care because the underground air is relatively humid and its temperature is low. For the present study, the heating performance of an air-to-water heat pump which used underground air as a heat source for greenhouse farming during the winter was assessed through measurements. In addition, the economic impact of the air-to-water heat pump (AWHP) was compared with a conventional air heater. According to the results, an AWHP can save more than 70% of the tota... [more]

Hydrogen-based engines are progressively becoming more important with the increasing utilization of hydrogen and layouts (e.g., onboard reforming systems) in internal combustion engines. To investigate the possibility of HICE (hydrogen fueled internal combustion engine), such as an engine with an onboard reforming system, which is introduced as recent technologies, various operating areas and parameters should be considered to obtain feasible hydrogen contents itself. In this study, a virtual hydrogen-added compressed natural gas (HCNG) model is built from a modified 11-L CNG (Compressed Natural Gas) engine, and a response surface model is derived through a parametric study via the Latin hypercube sampling method. Based on the results, performance and emission trends relative to hydrogen in the HCNG engine system are suggested. The operating conditions are 1000, 1300, and 1500 rpm under full load. For the Latin hypercube sampling method, the dominant variables include spark timing, exc... [more]

The sustainable development of the energy sector through the implementation of renewable energy (RE) technology has been a primary concern for the government of Malaysia since the 1990s. Developing RE technology in rural areas is also one of the most important energy strategies. One of the most important requirements for the successful adoption of renewable energy technology is the public acceptance of this technology. This article examines the public acceptance of RE (wind and solar) technologies among rural residents in Mersing, Malaysia. This study is conducted in conjunction with the development of the hybrid wind−solar RE generation system for the Marine Ecosystem Research Centre (EKOMAR), which located in Mersing. To investigate the public acceptance of RE technologies, two surveys were conducted, before and after the installation of the hybrid wind−solar RE generation system. The findings revealed that RE innovations, such as wind and solar energy, were well known among 54.7% an... [more]

This paper investigates the bottom-hole pressure (BHP) performance of a fractured well with multiple radial fracture wings in a coalbed methane (CBM) reservoir with consideration of stress sensitivity. The fluid flow in the matrix simultaneously considers adsorption−desorption and diffusion, whereas fluid flow in the natural fracture system and the induced fracture network obeys Darcy’s law. The continuous line-source function in the CBM reservoir associated with the discretization method is employed in the Laplace domain. With the aid of Stehfest numerical inversion technology and Gauss elimination, the transient BHP responses are determined and analyzed. It is found that the main flow regimes for the proposed model in the CBM reservoir are as follows: linear flow between adjacent radial fracture wings, pseudo-radial flow in the inner region or Stimulated Reservoir Volume (SRV), and radial flow in outer region (un-stimulated region). The effects of permeability modulus, radius of SRV,... [more]

The limitation of fossil fuel uses and GHG (greenhouse gases) emissions reduction are two of the main objectives of the European energy policy and global agreements that aim to contain climate changes. To this end, the building sector, responsible for important energy consumption rates, requires a significant improvement of its energetic performance, an obtainable increase of its energy efficiency and the use of renewable sources. Within this framework, in this study, we analysed the economic feasibility of a stand-alone photovoltaic (PV) plant, dimensioned in two configurations with decreasing autonomy. Their Net Present Value at the end of their life span was compared with that of the same plant in both grid-connected and storage-on-grid configurations, as well as being compared with a grid connection without PV. The analysis confirms that currently, for short distances from the grid, the most suitable PV configuration is the grid-connected one, but also that the additional use of a... [more]

This paper discusses three methods of modulation for a single-phase isolated matrix converter. The matrix converter is combined with a transformer integration to perform power decoupling control in order to reduce the number of component and capacitor volumes. Due to the reason of (i) Alternating current (AC/AC) direct conversion and (ii) transformer integration, obtaining a clean sinusoidal grid current waveform in the modulation of matrix converter (MC) is important. Three methods of modulation are compared in terms of control complexity, quality waveform, and inductive-capacitive-inductive (LCL) filter sizing. The principal control of each method is described. Finally, a prototype was tested to verify the validity and the effectiveness of grid current control and power decoupling in the spoken circuit structure.

According to the International Energy Agency (IEA)’s forecast, China will fully electrify its railway system by 2050. However, the development of electrified railways is limited in the weak areas of China’s power grid. To surpass these limitations, we turn our attention to new railway energy sources, among which the most suitable is photovoltaic power generation. To evaluate the feasibility of integrating railway systems and photovoltaic power generation in China, this paper analyzes the geographical conditions and railway layout of China, gives a potential method for evaluating railway asset energy transformation measures and asset energy transformations that are suitable for China’s national conditions, and proposes an application of railway system energy transformation on this basis. Then, this method is used to evaluate the potential of a substation section of the Lanxin high-speed railway in China for reference. The results show that the green energy potential and scheduling poten... [more]

