An air-independent propulsion system containing fuel cells is applied to improve the operational performance of underwater vehicles in an underwater environment. Fuel-reforming efficiently stores and supplies hydrogen required to operate fuel cells. In this study, the applicability of a fuel-reforming system using various fuels for underwater vehicles was analyzed by calculating the fuel and water consumptions, the amount of CO2 generated as a byproduct, and the amount of water required to dissolve the CO2 using aspen HYSYS (Aspen Technology, Inc., Bedford, MA, USA). In addition, the performance of the fuel-reforming system for methanol, which occupies the smallest volume in the system, was researched by analyzing performance indicators such as methanol conversion rate, hydrogen, yield and selectivity, and reforming efficiency under conditions at which pressure, temperature, steam-to-carbon ratio (SCR), and hydrogen separation efficiency vary. The highest reforming efficiency was 77.7−... [more]

The increasing integration of renewable energies reduces the inertia of power systems and thus adds stiffness to grid dynamics. For this reason, methods to obtain virtual inertia have been proposed to imitate mechanical behavior of rotating generators, but, usually, these methods rely on extra power reserves. In this paper, a novel ancillary service is proposed to alleviate frequency transients by smoothing the electromagnetic torque of synchronous generators due to change of active power consumed by loads. Being implemented by grid-tied inverters of renewables, the ancillary service regulates the reactive power flow in response to frequency transients, thereby demanding no additional power reserves and having little impact on renewables’ active power generation. Differently from the active power compensation by virtual inertia methods, it aims to low-pass filter the transients of the active power required to synchronous generators. The proposed ancillary service is firstly verified in... [more]

Different concepts and methods have been proposed and developed by many researchers to harvest ocean wave energy. In this paper, a new self-adjustable wave energy converter concept is presented, which changes its inertia through ballasting and de-ballasting using sea water. The trigger of ballasting and de-ballasting is controlled by the critical wave period. Therefore, the self-adjustable wave energy converter is able to interact at resonance with the ocean waves at two different resonant bandwidths. Ten years real wave data with hourly resolution from a selected location in Gulf of Mexico was used in this paper to decide the critical wave period and other parameters of the wave energy converter. The annual energy performance of the self-adjustable wave energy converter was also estimated and compared with non-adjustable wave energy converter with similar dimensions. Structural analysis including both static and fatigue analysis was performed on the self-adjustable wave energy convert... [more]

Photovoltaic-Thermal (PVT) is a type of technology that generates electricity and heat simultaneously at the point of use. The generated electricity could be used on site or exported to the grid while the thermal output could be utilized for space and water heating. There is a lot of research for solar air heating with experiment or CFD (Computational Fluid Dynamics), but CFD has the disadvantage that it would indicate impractical results. In this paper, a numerical PVT baseline model was developed and validated with Separate Effect Test (SET) data to increase reliability. The numerical study was conducted by considering the effect of baffle lengths and baffle slopes on outlet temperature, total heat transfer and pressure drop inside PVT air module. An optimum PVT baffle length and slope design were suggested. The baseline numerical PVT model agreed well with the test data set as indicated by 1.25% error for inlet−outlet temperatures difference. The sensitivity study was conducted by c... [more]

This paper studies the system unbalance caused by rooftop Photovoltaic Generation Systems (PVGSs) in distribution networks and proposes an improved method. The voltage and current unbalance studies for three extreme cases considering all rooftop PVGSs being connected to one single phase and then the stochastic analyses for the integration cases of rooftop PVGSs are considered. These three extreme cases lead to severe system unbalance problems. An improving method that combines the On Load Tap Changer (OLTC) and the optimal phase arrangement of distribution transformers is proposed in this paper to mitigate the system unbalance. The OLTC-based improving method is applied first. If the system unbalance is still out of range, the optimal phase arrangement of distribution transformers is further used to mitigate the system unbalance problem. The objective function of optimal phase arrangement is to minimize the system unbalance with the constraints of voltage limits, line flow limit, etc.... [more]

