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Two-phase closed thermosyphon heat exchangers (TPCTs) have considerable potential for use in ground source heat pump systems. This paper proposes a new metal-polyethylene TPCT that uses water as the working fluid and is composed of a galvanized steel pipe and a polyethylene pipe. The heat transfer rate characteristics of the metal-polyethylene TPCT were studied using a constant-temperature water bath test bench. The experimental results show that the metal-polyethylene TPCT has the best heat transfer rate when the vacuum degree and filling ratio are 1.00 kPa and 12.5%, respectively. The average heat transfer rate increased as the temperature of the heat source and the flow rate of the cooling water increased. Finally, a sandbox test bench was built, which provided seepage and non-seepage experimental conditions for the metal-polyethylene TPCT. In the sandbox experiment, the heat transfer rate capacity of the metal-polyethylene TPCT was initially studied and compared with that of a single U-tube heat exchanger, and the heat transfer rates were similar. When the evaporation section length was 0.5 m, the heat transfer rates were 34.89 W/m and 111.75 W/m under non-seepage and seepage conditions, respectively. The experimental results show that the metal-polyethylene TPCT is feasible as a new type of ground heat exchanger.

Tidal stream turbines (TST) deployed in open-water energetic sites are often unintentionally at yaw to the incoming flow that causes performance degradation and deflection of the wake. Wake steering is a popular concept in wind arrays where the upstream turbine is operated intentionally at yaw to steer the wake away from a downstream turbine. To explore such arrangements for TST arrays, a synergistic experimental and numerical campaign was undertaken to characterize a TST performance and wake deflection subjected to ±15° yawed inflow. The near-wake characterization study was performed using complementary acoustic Doppler velocimetry measurements and 3D computational fluid dynamics. The experiments show a ∼10% reduction in the maximum power coefficient. In the near field, the deflected wake morphed into an elliptical shape due to the formation of two counter-rotating vortices. The wake deflection results in enhanced momentum transfer and dissipation, leading to accelerated energy recovery. When the upstream turbine is yawed, available kinetic energy in the flow for the downstream turbine is at least 50% higher with the turbine array in a staggered configuration compared to the inline configuration. Our results provide guidance in reducing the cross-stream and downstream spacing between turbine units in an array.

Catalytic processes play an important role in the valorization of biomass for the production of biofuels. In this context, the effect of desilication of MOR zeolite (H-MOR-D) on the esterification of oleic acid as a model reaction for biomass conversion was investigated. Zeolite catalysts were characterized by BET, TG, NH3-TPD, XRD, XRF, FTIR and 27Al MAS NMR analysis and the results showed that the alkaline treatment caused a decrease in crystallinity and removal of sites with greater acid strength of the zeolite precursor. The conversion of oleic acid into methyl oleate catalyzed by H-MOR was less (44%) than that obtained by the treated zeolite H-MOR-D (70%), suggesting that the catalytic activity in the MOR structure does not depend only on the high density of strong acid sites. DFT calculations showed that, bulky molecules suffer molecular distortions within the confined voids, consequently the adsorption enthalpy is highly unstable limiting the formation of intermediates and thus contributing to the lower reaction rate observed experimentally in H-MOR zeolite. Desilication should be considered in projects for the synthesis of new catalysts type zeolite for the conversion of biomass crude or pre-treated, in which bulky molecules prevail.

The viability of the store-on grid (SoG) scheme model across 13 selected Sub-Saharan African (SSA) countries was investigated. The individual country's datasets applicable to the SoG scheme and a typical industrial building as a baseline prosumer were used in the evaluation. Two SoG scheme scenarios (A and B) based on solar photovoltaic (PV) module prices were used in this analysis. The electricity tariffs under the SoG scheme were compared with the time of use rates for the selected SSA countries. The analysis results revealed that the scheme could be viable in only nine and four out of 13 countries under scenario A and scenario B, respectively, with high lending interest rate in some countries being the key hindrance. Under the SoG scheme model, solar PV systems in all the selected countries could feed about 15.65–39.25% of the generated energy to the grid. The government tax in the range of 1.95–3.38 and 2.48–4.31 c$/kWh could be collected from the energy fed to the grid under SoG scheme scenario A and scenario B, respectively. Overall, the SoG scheme exhibits greater potential as an energy business model to foster rooftop solar PV technology adoption in developing countries.

A barium-modified zeolite (Ba-ZEL) catalyst was developed via co-precipitation technique followed by thermal treatment (calcination) at different temperatures (600, 700 and 800 °C). The thermal stability, elemental composition, surface functional groups, crystallographic structure, textural characteristics, basic strength and surface morphology of the Ba-ZEL catalyst were determined using TGA/DTA, EDX, FTIR, XRD, BET, CO2-TPD and SEM techniques, respectively. The biodiesel production process conditions, such as catalyst loading, alcohol to oil ratio, temperature and time, were optimized using a central composite design approach. The Ba-ZEL composite calcined at 700 °C was selected as a representative catalyst due to its high activity for the waste frying oil (WFO) conversion, resulting in a maximum biodiesel yield of 93.17 ± 0.02% under optimum conditions (3.0 wt% catalyst loading, 12:1 methanol to WFO ratio, 65.38 °C reaction temperature and 2 h reaction time). The produced biodiesel, which was characterized by the FTIR and GC-FID analyses, contained sufficient ester groups and was in accordance with the specifications of EN 14214. Additionally, its physicochemical properties met ASTM D6751 specifications. Moreover, the Ba-ZEL700 catalyst was reused for five cycles upon regeneration using n-hexane washing followed by reactivation at 110 °C for 12 h.

This paper examines the gap between the design and in-situ performance of solar streetlight interventions in two humanitarian settings. Displaced settlements often lack street lighting and electricity. Given that off-grid solar streetlights produce surplus energy, we hypothesized that this energy could be made available for daily usage, to improve system performance and provide further energy access to displaced populations. We recognize, however, that solar streetlight performance and longevity have typically been poor in remote and refugee settings. Eleven solar streetlights were fitted with ground-level sockets and their performance monitored, in two displaced settlements: a refugee camp in Rwanda and an internally displaced population settlement in Nepal. Considerable performance gaps were found across all eleven systems. Inefficient lights and mismatching system components were major issues at both sites, reducing targeted designed performance ratios by 33% and 53% on average in Rwanda and Nepal, respectively. The challenges of deploying these types of systems in temporary settlements are outlined and a number of suggestions are made to guide future developments in the design and implementation of sustainable solar streetlight interventions.