In this paper, we examine the energy efficiency performance of the Belt and Road Initiative (BRI) countries using a newly developed panel data stochastic frontier model that allows for estimation of both persistent and transient efficiency while controlling for random country effects and noise. By this, we contribute to the energy economic literature by providing a complete picture of the level of persistent, transient, and total energy efficiency estimates from a cross country perspective for a panel of 48 BRI countries during the period 1990−2015. Adding that there is little evidence to support energy efficiency convergence in the energy economic literature, we went further to check whether energy efficiency converges in the BRI countries. The results show that (1) persistent efficiencies are much lower than transient efficiencies, suggesting that the energy problem in the BRI countries is more of a structural issue; (2) while energy efficiency varies widely across the countries, hig... [more]

There is a significant interaction between wind and earthquakes for large-scaled wind turbines due to an aeroelastic effect. This study evaluates the accuracy of an uncoupled method extensively utilized to analyze the seismic response of wind turbines at the operational state. Initially, the oscillation of the blade for the National Renewable Energy Laboratory (NREL) 5 MW wind turbine excited by wind and wind-earthquake combination, respectively, is compared using the fully coupled method to verify the assumption in this uncoupled method. Subsequently, the influence of ground motions on the aerodynamic loadings of the rotor is discussed to evaluate the interaction between wind and earthquake loads. In addition, the accuracy of the uncoupled method is assessed by comparing the analysis results of the coupled and uncoupled methods, where different mean wind speed and equivalent aerodynamic damping ratio are considered. The results indicate that the oscillation velocity of blades and thru... [more]

Photovoltaic systems have been explored as a solution to meet the growing demand for electricity from a clean and renewable source. However, the low energy conversion efficiency of photovoltaic panels is one of the critical factors that hinder the competitiveness of this energy source concerning the others. An effective way to improve the efficiency of photovoltaic systems is by using solar trackers. The tracking strategy most used in photovoltaic plants employs algorithms to calculate the Sun position. This work presents energy generation estimation applying six algorithms in horizontal single-axis solar tracking: the Solar Position Algorithm (SPA) and Grena 1−5 algorithms. The aim is to evaluate the influence of these algorithms on energy generation. For all simulated locations, comparing to an ideal scenario, the SPA presented the best energy generation results. However, the other algorithms showed negligible differences between themselves, which allows us to conclude that any of th... [more]

This research put forth exergy-based economic and sustainability analyses of a (J85-GE-5H) military turbojet engine (TJE). Firstly, sustainability, conventional exergoeconomic and advanced exergoeconomic cost analyses were executed utilizing kerosene fuel according to real engine working circumstances. The engine was likewise investigated parametrically, considering H2 fuel utilization. The sustainable economic analysis assessment of the TJE was finally actualized by comparing the acquired outcomes for both fuels. The entire engine’s unit exergy cost of product (cPr) with kerosene was determined 76.45 $/GJ for the military (MIL) process mode (PM), whereas it was computed 94.97 $/GJ for the afterburner (AB) PM. Given the use of H2, the cPr increased to 179 and 288 $/GJ for the aforementioned two modes, seriatim. While the sustainability cost index (SCI) values were obtained 52.86 and 78.84 $/GJ for the MIL and AB PM, seriatim, they became 128 and 244 $/GJ when considering H2. Consequent... [more]

The pump turbine is prone to stall when running at part-load operation. Stalls would cause a hump-like head characteristic curve, low-frequency high-amplitude pressure pulsation, and surge or resonance in the system. There is a lack of efficient methods for pump turbine stall suppression. The traditional blade hydrodynamic optimization method has limited effect and would influence the other characteristics. As the essence of stall is flow separation, forming a severe backflow vortex, a “Groove Method” is put forward and employed to suppress stall in a pump turbine with the full consideration of the mechanical structure, flow field, and pressure field. Both experiments and calculations are carried out to test the effectiveness of this new method. Furthermore, its deep mechanisms are revealed. This method can weaken the head hump to a certain extent and reduce the pressure pulse amplitude induced by stall. Meanwhile, the performance at the design operating point is not disturbed much.

The alcohols ethanol and 1-butanol are interesting options as blending components for renewable fuels. We studied whether it is possible to mix these alcohols with a little refined material, rapeseed oil, to obtain stable fuel samples. At room temperature, the stable samples consisted of rapeseed oil blended with butanol at 5 vol-%, 10 vol-%, 20 vol-%, 30 vol-% and one sample of rapeseed oil with 5 vol-% of ethanol. The samples’ fuel properties analysed were kinematic viscosity (at 40 °C), density (at 15 °C) and surface tension. Cold filter plugging point was measured for rapeseed oil with 20 vol-% and 30 vol-% of butanol. Stability of butanol or ethanol and rapeseed oil blends can be achieved at the studied volumes. The density of neat rapeseed oil and all the alcohol−rapeseed oil blends met the requirements set for residual marine fuels. The 30 vol-% butanol−rapeseed oil blend met the requirements for distillate marine oil for density, and almost for kinematic viscosity. The blends a... [more]

