Combined with the negative pressure zone outside the duct, a new method based on the converging-diverging tube using for speeding up the low-grade wind is proposed in this paper. Firstly, a 3D CFD model of the converging-diverging air duct is developed, and the validation of the numerical model is also shown by comparing the experimental and numerical data. Secondly, based on the method of velocity stratification analysis at the air duct throat, the effect of the outlet angle on the speed increase is studied, and the mechanism of the negative pressure zone on changes to the wind speed is also analyzed and discussed. The air duct geometry was optimized, and the simulation study results were verified through experimental tests with a prototype duct and a wind tunnel. The results show that air ducts can significantly focus and increase wind speeds, offering insight for the future use low-speed winds for electricity generation.

Solar reflectors are exposed to outdoor environments where dust accumulation is a primary degrading factor on optical performance. In this study, the effect of dust accumulation on reflectivity at different positions on the reflector of a parabolic trough solar thermal power plant in Hohhot, China was investigated and analyzed. The physical and chemical properties of dust accumulation were tested using a combination of spectrophotometer, scanning electron microscopy, and X-ray diffraction. The results showed that dust accumulation on the bottom edge of the reflector caused the largest decrease in reflectivity compared to dust on the center and top edge. In addition, dust particles at Hohhot were dominated by quartz (SiO2, 53.5%), followed by calcium oxide (CaCO3, 25.4%), and some minor feldspar minerals (NaAlSi3O8, 21.1%). However, some characteristics of the dust could not be determined by experimental measurements. To address this gap, a physical model was proposed to predict the impact of dust accumulation on light reflectivity of the reflector. Different physical parameters of the model are discussed, such as the size of the particles, diaphaneity, the incidence light angle, and tilt angle. The maximum relative deviation between the mathematical model and the experimental results was only 1%.

Although regular curtailment of wind power has not been necessary in the Nordic power system so far, rapidly increasing wind power capacity means that it may be needed in the future. To estimate the amount of curtailment in the future Nordic power system we develop an hourly dispatch model based on open data. The model is validated against historical data and used to perform a case study for the Nordic power system in 2025 to estimate the amount of wind power curtailment under different assumptions. Curtailment is found to be below 0.3% of available generation for a 26 GW wind scenario and below 1.7% for a 33 GW wind scenario, when considering trade with neighbouring systems. The most important measures for decreasing curtailment are found to be increased transmission capacity, particularly between the areas in Sweden and those in Norway and Denmark, as well as flexibility of nuclear generation. Inertia requirements are found to have a limited impact on curtailments.

In this paper, the accelerated degradation and oxidation of Jatropha biodiesel were carried out at 110 °C through the Rancimat method. The applicability of surface tension and UV absorbance in the fuel oxidation degree detection was studied through Gas Chromatography-Mass Spectrometer( GC-MS) and acid value titration. The analysis of experimental data demonstrated that the acid value, surface tension and density of Jatropha biodiesel increased by 551%, 3.8% and 0.91% following oxidation, respectively, while the UV absorption intensity at 230 nm increased nearly 2 times. Subsequently to oxidation, the correlations among surface tension, UV absorbance and acid value of Jatropha biodiesel were 0.9743 and 0.9702. Based on this fact, four prediction models for the degree prediction of fuel oxidation through surface tension and UV absorbance were proposed, while the cross-validation method was utilized. The test analysis finally determined that the two models were Logarithm model and Power model, while the RMESP and R values were 0.093, 0.9875, 0.0705 and 0.9928. Both the accuracy and correlation were high. The acid value prediction model based on surface tension was 7.8%, while the acid value prediction model based on UV absorbance was 3.8%. Both could accurately determine the oxidation degree of biodiesel.