The paper deals with the cavitation at tongue of a pump-turbine in pump mode, including the typical patterns, unsteady behaviors, and the influence on pump performance and fluid-borne noise. Visualization experiments were conducted under different flow rates and rotational speeds for variation cavity regimes. The results show the patterns can be divided into three regimes with cavitation development: bubble cavitation, cloud cavitation, and lock cavitation for the gas-lock phenomenon and performance plummet. The rotor-stator interaction and jet-wake flow could affect the cavitation generation. The blade passing effect is the leading cause of bubble clusters periodic collapsing or shedding at the early stages of cavitation, while playing a small role as cavities become thick and evaporation rate rises. The combined action of the attached vortex (re-entrant jet) and the depression by pressure gradient outside cavity surface account for the shedding at the developed cloud cavitation stage. Based on the noise measurement by hydrophone at the outlet, the broadband sound in the range of 1000 HZ-2000 Hz can be used for cavitation detection since it can be rarely influenced by operating conditions under non-cavitation.

In discussion over the dating of theBucolicsof Calpurnius Siculus, an important role has always been played by attempts to identify the character of Meliboeus, who is to be read as a bucolic allegory of the poet's patron. By providing a new interpretation of the description of Meliboeus’ literary production, I argue that he must be the agricultural writer Columella. A consideration of other aspects of Meliboeus confirms this identification, as does the analysis of a number of significant allusions toDe cultu hortorum, the poem that makes up the tenth book of Columella'sDe re rustica. I then establish the date of Columella and discuss the consequences for dating Calpurnius, placing some parts of his book later in the reign of Nero than has been customary.

Solar tower systems show significant prospects based on their room for improvement in the solar thermal industry. Despite not being an entirely new concept, multi-tower systems have not been extensively studied in the literature yet. An optical optimization model is presented to evaluate the feasibility of dual-tower systems, where each heliostat can select the most convenient receiver. There is a number of optimization variables, which makes it essential to implement a fast optical algorithm capable of evaluating the field optical efficiency. Taking advantage of the tower central receiver's axial symmetry, an integration method is proposed to work out the individual spillage for each heliostat. As a result, an optimal design has been accomplished where 32 representative days (with several time-points each) have been taken into account to assess the yearly-averaged optical efficiency of the whole solar field. Thus, it can be concluded that a ∽1.5% increase in the annual optical efficiency can be achieved with respect to the analogous single tower system.

The recent increase in Renewable Generation (RG) has prompted many states, utilities, and other stakeholders to improve the methods used to determine the value of RG in efforts of replacing the Net Metering approach. However, these studies result in a wide range of values. This paper proposes a methodology based on the RG valuation studies conducted in recent years. The method includes the most common cost and benefit components considered in these studies and adopts a comprehensive method to calculate each component. The main categories include avoided energy, avoided generation capacity, avoided transmission capacity, avoided system losses, price hedging benefits, environmental benefits, and grid integration costs. A realistic case study emulating a large utility is also conducted to illustrate the application of the proposed method. The results show that all the main components can be estimated based on detailed system models or simulations. The results also illustrate some of the data challenges associated with such a study.

Due to the large size of free fatty acid molecules, they cannot diffuse into Al–Si–P Zeotype pores in the biofuel production process. Therefore, in the current work, to rectify this problem, in the synthesis of Al–Si–P zeotype by hydrothermal method, various weight percentages of the carbon casting and ultrasound waves for the uniform of the materials were used. Moreover, to enhancement the acidic strength and catalyst performance, Ceric oxide was accommodated on the Al–Si–P zeotype structure by sono-solvothermal synthesis. TPD-NH3, FESEM, HRTEM, BET-BJH, and EDX analyses were utilized for characterizing the samples developed in the present work. BET analysis has revealed that the optimized percentage of charcoal active is 4 wt %. By adding the sonication technique at the stage accommodating Ceric oxide on Al–Si–P zeotype, the conversion percentage increased from 77 to 94%. Test of the capability of modified Al–Si–P Zeotype with sonication and carbon casting to produce biofuel from waste oil delivered a conversion of 91.5%. Kinetic studies have shown that reaction of oil to biofuel is of the first degree, and the modified Al–Si–P Zeotype with sonication and carbon casting has the highest rate constant (0.0014 min−1) among all of the synthesized samples.

Geothermal energy resources are necessary to meet the increasing energy requirements worldwide and reduce the impact of climate change, particularly in developing countries. The aim of this study is the investigation of the low-enthalpy geothermal system of Pismanta, in the Central Andes of Argentina, to evaluate the possibility of power generation or direct use applications. Results indicate a circulation of meteoric water to the reservoir located in the Iglesia Basin, reaching a maximum depth of 2500 m. A background heat flow of 60 mW/m2 raises the temperature of the reservoir to approximately 95 °C resulting in a mean thermal gradient of 30 °C/km. The preliminary evaluation of four binary cycle energy conversion plants suggests a gross power generation range of 30–280 kW and the capacity of using the remaining heat for direct use applications such as drying of fruits, greenhouses, food processing and membrane distillation processes to solve arsenic problems in freshwater, among others.

In this study, three SBCs are developed as (i) SBC with phase change material (PCM: waste cooking oil and C4H4O3), (ii) a novel SBC with nanocomposite PCM (NPCM), and (iii) a SBC without NPCM. The novel proposed cooker integrated with NPCM (MgAl2O4/Ni/Fe2O3-PCM) was experimentally developed and its performance was evaluated using fuzzy logic and Cramer's rules, and image processing techniques. The results indicated that the implementation of a bar plate absorber coated with MgAl2O4/Ni-doped, Fe2O3 nanoparticles, and integrated with PCM increases the cooker's internal temperature up to 164.12 °C. The used nanocomposite materials were in the average particle size of 20 μm. The cooking materials were verified with the temperature in the segmentation process. The NPCM indicated the SBC's thermal performance enhancement of 11% in comparison with the SBC with PCM and without NPCM. Additionally, the overall thermal performance of SBCs without NPCM, with PCM, and with NPCM was obtained as 24.90–33.90%, 24.77–45.20%, and 31.77–56.21%, respectively. Moreover, the temperature of the bar plate absorber was achieved as 163.74 °C, 147 °C, and 113.34 °C for the SBC with NPCM, PCM, and without NPCM, respectively, under the solar radiation of 1,037 W/m2.