The European Commission’s call for energy communities has motivated academia to focus research on design and trading concepts of local electricity markets. The literature provides a wide range of conceptual ideas and analyses on the technical and economic framework of single market features such as peer-to-peer trading. The feasible, system-wide integration of energy communities into existing market structures requires, however, a set of legal adjustments to national regulation. In this paper, we test the implications of recently proposed market designs under the current rules in the context of the German market. The analysis is facilitated by a simplistic equilibrium model representing heterogeneous market participants in an energy community with their respective objectives. We find that, on the one hand, these proposed designs are financially unattractive to prosumers and consumers under the current regulatory framework. On the other hand, they even cause distributional effects withi... [more]

Diffuse Ceiling Ventilation (DCV) is a promising concept to address internal air quality and thermal comfort requirements in contemporary buildings. Sound-absorbing perforated ceiling panels are common in office rooms and can be used as air diffusers without modifications. The optimization of such systems is not a trivial procedure, and numerical simulation can represent an important tool to carry out this task. Today, most of the numerical studies on DCV are performed using porous medium models and focus on the general system performance rather than on the optimization of the diffuser design. In previous studies, a CFD model was used to optimize the size and distribution of the ceiling perforation. In the study presented in this paper, the results of simulations conducted on a full-scale three-dimensional domain and the performance comparison between a continuous and non-continuous perforation distribution are given. The results show that the non-continuous diffuser design does not di... [more]

Biowaste represents a significant fraction of municipal solid waste (MSW). Its separate collection is considered as a useful measure to enhance waste management systems in both the developed and developing world. This paper aims to compare the environmental performance of three market-ready technologies currently used to treat biowaste—biowaste composting, fermentation, and biowaste incineration in waste-to-energy (WtE) plants as a component of residual municipal solid waste (RES). Global warming potential (GWP) was applied as an indicator and burdens related to the operation of facilities and credits obtained through the products were identified. The environmental performance of a WtE plant was investigated in detail using a model, implementing an approach similar to marginal-cost and revenues, which is a concept widely applied in economics. The results show that all of the treatment options offer an environmentally friendly treatment (their net GWP is negative). The environmental per... [more]

The amount of solar radiation reaching the front cover of a photovoltaic module is crucial for its performance. A number of factors must be taken into account at the design stage of the solar installation, which will ensure maximum utilization of the potential arising from the location. During the operation of a photovoltaic installation, it is necessary to limit the shading of the modules caused by both dust and shadowing by trees or other objects. The article presents an analysis of the impact of the radiation reaching the surface of the radiation module on the efficiency obtained. Each of the analyzed aspects is important for obtaining the greatest amount of energy in specific geographical conditions. Modules contaminated by settling dust will be less efficient than those without deposits. The results of experimental studies of this effect are presented, depending on the amount of impurities, including their origins and morphologies. In practice, it is impossible to completely elimi... [more]

Fin arrays are widely utilized in many engineering applications, such as heat exchangers and micro-post reactors, for higher level of fluid−solid contacts. However, high fluid pressure loss is reportedly the major drawback of fin arrays and a challenge for pumping supply, particularly at micro-scales. Previous studies also indicate that fin shapes, spacing and alignment play an important role on the overall pressure losses. Therefore, we present a numerical tool to minimize pressure losses, considering the geometrical aspects related to fin arrays. In this regard, a density-based topology optimization approach is developed based on the pseudo-spectral scheme and Brinkman penalization in 2D periodic domains. Discrete sensitives are derived analytically and computed at relatively low cost using a factorization technique. We study different test cases to demonstrate the flexibility, robustness and accuracy of the present tool. In-line and staggered arrays are considered at various Reynold... [more]