As the world moves to a greater reliance on renewable energy, a vital component will be the predictability and dependability of the energy source; tidal energy provides such a solution. Horizontal axis tidal turbines are the most mature technology of all the marine renewable energy devices currently under development, as full-scale porotypes are already being tested and operated. As the industry develops and strives for commercial viability, it is becoming increasingly vital to develop a robust understanding of the complex interaction between the tidal flow, turbine blades and the support structure. This study uses an advanced computational fluid dynamics model to explore the operational fatigue loadings induced on tidal turbine blades. Two factors are considered, the presence of a support structure and varying vertical velocity profile of the tidal current. In order to perform the investigation, a model of a concept 16m diameter horizontal axis tidal turbine with a monopile support structure is created. An investigation of the operational fatigue loadings due to variations in the positioning and the diameter of the support structure, the tidal turbine blade loads were found to varying by up to 43% of the maximum total thrust force.

Efficient heating system is critical for electric vehicles to extend the driving range. In this paper, an air source heat pump system with waste heat recovery (WHR) for the electric bus was proposed to improve the heating performance. According to the experimental results of the prototype, it’s found that the pressure drop of waste heat exchanger (WHX) has great effects on the heating performance and the heat exchanger is required to be optimized. The simulation model of this series system was developed and validated to study the heating performance of the series waste heat recovery system with low pressure drop WHX. The simulation results showed that heat recovery can improve the heating performance at the ambient temperature of −5 °C. Compared with the vapor injection heat pump without WHR, the heating capacity and COP of the heat pump at 2kW waste heat were increased by 1.61% and 1.38%, respectively. The improvements of heating capacity and COP at 6kW waste heat were 5.12% and 2.56%, respectively. As the ambient temperature is lower than 0 °C, the heating performance of heat pump system with 2kW waste heat is better than that of system without WHR. However, as the ambient temperature rises, the heating performance of heat pump with WHR becomes worse.

Solar collector with horizontal double-row all-glass evacuated tubes has been extensively implemented in the solar water heating system engineering. The temperature distribution and stratification of horizontal double-row all-glass evacuated tubes collector with 24 evacuated tubes have been studied. Validation of instantaneous efficiency under different declination angle θm were studied by means of experiments. Moreover, numerical simulations are carried out for four different declination angle θm (0°/2°/4°/6°). The results showed that the declination angle θm has significant effect on energy conversion efficiency, flow patterns and stratification inside evacuated tubes. When θm > 0, with the declination angle increased, instantaneous efficiency increased, the less obvious the temperature stratification, and not a significant change in heat loss coefficient. Declination angle 6° allowed to achieve significant higher temperatures, nevertheless, along with inactive area at the bottom of evacuated tubes appears. If declination angle θm < 0, inversion phenomenon appears, with the increase of |θm|, more heat is trapped in the sealed end of the evacuated tube, which is not conducive to the flow heat transfer in evacuated tube solar collector.

Previous studies found mineral wastes (MW; incineration bottom ash (IBA), cement based waste (CBW), Fly ash (FA) and boiler ash (BA) are a promising resource for the macro-/micronutrients necessary for anaerobic digestion (AD) processes. The current study used first-order and modified Gompertz models from BMP assays to investigate the effects of integrating MW on the AD of OFMSW at 37 °C. Results from the first-order model showed a 45% increase in the specific growth rate of microorganisms (μ) in the MW- supplemented BMP compared to the control. Gompertz model results indicated that the IBA, CBW, FA and BA BMP amended assays obtained the highest K values (45–54 mL CH4 g VS−1 d−1) than the control (K ∼ 31 mL CH4 g VS−1 d−1), with no significant adverse effects of co-digestion of OFMSW with MW on the length of the lag phase (λ) in BMP assays (λ = 1.89 ± 0.07 days for IBA, CBW and BA amended assays compared to 1.5 ± 0.01 days for the control). However, FA amended assays had a greater λ value (3.66 ± 0.1 days). The MW provided both alkalinity and released several trace elements at concentrations within the optimal ranges for methanogenic archaea.