Shadow-bands are a low cost alternative when a precision solar tracker is not available. Adequate precision may be achieved if the measured diffuse irradiance is corrected to account for the sky portion blocked by the shadow-band. The isotropic sky assumption leads to a systematic under estimation of diffuse irradiance. Several correction methods have been proposed to take into account the anisotropic effects. However, their performance at a given site depends on the dominant local climate. In this work, it is shown that the local adaptation of shadow band correction methods results in a significant improvement in the diffuse irradiance measurement's accuracy. Nine well-known correction methods are implemented and tested (both in their original and locally adapted versions) for the Pampa Humeda region of southeastern South America. In absence of local adaptation, only one of the pre-existing methods improves the simple isotropic model. All locally adapted versions perform similarly well and outperform significantly the original methods. A new model based on the parametrization of Battle's model is proposed. It provides the best performance compared to all locally adapted pre-existing models, under all-sky and discriminated sky conditions.

Recently, Biodiesels are found high popularity as environmentally friendly and renewable fuels. Suitable combustion, appropriate atomization process, high flash point, and proper cetane number approved biodiesels as potential alternative for petroleum-based diesel fuels. Since, characteristics of biodiesels as well as biodiesel-diesel blends are directly related to their viscosity, an accurate approach is required for prediction of this important transport property. Therefore, this study tries to compare the accuracy of different empirical and intelligent paradigms for estimation of biodiesel-diesel blends. For this regard, the best topology of adaptive neuro-fuzzy inference systems (ANFIS) and least squares support vector machines (LSSVM) are determined at first, and then their predictive performances are compared with five empirical correlations in literatures. Combination of statistical study and ranking analysis justified that the LSSVM with polynomial kernel is the most accurate approach for the considered matter. The designed model estimated kinematic viscosity of 636 biodiesel-diesel blends with an excellent AARD = 0.754%, MAE = 0.03, RAE = 1.98%, RRSE = 2.3%, MSE = 0.003, RMSE = 0.05, and R2-value of 0.9997.

Access to sustainable energy source is crucial for healthcare facilities to deliver their services. Hybrid solar energy systems (HSES) are seen as a strong solution given the proximity of the Philippines to the equator. This study addresses the knowledge gap in the estimated energy consumption profile of Philippine rural health units (RHU) using easily replicable questionnaire and work sampling technique. The estimated energy consumption profile was used to determine the optimal HSES design and benefits. The RHU of Los Banos, Laguna was considered, and simulation of different energy system configurations was performed in the HOMER Pro software. Two scenarios were considered: a grid-connected and an off-grid RHU. The estimated average scaled load of the facility is ∼92 kWh per day. Estimates were validated against actual consumption, with 15–21% error. Results of the simulations show that a solar photovoltaic panel-grid system is optimal for the grid-connected scenario and can reduce cost of electricity by ∼35%. Meanwhile, a solar photovoltaic panel-generator-battery system is optimal for the off-grid scenario and can reduce cost of electricity by ∼61%. In both scenarios, the solar component is estimated to contribute ∼71–85% of the total annual energy production and can help reduce greenhouse gas emissions.

In urban areas, vertical axis wind turbines have been installed on both sides of the road and rooftop. Compared with rooftop, vertical axis wind turbines mounted on the side of a building have a larger swept area with longer blades, and the effect of tip vortices can be reduced at the same time. Around the building, there are several high wind speed regions that can provide more wind energy. In this paper, a high-resolution numerical method composed of overset grid and adaptive mesh refinement techniques is adopted to verify the feasibility of vertical axis wind turbines mounted on the side of the building. Firstly, the complex flow field around the building is simplified into the flow field around the cylindrical building. Five typical flow regions with different flow conditions are determined: windward zone, crosswind zone, tailwind zone, recirculation zone and leeward zone. Secondly, wind turbines are installed evenly around the building. The simulation results show that the energy output of wind turbines in tailwind zone can be increased by 120% compared with the reference value. Thirdly, multiple wind turbines are coupled with the building. In order to get the optimal arrangement, power outputs of four arrangements are compared for the best choice. The results indicate that the arrangement with six wind turbines in crosswind zone and tailwind zone can achieve the best performance. Through changing the rotational directions, the forward blades of wind turbines can be close to the wall, and the energy output of all the wind turbines around the building can be improved.

An effective approach for synthesizing green and sustainable biodiesel fuel from low-value vegetable oils has been explored. Herein, a series of catalysts of zinc supported on zirconia (xZn/ZrO2) were successfully synthesized, characterized, and applied for the production of biodiesel from Litsea cubeba kernel oil (LCKO) through the transesterification process. The results showed that the monoclinic phase structure of the prepared catalysts transformed to the more stable tetragonal phase structure after supporting different Zn loadings (≥5%). Compared with the pure ZrO2, the highly dispersed Zn species on the surface of xZn/ZrO2 could be divided into Zn oxide and ZnOH+, which could promote the transesterification of LCKO. Thus, the 7%Zn/ZrO2 catalyst exhibited the best catalytic activity of the LCKO conversion 82.5%, which was attributed to the positive effects of both the ZrO2 support and Zn species. Furthermore, the various reaction parameters (such as reaction time, stirring rate, nCH3OH:nLCKO, catalyst amount, and reaction temperature) were investigated systematically and optimized carefully. And a possible mechanism of the transesterification process catalyzed by Zn/ZrO2 catalysts was also proposed. Finally, the physical properties of the as-synthesized biodiesel accorded with the current international biodiesel standards.

Recent investigations verified CaO2 accelerated hydrolysis of lignocellulose, but its residue caused a harmful oxidizing environment. This study therefore proposed the combined CaO2 pretreatment and zero-valent iron (ZVI) addition to enhance high-solid anaerobic digestion of wheat straw, trying to eliminate negative effect of residual oxides. Effects of CaO2 pretreatment without/with ZVI addition on digestion performance were investigated. Results showed that in non-ZVI added digesters, as CaO2 dosage increased, total production of SCOD and VFAs increased linearly, while activities of coenzyme F420 and electron transport system were negatively correlated. Pretreatment using appropriate CaO2 dosage indirectly increased biogas production by promoting hydrolysis and acidification. Comparably, initial ORP in ZVI-added digesters sharply declined below −350 mV, which was suitable for methanogen growth. ZVI significantly improved activities of cellulase, hemicellulase, acetic kinase and coenzyme F420, with the highest improvement percentages of 138%, 48%, 35% and 58%, respectively. Since ZVI could provide electrons for conversion of CO2 to CH4, compared with non-ZVI added digesters (R0-R4), methane content in ZVI-added digesters (RZ0-RZ4) increased by 8.1%, 9.0%, 11.2%, 17.0% and 18.0% successively. Consequently, 0.6 g/g VS CaO2 pretreatment combined with 0.4 g/g VS ZVI addition achieved the maximum methane production, increasing by 35.6% compared to control digester.

