The European Union (EU) has made climate change mitigation a high priority though a policy framework called “Clean Energy for all Europeans “. The concept of primary energy for energy resources plays a critical role in how different energy technologies appear in the context of this policy. This study shows how the calculation methodologies of primary energy content and primary energy factors pose a possible negative implication on the future development of geothermal energy when comparing against EU’s key energy policy targets for 2030. Following the current definitions of primary energy, geothermal utilization becomes the most inefficient resource in terms of primary energy use, thus contradicting key targets of increased energy efficiency in buildings and in the overall energy use of member states. We use a case study of Hellisheidi, an existing geothermal power plant in Iceland, to demonstrate how the standard primary energy factor for geothermal in EU energy policy is highly overes... [more]

Many smart apartments and renovated residential buildings have installed Smart Meters (SMs), which collect interval data to accelerate more efficient energy management in multi-family residential buildings. SMs are widely used for electricity, but many utility companies have been working on systems for natural gas and water monitoring to be included in SMs. In this study, we analyze heating energy use data obtained from SMs for short-term monitoring and annual predictions using change-point models for the coefficient checking method. It was found that 9-month periods were required to search the best short-term heating energy monitoring periods when non-weather-related and weather-related heating loads and heating change-point temperatures are considered. In addition, the 9-month to 11-month periods were needed for the analysis to apply to other case study residences in the same high-rise apartment. For the accurate annual heating prediction, 11-month periods were necessary. Finally, th... [more]

A thermoelectric generator (TEG) is a clean electricity generator from a heat source, usually waste heat. However, it is not as widely utilized as other electricity generators due to low conversion efficiency from heat to electricity. One approach is a system-level net power optimization for a TEG system composed of TEGs, heat sink, and fans. In this paper, we propose airflow reuse after cooling preceding TEGs to maximize system net power. For the accurate system net power, we model the TEG system, air, and heat source with proper dimension and material characteristics, and simulate with a computational fluid dynamics program. Next, the TEG power generation and the fan power consumption are calculated in consideration of the Seebeck coefficient and internal electrical resistance varying with hot and cold side temperatures. Finally, we find the optimal number of TEGs and fan speed generating the most efficient system net power in various TEG systems. The results show that the system wit... [more]

Solar energy is a sustainable and low-cost renewable energy of enormous importance, especially at this time where non-renewable energy sources are unsustainable and costly. However, improving the thermal performance of a solar energy storage reactor poses some challenges. In this study, the location of fluid inlets and outlets in the given reactor design and its impact on the thermal performance were investigated. A P1 approximation radiation model coupled with shallow channel approximation of fluid flow was developed. By taking the frustum base as a reference, four fluid inlets along the edges of the frustum and two outlet locations at the base and side of the reactor were computed. Inlets located 4.81 cm from the base of the frustum and an outlet located at the side of the reactor were found to have a better thermal performance with a short conveyer energy flow system. It was also deduced that radiation applied at the edges of the frustum had better thermal performance than that appl... [more]

Smart grid operation schemes can integrate prosumers by offering economic rewards in exchange for the desired response. In order to activate prosumers appropriately, such operation schemes require models of the dynamic uncertain price-response relationships. In this study, we combine the system identification of nonlinear dynamics with control (SINDyc) algorithm with Bayesian inference techniques based on Markov-chain Monte-Carlo sampling. We demonstrate this combination of two algorithms on an exemplary system in order to obtain parsimonious models alongside parameter uncertainty estimates. The precision of the identified models depends on the identification experiment and the parameterization of the algorithms. Such models may characterize the prosumer response and its uncertainty, thereby facilitating the integration of such entities into smart grid operation schemes.

Previous studies have shown that different parameters such as reservoir conditions (e.g., pressure, temperature, and brine chemistry) and wellbore hydraulics influence the scaling tendency of minerals on the surfaces of completion tools in conventional resources. Although different studies have investigated the suitable conditions for the precipitation of scaling minerals, there is still a lack of understanding about the composition of the scaling materials deposited on the surfaces of completion tools in thermal wells. In this study, we presented a laboratory workflow combined with a predictive toolbox to evaluate the scaling tendency of minerals for different downhole conditions in thermal wells. First, the scaling indexes (SIs) of minerals are calculated for five water samples produced from thermal wells located in the Athabasca and Cold Lake areas in Canada using the Pitzer theory. Then, different characterization methods, including scanning electron microscopy (SEM) with energy di... [more]

