Energies — Open Access Journal

In the Internet of Things (IoT)-supported energy data management infrastructure, objects from various energy generation and consumption terminals in buildings produce a tremendous amount of data. However, this data is not useful unless it is available on-time for services that discover meaningful information in order to provide intelligent decisions. The microservices-based data caching, data virtualization, data processing, data analysis, and data ingestion methods can be applied to enhance the data availability for energy efficiency management services provision across buildings. To foster building energy efficiency management services (BEEMS), Web of Objects (WoO) provides data abstraction, aggregation, and ingestion mechanism with virtual objects (VOs) and composite virtual objects (CVOs) by using ontologies and availability and scalability of services with microservices. This article proposes the use of data processing microservices modeling to enhance data availability and expose services capabilities with microservices for BEEMS. We present a semantic web agent based on an ontology for linking, enhancement, reusability, and availability of data-objects, services, and microservices. For the evaluation, we present a use case, which includes heterogeneous data collection and processing and provision of various BEEMS. A prototype for the use case scenario has been built and the results have been evaluated in the laboratory to mimic the enhanced data availability for BEEMS. Full article

The data-driven method is an important tool in the field of underwater acoustic signal processing. In order to realize the feature extraction of ship-radiated noise (S-RN), we proposed a data-driven optimization method called improved variational mode decomposition (IVMD). IVMD, as an improved method of variational mode decomposition (VMD), solved the problem of choosing decomposition layers for VMD by using a frequency-aided method. Furthermore, a novel method of feature extraction for S-RN, which combines IVMD and sample entropy (SE), is put forward in this paper. In this study, four types of S-RN signals are decomposed into a group of intrinsic mode functions (IMFs) by IVMD. Then, SEs of all IMFs are calculated. SEs are different in the maximum energy IMFs (EIMFs), thus, SE of the EIMF is seen as a novel feature for S-RN. To verify the effectiveness of the proposed method, a comparison has been conducted by comparing features of center frequency and SE of the EIMF by IVMD, empirical mode decomposition (EMD) and ensemble EMD (EEMD). The analysis results show that the feature of S-RN can be obtain efficiently and accurately by using the proposed method. Full article

The extraction of the photovoltaic (PV) model parameters remains to this day a long-standing and popular research topic. Numerous methods are available in the literature, widely differing in accuracy, complexity, applicability, and their very nature. This paper focuses on the class of non-iterative parameter extraction methods and is limited to the single-diode PV model. These approaches consist of a few straightforward calculation steps that do not involve iterations; they are generally simple and easy to implement but exhibit moderate accuracy. Seventeen such methods are reviewed, implemented, and evaluated on a dataset of more than one million measured I-V curves of six different PV technologies provided by the National Renewable Energy Laboratories (NREL). A comprehensive comparative assessment takes place to evaluate these alternatives in terms of accuracy, robustness, calculation cost, and applicability to different PV technologies. For the first time, the irregularities found in the extracted parameters (negative or complex values) and the execution failures of these methods are recorded and are used as an assessment criterion. This comprehensive and up-to-date literature review will serve as a useful tool for researchers and engineers in selecting the appropriate parameter extraction method for their application. Full article

By integrating an Absorption Refrigerator (AR), a new hybrid system model is established to reuse the waste heat from a Molten Carbonate Direct Carbon Fuel Cell (MCDCFC) for additional cooling production. Various irreversible losses in each element of the system are numerically described. The operating current density span of the MCDCFC that allows the AR to work is derived. Under different operating conditions, the mathematical expressions for equivalently evaluating the hybrid system performance are derived. In comparison with the stand-alone MCDCFC, the maximum attainable power density of the proposed system and its corresponding efficiency are increased by 5.8% and 6.8%, respectively. The generic performance features and optimum operating regions of the proposed system are demonstrated. A number of sensitivity analyses are performed to study the dependences of the proposed system performance on some physical parameters and operating conditions such as operating temperature, operating current density, and pressure of the MCDCFC, cyclic working fluid internal irreversibility inside the AR, thermodynamic losses related parameters and the anode thickness of the MCDCFC. The obtained results may offer some new insights into the performance improvement of an MCDCFC through a reasonable heat management methodology. Full article