An hybrid floating platform concept, combining a wind turbine with wave energy converter devices, has been proposed. This paper conducts a further exploration of these synergies analyzing the utilization of the wave energy converters to assist the platform water ballast system on the compensation for variations on the sea state conditions. An experimental campaign has been performed for a preliminary evaluation of this approach. It is limited, for simplification, to five different sea state conditions in head wave situation. However, it allows the study of the main design principles that should be followed to develop the approach in a more complex scenario. The experimental results indicate that energy wave converters assist the water ballast system in the tested sea state conditions, and even extend the operational sea state range. Moreover, it indicates that wave energy converters located at downwind and upwind sides of the platform have different roles in the compensation of the platform dynamics. The first ones are dedicated to the production of platform restoring moments while the seconds are harvesting the power that should be supplied to the downwind of the wave converters. The case study considers the application of oil-hydraulic technology in wave energy converters.

An effective air staging strategy is of great importance for achieving low emissions and sensible heat losses through flue gas extraction. In cases where a commercially available system needs to be optimised, often the only viable measure is the modification of process parameters. In this work, the aim is to (1) Discover a combination of the most suitable process parameters based on a multi-criteria decision-making method and (2) To unveil relevant correlations between the two process parameters under study (PA/SA ratio and excess air), emissions and combustion temperatures. A modified commercial small-scale hot water wood pellet boiler was installed into a laboratory heating system. Nine different cases have been addressed within a parametric study, differing in the PA/SA ratio and overall excess air. Emissions, temperatures inside the combustion chamber and the flow rate of air entering the combustion chamber were measured. A low PA/SA ratio of 0.53 (54.7% reduction from factory settings), combined with a low O2 concentration in the flue gases of 5.26% (39.8% reduction from factory settings), and the elimination of infiltration air resulted in a simultaneous reduction of NOx and CO emissions by 14.4% and 93.9% respectively and a flue gas sensible heat loss reduction of 31.6%.

Hydrodynamic damping is a key factor that influencing the amplitude of structural vibration under resonance conditions. In this study, the one-way FSI energy balance method by loading structure mode onto flow field is applied to simulate the hydrodynamic damping. Based on the good solution of vortex shedding frequency, structure natural frequency and mode shape, it provides a good accuracy on both flow field and structural field by predicting the hydrodynamic damping well with deviations less than 10.4%. On the basis, the hydrodynamic damping characteristics of different vibration displacements and the lock-in region are studied and analyzed in detail. Results found that the hydrodynamic damping ratio increases with the increasing of vibration displacement. A displacement interval within 6 × 10−5 m–1.2 × 10−4 m can be detected when the hydrodynamic damping ratio is slightly affected by vibration displacement. It is proved that the value of hydrodynamic damping depends on the combined area of hydrodynamic force and structural velocities. The hydrodynamic damping in the lock-in region changes nonlinearly. Under the resonance condition, the disturbance of the fluid domain increases, and a negative damping value will appear, which will increase the structure vibration amplitude.

Systems involving more than one energy source, namely hybrid systems, can be arranged in different configurations and layouts depending on the available or used energy source, application and scale of the system. Despite an increasing awareness and penetration of renewable energy sources at different scales in many countries over the world, the adoption of hybrid and novel renewable systems is relatively scarce, especially at a small scale. This scenario is also presented from the point of view of the research of such systems. Therefore, the scope of the paper is to improve the knowledge regarding small-scale hybrid renewable energy systems performance and operation by investigating a novel trigeneration system based on a biomass fired steam cycle, wind turbine, photovoltaic panels and adsorption chiller. In the proposed system, the thermal energy recovered by the steam cycle is used to match the user thermal demand by means of a storage tank supplying directly heat to the user during winter, and driving the adsorption unit during summer. The electrical energy produced by the steam turbine, photovoltaic field and wind turbine is managed by a control system that integrates a bidirectional connection with the electric grid. The grid allows one to virtually store the electrical energy produced in excess and to recover it in part when needed by the user. In order to assess the system performance, a farm and residential buildings are considered as case study. The proposed system is modelled and dynamically simulated by means of Transient System Simulation software. In the paper, the dynamic operation of the system and the energy and economic performance of the system is assessed. The operation of the system is presented in a daily and monthly basis, while the global performance parameters of the system are reported considering a one-year period. The primary energy saving of the system is above 70% when a reference system based on natural gas, electric chiller and grid is considered. For this scenario, the Simple Pay Back of about 10 years is achieved. The results of the analysis show that the system is feasible from the technical and energy point of view, whereas its economic profitability is significantly affected by its cost and the reference system that is adopted by the user.

In this study, a new method of microwave-induced discharge over biomass-derived char (i.e., bio-char) spherical carriers was proposed. Bio-char spherical carriers were obtained through rational forming. The discharge intensity and temperature increase under discharge were measured to elaborate the quantitative relationship between microwave discharge and the temperature increase. The effect of bio-char properties on microwave-induced discharge was investigated. The results revealed that discharge achieved the highest electric–thermal conversion efficiency of 61.04%, and the heat generation ratio through the discharge in the initial 10 min was up to 69.08%. The graphitisation degree and transmission depth of microwaves can affect discharge intensity. A critical light intensity inducing hot spot effect exists under different working conditions, and exceeding the critical value led to the hot spot effect and a sudden increase in bed temperature, with a corresponding range of 2.48–5.76 V. The maximum temperature under microwave discharge reached 981 °C, with a heating rate of 376.4 °C/min. The method is potential in the field of value-added utilization of bio-char and microwave-promoted chemical processes.