Solid acid catalyst (SAC) was synthesized via direct treatment of cacao shells (CS) with concentrated sulfuric acid at varying temperature (80, 100, 120 °C) and time (4, 6, 8 h) settings. The synthesized catalysts were found to have sulfonic acid density ranging from 0.6326 to 0.8500 mmol SO3H/g dry CS-SAC and total acid density from 6.0509 to 7.1165 mmol H+/g dry CS-SAC. The catalytic activity is dependent on the sulfonic acid density of the catalyst. Catalyst synthesized at 120 °C for 6 h showed the highest sulfonic acid density (0.85 mmol SO3H/g catalyst) corresponding to highest catalytic activity (5.73 mmol OA converted/mmol SO3H·h) and a conversion of ∼39% after a fixed reaction time of 4 h and carried out at 65 °C. Conversions of up to 76% could be achieved after 24 h. The catalyst was reused for 4 cycles and was able to retain 78% of its catalytic activity from the 2nd to the 4th cycle. Direct sulfonation may be an alternative to conventional synthesis process.

Marine fouling changes the flow regime around sub-sea structures, such as Vortex-Induced Vibration Aquatic Clean Energy (VIVACE) converters. The present experimental study investigates the effects of marine fouling on mechanical power harvesting performance from the Vortex-Induced Vibration (VIV) of single circular cylinders. The towing tank VIV tests are conducted on elastically mounted rigid cylinders. Hard artificial marine fouling with aggregated spatial distribution is considered. Effects of coverage ratio and spatial distributions are investigated. The test results show that, on the whole, marine fouling suppresses the VIV oscillations. Over the upper branch, lower branch and the de-synchronization zone of the VIV response, energy transfer ratio (η) with the biofouled cylinders stay around 15 to 36% below that from the corresponding clean cylinder. It is also found that the coverage percentage of the fouling and the fouling irregularity negatively affect the VIV hydro energy transfer ratio. The fouling irregularity effects, however, are less significant than those from the coverage percentage. The results of the study suggest that biofouling growth may considerably degrade the long-term energy extraction performance of a VIVACE device.

The actual requirements of the energy market enforce the hydraulic turbine to operate far from the best efficiency point. When hydraulic turbines operate at partial discharge, downstream of the runner (in the conical diffuser), the decelerated swirling flow becomes highly unstable. In these conditions a spiral vortex breakdown occurs, also known in engineering literature as the precessing vortex rope. The flow unsteadiness produced by the vortex rope results in severe pressure fluctuations that hinder the turbine operation or may cause accidents. We propose the water jet method for decelerated swirling flow with vortex rope from conical diffuser to mitigate the unsteadiness. The method involves injecting water at the inlet of the conical diffuser. Initial experimental investigations of the unsteady pressure field at conical diffuser wall reveal that the water injection method mitigates the pressure pulsations associated to the precessing vortex rope. In this paper, we investigate experimental measurements of the unsteady velocity field in a conical diffuser using LDA (Laser Doppler Anemometry). The main goal of the paper is to show how different water-jet discharge rates change the velocity field and the characteristics of the vortex rope in the wake.

The high emissions of substances harmful to the environment associated with the activity of people, has become a point of extreme importance, since it depends on the subsistence of life on the planet [1]. Manufacturing processes and the application of new technologies improve substantially the life, but some processes contribute more to the damage to the environment. These manufacturing processes require a high consumption of energy and resources, which entail environmental impacts, some of them not quantified. For this reason, the reduction of emissions has become the battlefield in the fight for the preservation of planet. To determine and quantify the impacts that occur in a product, process or system, it is necessary to perform an analysis of the flows of energy and resources that occur throughout its life cycle. That is why the LCA has become a very important tool in the process of transition to a low-emission production economy [2]. There are systems that, although considered renewable, also produce impacts on the environment. That is why, the present work, and through the LCA, determines the impacts produced by two heat generation systems, to later be able to compare them with each other.