Currently, lipid extraction remains a major bottleneck in microalgae technology for biofuel production. In this study, an effective and easily controlled cell wall disruption method based on electro-Fenton reaction was used to enhance lipid extraction from the wet biomass of Nannochloropsis oceanica IMET1. The results showed that 1.27 mM of hydroxide radical (HO•) was generated under the optimal conditions with 9.1 mM FeSO4 in a 16.4 mA·cm−2 current density for 37.0 min. After the electro-Fenton treatment, the neutral lipid extraction yield of microalgae (~155 mg) increased from 40% to 87.5%, equal to from 12.2% to 26.7% dry cell weight (DCW). In particular, the fatty acid composition remained stable. The cell wall disruption and lipid extraction processes were displayed by the transmission electron microscope (TEM) and fluorescence microscopy (FM) observations, respectively. Meanwhile, the removal efficiency of algal cells reached 85.2% within 2 h after the reaction was terminated. Fu... [more]

The internal combustion engine (ICE) as a main power source for transportation needs to improve its efficiency and reduce emissions. The Organic Rankine Cycle (ORC) is a promising technique for exhaust heat recovery. However, vehicle engines normally operate under transient conditions with both the engine speed and torque varying in a large range, which creates obstacles to the application of ORC in vehicles. It is important to investigate the dynamic performance of an ORC when matching with an ICE. In this study, the dynamic performance of an ICE-ORC combined system is investigated based on a heavy-duty diesel engine and a 5 kW ORC with a single-screw expander. First, dynamic simulation models of the ICE and the ORC are built in the software GT-Power. Then, the working parameters of the ORC system are optimized over the entire operation scope of the ICE. A closed-loop proportional-integral (PI) control together with a feedforward control is designed to regulate the operation of the OR... [more]

There is the potential for hybridised gas engine-energy storage systems to participate in the Balancing Mechanism (BM) by offering a product that marries the advantages of both units. The higher price offerings are currently dominated by pumped storage (PS) assets. Given their high-flexibility, PS plants mostly offer at higher prices, but respond quicker and can run for a smaller minimum run time than a gas engine on its own. The operation of the hybrid system must match the operation of the pumped storage plants, to be able to claim a space in this part of the BM market including meeting a minimum run time and minimum start time. The business case is dependent on battery costs which in turn depend on size and operational strategy. This paper uses a case study approach to estimate Net Present Value of a hybrid system. The paper uses a mixture of publicly available data and industrially provided data within its analysis. The paper concludes that battery cost and lifespan are still issue... [more]

With an elevation of 1000 m above sea level, once the coastal mountain range is crossed, the Atacama Desert receives the highest levels of solar radiation in the world. Global horizontal irradiations over 2500 kWh/(m2 year) and a cloudiness index below 3% were determined. However, this index rises to 45% in the coastal area, where the influence of the Pacific Ocean exists with a large presence of marine aerosols. It is on the coastal area that residential photovoltaic (PV) applications are concentrated. This work presents a study of the soiling impact on PV modules at the coastline of Atacama Desert. The current−voltage characteristics of two multicrystalline PV modules exposed to outdoor conditions were compared, while one of them was cleaned daily. Asymptotic behavior was observed in the accumulated surface dust density, over 6 months. This behavior was explained by the fact that as the glass became soiled, the probability of glass-to-particle interaction decreased in favor of a more... [more]

Hydropower units undertake tasks such as peak shaving, frequency modulation, and providing accident reserves in the power system. With the increasing capacity and structural complexity of power systems, hydropower units have become more important. Hydraulic-turbine-governing systems (HTGSs) need to have higher control performance and automation levels to meet the higher regulatory requirements of the power system. To achieve high-quality control, we proposed a new finite-time, fault-tolerant control method for HTGSs with an actuator fault. First, a fractional-order model for HTGSs with uncertainty, external disturbance, and an actuator fault was introduced. Second, a fault estimator that could quickly track the fault signal for an actuator fault was proposed. Then, based on the fractional-order finite-time stability theorem, a finite-time, fault-tolerant controller was proposed for the stabilization of an HTGS. Furthermore, a controller was developed as a fractional differential form c... [more]

Soiling of solar module cover glass is a serious problem for solar asset managers. It causes a reduction in power output due to attenuation of the incident light, and reduces the return on investment. Regular cleaning is required to mitigate the effect but this is a costly procedure. The application of transparent hydrophobic, anti-soiling coatings to the cover glass is a promising solution. These coatings have low surface energy and contaminants do not adhere well. Even if soiling does remain on the coated surface, it is much more easily removed during cleaning. The performance of the coatings is determined using the water contact angle and roll-off angle measurements. However, although hydrophobic coatings hold out great promise, outdoor testing revealed degradation that occurs surprisingly quickly. In this study, we report on results using laboratory-based damp heat and UV exposure environmental tests. We used SEM surface imaging and XPS surface chemical analysis to study the mechan... [more]