Polyisocyanurate (PIR) thermal insulation boards faced with carboard, plastic, aluminum, or multilayer facings are used for thermal insulation of buildings. Facing materials are selected according to the conditions of use of PIR products. At the corners of the building where these products are joined, facings can be in the direction of the heat flux movement and significantly increase heat transfer through the linear thermal bridge formed in the connection of PIR boards with facing of both walls. Analyzing the installation of PIR thermal insulation products on the walls of a building, the structural schemes of linear thermal bridges were created, numerical calculations of the heat transfer coefficients of the linear thermal bridges were performed, and the influence of various facings on the heat transfer through the thermal bridge was evaluated. Furthermore, an experimental measurement using a heat flow meter apparatus was performed in order to confirm the results obtained by numerical... [more]

Energy consumption is directly related to the energy supply and production costs of gas-based direct reduction ironmaking, which is an effective choice to reduce the energy consumption of iron making. In this paper, the minimum Gibbs free energy principle was used to calculate the equilibrium composition under the conditions of reduction gas consisting of hydrogen and carbon monoxide (hydrogen concentration of 0−100%, reduction gas amount of 0−6.0 mol, reduction temperature of 790−1100 °C, and 0.5 mol Fe2O3). According to the enthalpy change, a simplified energy consumption model of a gas-based direct reduction ironmaking process was established, and the energy consumption per mole of metallic iron produced was calculated in detail. The following conclusions were drawn: at the stage when the reduction reaction occurred, the utilization rate of hydrogen or carbon monoxide remained unchanged with the increase in the amount of reduction gas or the increase in the hydrogen concentration of... [more]

Metal/NiO-Smarium-doped ceria (SDC) nano-composite thin film anodes were deposited on anodic aluminum oxide by co-sputtering to enhance the in-plane current-collecting ability and investigated by varying the composition of metal materials (Pt and Au). Full fuel cells with these nano-composites were fabricated and tested at 500 °C. Columnar anodes with a sponge structure were fabricated by varying the DC sputtering source power and they were thermally stable at the operating temperature. By adding metal material, the ohmic resistance, including the current collecting resistance, was drastically reduced and the polarization resistance also decreased. The nano-composite electrode with a Pt content of 61 at% showed the highest performance, which is a maximum power density of 212.5 mW/cm2 at 500 °C. In addition, Au was considered to reduce the current collecting resistance and the corresponding power density was 3 times higher than that with the NiO-SDC anode.

Decreasing the levelized cost of renewable energy and improving the stability of power systems are the key requirements for realizing the sustainable growth of power production capacity. Concentrating solar power (CSP) technology with thermal energy storage can overcome the intermittent and unstable nature of solar energy, and its development is of great significance for the sustainable development of human society. In this paper, topic discovery and clustering were studied using bibliometric, social network analysis and information visualization technology based on the Web of Science database (SCI-Expanded) and the incoPat global patent database. The technology searched for papers and patents related to CSP technology to reveal the development trends of CSP technology and provide the references for related technical layout and hot spot tracking. The results show that the global output of CSP technology papers has continued to grow steadily, whereas the number of patent applications sh... [more]

The present paper deals with the theoretical evaluation of the efficiency of an array of cylindrical Wave Energy Converters (WECs) having a vertical symmetry axis and placed in front of a reflecting vertical breakwater. Linear potential theory is assumed, and the associated diffraction and motion radiation problems are solved in the frequency domain. Axisymmetric eigenfunction expansions of the velocity potential are introduced into properly defined ring-shaped fluid regions surrounding each body of the array. The potential solutions are matched at the boundaries of adjacent fluid regions by enforcing continuity of the hydrodynamic pressures and redial velocities. A theoretical model for the evaluation of the WECs’ performance is developed. The model properly accounts for the effect of the breakwater on each body’s hydrodynamic characteristics and the coupling between the bodies’ motions and the power take-off mechanism. Numerical results are presented and discussed in terms of the exp... [more]