With the increasing demand for environmental protection, CO2, as a natural refrigerant, has always been environmentally friendly and safe, which makes transcritical CO2 heat pump system attract more attention. The internal heat exchanger is employed to improve the performance of transcritical CO2 heat pump system to match the traditional heat pump circulation system. In this work, two evaluation methods are proposed, one is the actual operation thermal effectiveness of internal heat exchanger, the other is the actual increase rate of COP. Compared with the experimental results, the conclusions can be extracted that the actual increase rate of COP can effectively evaluate the impact of the internal heat exchanger on system performance. In addition, this research deeply analyzes the influence of the internal heat exchanger on exergy efficiency. The results show that the internal heat exchanger greatly reduces the exergy efficiency under the discharge pressure of 7310 kPa and the ambient temperature of 15 °C, and the difference value between the system with and without internal heat exchanger reaches 39%. However, the influence of the internal heat exchanger on exergy efficiency decreases with the increase of discharge pressure and ambient temperature, the minimum difference value is only 0.1% at 11000 kPa and 30 °C.

The peak period of an energy-generating wave is one of the most important parameters that describe the spectral shape of the oceanic wave, as this indicates the duration for which the waves prevail with respect to their maximum extractable energy. In this paper, a half-hourly peak wave energy period (TP) forecast model is constructed using a suite of statistically significant lagged inputs based on the partial auto-correlation function with an extreme learning machine model developed and its predictive utility is benchmarked against deep learning models, i.e., convolutional neural network (CNN/CovNet) and recurrent neural network (RNN) models and other traditional M5tree, Conditional Maximization based Multiple Linear Regression (MLR-ECM) and MLR models. The objective model (ELM) vs. the comparison models (CNN, RNN, M5tree, MLR-ECM, and MLR) were trained and validated independently on the test dataset obtained from coastal zones of eastern Australia that have a high potential for implementation of wave energy generation systems. The outcomes ascertain that the ELM model can generate significantly accurate predictions of the half-hourly peak wave energy period, providing a good level of accuracy relative to deep learning models in selected coastal study zones. The study establishes the practical usefulness of the ELM model as being a noteworthy methodology for the applications in renewable and sustainable energy resource management systems.

This study investigates the impact of monetary policy on renewable energy generation in Iran. It examines three types of renewable energy generation: total renewable energy generation; solid biomass and biogas energy generation; and the hydropower, solar, and wind group energy generation. The study uses the Kalman filter and vector autoregression (VAR) models to examine annual data from 1984 to 2016. The Kalman filter model showed that the money supply parameter moved with a steady trend, except for a sharp point during the Iran-Iraq War. A sharp point can be found for real interest rate parameter as well, although the time of global crisis and sanctions also affects this coefficient. The VAR model results indicate that only a shock to money supply can affect all the three renewable energy generation types.

A novel model reference adaptive system for the rotor position/speed estimation and sensorless operation of a brushless doubly fed reluctance generator with maximum power point tracking is presented. Its main advantage over the existing designs are the inherent robustness and stability afforded by the complete parameter independence of the reference model using only the measured currents of the converter-fed (secondary) winding. In addition, the respective stationary frame current components are estimated by the adaptive model using the voltage and current measurements of the grid-connected (primary) winding at line frequency, offering higher accuracy. The simulation and experimental results have demonstrated the excellent real and reactive power controller performance for typical operating characteristics of wind turbines.

Energy consumption and economic growth play an important role in the global policy debate among policymakers around the world. This is the first study to investigate the relationship between economic growth and energy consumption at the state level for the U.S. from 2000 to 2016. As opposed to country-level studies, a focus on states within a country allows for comparisons across more homogeneous entities. The four known hypotheses are tested: growth, conservative, feedback, and neutral, differentiating between renewable and non-renewable energy consumption. In order to address endogeneity, two strategies are developed: (1) a static analysis for 2016 where key policy covariates are gradually added to the model, and (2) a dynamic analysis using different generalized method of moments (GMM) estimators. The model is augmented using socioeconomic, regulatory and climatic variables, which allows for the evaluation of policies while facilitating a transition to renewable energy use. Overall, the results show that total energy consumption and non-renewable energy consumption support the feedback hypothesis. Results for renewable energy, industrial energy, and residential energy consumption show more support for the growth hypothesis. These results have policy implications in terms of optimizing decisions and investments to efficiently improve economic growth while reducing energy consumption.

The plague of 1630–1632 was one of the deadliest plague epidemics to ever hit Northern Italy, and for many of the affected regions, it was also the last. While accounts on plague during the early 1630s in Florence and Milan are frequent, much less is known about the city of Imola. We analyzed the full skeletal assemblage of four mass graves (n = 133 individuals) at the Lazaretto dell’Osservanza, which date back to the outbreak of 1630–1632 in Imola and evaluated our results by integrating new archival sources. The skeletons showed little evidence of physical trauma and were covered by multiple layers of lime, which is characteristic for epidemic mass mortality sites. We screened 15 teeth for Yersinia pestis aDNA and were able to confirm the presence of plague in Imola via metagenomic analysis. Additionally, we studied a contemporaneous register, in which a friar recorded patient outcomes at the lazaretto during the last year of the epidemic. Our multidisciplinary approach combining historical, osteological and genomic data provided a unique opportunity to reconstruct an in-depth picture of the last plague of Imola through the city's main lazaretto.

Microalga biomass is a reliable bioenergy feedstock to produce green fuel owing to its high lipid and organic content. On the other hand, the microalgal biomass productivity as well as lipid accumulation widely depends on various cultivation factors - including nitrogen/phosphorus ratio and light-dark cycles (LD). This study investigated the effects of LD and NaNO3 (nitrogen) dose on the specific growth rate (SGR), biomass productivity (P), and intracellular lipid productivity (LP) of Chlorella kessleri. Response surface methodology (RSM) and support vector regression (SVR) based nonlinear empirical models were developed to forecast SGR, P, and LP. The laboratory data acquired based on central composite design (CCD) matrix, was utilized to establish the adequacy of the models. Bayesian optimization algorithm (BOA) was coupled with SVR to tune the hyperparameters automatically. The performance of the hybrid intelligence model (BOA-SVR) was better than RSM model for anticipating all the responses. Lastly, the crow search algorithm was combined with BOA-SVR to achieve the global optimal solution for maximizing SGR, P and LP, simultaneously. The maximum SGR, P, and LP were found to be 0.302 d−1, 45.31 mgL−1d−1, and 16.3 mgL−1d−1, respectively at the operating environments of LD of 12/12 (h/h) and NaNO3 dose of 10.92 gL-1.