The feasibility of installation and performance of vertical ground source heat pump (GSHP) systems for heating and cooling of a typical 9000 m2 office building located in ten metropolitan cities with tropical and subtropical climates are investigated. The heating and cooling loads of the identical building in the ten cities are simulated using the EnergyPlus software. For each location, the design of the GSHP system is performed using the ground loop design (GLD) software, and the performance of the GSHP system is assessed. A multi-year cost analysis is also carried out to assess the feasibility of installation of GSHP systems from an economic point of view. It is found that GSHP systems may not be economically viable for the cities in tropical climates, particularly those near the equator, because of inefficient performance and high cooling demand. Thermal imbalance in soil caused by significantly greater cooling demand than heating demand may further exacerbate the system in tropical cities. However, the implementation of GSHP may turn into a feasible option for some of the tropical cities located near the Tropic of Cancer by adopting special design techniques or including additional hybrid energy sources. GSHP systems seem to be economically feasible and operationally efficient in the cities with subtropical climates where more balance between heating and cooling loads exist.

Batch experiments were conducted to study bioelectrochemical enhancement of the anaerobic digestion (AD) of alkaline-pretreated sewage sludge in microbial electrolysis cell (MEC) in the presence or absence of phosphate buffer solution (PBS). Experimental results showed that the maximum methane production rate was increased from 0.18 mL-CH4/(mLreactor·d) (control) to 0.2 mL-CH4/(mLreactor·d) in the presence of PBS and cumulative methane production was 1.4-fold higher than that of control. The initial concentrations of SCOD, protein, polysaccharide and VFAs in the presence of PBS were slightly higher than those of control, suggesting that PBS might facilitate the release of organics into mixed liquor. The microbial community analysis results showed that the microbial community with PBS had higher diversity and Bacteroidetes and Firmicutes were the two most abundant phyla in the communities. Moreover, the PBS addition could enhance the growth of aceticlastic methanogens (Methanosaeta) and inhibit a portion of hydrogenotrophic methanogens (Methanobacterium), possibly due to the different cell wall composition.

Supplying the energy needs of a community through renewable energy sources is a vital aspect in developing sustainable communities. Many variations and uncertainties affect the development of a renewable-powered net-zero energy system. Community developers face challenges in making the investment decisions when planning community-level renewable energy (RE) projects. This study aims to address the need for reliable methods to assess RE project deployment strategies. To achieve this, the key decision variables were identified and dynamic project performance was assessed for a Canadian RE case study. A framework was developed using system dynamics for rating renewable energy project deployment scenarios. A fuzzy logic-based optimization process was used to identify the optimal system capacities and energy mix. The optimal energy supply mix was identified as follows for the case study: grid electricity- 56%, solar PV – 28%, biomass – 11%, and waste-to-energy– 5%. The results of the system dynamics based rating indicated that stage-by-stage construction that also accounts for community growth in facility capacity sizing provides the best outcomes for the community, with 42.8% of the community's energy demand supplied with renewables. The developed model can help community developers to identify the best energy choices and investment strategies when planning community energy systems.

In this study, a model is developed to estimate the cost-optimal large-scale economic potential of shared rooftop PV systems based on neighbourhood energy communities (ECs). In a first step, an optimisation model determines the cost-optimal rooftop PV capacities for representative neighbourhood ECs in characteristic settlement patterns (SPs). Next, the number of ECs in the large-scale area of investigation is determined by allocating buildings to SPs and ECs. Finally, the optimal large-scale, EC-based rooftop PV potential is determined by upscaling. A case study is provided for Austria, identifying a cost-optimal economic rooftop PV potential of approximately 10GWp. This PV capacity would already be sufficient (in terms of expected PV deployment) to meet the Austrian 2030 policy goal of a 100% renewable electricity generation. However, results also indicate that accommodating the cost-optimal rooftop PV capacity is difficult in cities/towns in contrast to rural areas. Thus, future ECs should be implemented not only on neighbourhood level, but across the boundaries of different SPs. Different sensitivity analyses are conducted, notably in terms of varying retail electricity prices, including a variation of distribution grid tariff structures, and PV system cost. The trade-off between these sensitivity parameters is critically discussed and provides recommendations for future work.