For many years, primary weather forecasting services (Global Forecast System (GFS) and the European Centre for Medium-Range Weather Forecasts (ECMWF)) have been made available to the public through global Numerical Weather Prediction (NWP) models estimating a multitude of general weather variables in a variety of resolutions. Secondary services such as weather experts Meteomatics AG use data and improve the forecasts through various methods. They tailor for the specific needs of customers in the wind and solar power generation sector as well as data scientists, analysts, and meteorologists in all areas of business. These auxiliary services have improved performance and provide reliable data. However, this work extended these auxiliary services to so-called tertiary services in which the weather forecasts were further conditioned for the very niche application environment of mobile solar technology in solar car energy management. The Gridded Model Output Statistics (GMOS) Global Horizon... [more]

To meet the rapid-growing demand for electricity in Kuwait, utility planners need to be informed on the energy consumption to implement energy efficiency measures to manage sustainable load growth and avoid the high costs of increasing generation capacities. The first step of forecasting the future energy profile is to establish a baseline for Kuwait (i.e., a business-as-usual reference scenario where no energy efficiency incentives were given and the adoption of energy efficient equipment is purely market-driven). This paper presents an investigation of creating a baseline end-use energy profile until 2040 for the residential sector in Kuwait by using a bottom-up approach. The forecast consists of mainly two steps: (1) Forecasting the quantity of the residential energy-consuming equipment in the entire sector until 2040 where this paper used a stock-and-flow model that accounted for the income level, electrification, and urbanization rate to predict the quantify of the equipment over... [more]

This paper presents a reinforcement learning framework for solving battery scheduling problems in order to extend the lifetime of batteries used in electrical vehicles (EVs), cellular phones, and embedded systems. Battery pack lifetime has often been the limiting factor in many of today’s smart systems, from mobile devices and wireless sensor networks to EVs. Smart charge-discharge scheduling of battery packs is essential to obtain super linear gain of overall system lifetime, due to the recovery effect and nonlinearity in the battery characteristics. Additionally, smart scheduling has also been shown to be beneficial for optimizing the system’s thermal profile and minimizing chances of irreversible battery damage. The recent rapidly-growing community and development infrastructure have added deep reinforcement learning (DRL) to the available tools for designing battery management systems. Through leveraging the representation powers of deep neural networks and the flexibility and vers... [more]

A modern renewable energy forecasting system blends physical models with artificial intelligence to aid in system operation and grid integration. This paper describes such a system being developed for the Shagaya Renewable Energy Park, which is being developed by the State of Kuwait. The park contains wind turbines, photovoltaic panels, and concentrated solar renewable energy technologies with storage capabilities. The fully operational Kuwait Renewable Energy Prediction System (KREPS) employs artificial intelligence (AI) in multiple portions of the forecasting structure and processes, both for short-range forecasting (i.e., the next six hours) as well as for forecasts several days out. These AI methods work synergistically with the dynamical/physical models employed. This paper briefly describes the methodology used for each of the AI methods, how they are blended, and provides a preliminary assessment of their relative value to the prediction system. Each operational AI component add... [more]

Blockchain, as an emerging technology and a disruptive innovation, has attracted attention from both academia and industry. However, there are many potential risks associated with it, such as the technical risk, the legal risk and the privacy risk. A comprehensive risk analysis is crucial for cost-effective deployment of blockchain technology. Important adoption decisions, including when to deploy blockchain, how to plan the investment, how to transfer current businesses onto blockchain, and how to price the blockchain service depend on this risk analysis. Yet very little study exists concerning the blockchain adoption planning with risks analysis. This research presents a cost-and-risk analysis framework and an adoption planning method for the case of blockchain application in carbon trading. Design requirements implied by the analysis are inferred and the architecture of a novel hybrid blockchain system is proposed. The system leverages the advantages of blockchain technology and inc... [more]