In this paper, an innovative modeling approach for Li-ion battery packs is proposed by considering intrinsic cell unbalances and packaging elements. The proposed modeling method shows that the accurate battery pack model can be achieved if the overall influences of intrinsic cell unbalances and packaging elements are taken account. Concurrently, the proposed method takes a practical model structure, resulting in the reduction of computational burden in a battery management system. Furthermore, because the proposed method utilizes cell information without a manufactured battery pack, it can be helpful to design optimal battery packs. The proposed method is verified through simulation and experimental results of the Li-ion battery pack along with the battery cycler. In three test profiles, the mean absolute percentage errors and root mean square errors of the proposed pack model do not exceed 0.5% and 0.07 V, respectively. Full article

With the increasing consumption of fossil energy and changes in the ecological environment, meeting the energy demands required for industrial and economic development with clean and efficient power generation is a major challenge of our society. Solar energy is considered to be one of the most renewable and sustainable energy sources, and photovoltaic power generation has become an important research topic. This study combines data envelopment analysis (DEA) with Tobit regression analysis to assess the efficiency of photovoltaic power generation in China and analyze factors affecting efficiency to improve the efficiency of photovoltaic power generation. The results show that there are obvious regional differences in photovoltaic power generation efficiency in China. The phenomenon of focusing on economic development at the expense of the use of solar power generation still exists. The establishment of photovoltaic demonstration projects, the implementation of differential electricity price policies, and the promotion of photovoltaic precision poverty alleviation can alleviate economic pressure and effectively improve the efficiency of photovoltaic power generation. Full article

After the recent renewed interest in CO₂ as the refrigerant (R744) for the food retail industry, many researchers have focused on the performance enhancement of the basic transcritical R744 supermarket refrigeration unit in warm climates. This task is generally fulfilled with the aid of energy-based methods. However, the implementation of an advanced exergy analysis is mandatory to properly evaluate the best strategies needing to be implemented to achieve the greatest thermodynamic performance improvements. Such an assessment, in fact, is widely recognized as the most powerful thermodynamic tool for this purpose. In this work, the advanced exergy analysis was applied to a conventional R744 booster supermarket refrigerating system at the outdoor temperature of 40 °C. The results obtained suggested the adoption of a more sophisticated layout, i.e. the one outfitted with the multi-ejector block. It was found that the multi-ejector supported CO₂ system can reduce the total exergy destruction rate by about 39% in comparison with the conventional booster unit. Additionally, the total avoidable exergy destruction rate was decreased from 67.60 to 45.57 kW as well as the total unavoidable exergy destruction rate was brought from 42.67 down to 21.91 kW. Full article

The characterization of a spectrum splitter of both hot and cold mirror, type TechSpec AOI 50.0, using a 50-Watt halogen bulb light has been done. Both the bulb spectrum, prior to and after spectrum splitting, are described in this study to see the degradation of radiation that occurs because partial energy is absorbed by the splitter. This characterization plays an important role in determining the best position of a photovoltaic (PV) and thermoelectric generator (TEG) in a PV-TEG system. The light spectrum was recorded using mini USB spectrometer hardware and Spectragryph version 1.2.8 software as optical spectroscopic software that displays light records coming with wavelength (nm) on the x-axis and light spectrum intensity in arbitrary units (a.u.) on the y-axis. The measurement results show that the light intensity in the visible light region (300–750) nm is more dominant than the intensity in infrared light (>750 nm), so that the PV placement is preferred over TEG. Furthermore, with a cold mirror, PV is more suitable if placed in a position to receive reflected light, while using a hot mirror is more suitable in the position transmitted light. For TEG, it is placed in a position opposite to PV. As a result, the maximum intensity of the PV light spectrum with cold mirrors is 46.52 a.u at a wavelength of 479.6 nm, while with hot mirrors it is 42.07 a.u with a 457.6 nm wavelength. It can be concluded that the value of the light intensity with a cold mirror is better than that with a hot mirror on the visible light (Vis) spectrum, and the current and voltage are equivalent to the results of the radiation energy area. It was proven that the maximum total output of a hybrid PV-TEG system with Cold Mirror is greater than that with Hot Mirror (100.53 > 68.77) × 10⁻³ µW. Based on the result of this study, it is recommended that further research can be conducted to increase radiation energy and output power in TEG. Full article