Solar air collectors (SAC) convert the available solar energy into useful thermal energy for different heating applications such as drying, space heating, hot water etc. The study aims to enhance the thermal performance of a flat plate SAC by modifying the absorber surface. The experimental performance of two variant SACs (a sand coated absorber to increase surface roughness and a conventional plain absorber) was compared under controlled laboratory conditions The experimental tests were performed under a solar simulator for radiation levels of 400, 600, and 800 W/m2 and variable air mass flow rate ranging from 0.01 to 0.02 kg/s/m2. Results indicated that increasing the air flow rate by 90% enhanced the thermal efficiency on a plain absorber SAC by almost 68%, and the rate of increase was higher for the sand coated absorber. SAC with the sand coated absorber provided additional surface area resulting in an increase in the effective heat transfer. The thermal efficiency of the collector was improved by up to 17% for the sand coated absorber compared to the plain absorber. The absolute thermal efficiency of the SAC varied from 19% to 41% under the different tests conditions.

Knowledge of borehole heat exchanger efficiency is necessary to optimize the design and performance of ground source heat pump systems. To evaluate the heat transfer performance of the wildly-used vertical U-pipe BHE, a novel one-dimensional numerical model was developed to assess the thermal transfer performance of the BHE from short-term (thermal response test) to long-term (a heating period) for engineering application. The proposed numerical model took into account the internal capacity of the borehole and the thermal resistance between the two legs of U-pipe which are often negligible in traditional one-dimensional numerical models. A thermal response test data from a case at Vorbasse, Denmark and the data from the TRNSYS model were used to validate the feasibility and reliability of the presented model. Then, both a short-term thermal response and a long-term temperature development of the fluid in BHE and surrounding ground were simulated and analyzed based on the model. Additionally, this study did a sensitivity analysis to see what effect the parameters have on the BHE efficiency. Hereby the impact of given assumptions can be able to estimate and the results can serve for the optimum design and control of GSHP systems.

Gearbox is one of critical transmission components in wind turbine (WT) having a high downtime rate among all subcomponents. Fault prognostics and health management (PHM) of WT gearbox is crucial to their high reliability operation. However, presence of background noise in WT signals restricts the applicability of existing PHM approaches in feature extraction. To solve this problem, a novel performance degradation assessment method based on deep belief network (DBN) and self-organizing map (SOM) is proposed to de-noise and merge multi-sensor vibration signals. Minimum quantization error (MQE) is defined as health indicator to detect incipient fault of WT gearbox. After health indicator construction, an improved particle filtering (PF) optimized by fruit fly optimization algorithm (FOA) is employed to predict the remaining use life (RUL) of WT gearbox. To take advantage of dynamic and random operation process of WT gearbox, Wiener-process-based degradation model is developed to improving RUL prediction efficiency. The effectiveness is validated by using simulated as well as experimental vibration signals obtained through a WT gearbox highly accelerated life test. The results illustrate that proposed method can evaluate performance degradation process and predict RUL of WT gearbox effectively.

A variable speed photovoltaic direct-current (DC) refrigerator (VSPVDR) system is proposed in this paper. In the VSPVDR system, the photovoltaic (PV) cells are directly connected to the compressor without batteries and inverter, and the DC compressor speed changes with the radiation intensity. In the paper, a dynamic model is presented to simulate the behavior of the VSPVDR, and several prototype experiments are conducted to validate the model. On this basis, the impacts of the compressor speed control strategy, ambient temperature and the radiation intensity have been studied. Compared with the fixed speed mode, the cooling capacity of the variable speed mode increases by 32.76% and the average PV utilization efficiency increases by 45.69%. When ambient temperature increases, the average cooling capacity decreases significantly, but the increase of average power consumption is not obvious, which reveals that the ambient temperature has greater influence on the cooling capacity and has less influence on the power consumption. The radiation intensity has a significant impact on system performance. When the radiation intensity increases, the cooling capacity increases significantly.