We suggest an alternative to conventional coating methods for accident-tolerant fuel (ATF) cladding. A Zircaloy-4 tube was inserted into metal tubes of different materials and the inserted tubes were subjected to physical force at room temperature. The manufactured tube exhibited a pseudo-single tube (PST) structure and had higher thermal stability than a Zircaloy-4 tube. Optical microscopy and scanning electron microscopy images showed that the PST had a uniform and well-bonded interface structure, i.e., no gaps or voids were found at the interface between the inner and outer tubes. Energy-dispersive X-ray spectroscopy analysis confirmed that the metal components did not interdiffuse at the interface of the PST, even after being kept at 600 and 900 °C for 1 h and rapidly cooled to room temperature. Unlike pure Zircaloy-4 tubes, Zircaloy-4/stainless use steel (SUS) 316 PST did not show significant structural collapse, even after being stored at 1200 °C for 1 h. Based on these results,... [more]

This paper intends to prepare a nanofluid sample by suspending Multi-walled Carbon Nanotubes (MWCNTs) at 0.005g/L concentration and analyze the behavior of electrical and dielectric properties based on the International Electrotechnical Commision test method. In order to validate the effectiveness of MWCNT nanofluid, alternating current breakdown voltage (BDV), negative polarity lightning impulse (LI), dielectric permittivity, dissipation factor (DF), DC resistivity and Raman structural measurement are executed accordingly. In the following, an analysis of the statistical distribution using the two-parameter Weibull distribution law of BDV and LI are evaluated at four experimental conditions to predict the probability of breakdown occurring at different percentages. Based on the observation, the MWCNT filler has a substantial effect in improving the BDV and LI characteristics of disposed mineral oil. The permittivity, DF and resistivity performance of MWCNT nanofluid from 25 °C to 90 °... [more]

Predicting actual energy harvesting of a photovoltaic (PV) installation as per site-specific conditions is essential, from the customer’s point of view, to choose suitable PV technologies as well as orientations, since most PVs usually have been designed and evaluated under standard illumination. Hence, the tendency lives in the PV community to evaluate the performance on the energy yield and not purely on the efficiency. The major drawback is that weather conditions play an important role, and recording solar spectra in different orientations is an expensive and time-consuming business. We, therefore, present a model to calculate the daily, monthly and annual energy yield of Si-based PV installations included in commercial panels as well as tandem solar cells. This methodology will be used to evaluate the benefit of potential new technologies for domestic and building integrated applications. The first advantage of such a numerical model is that the orientation of solar panels and the... [more]

Axial flow fans play key roles in the thermo-flow performance of direct dry cooling system under windy conditions, so the energy efficiency of a power generating unit can be improved by optimizing the operation strategies of the axial flow fans. In this work, various measures based on the partition adjustment of axial flow fans with constant power consumption of a 2 × 660 MW power plant are studied by computational fluid dynamics (CFD) methods. The results show that increasing the rotational speed of the windward fans is beneficial to reduce the inlet air temperature and increase the mass flow rates of the fans, which enhance the heat rejections of the air-cooled condensers, especially at high wind speeds. Moreover, the turbine back pressures for the optimal and original cases are achieved by iterative methods, with the largest drop of 2.77 kPa at the wind speed of 12 m/s for 110-case 3 in the wind direction of −90°. It is recommended to adopt 110-case 1 and 110-case 3 at low and high... [more]

During the last few years, electric power systems have undergone a widespread shift from conventional fossil-based generation toward renewable energy-based generation. Variable speed wind generators utilizing full-scale power electronics converters are becoming the preferred technology among other types of renewable-based generation, due to the high flexibility to implement different control functions that can support the stabilization of electrical power systems. This paper presents a fundamental study on the enhancement of transient stability in electrical power systems with increasing high share (i.e., above 50%) of power electronic interfaced generation. The wind generator type IV is taken as a representative form of power electronic interfaced generation, and the goal is to investigate how to mitigate the magnitude of the first swing while enhancing the damping of rotor angle oscillations triggered by major electrical disturbances. To perform such mitigation, this paper proposes a... [more]

Thin films and coatings which have a high demand in a variety of industries—such as manufacturing, optics, and photonics—need regular improvement to sustain industrial productivity. Thus, the present work examined the problem of the Carreau thin film flow and heat transfer with the influence of thermocapillarity over an unsteady stretching sheet, numerically. The sheet is permeable, and there is an injection effect at the surface of the stretching sheet. The similarity transformation reduced the partial differential equations into a system of ordinary differential equations which is then solved numerically by the MATLAB boundary value problem solver bvp4c. The more substantial effect of injection was found to be the reduction of the film thickness at the free surface and development of a better rate of convective heat transfer. However, the increment in the thermocapillarity number thickens the film, reduces the drag force, and weakens the rate of heat transfer past the stretching shee... [more]