This paper presents the system analysis and the techno-economic assessment of selected solar hydrogen production paths based on thermochemical cycles. The analyzed solar technology is Concentrated Solar Power (CSP). Solar energy is used in order to run a two-step thermochemical cycle based on two different red-ox materials, namely nickel-ferrite and cerium dioxide (ceria). Firstly, a flexible mathematical model has been implemented to design and to operate the system. The tool is able to perform annual yield calculations based on hourly meteorological data. Secondly, a sensitivity analysis over key-design and operational techno-economic parameters has been carried out. The main outcomes are presented and critically discussed. The technical comparison of nickel-ferrite and ceria cycles showed that the integration of a large number of reactors can be optimized by considering a suitable time displacement among the activation of the single reactors working in parallel. In addition the comparison demonstrated that ceria achieves higher efficiency than nickel-ferrite (13.4% instead 6.4%), mainly because of the different kinetics. This difference leads to a lower LCOH for ceria (13.06 €/kg and 6.68 €/kg in the base case and in the best case scenario, respectively). Full article

A better design of gas supply chains may lead to a more efficient use of locally available resources, cost savings, higher energy efficiency and lower impact on the environment. In optimizing the supply chain of liquefied natural gas (LNG), compressed natural gas (CNG) or biogas for smaller regions, the task is to find the best supplier and the most efficient way to transport the gas to the customers to cover their demands, including the design of pipeline networks, truck transportation and storage systems. The analysis also has to consider supporting facilities, such as gasification units, truck loading lines and CNG tanking and filling stations. In this work a mathematical model of a gas supply chain is developed, where gas may be supplied by pipeline, as compressed gas in containers or as LNG by tank trucks, with the goal to find the solution that corresponds to lowest overall costs. In order to efficiently solve the combinatorial optimization problem, it is linearized and tacked by mixed integer linear programming. The resulting model is flexible and can easily be adapted to tackle local supply chain problems with multiple gas sources and distributed consumers of very different energy demands. The model is illustrated by applying it on a local gas distribution problem in western Finland. The dependence of the optimal supply chain on the conditions is demonstrated by a sensitivity analysis, which reveals how the model can be used to evaluate different aspects of the resulting supply chains. Full article

In order for electrolysis cells to operate optimally, mass transport must be improved. The key initial component for optimal operation is the current collector, which is also essential for mass transport. Water as an educt of the reaction must be evenly distributed by the current collector to the membrane electrode assembly. As products of the reaction, hydrogen and oxygen must also be directed quickly and efficiently through the current collector into the channel and removed from the cell. The second key component is the stoichiometry, which includes the current density and water volume flow rate and represents the ratio between the water supplied and water consumed. This study presents the correlation of the stoichiometry, two-phase flow in the channel and gas fraction in the porous transport layer for the first time. The gas-water ratio in the channel and porous transport layer during cell operation with various stoichiometries was investigated by means of a model in the form of an ex situ cell without electrochemical processes. Bubble formation in the channel was observed using a transparent cell. The gas-water exchange in the porous transport layer was then investigated using neutron radiography. Full article

Techno-economic, social, and environmental factors influence a large part of society, predominantly in developing countries. Due to energy poverty and bloating populations, developing countries like India are striving to meet the energy balance. One initiative of India to achieve the country’s Renewable Energy Target (RET) is the setting up of the National Solar Mission (NSM) to meet a target of 175 GW (non-hydro) by the year 2022. Prioritizing Renewable Energy (RE) utilization to achieve techno-economic balance is India’s primary objective and creating a positive environmental impact is a bonus. In this study, various scenarios are explored by investigating the techno-economic and environmental impact on RE adoption for a small community in India by optimally sizing the Hybrid Renewable Energy System (HRES). This study is an exemplar in understanding and exploring RE utilization, whilst examining the recent RE market in depth and exploring the advantages and disadvantages of the current RE situation by initiating it in a smaller community. Improved Hybrid Optimization using Genetic Algorithm (iHOGA) PRO+ software, (Version 2.4 -Pro+ , Created by Dr Rodolfo Dufo López, University Zaragoza (Spain)) is used to size the RE systems. The results are categorized using triple bottom line analysis (TBL analysis) and for different scenarios, the techno-economic, environmental, and social merits are weighed upon. The probable hurdles that India has to surpass to achieve easy RE adoption are also discussed in this work. The influential merits for analyzing the TBL for a real-time scenario are Net Present Cost (NPC), Carbon-di-oxide (CO₂) emissions, and job criteria. Compared to Hybrid Optimization of Multiple Energy Resources (HOMER) software, iHOGA remains less explored in the literature, specifically for the grid-connected systems. The current study provides a feasibility analysis of grid-connected RE systems for the desired location. iHOGA software simulated 15 sets of results for different values of loads considered and various acquisition costs of HRES. At least 70% of RE can be penetrated for the Aralvaimozhi community with the lowest value of NPC of the HRES. From the TBL analysis conducted, integrating HRES into a micro-grid for the community would result in mitigating CO₂ emissions and provide job opportunities to the local community; although, the economic impact should be minimized if the acquisition costs of the HRES are reduced, as has been established through this study. Full article