Thermoelectric generators (TEGs) can convert heat into electricity directly. However, the thermal boundary conditions are intermittent and high temperature in most TEG systems. Therefore, thermal management of TEG systems is of great significance. It is an efficient technology to use phase change material (PCM) for thermal management of the TEG systems. PCM is applied to hot side of TEG in this study, and the phase change material-thermoelectric generation (PCM-TEG) system is set up. For the purpose of exploring the effect of the PCM on the output performance of TEG, the common TEG system is established to compare with PCM-TEG system. Furthermore, the effect of the heat transfer characteristics of PCM on TEG output performance is investigated and discussed in detail under different pulse transient thermal boundary conditions. Experimental results show that PCM can reduce the temperature fluctuation to protect TEG and extend the temperature difference operation time. The PCM of solid state, solid-liquid coexistence state and liquid state have different effects on reducing the temperature fluctuation. Besides, the PCM-TEG system cannot provide the peak output power provided by the common TEG system, but it is still beneficial to provide a stable output power.

Integration of solar photovoltaic systems to low-voltage distribution networks is witnessing an unprecedented growth in many parts of the world. Although solar photovoltaic generation is of significant benefit from a number of angles, exceedance of hosting capacity levels by such installations in low-voltage distribution networks continue to cause significant technical challenges in network operation, especially to the management of network voltage. Modern smart inverters are equipped with Volt-VAr and Volt-Watt control capabilities, which can assist in the management of network voltage levels. This paper provides a detailed analysis of the influence of different connection standards which cover these strategies on solar photovoltaic hosting capacity and their applicability in low-voltage distribution networks. Smart inverters with differing Volt-VAr and Volt-Watt control functions are modelled in the DIgSILENT PowerFactory platform. Influence of different connection standards on solar photovoltaic hosting capacity is analysed to investigate the most beneficial connection approach/es to address the issue of voltage violations. Furthermore, the work presented in this paper provides a greater understanding on the hosting capacity improvement by employing advanced inverter control functions where such improvements are subjected to locational aspects of inverters in low-voltage distribution systems.

Global electricity consumption has raised in the last century due to many reasons such as the increase in human population and technological development. To keep up with this increasing trend, the use of fossil resources has increased. But these resources are not environmentally friendly, and for this reason, many countries and governments are encouraging the use of green sources. Among these sources, PV technology is widely promoted and used due to its improved efficiency and lower prices for photovoltaic panels. Therefore, the importance of forecasting power production for these plants is necessary. In this work, two hybrid models were proposed (CNN-LSTM and ConvLSTM) to effectively predict the power production of a self-consumption PV plant. To confirm the efficiency of the proposed models, the LSTM model was used as a baseline for comparison. The three models were trained on two datasets, a univariate dataset containing only the power output of the previous days, while the multivariate dataset contains more features (weather features) that affect the production of the PV plant. The time frames for the forecast ranged from one day to one week ahead of time. The results show that the proposed methods are more accurate than a normal LSTM model.

Presented paper identifies the possible corrosion problems related to animal waste incineration since it is a key issue for their use in the power sector. Cow dung as an example of animal-origin biomass is examined in terms of high-temperature corrosion and slagging hazards in comparison with commonly used mixed straw. Results of the laboratory-scale corrosion studies of pure ash deposits on two steel alloys: 16Mo3 and 10CrMo9–10 are reported. Selected steel types are commonly used in boiler construction for superheaters and waterwalls – parts of a boiler that are most exposed to the high-temperature corrosion risk. The corrosion experiments were carried out under oxidizing conditions at 460 °C, 510 °C and 560 °C for 168 h. To determine the corrosion rate the mass of steel samples was measured after 24, 72 and 168 h. For a better understanding of the corrosion process, a detailed chemical analysis of ashes was conducted together with SEM-EDS analysis of the corrosion products. Ash melting and deposition behavior of both ashes were predicted according to 11 indices. It was found that cow dung and mixed straw ash differ significantly in terms of quantitative chemical compositions and ash melting characteristics. Cow dung ash is characterized by a high concentration of alkali compounds (2.57 wt% Cl, 30.6 wt% CaO, 5.56 wt% K2O) together with high phosphorus content typical for animal manure. The presence of alkali chlorides in the cow dung ash deposits led to a build-up of chlorides on the steel surface, which caused accelerated corrosion. At 560 °C the corrosion rate was over 3 times higher for cow dung ash than for mixed straw ash. The corrosion occurred due to the formation of low-melting FeCl2 mixtures since chlorine- and iron-rich particles were found in the crevices and cracks within deposits. The results clearly demonstrated the high corrosive potential of animal-origin biomass and therefore indicate the potential problems related to its thermal conversion process. These adverse effects can be reduced by ash removal and maintaining the temperature of the heating surfaces below 560 °C.

In response to the rapid growth of energy consumption in urban cities, rooftop wind turbines (RWT) have emerged as a powerful technique for providing sustainable energy and strategically minimizing the carbon footprint of buildings. However, significant knowledge gaps exist regarding how RWT respond to the complex urban environmental flows modified by the coexisting buildings and trees. This study conducts idealized numerical experiments using an open-source large-eddy simulation model to investigate the interactions between actuator-disc turbines, street trees and buildings. We found that trees taller than the mean building height modifies the existing roof-level strong shear layer by extracting energy from the mean momentum. A significant change in the mean kinetic energy budget is induced, drastically increasing turbulence production of the flow, which leads to lower power output of RWT. Trees lower than the buildings hardly alter the mean flow field but they reduce turbulence production near the roof level. As a result, improved power output (16%) and decreased normalized power fluctuation (5.2%) are observed compared to the control case without trees. The results highlight that it is important to assess effects of different street tree morphologies on the performance of RWT in their design and implementation processes.

Graphitic carbon nitride (g-C3N4) with unique physicochemical features has garnered much attention in artificial photosynthesis, yet the photoactivity of pristine g-C3N4 (PCN) is severely restricted because of its rapid charge recombination rate and narrow visible-light absorption. To this end, for the first time, here we reported a rational one-step copolymerization strategy for the fabrication of carbon self-doped g-C3N4 (CCN) by using melamine and chitosan as the starting materials. Experimental results indicated that the bridged N atoms were substituted by C atoms in the g-C3N4 matrix, resulting in the formation of delocalized big π bonds, thereby the obviously increased the electrical conductivity, remarkably extended the visible-light absorption region, and significantly improved the mobility of photoinduced electron-hole pairs. Consequently, the as-engineered CCN with abundant mesopores structure showed a dramatically boosting photocatalytic H2-evolved activity (1224 μmol g−1 h−1), 4.5-folds than PCN powders. Eventually, the resulting CCN exhibited an extremely long-term durable stability after storing in reaction solution for 90 days. Our work will bring about potential application in designing of high-performance g-C3N4 photocatalyst for renewable solar-to-H2 conversion.

