Organic−inorganic perovskites are crystalline light absorbers which are gaining great attraction from the photovoltaic community. Surprisingly, the power conversion efficiencies of these perovskite solar cells have rapidly increased by over 25% in 2019, which is comparable to silicon solar cells. Despite the many advances in efficiency, there are still many areas to be improved to increase the efficiency and stability of commercialization. For commercialization and enhancement of applicability, the development of electron transport layer (ETL) and its interface for low temperature processes and efficient charge transfer are very important. In particular, understanding the ETL and its interface is of utmost importance, and when this understanding has been made enough, excellent research results have been published that can improve the efficiency and stability of the device. Here, we review the progress of perovskite solar cells. Especially we discuss recent important development of pero... [more]

The growing rate of electricity generation from renewables is leading to new operational and management issues on the power grid because the electricity generated exceeds local requirements and the transportation or storage capacities are inadequate. An interesting option that is under investigation by several years is the opportunity to use the renewable electricity surplus to power electrolyzers that split water into its component parts, with the hydrogen being directly injected into natural gas pipelines for both storage and transportation. This innovative approach merges together the concepts of (i) renewable power-to-hydrogen (P2H) and of (ii) hydrogen blending into natural gas networks. The combination of renewable P2H and hydrogen blending into natural gas networks has a huge potential in terms of environmental and social benefits, but it is still facing several barriers that are technological, economic, legislative. In the framework of the new hydrogen strategy for a climate-ne... [more]

“One-pot regeneration”, which is simple regneneration method of ammonia borane (AB) using hydrazine and liquid ammonia, enables conversion of AB from hexagonal boron nitride (h-BN) after milling hydrogenation. Solution 11B-NMR revealed the presence of AB after NH3/N2H4 treatment of milled h-BN (BNH) although the yield of AB was less than 5%. The conversion mechanism was clarified as B-H bonds on the h-BN surface created by ball-milling under hydrogen pressure have an ability to form AB, which was confirmed by Thermogravimetry-Residual Gas Analysis (TG-RGA) and Infrared (IR) analysis. The reaction routes are also the same as regeneration route of polyborazylene because intermediates of AB such as (B(NH2)3 and hydrazine borane were found by solution 11B-NMR after soaking BNH in liquid NH3 and hydrazine, respectively. Because of the fact that all reactions proceed on the h-BN surface and no reaction proceeds when neat h-BN is treated, breaking of B3N3 ring structure and then creation of B... [more]

The relative permeability of coal to gas and water is an essential parameter for characterizing coalbed methane (CBM) reservoirs and predicting coal seam gas production, particularly in numerical simulations. Although a variety of studies related to the relative permeability of coals have been conducted, the results hardly meet the needs of practical engineering applications. To track the dynamic development of relative permeability measurements in the laboratory, discover the deficiencies, and discuss further work in this field, this paper investigates the relative permeability measurement preparation work and laboratory methods and summarizes the development of techniques used to determine the water saturation during experimentation. The previously determined relative permeability curves are also assembled and classified according to coal rank and the absolute permeability. It is found that the general operations in the relative permeability measurement process are still not standard... [more]

The worldwide growing development of PV capacity requires an accurate forecast for a safer and cheaper PV grid penetration. Solar energy variability mainly depends on cloud cover evolution. Thus, relationships between weather variables and forecast uncertainties may be quantified to optimize forecast use. An intraday solar energy forecast algorithm using satellite images is fully described and validated over three years in the Paris (France) area. For all tested horizons (up to 6 h), the method shows a positive forecast skill score compared to persistence (up to 15%) and numerical weather predictions (between 20% and 40%). Different variables, such as the clear-sky index (Kc), solar zenith angle (SZA), surrounding cloud pattern observed by satellites and northern Atlantic weather regimes have been tested as predictors for this forecast method. Results highlighted an increasing absolute error with a decreasing SZA and Kc. Root mean square error (RMSE) is significantly affected by the me... [more]

We present the concept of a novel thermal power plant process in conjunction with low-temperature selective catalytic reduction (SCR). This process can be employed to achieve modern standards for NOx emissions and solve problems related to post-gas cleaning processes, such as thermal fatigue, catalyst damage, and an increase in differential pressure in the boiler. Therefore, this study is aimed at evaluating the performance of a novel flue-gas cleaning process for use in a thermal power plant, where a low-temperature SCR is implemented, along with the existing SCR. We developed a process model for a large-scale power plant, in which the thermal power plant was divided into a series of heat exchanger block models. The mass and energy balances were solved by considering the heat transfer interaction between the hot and cold sides to obtain the properties of each material flow. Using the process model, we performed a simulation of the new process. New optimal operating conditions were der... [more]