Dark fermentation is an anaerobic digestion process of biowaste, used to produce hydrogen as a fuel, which however releases high amounts of polluting volatile fatty acids in the environment. In order for the process to become more competitive, the acids stream can be utilized through conversion to high added-value docosahexaenoic acid by the microalga Crypthecodinium cohnii. Docosahexaenoic acid is one of the two main omega-3 fatty acids, necessary for human nutrition. The purpose of this work was to optimize the production of omega-3 fatty acids by the cells, utilizing the organic content of a dark fermentation effluent. For that purpose, the effect of different fermentation conditions was examined, such as incubation temperature, nitrogen source and concentration, the addition of chemical modulators, as well as the feeding composition. The volatile fatty acid content of the effluent was totally depleted in a fed-batch culture of the microalga, while the cells accumulated DHA in a percentage of 35.6% of total lipids, when fed with yeast extract or 34.2% when fed with ammonium sulfate. Taking into consideration the economic feasibility of the culture conditions proposed it was concluded that the use of yeast extract could be substituted by the much economic ammonium sulfate.

New systems using solid particles for solar energy capturing, heat transfer and thermal energy storage have been proposed and analysed in direct particle solar receivers. In this work, black coloured silica sand was investigated as a possible solid particle for such combined systems. Two different methods based on a carbon coating approach were implemented to black colour the initial material to improve their solar absorption characteristics. The morphology of the raw and coloured sands was analysed by scanning electron microscopy (SEM), particle size characterisation and porosity measurements. The coating of the black-coloured silica sands was evaluated by thermogravimetry. Solar absorption was characterised in a double-beam UV-VIS spectrophotometer combined with an integrating sphere, and with enhancements of approximately 100%, found for both coloured sands. The thermal storage and heat transfer capabilities of the initial and coated sands were measured at different temperatures. Some improvements in the specific heat capacity and reductions in thermal conductivity due to porosity changes were observed.

Macroalgae are promising renewable energy resources due to their high biomass production rate, high photosynthetic efficiency, faster growth rate, low lignin content, and higher CO2 fixation capability. The conventional methods for macroalgae pre-treatment involve energy-intensive processes which require high pressure and elevated temperatures, often requiring alkali or acidic compounds. Recently, ionic liquids are gaining interest as environmentally benign solvents due to their ability to deconstruct the biomass cell wall under relatively milder conditions. In this review, current developments involving IL-based pre-treatment technologies are discussed. A brief background about macroalgae and its traditional pre-treatment methods are presented. Different IL pre-treatment approaches are then discussed, highlighting the dissolution mechanism and selection criteria for an effective IL. Unique pre-treatment strategies, such as acidic ILs, IL blends, task specific ILs and bio-ILs are also explored. Finally, challenges and opportunities related to macroalgae processing using ILs are addressed.

Fast pyrolysis has been recognized as an efficient and feasible way to produce liquid fuels from biomass. For the aim to upgrade the products from fast pyrolysis of hemicellulose, reduced graphene oxide supported Pt nanoparticles (Pt/RGO) was adopted as catalyst for in situ catalytic fast pyrolysis (CFP). Pt/RGO was prepared by one-step thermal reduction method, and further employed as catalyst for in situ CFP of xylan. Online single-photon ionization time-of-flight mass spectrometry was employed to detect the volatile products, and furans were chosen as the model compounds. The experimental results showed that Pt/RGO distinctly increased the intensity of furans products from xylan pyrolysis, as the increase rates were respectively 80.5%, 64.4% and 50.2% in 400 °C, 500 °C and 600 °C. Furthermore, Pt/RGO can accelerate the process of xylan pyrolysis and be effective in eliminating oxygen for furans products. With addition of Pt/RGO, O/C ratio for furans products decreased from 0.38 to 0.32 in 400 °C, 0.37 to 0.32 in 500 °C, and 0.35 to 0.32 in 600 °C, respectively. This work proved that Pt/RGO had the potential to be a highly efficient catalyst for upgrading of the volatile products from in situ CFP of biomass.