This work proposes and employs a mixed-complexity modeling approach to creating a 3D computational fluid dynamics (CFD) model to predict the syngas production from Miscanthus briquettes in a two-stage downdraft gasifier operating with different gasification fluids. The study was performed at steady state regime in the Ansys Fluent environment considering the non-premixed combustion model. A probability density function is also included as a tool for the description of the chemical kinetics to predict the syngas composition following the main chemical reactions involved in the gasification process. The goal of this approach is to reduce the computational cost while still providing accurate predictions. In comparison to experimental gasification with air, the model correctly predicts the temperature profile inside the reactor, the composition of the syngas (CO, H2 and CH4), and therefore the lower heating value (LHV). For cases involving the use of saturated steam and oxygen as gasification fluids, the model predicted key species concentrations in the gasification zone and the reactor core and accurately described the significant increase in the LHV of the syngas. This approach opens the possibility of studying the gasification process in moving-bed reactors using different gasification fluids and feedstocks based on their elemental and proximate analysis.

This essay applies Karl Polanyi’s concepts of embedding and countermovement to provincial Hungary during and after socialism. Comprehensive state socialist repression in the 1950s was a politics-led disembedding. An economy-led countermovement began in the 1960s, later augmented by elite discourses of civil society. The 1970s and 1980s were decades of socialist embeddedness. Neoliberal configurations after 1990 dislocated both economic and associational life. The illiberal democracy of Viktor Orbán is a more consequential countermovement than the earlier countermovements to state socialism. The argument is illustrated with data from long-term fieldwork in southern Hungary, in the region of the Danube-Tisza Interfluve.

To solve the problems of high energy consumed by the cooling system in the data center, this article puts forward a composite air conditioning system. The simulation platform for system operation performance is established, and the accuracy of the simulation platform is verified by experiments. The influence of operation parameters on system performance is analyzed by simulation. Finally, the optimal operation control parameters are determined. The results show that the system can adjust the condenser wind speed and the refrigerant pump operating frequency to meet the cooling requirements and solve the problem of low evaporation temperature in the heat pipe. The evaporative cooling effectively expands the working range of the heat pipe mode and raises the upper limit of outdoor temperature from 8 °C to 15 °C. In the vapor compression mode, when the ambient temperature is lower than 26 °C, the performance of the air-cooled mode is better than that of the evaporative-cooled mode. The condensation temperature can be ensured within a reasonable range by adjusting the condenser cooling wind speed and the compressor frequency. When the outdoor temperature is not less than 26 °C, the evaporative cooling can effectively improve the operation performance

One feasible solution to reduce the cost of concentrated solar power is to employ a higher temperature and efficiency supercritical carbon dioxide Brayton power cycle. An alternative heat transfer medium and thermal energy storage (TES) system therefore needs to be explored. This work considered a variety of phase change materials (PCMs) and graphite as the storage media in four indirect shell-and-tube storage configurations, including a 3-PCM and 5-PCM cascade storage, a PCM-graphite-PCM hybrid storage and a single graphite storage. The sizing and design of the TES systems were performed by using a dynamic cycling methodology based on a transient 2D numerical model. The cost of those designs were then determined by using an economic model developed inhouse. This work also investigates the impact of some geometric parameters and cost assumptions on the techno-economic performance of the TES system. The analysis suggests a scenario exists whereby a low thermal efficiency storage system which therefore utilises less tube or storage material could be more cost-effective. Overall, the cost of hybrid TES is the lowest among all studied systems, at $26.96/kWht and $21.49/kWht for charging temperature of 720 °C and 750 °C, respectively, followed by the 5-PCM storage at $28.06/kWht and $21.82/kWht, respectively Refereed/Peer-reviewed

Renewable energy has become very prominent these days because of its sustainable and environment-friendly nature. The soil heat storage system plays an important role in the long-term storage of solar energy to ensure a consistent power supply. The experimental analysis and practical implementation of soil heat storage system are very difficult due to its large size and the simulation-based calculation is also very complex for the entire storage system. In order to reduce the system from the perspective of space and time, this paper has applied a similar function relationship for soil heat storage system and develops the traditional CFD simulation model and similar model. According to the dimensions of similar model, the corresponding experimental setup is constructed and the experimental results of long-term heat storage in the soil are compared with the calculation results of a CFD similar model. The relative error of inlet and outlet temperature difference is measured 10% and the error for soil temperature rise is below 1 °C. The proposed method has reduced the simulation and experimental workload for soil heat storage using similarity theory. Hence, the proposed method has great significance in the research domain of soil heat storage and the application of similarity theory.

Improving efficiency and yield of a parabolic trough collector (PTC) field is of paramount technological importance. Here, an attempt toward this goal is made through combined optical and thermal simulation. Two major factors that affect the performance of an individual trough are mass flow rate and aperture width, which scales with rim angle. Performance of PTC-field is observed to have a non-linear scale-up rule as opposed to the same for an individual trough. Wider aperture leads to higher heat collection for individual trough; however, the same results in higher inter-trough shading limiting the number of troughs in a field and the effective unshaded hours. It also depends on insolation and latitude. Therefore, there lies a possibility of trade-off where flow rate, rim angle and design hours of operation require careful tuning to maximize annual energy yield. Here, a step by step procedure is demonstrated for Kanpur, India where optimal values of flow rate, rim angle and hours of operation are obtained to be 1.1 kg/s (for Syltherm 800 as the heat transfer fluid), 70° and 4 h around solar noon on winter solstice day, respectively. The methodology is illustrated to be generally applicable to any location or working fluid.