Hydrogen can be produced in undesired ways such as a high temperature metal oxidation during an accident. In this case, the hydrogen must be carefully managed. A hydrogen mitigation system (HMS) should be installed to protect a containment of a nuclear power plant (NPP) from hazards of hydrogen produced by an oxidation of the fuel cladding during a severe accident in an NPP. Among hydrogen removal devices, passive auto-catalytic recombiners (PARs) are currently applied to many NPPs because of passive characteristics, such as not requiring a power supply nor an operators’ manipulations. However, they offer several disadvantages, resulting in issues related to hydrogen control by PARs. One of the issues is a hydrogen stratification in which hydrogen is not well-mixed in a compartment due to the high temperature exhaust gas of PARs and accumulation in the lower part. Therefore, experimental simulation on hydrogen stratification phenomenon by PARs is required. When the hydrogen stratificat... [more]

In this paper, hard magnetic materials for future use in electrical machines are discussed. Commercialized permanent magnets used today are presented and new magnets are reviewed shortly. Specifically, the magnetic MnAl compound is investigated as a potential material for future generator designs. Experimental results of synthesized MnAl, carbon-doped MnAl and calculated values for MnAl are compared regarding their energy products. The results show that the experimental energy products are far from the theoretically calculated values with ideal conditions due to microstructure-related reasons. The performance of MnAl in a future permanent magnet (PM) generator is investigated with COMSOL, assuming ideal conditions. Simplifications, such as using an ideal hysteresis loop based on measured and calculated saturation magnetization values were done for the COMSOL simulation. The results are compared to those for a ferrite magnet and an NdFeB magnet. For an ideal MnAl hysteresis loop, it wou... [more]

Stringent exhaust emission and fuel consumption regulations impose the need for new solutions for further development of internal combustion engines. With this in mind, a refined control of the combustion process in each cylinder can represent a useful and affordable way to limit cycle-to-cycle and cylinder-to-cylinder variation reducing CO2 emission. In this paper, a twin-cylinder turbocharged Port Fuel Injection−Spark Ignition engine is experimentally and numerically characterized under different operating conditions in order to investigate the influence of cycle-to-cycle variation and cylinder-to-cylinder variability on the combustion and performance. Significant differences in the combustion behavior between cylinders were found, mainly due to a non-uniform effective in-cylinder air/fuel (A/F) ratio. For each cylinder, the coefficients of variation (CoVs) of selected combustion parameters are used to quantify the cyclic dispersion. Experimental-derived CoV correlations representati... [more]

The modular multilevel matrix converter is a relatively new power converter topology suitable for high-power alternating current (AC)-to-AC applications. Several publications in the literature have highlighted the converter capabilities, such as full modularity, fault-redundancy, control flexibility and input/output power quality. However, the topology and control of this converter are relatively complex to realise, considering that the converter has a large number of power-cells and floating capacitors. To the best of the authors’ knowledge, there are no review papers where the applications of the modular multilevel matrix converter are discussed. Hence, this paper aims to provide a comprehensive review of the state-of-the-art of the modular multilevel matrix converter, focusing on implementation issues and applications. Guidelines to dimensioning the key components of this converter are described and compared to other modular multilevel topologies, highlighting the versatility and co... [more]

Controversy exists as to whether renewable energy (RE) can provide for all the world’s energy needs. The purpose of this paper is to help resolve this vital question. Official forecasts see a resumption of a business-as-usual world after the pandemic-induced recession, with further economic growth out to at least 2050. The novel approach taken in this paper is to assume that such a world is fueled entirely with RE at global energy levels at or above those of today, and then to examine whether this scenario is feasible. Because the intermittent primary electricity sources, wind, and solar power, would have to supply nearly all this energy, a simplification made for this analysis is that they do supply 100% of all energy, including non-electrical energy needs. It is found that the energy that could be delivered by these two sources is much less than often assumed, for several reasons: The declining quality of inputs; the need for inclusion of uncounted environmental costs; the need for e... [more]

Declining costs for high-performance batteries are leading to a global increased use of storage systems in residential buildings. Especially in conjunction with reduced photovoltaic (PV) feed-in tariffs, a large market has been developed for PV battery systems to increase self-sufficiency. They differ in the type of coupling between PV and battery, the nominal capacities of their components, and their degree of integration. High system performance is particularly important to achieve profitability for the operator. This paper presents and evaluates methods for a uniform determination of PV battery system performance. Already the requirement analysis reveals that a performance comparison of PV battery systems must cover the efficiency and effectiveness during system operation. A method based on a derivation of key performance indicators (KPIs) for these two criteria through an application test is proposed. It is evaluated by comparison to other methods, such as the System Performance In... [more]