The article presents the results of experimental and numerical investigation of turbulent premixed methane flames diluted by carbon dioxide (up to 30%) at atmospheric and elevated pressures (up to 0.5 MPa). The study included the influence of fuel properties and operation parameters on the emission of NO_x and CO as well as flame properties. The investigation has been prepared for two combustion system configurations (axisymmetric flames and flames supported by a pilot flame) in a wide range of air/fuel equivalence ratios (ϕ = 0.42 ÷ 0.85). It has been reported that reduction of NO_x emission by CO₂ fuel dilution reached a level of up to 45% in atmospheric conditions and 30% at elevated pressure, decreasing with a drop in the equivalence ratio. The results have shown influence of pressure on NO_x composition, where for pressurized tests, NO₂ was doubled compared to atmospheric tests. Carbon monoxide emission rises with CO₂ content in the fuel as a result of thermal dissociation, but this phenomenon is mitigated by a pressure increase. Planar laser induced fluorescence (PLIF) study has shown that flame length decreases with an increase in pressure and CO₂ content in the fuel. Fuel staging increased NO_x emission, especially for richer flames (ϕ > 0.6) at low pressure, while CO increased in the whole range of equivalence ratios. Full article

In a commercial building, a significant amount of energy is used by the ventilation systems to condition the air for the ‎indoor environments to satisfy the required quantity (temperature ‎and humidity) and quality (amount of fresh air). For many years, Variable Air Volume ‎‎(VAV) systems have been considered as the most efficient solutions by balancing the airflow volume based on the demand making them energy efficient when compared with the traditional Constant Air Volume (CAV) systems. However, the setpoints in VAV systems are ‎often misread by the sensors due to stratification and formation of pollutant pockets and ‎responding to design levels that overestimate the real-time demand conditions, which result in ‎waste of energy, thermal discomfort and unhealthy air. In general, VAV devices are expensive, complicated and prone to failures and ‎they are used only in medium and large projects. More recently, new technologies have evolved to solve this issue. In one of the new solutions, VAV motors terminals are replaced with flaps which are simpler and less expensive thus, they can be implemented ‎in a wider range of projects. In systems, balancing and supplying the optimal airflow ‎to reduce the energy consumption while delivering ideal thermal and Indoor Air Quality (IAQ) levels are the ‎main challenges. In this paper, a comparison of the recent technologies with traditional VAV systems is presented to be used as a guild line for researchers and designers in the field of Heating Ventilation Air Conditioning (HVAC)‎. Full article

This work reports the synthesis of N-doped porous carbon (NPC) with a high surface area from Sargassum spp. as a low-cost alternative for electrocatalyst production for the oxygen reduction reaction (ORR). Sargassum spp. was activated with potassium hydroxide at different temperatures (700, 750, and 800 °C) and then doped with pyridine (N700, N750, and N800). As a result of the activation process, the 800 °C sample showed a high surface area (2765 m² g⁻¹) and good onset potential (0.870 V) and current density (4.87 mA cm⁻²). The ORR performance of the electrocatalysts in terms of their current density was N800 > N750 > N700 > 750 > 800 > 700, while the onset potential decreased in the following order: N800 > 800 > 750 > 700 > N700 > N750. The fuel cell performance of the membrane electrode assembly (MEA) prepared with electrocatalyst synthesized at 750 °C and doped with pyridine was 12.72 mW cm⁻², which was close to that from Pt/C MEA on both the anode and cathode (14.42 mW cm⁻²). These results indicate that NPCs are an alternative to the problem of Sargassum spp. accumulation in the Caribbean due to their high efficiency as electrocatalysts for ORR. Full article