Thermal energy storage using phase change materials (PCMs) plays a crucial role in solving the contradiction between energy supply and demand. In this paper, we proposed a novel approach to design a functionalized process for the matrix which was modified with polydopamine and silver nanoparticles for improving the crystallization process of polyethylene glycol (PEG) PCMs which were bound onto the surface and the interior of the mesoporous silica by adjusting the size and shape of pore systems, the hydrogen bonding force between PEG molecules and carriers. And the results suggested that the prepared supporting materials exhibited prominent chemical compatibility with PEG and a great enhancement for the thermal conductivity (34.0%) with the sequential modification of polydopamine and silver nanoparticles. The composite ss-PCMs also exhibited excellent thermal reliability after 10 thermal cycles, indicating that the emerging composite ss-PCMs had favorable potential in the practical applications.

Water and electricity distribution networks are two highly interdependent and critical infrastructures in the world today. This paper investigates the coupling of water and electricity distribution networks through the electrical energy demand of water pumps. Further, with additional variable renewable energy (VRE) sources in the distribution system, utilities face significant challenges stemming from the VRE stochasticity. In this paper, a coordinated operational model of urban water and electricity distribution networks is proposed. Stochastic VRE generation is handled by using a data-driven probability efficient point (PEP) method based on historical wind and solar datasets without the need for any probability distribution function. Case studies are performed on a modified Institute of Electrical and Electronics Engineers (IEEE) 13-node electricity distribution network coupled with a 10-node water distribution network, typical of a small-town setting. Results show the impact of coordinating water and energy networks on the cost of operation and the distribution locational marginal prices (DLMPs). The inclusion of water tanks as alternative storage devices in the electricity distribution network are shown to slightly reduce voltage violations, line congestion, and VRE curtailments in a case with high VRE penetration.

The utilization of renewable energy to run desalination plants has enormously expanded in the last two decades. In this study, a grid-connected hybrid solar-wind system is proposed to power a small-scale Reverse Osmosis (RO) desalination unit. In a case study, the system's performance has been analyzed under the weather conditions of the Eastern Province, Saudi Arabia. A numerical model has been developed based on a mixed-integer linear programming (MILP) approach to design and size the proposed system. The developed model is solved on an hourly basis to capture hourly variations of weather conditions with the aim to obtain an efficient design to operate the RO plant and supply freshwater to a small community living in a remote area at minimum cost. The developed model allows finding the optimal number of wind turbines, the number of photovoltaic (PV) modules, and the energy purchased from the national grid. Since the desalination energy consumption depends on the feed water conditions, two energy consumption rates are considered, namely, 2 and 4 kWh/m3. The results show that brackish water can be purified for the two different energy requirements at a cost varying between 1.72 and 1.84 $/m3, respectively.

This paper presents a case study of photovoltaic (PV) module failures after over 10 years of operation in the tropical climate of Singapore. Three types of modules (two samples from each type) were analysed: multi-crystalline silicon (multi-Si), mono-crystalline silicon (mono-Si), and copper indium selenide (CIS). Visual inspection revealed several problems, including encapsulant discoloration (to different extents), backsheet yellowing, and soiling among others. Different degradation behaviour of the samples was observed from current-voltage (IV) and electroluminescence characterization. The maximum power of the multi-Si samples degraded by more than 9% (on average), likely due to corrosion around the cell edges. The mono-Si modules suffered a catastrophic power reduction (>40%) that could be ascribed to a combination of encapsulant discoloration, potential-induced degradation (PID), and corrosion. While one CIS module was primarily affected by encapsulant discoloration and possibly corrosion, the other sample also exhibited signatures of PID and experienced about 45% power drop. Furthermore, external quantum efficiency measurements of the multi-Si modules identified cell mismatch and changes to the additives in the encapsulant. Overall, PID, corrosion and encapsulant degradation are found to be the most detrimental degradation processes for PV modules in the tropical climate of Singapore.

A-site deficiency perovskite oxides, Pr0.35Sr0.6Co0.2Fe0.7Nb0.1O3-δ, and Pr0.4Sr0.55Co0.2Fe0.7Nb0.1O3-δ are prepared and act as the semiconductor for single-component fuel cell (SCFC) and reversible single-component cell (RSCC). After reduction, the perovskite oxides can in situ exsolve Co3Fe7 alloy nanoparticles on perovskite and Ruddlesden−Popper structure oxide matrix, further facilitating the hydrogen oxidation reaction. In addition, Pr0.4Sr0.55Co0.2Fe0.7Nb0.1O3-δ and reduced Pr0.4Sr0.55Co0.2Fe0.7Nb0.1O3-δ have the most oxygen vacancies. Furthermore, Pr0.4Sr0.55Co0.2Fe0.7Nb0.1O3-δ based SCFC exhibits the highest cell performance and the mximum power densities (Pmax) are 109.6, 145.2, and 211.1 mW cm−2 at 600, 650, and 700 °C, respectively. It is because Pr0.4Sr0.55Co0.2Fe0.7Nb0.1O3-δ shows the highest catalytic activity for oxygen reduction reaction (ORR) and the reduced Pr0.4Sr0.55Co0.2Fe0.7Nb0.1O3-δ exhibits the highest catalytic activity for hydrogen oxidation reaction (HOR). For RSCC, when 53%H2-47%H2O fuel is applied and the Pmax values are 105.7, 143.0, and 179.6 mW cm−2 at 700, 650, and 600 °C, respectively in solid oxide fuel cell (SOFC) mode and the current densities are −127.2, −205.8, and −265.0 mA cm−2 under 1.3 V at 600, 650, and 700 °C, respectively in solid oxide electrolysis cell (SOEC) mode, indicating that Pr0.4Sr0.55Co0.2Fe0.7Nb0.1O3-δ based RSCC can generate the most hydrogen in SOEC mode.

A mirror-image rotating piezoelectric energy harvester is proposed, and it can adapt to 2.8 m/s — 13.6 m/s wind speed. It is arranged by the mirror image of two piezoelectric elements, so it has multiple resonant frequencies. The multiple resonant frequencies make the bandwidth of the energy harvester be broadened. The force applied on the piezoelectric beam is aperiodic and an evaluable analytical model is established based on Fourier series and superposition principle. The influence of the system parameters on the piezoelectric beam is deduced by the Bernoulli beam formula of axial direction, and a prototype is made for experiment and application. The results show that when the distance between the two magnets is kept at 15 mm, the torsion angle of the blades is 15°, three blades are selected, and the height of each blade is 50 mm, the power generation effect is optimal, and the power can reach 12.5 mW. Under the optimal power, it only takes 100s to charge the capacitor of 220 μF to 15V, the prototype can directly power 98 light emitting diodes (LEDs) and make the calculator work. This technology can also be extended for harvesting water energy.