Acrylic acid, a versatile chemical intermediate, is typically manufactured via a two-step process involving the selective oxidation of propylene and acrolein. This work presents an optimized simulation on Aspen Plus® (AspenTech, Bedford, MA, USA) of the production of acrylic acid, with focus on the optimum design and operation of the reactor train, and modification for reduction in energy usage. In the propylene oxidation reactor, an inert pre-heating zone was designed to make use of the excess energy present in the exothermic process fluid and carried within the molten salt cooling fluid circuit. In the acrolein oxidation reactor, injection of cold air was used as a means to absorb the reaction heat. The optimization methodology employed aimed to minimize the total capital expenditure (i.e., equipment sizing) and operating costs (heat exchange network) for the required acrylic acid production and design constraints. The design constraints were based on the selected reaction kinetics a... [more]

Modular multilevel converters (MMCs) play an important role in the power electronics industry due to their many advantages such as modularity and reliability. However, one of the challenges is to suppress fluctuations of circulating current and capacitor voltage and to ensure the quality of the output current. In this paper, the upper and lower arm voltages are employed as control inputs to control the output current and circulating current which are fed back to track the desired value. Based on linear matrix inequality (LMI), the control law of the MMC with multi-input system is designed to optimize the control value. The optimum arm voltage is divided by the SM nominal capacitor voltage to determine the number of SMs inserted into the upper/lower arm. The Voltage Sorting Algorithm (VSA) is then used to suppress the capacitor voltage fluctuation. The proposed tracking control strategy is implemented in MATLAB/Simulink. The results show that even under a small number of SMs (4 per arm)... [more]

Tidal stream turbines are subject to complex flow conditions, particularly when installed in staggered array configurations where the downstream turbines are affected by the wake and/or bypass flow of upstream turbines. This work presents, for the first time, methods for and results from the physical testing of three 1/15 scale instrumented turbines configured in a closely-spaced staggered array, and demonstrates experimentally that increased power extraction can be achieved through reduced array separation. A comprehensive set of flow measurements was taken during several weeks testing in the FloWave Ocean Energy Research Facility, with different configurations of turbines installed in the tank in a current of 0.8 m/s, to understand the effect that the front turbines have on flow through the array and on the inflow to the centrally placed rearmost turbine. Loads on the turbine structure, rotor, and blade roots were measured along with the rotational speed of the rotor to asses... [more]

The complexity of floating offshore wind turbine (FOWT) systems, with their coupled motions, aero-hydro-servo-elastic dynamics, as well as non-linear system behavior and components, makes modeling and simulation indispensable. To ensure the correct implementation of the multi-physics, the engineering models and codes have to be verified and, subsequently, validated for proving the realistic representation of the real system behavior. Within the IEA (International Energy Agency) Wind Task 23 Subtask 2 offshore code-to-code comparisons have been performed. Based on these studies, using the OC3 phase IV spar-buoy FOWT system, the Modelica for Wind Turbines (MoWiT) library, developed at Fraunhofer IWES, is verified. MoWiT is capable of fully-coupled aero-hydro-servo-elastic simulations of wind turbine systems, onshore, offshore bottom-fixed, or even offshore floating. The hierarchical programing and multibody approach in the object-oriented and equation-based modeling language Modelica hav... [more]

Power system stability is a topic which is attracting considerable interest due to the increase of both electrical demand and distributed variable generation. Since Flexible AC Transmission Systems (FACTS) devices are an increasingly widespread solution to these issues, it is important to study how their allocation procedure should be done. This paper seeks to assess the influence of load share in FACTS devices allocation. Despite this interest, researchers, as well as system planners, have mainly focused on studying single power system configuration rather than using a wider approach. Keeping this in mind, we have iteratively created several load share scenarios based on an IEEE 14-bus test system. Subsequently, we have applied an heuristic procedure in order to demonstrate how load share may affect the results of the FACTS devices allocation procedure. Additionally, we have compared results from two different objective functions so as to evaluate our proposal. Finally, we have propos... [more]