Energy cooperation is an important part of the Belt and Road Initiative (BRI). As China’s investment in One Belt One Road countries has increased substantially, a natural question is whether the investment in the BRI countries can contribute to its oil import since it is the most critical part of the national energy security strategy. By employing a dataset that includes the oil import from BRI countries and the oil-related investment in these countries, along with other control variables, an econometric analysis is conducted to investigate the relationship between these two variables. The estimation results provide supporting evidence for the hypothesis that China’s oil investment in BRI countries has helped enhance its oil security. Specifically, investment in BRI countries increases the oil import volume from the host country and diversifies China’s sources of imports. Further analysis also reveals that the effects do not differ by investment mode, e.g., greenfield or mergers and ac... [more]

To improve the low viscosity and poor lubrication characteristics of high-water-based hydraulic liquid, the abrasion and leakage problems in hydraulic components need to be addressed. In a high water-based hydraulic motor with self-balanced distribution valve (HWBHM-SDV), there are two key friction pairs: the piston-crankshaft pair and piston-swivelling-cylinder (PSC) pair. To study the working performance of the PSC pair in HWBHM-SDV, we firstly designed the structural parameters. We found that, within the working speed 0−100 rpm, the leakage in the PSC pair is mainly caused by pressure-gradient flow, and the influence of the seal will not be significant when the seal length is 24 mm. Then, the friction coefficients of different matching materials were tested. It was found that the friction coefficient of 316L stainless steel with OVINO-GIC (OVINO-graphite intercalated compound) coating (316L-GIC)/PEEK reinforced with 30% carbon fibre (PEEK-30CF) is about 0.02~0.04, and the friction c... [more]

Short-circuit faults in a receiving-end power system can lead to blocking events of the feed-in high-voltage direct-current (HVDC) systems, which may further result in system instability. However, security assessment methods based on the transient stability (TS) simulation can hardly catch the fault propagation phenomena between AC and DC subsystems. Moreover, effective emergency control strategies are needed to prevent such undesired cascading events. This paper focuses on power systems with multi-infeed HVDCs. An on-line security assessment method based on the electromagnetic transient (EMT)-TS hybrid simulation is proposed. DC and AC subsystems are modeled in EMTDC/PSCAD and PSS/E, respectively. In this way, interactions between AC and DC subsystems can be well reflected. Meanwhile, high computational efficiency is maintained for the on-line application. In addition, an emergency control strategy is developed, which coordinates multiple control resources, including HVDCs, pumped sto... [more]

This paper proposes a virtual tool for load flow analysis in energy distribution systems of micro-grids. The solution is based on a low-cost measurement architecture, which entails low-voltage power measurements in each secondary substation and a voltage measurement at the beginning of the medium voltage (MV) feeder. The proposed virtual tool periodically queries these instruments to acquire the measurements. Then, it implements a backward−forward load flow algorithm, to evaluate the power flow in each branch and the voltage at each node. The virtual tool performances are validated using power measurements acquired at the beginning of each MV feeder. The uncertainties on each calculated quantity are also evaluated starting from the uncertainties due to the used measurement instruments. Moreover, the influence of the line parameter uncertainties on the evaluated quantities is also considered. The validated tool is useful for the online analysis of power flows and also for planning purpo... [more]

Water-based polymer drilling fluids are commonly used for drilling long horizontal wells where eliminating the drilling fluid-related formation damage and minimizing the environmental impact of the drilling fluids are the main concerns. An experimental study was conducted to investigate the turbulent flow of a polymer fluid over a stationary sand bed deposited in a horizontal pipeline. The main objectives of the study were to determine the effects of sand particle size on the critical velocity required for the onset of the bed erosion and the near-wall turbulence characteristics of the polymer fluid flow over the sand bed. Industrial sand particles having three different size ranges (20/40, 30/50, 40/70) were used for the experiments. The particle image velocimetry (PIV) technique was used to determine instantaneous local velocity distributions and near-wall turbulence characteristics (such as Reynolds stress, axial and turbulence intensity profiles) of the polymer fluid flow over the... [more]

This study aimed to develop a building-integrated photovoltaic (BIPV) device and optimal control methods that increase the photovoltaic (PV) efficiency and visual comfort of the indoor space. A louver-type PV-integrated shading device was suggested and an artificial neural networks (ANN) model was developed to predict PV electricity output, work plane illuminance, and daylight glare index (DGI). The slat tilt angle of the shading device was controlled to maximize PV electricity output based on three different strategies: one without visual comfort constraints, and the other two with visual comfort constraints: work plane illuminance and DGI. Optimal tilt angle was calculated using predictions of the ANN. Experiments were conducted to verify the system modeling and to evaluate the performance of the shading device. Experiment results revealed that the ANN model successfully predicted the PV output, work plane illuminance, and DGI. The PV-integrated shading device was more efficient in p... [more]