Nowadays, the integration of photovoltaic (PV) systems into the grid involves new and competitive ways to realize this. Thus, it is necessary to define procedures that not only include energy calculations but also incorporate economic and funding feasibility features. According to the literature review, there are numerous tools that are available to carry out a profitability analysis of a photovoltaic system. However, certain shortcomings have been identified, either in the definition of the economic and financial scenarios or in the results obtained, as they do not provide all the necessary information, do not use all the most common economic criteria, or in some cases the complexity and training requirements for their correct implementation may discourage their use. Therefore, in this paper a complete procedure that can be used as a preliminary decision tool prior to the design of an in-depth PV self-consumption system is proposed. Realistic input data makes it possible to not only obtain results for common economic and financial feasibility criteria (Net Present Value, Internal Rate of Return, Discounted Pay-Back Time and Net Cash Balance), but it also allow for a cost-competitiveness evaluation based on the Levelised Cost of Electricity (LCOE). The novel concept of the direct cost of PV self-consumed electricity is also introduced. Full article

The scope of this study is to assess how different energy efficient renovation strategies affect the environmental impacts of a multi-family house in a Nordic climate within district heating systems. The European Union has set ambitious targets to reduce energy use and greenhouse gas emissions by the year 2030. There is special attention on reducing the life cycle emissions in the buildings sector. However, the focus has often been on new buildings, although existing buildings represent great potential within the building stock in Europe. In this study, four different renovation scenarios were analyzed with the commercially available life cycle assessment software that follows the European Committee for Standardization (CEN) standard. This study covers all life cycle steps from the cradle to the grave for a residential building in Borlänge, Sweden, where renewable energy dominates. The four scenarios included reduced indoor temperature, improved thermal properties of building material components and heat recovery for the ventilation system. One finding is that changing installations gives an environmental impact comparable to renovations that include both ventilation and building facilities. In addition, the life cycle steps that have the greatest environmental impact in all scenarios are the operational energy use and the building and installation processes. Renovation measures had a major impact on energy use due to the cold climate and low solar irradiation in the heating season. An interesting aspect, however, is that the building materials and the construction processes gave a significant amount of environmental impact. Full article

This paper presents the reliability evaluation for a microgrid composed of conventional generators (CGs), a photovoltaic (PV) system, and a small hydropower plant (HPP). The PV system has an intermittent output and the HPP output is limited depending on several constraints. Therefore, their reliability evaluation should be performed according to the CGs. This paper proposes a methodology to evaluate the reliability of the microgrid based on Monte Carlo simulations. To this end, a simple operational strategy for the HPP and reliability models for each component of the grid are introduced. By the operational strategy consisting of two stages, the HPP would be operated to generate power whenever water stored in the reservoir exceeds a certain threshold (called volume reference) or to discharge extra water when it is beyond the maximum volume of the reservoir. To demonstrate the proposed methodology, a case study is performed according to various volume references, and the results are obtained in terms of several reliability indices. Further, the appropriate volume reference is determined considering a trade-off relationship between the reliability and economics aspects. Full article

As a critical infrastructure, the modern electrical network is faced with various types of threats, such as accidental natural disaster attacks and deliberate artificial attacks, thus the power system fortification has attracted great concerns in the community of academic, industry, and military. Nevertheless, the attacker is commonly assumed to be capable of accessing all information in the literature (e.g., network configuration and defensive plan are explicitly provided to the attacker), which might always be the truth since the grid data access permission is usually restricted. In this paper, the information asymmetry between defender and attacker is investigated, leading to an optimal deception strategy problem for power system fortification. Both the proposed deception and traditional protection strategies are formulated as a tri-level mixed-integer linear programming (MILP) problem and solved via two-stage robust optimization (RO) framework and the column-and-constraint generation (CCG) algorithm. Comprehensive case studies on the 6-bus system and IEEE 57-bus system are implemented to reveal the difference between these two strategies and identify the significance of information deception. Numerical results indicate that deception strategy is superior to protection strategy. In addition, detailed discussions on the performance evaluation and convergence analysis are presented as well. Full article