The viability of thermochemical energy storage for a given application is often determined by the reaction kinetics under process conditions. For high exergetic efficiency the process needs to operate in close proximity to the reaction equilibrium. Thus, accurate kinetic models that include the effect of the reaction equilibrium are required. In the present work, different parametrization methods for the equilibrium term in the General Kinetic Equation are evaluated by modeling the kinetics of two reaction systems relevant for thermochemical energy storage (CaC2O4 and CuO) from experimental data. A non-parametric modeling method based on tensor decompositions is used that allows for a purely data driven assessment of different parametrization methods. Our analysis shows that including a suitable equilibrium term is crucial. Omitting the equilibrium term when modeling formation reactions can lead to seemingly negative activation energies. Our tests also show that for formation reactions, the reaction rate decreases much faster towards the equilibrium than theory predicts. We present an empirical modeling approach that can predict the reaction rate of gas-solid reactions, regardless of the shortcomings of theory. In this way, non-parametric modeling offers a powerful tool for applied research and may contribute to the advancement of the thermochemical energy storage technology.

In this study, a solar-powered absorption cooling system was modelled using the TRNSYS software. The performance of the system was investigated using dynamic modelling under the weather conditions of Mugla, Trabzon, Izmir, Konya, Canakkale and Istanbul. The external catalog data file of the absorption chiller model was created to get more realistic results. A parametric study was carried out to evaluate the selected parameters’ influence on system efficiency. Various parameters such as solar collector type, area, storage tank volume, collector slope, boiler setpoint temperature, room thermostat set point temperature were investigated to see their impact on the performance of the solar-absorption system, in every city. Instead of using a constant boiler setpoint temperature, a novel control strategy is proposed. Besides, the payback period and the levelized cost of cooling of the optimized systems were studied. Results showed that, in terms of financial analysis, Izmir is the most suitable city for solar-based absorption cooling system applications with a payback period of 10.7 years. Trabzon is found to be the least suitable city due to the longest payback period, and the highest levelized cost of cooling among all locations.

Solar storage tanks are key to ensuring the high efficiency of concentrated solar power plants, and phase change materials are the most important storage energy media influencing system efficiency. Therefore, as energy storage or release mechanisms are a focus of related research. In this study, numerically analysed the thermal performance of a small capsule of three different phase change materials for a packed bed solar energy storage system. Air and molten salt are used as the heat transfer fluid (HTF) and the phase change material (PCM), respectively. A model based on a concentric-dispersion model and the enthalpy method was used to analyse the phase transition of the PCM. The equation was solved using the finite- difference method, and the results were verified using previous experimental data. The influence of particle diameter, porosity, and height-to-diameter ratio of the storage tank on the total storage energy, storage capacity ratio, axial temperature curve, and utilization ratio of the PCM were studied. It was found that he storage capacity and utilization rate of 3-PCM energy storage tanks are relatively high. And that increase from 86.07% to 86.65% and 86.07% to 86.67%, respectively, when the porosity is reduced from 0.6 to 0.1. This results in an increase in the total storage energy of 5.2 ×1012 Wh to 1.3 ×1013 Wh. Similarly, when the particle diameter decreases from 0.6 to 0.1, the storage capacity ratio and utilization rate increase from 85.8% to 87.3% and 85.6% to 87.4%, respectively. However, although these increases are larger, the increase in total energy storage is small. Finally, it was found that the shape of the tank has no effect on the storage capacity at a fixed tank volume. The proposed model provides a reference value for energy storage in a concentrating solar thermal power (CSP) system.