Optimization-based methods are of interest for developing energy management strategies due to their high performance for hybrid electric vehicles. However, these methods are often complicated and may require strong computational efforts, which can prevent them from real-world applications. This paper proposes a novel real-time optimization-based torque distribution strategy for a parallel hybrid truck. The strategy aims to minimize the engine fuel consumption while ensuring battery charge-sustaining by using linear quadratic regulation in a closed-loop control scheme. Furthermore, by reformulating the problem, the obtained strategy does not require the information of the engine efficiency map like the previous works in literature. The obtained strategy is simple, straightforward, and therefore easy to be implemented in real-time platforms. The proposed method is evaluated via simulation by comparison to dynamic programming as a benchmark. Furthermore, the real-time ability of the propo... [more]

The biomass combustion process is inevitably accompanied by the emission of pollutant gasses. This paper gives a comprehensive analysis of the external variables and combustion products of the biomass plant. The analyzed data were collected from 18 MWt boiler in combined heat and power plant Sremska Mitrovica over a period of four months. The correlations between the recorded data were determined using a unique methodology, which is based on association rule mining. The results of the study can be further used for the reduction of the harmful combustion products, as well as for the optimization of the operation process.

This paper presents a numerical investigation of the ignition and combustion process of a primary reference fuel in a partially premixed light-duty internal combustion (PPC) engine. Partially pre-mixed combustion is achieved by employing a multiple injection strategy with three short injection events of fuel pulses. The timing of the first two fuel pulses, 48 and 22 crank angle degrees before top dead center, are chosen with the purpose to stratify the fuel and air charge, whereas the third injection, at five crank angle degrees before top dead center, serves as an actuator of the main heat release. In addition to this baseline injection, three alternative injection strategies are studied, including a split-fuel two-injection strategy and modified triple-injection strategies. Large eddy simulations are employed utilizing a skeletal chemical kinetic mechanism for primary reference fuel capable of capturing the low-temperature ignition and the high temperature combustion. The large eddy... [more]

The weakening of hard coal−rock mass is the core common problem that is involved in the top coal weakening in hard and thick coal seams, the hard roof control during the initial mining stage in the longwall mining face, and the hanging roof control in the gob of non-coal mine. Based on the characteristics of pulse hydraulic fracturing and constant pumping rate hydraulic fracturing, a weakening method for hard coal−rock mass by combining pre-pulse and constant pumping rate hydraulic fracturing is proposed. A complete set of equipment for the combined pulse and constant pumping rate hydraulic fracturing construction in the underground coal mine is developed. The pulse and constant pumping rate hydraulic fracturing technology and equipment were applied in the top coal weakening of the shallow buried thick coal seam. Compared with no weakening measures for top coal, the average block size of the top coal caving was reduced by 42% after top coal hydraulic fracturing. The recovery rate of th... [more]

The internet of things (IoT) manages a large infrastructure of web-enabled smart devices, small devices that use embedded systems, such as processors, sensors, and communication hardware to collect, send, and elaborate on data acquired from their environment. Thus, from a practical point of view, such devices are composed of power-efficient storage, scalable, and lightweight nodes needing power and batteries to operate. From the above reason, it appears clear that energy harvesting plays an important role in increasing the efficiency and lifetime of IoT devices. Moreover, from acquiring energy by the surrounding operational environment, energy harvesting is important to make the IoT device network more sustainable from the environmental point of view. Different state-of-the-art energy harvesters based on mechanical, aeroelastic, wind, solar, radiofrequency, and pyroelectric mechanisms are discussed in this review article. To reduce the power consumption of the batteries, a vital role i... [more]

The grid integration of large scale photovoltaic (PV) power plants represents many challenging tasks for system stability, reliability and power quality due to the intermittent nature of solar radiation and the site accessibility issues where most PV power plants are located over a wide area. In order to enable real-time monitoring and control of large scale PV power plants, reliable two-way communications with low latency are required which provide accurate information for the electrical and environmental parameters as well as enabling the system operator to evaluate the overall performance and identify any abnormal conditions and faults. This work aims to design a communication network architecture for the remote monitoring of large-scale PV power plants based on the IEC 61850 Standard. The proposed architecture consists of three layers: the PV power system layer, the communication network layer, and the application layer. The PV power system layer consists of solar arrays, inverters... [more]

One of the main methods used to generate thermal energy is the combustion process. Burners are used in both industrial and residential applications of the open combustion process. The use of fuels that reduce polluting gas emissions and costs in industrial and residential processes is currently a topic of significant interest. Hydrogen is considered an attractive fuel for application in combustion systems due to its high energy density, wide flammability range, and only produces water vapor as waste. Compared to research conducted regarding hydrocarbon combustion, studies on hydrogen burners have been limited. This paper presents the design and evaluation of an oxyhydrogen gas burner for the atmospheric combustion process. The gas is generated in situ with an alkaline electrolyzer with a production rate of up to 3 sL min−1. The thermal efficiency of a gas burner is defined as the percentage of the input thermal energy transferred to the desired load with respect to a given time interva... [more]