A prerequisite for the proper and safe designing of a grounding system is the full knowledge of the ground structure in the terrain of installation. Through soil resistivity measurements, engineers are able to illustrate the ground profile, which constitutes the most significant parameter for the design of a grounding system and for determining the maximum permissible limits of step and touch voltages. This paper highlights the high importance and necessity for engineers to choose the proper measurement axes of soil resistivity in the terrain of interest and to choose suitable measurement depths, as well the combination of axes for the final determination of the ground profile. The variance of soil resistivity values, as a function of axis distance and the impact of axis placement on determining the uncertainty of measurements, is also analyzed in detail in this study. Furthermore, this work studies the value variance of step and touch voltages as a function of measurement axes, consid... [more]

This paper deals with the computation of the performance characteristics of the single-phase self-excited induction generator by field−circuit method. It presents and compares previously unpublished results—self-excitation and no-load characteristics of the generator for different rotor speeds, and complete load steady-state performance characteristics for various types of the core materials. The discrepancies between the performance characteristics of the generator for the catalog’s magnetization curves of different types of electrical sheets and for an actual magnetic core of the generator for self-excitation transients and load steady-state are presented. The results may be useful for designing new constructions of single-phase self-excited induction generators.

The paper presents an analysis of local and global forces acting on the ferromagnetic material of a modulator in a co-axial magnetic gear, taking several design variants and the impact of loading into account. The analyses include a modulator with cores manufactured from a soft-magnetic composite material and two variants made from electrical steel with laminations stacked in different directions. Variations of local forces acting on individual pole pieces of the modulator are analyzed at different loads, showing that the force spectra are subject to significant variation with an increasing load. The presented magnetostatic analyses are extended by structural analysis that provides estimation of stress and displacement for the modulator assembled from additively manufactured acrylonitrile butadiene styrene (ABS)-plastic parts. The analysis carried out for the least favorable design case of the magnetic circuit of the modulator shows that an application of the technology is significantl... [more]

This paper is concerned with the derivation of a one-cycle controller for driving a single-stage buck-boost DC-AC micro-inverter in grid-tied applications. The topology under study is based on a full-bridge switch arrangement with no unfolder circuit. The proposed micro-inverter attains a high gain by applying a multi-winding tapped inductor and, therefore, can operate at grid-level voltage without using a DC-DC step-up stage. To minimize the switching loss, the proposed inverter is operated in the discontinuous conduction mode. The operation principles of the proposed topology in the discontinuous conduction mode are discussed and analyzed. Based on the analysis, the one-cycle control law and modulator circuitry needed to control the proposed micro-inverter are developed. The feasibility of the proposed modulation scheme is verified by simulation.

Since the voltages and currents in dc grids do not have a natural zero-crossing, the protection of these grids is more challenging than the protection of conventional ac grids. Literature presents several unit and non-unit protection schemes that rely on communication, or knowledge about the system’s topology and parameters in order to achieve selective protection in these grids. However, communication complicates fast fault detection and interruption, and a system’s parameters are subject to uncertainty and change. This paper demonstrates that, in low voltage dc grids, faults propagate fast through the grid and interrupted inductive currents commutate to non-faulted sections of the grid, which both can cause circuit breakers in non-faulted sections to trip. A decentralized plug-and-play protection scheme is proposed that ensures selectivity via an augmented solid-state circuit breaker topology and by utilizing the proposed time-current characteristic. It is experimentally shown that t... [more]

In this paper, a direct power predictive controller (DPPC) is derived for a current source inverter (CSI) based single stage photovoltaic (PV) system. The equations of the dynamics, including AC and DC filters, are formulated directly for the PV power and for the active and reactive power injected in the grid. Then, the prediction equations are synthesized straight for the power, and, at each time instant, the optimal switching vector that guarantees simultaneously the control of the power generated by the PV arrays, and the control of the reactive power in the connection to the grid is chosen. This approach aims to guarantee fast and accurate tracking of the power. The proposed system is then validated through simulation and experimental results, showing that the PV system is able to follow the power references, guaranteeing a fast response to a step in the power, and decoupled active and reactive power control, with minimum total harmonic distortion (<5%) of the currents injected... [more]

The computing devices in data centers of cloud and fog remain in continues running cycle to provide services. The long execution state of large number of computing devices consumes a significant amount of power, which emits an equivalent amount of heat in the environment. The performance of the devices is compromised in heating environment. The high powered cooling systems are installed to cool the data centers. Accordingly, data centers demand high electricity for computing devices and cooling systems. Moreover, in Smart Grid (SG) managing energy consumption to reduce the electricity cost for consumers and minimum rely on fossil fuel based power supply (utility) is an interesting domain for researchers. The SG applications are time-sensitive. In this paper, fog based model is proposed for a community to ensure real-time energy management service provision. Three scenarios are implemented to analyze cost efficient energy management for power-users. In first scenario, community’s and fo... [more]