The zero-energy building (ZEB) concept has a high potential for securing energy savings in the building sector. To achieve ZEB, various active systems, including renewable systems such as photovoltaic, solar heating, and geothermal systems, have been developed. However, the existing systems are costly or not optimized. To overcome these issues, the authors previously developed an integrated tri-generation system. In this research, the previously developed system was comprehensively analyzed considering the indoor thermal comfort and energy efficiency to develop a design and operation method for the integrated system. Two different heating systems (convective heating and radiant floor heating) were employed in the tri-generation system, and their system performance, predicted mean vote (PMV), and predicted percentage of dissatisfied (PPD) were compared using simulations. The results showed that the heating coefficient of power of the radiant floor heating system was 18.8% higher than th... [more]

Offshore oil multi-platform interconnected power system is developing rapidly. The proposal of an effective economic evaluation method that fits the actual production situation of offshore oilfields is very meaningful for the planning and construction of multi-platform interconnected power systems. This article proposes the electric depreciation, depletion, and amortization (DD&A) barrel oil cost S and maximum expected benefit per unit power generation Ie as economic indicators, considering the actual production characteristics and life cycle of the oil field. In order to build a complete economic evaluation system, this article also introduces the N−1 pass rate ηN−1, voltage qualification rate γ, power supply reliability ASAI (Average Service Availability Index), and other reliability indicators to evaluate the offshore power system. When calculating the weight of the indicators, analytic hierarchy method (AHP) was applied to calculate subjective weights, and an entropy method was app... [more]

This paper presents a multiagent system (MAS) day-ahead co-operation framework between renewable energy resources (RESs) and Battery Energy Storage Systems (BESSs) owned by different stakeholders. BESSs offer their storage services to RESs by shifting RES power to sell it during profitable peak-hours (aka; time-shifting). The MAS framework consists of three phases. Phase-one is a pre-auction phase that defines the maximum charging and discharging BESS power limits. These limits guarantee a reliable distribution system operation without violating the buses’ voltage limits or the ampacity of the branches. Phase-two is an auctioning phase between the BESS-agents and the RES-agents. Each agent has a different owner with a specific profit agenda and risk levels. The agent tries to maximize the profit potential of the owner. The agents use historical trade data and expected weather conditions to maximize profitability. Phase-three is called the post-auctioning phase, in which the agreement b... [more]

This study investigates the frequency−temperature relations between the phase angle φ and admittance Y for composites of cellulose, synthetic ester, and water nanoparticles. We determined the activation energy value for the relaxation time of a phase shift angle ΔWφ ≈ (0.783 ± 0.0744) eV, which was related to the shift of φ(f) waveforms in higher frequency area with increasing temperature. We found that the position of admittance frequency waveforms in double logarithmic coordinates was simultaneously influenced by the temperature dependence of admittance and its relaxation time. Activation energy values for the relaxation time of admittance ΔWτ ≈ (0.796 ± 0.0139) eV and the activation energy value of admittance ∆WY ≈ (0.800 ± 0.0162) eV were determined. It was found that all three activation energy values were identical and their average was ΔW ≈ (0.793 ± 0.0453) eV. Impregnation with synthetic ester resulted in a decrease of activation energy by 0.26 eV compared to the impregnation w... [more]

The proliferation of solar power systems could cause instability within existing power grids due to the variable nature of solar power. A well-defined statistical model is important for managing the supply-and-demand dynamics of a power system that contains a significant variable renewable energy component. It is furthermore important to consider the inherent uncertainty in the data when modeling such a complex power system. Gaussian process regression has the potential to address both of these concerns: the probabilistic modeling of solar radiation data could assist in managing the variability of solar power, as well as provide a mechanism to deal with uncertainty. In this paper, solar radiation data was obtained from the Southern African Universities Radiometric Network and used to train a Gaussian process regression model which was developed especially for this purpose. Attention was given to constructing an appropriate Gaussian process kernel. It was found that a carefully construc... [more]

The cost of solar PV has been reduced to a level such that the levelized cost of solar electricity is either cheaper or competitive relative to the grid electricity. So, a low-cost integration of solar PV with grid can be a cost-effective solution for clean cooking. The usual technique of using grid-tied inverters contribute ~20% towards the energy cost. The proposed system incorporates a control circuit that connects grid electricity to the solar PV via a DC link and provides a DC output eliminating the requirement of grid-tied inverters. Most of the cooking utensils either have a resistive heating element or an electronic control circuit that is insensitive to input AC or DC and no modification is needed for the cooking utensils while using with DC voltage. In the proposed system, preference for power delivery is always given to the solar PV and the grid effectively operates as the backup for the system when solar PV output fluctuates due to varying weather and climatic conditions. A... [more]