Lidar based wind measurement is an integral part of wind farm control. The major issues and challenges in power maximization include the potential losses due to wake effect observed among wind turbines. This manuscript presents a wake management technique that utilizes lidar simulations for wake redirection. The proposed methodology is validated for 2-turbine and 15-turbine wind farm layouts involving a PI control based yaw angle correction. Yaw angle misalignment using wake center tracking of the upstream turbines is used to increase the power generation levels. Results of wake center estimation are compared with a Kalman filter based method. Further, the velocity deficit and overall farm power improvement by yaw angle correction is calculated. Results reveal a 1.7% and 0.675% increase in total wind farm power for two different wind speed cases.

This paper proposes a generalized methodology to calculate the parameters of the single-diode or double-diode models of a photovoltaic module. The presented method relies in the solution by a simple iterative process of the set of equations obtained from the photovoltaic-module's equivalent circuit. The use of the generalized form of Tellegen's theorem allows the solving of the equivalent circuit's equations in an exact way, without making considerations or approximations commonly used in previous works. The parameters of the equivalent circuit are obtained from the standard conditions of: open-circuit, short-circuit and maximum power, provided by the manufacturer in the data sheet of the photovoltaic module. The presented method is applied to obtain the models of several commercial modules. The accuracy of the obtained parameters is greater than that of the results previously determined by other authors. The curves calculated with the obtained models matches the experimental curves supplied in the manufacturer's data.

This work presents a simplified model for the rapid computation of the yearly solar fraction of direct solar water heating systems using on-off control. Thermal stratification was included using a simple one-dimensional multi-node model. A time-step dependency analysis showed that a time step of 0.05h is a good compromise between accuracy and computation speed. The solar fraction increases with collector flow rate when the flow rate is low. In fully-mixed storage, the solar fraction keeps increasing with flow rate, although with a decreasing rate of increase. However, in stratified storage, the solar fraction reaches a maximum at an optimum flow rate, before it starts decreasing with flow rate. When the number of tank nodes increases from 1 to 4, the maximum solar fraction increases 5–28%; this increase is superior for less efficient collectors and lower collector areas. In low-stratified systems, the optimum flow rate is the maximum allowed by the system. However, in stratified systems, the optimum flow rate is reduced to values of 0.006–0.016m3h−1 per square meter of collector area. Unless the tank walls are covered by a rather thick layer of thermal insulation (about 0.2m), storage tank losses cannot be ignored.

In this study, banana slices were dried at different temperatures in a closed-loop heat pump drying system. As the temperature and the slice thickness increased, the drying time also increased. Midilli & Kucuk model was found to be the best model to explain the experimental data. The effective moisture diffusivity ranged from 1.12 × 10−10 to 1.64 × 10−10 m2/s. The dependence of moisture diffusivity on temperature was described by an Arrhenius-type equation and the activation energy was found to be 51.43 kJ/mol. The highest mean specific moisture extraction ratio (SMER) and coefficient of performance (COP) of HPD system were obtained as 0.212 kg/kWh and 3.059, respectively, at the highest drying air temperature.

Most of the k−ε closures for modeling stratified surface layer are derived from the classical similarity functions and might fail in complex terrain due to limitations of the classical similarity functions. Despite the classical similarity functions to limit the flux Richardson number Rf, we present new similarity functions estimated from field measurement in full range of Rf and propose a k−ε model using the new similarity functions to improve predictions of stratified surface layer flows in complex terrain. Measurements show that the classical similarity functions are partially valid in complex terrain and the wind shear under strongly stable conditions is constrained at large Rf. According to numerical studies in two areas of complex terrain, models using the classical similarity functions and the new similarity functions both present good predictions of convective airflows in complex terrain. The new similarity functions are shown to significantly improve the k−ε model in predicting stably stratified airflows in complex terrain by constraining the wind shear at large Rf, while the classical similarity functions without limiting the wind shear lead to significantly misestimating the wind speedup factor under stable conditions. Using the proposed model to predict flows in wind farm could benefit wind resource estimation and wind power forecasting.

Local fish markets are often saturated during periods of full production. Solar drying offers a suitable alternative to reduce losses of surpluses, and to preserve products for a longer period. In this respect, this work was carried out to study the effect of the air indirect solar convective drying process on the dehydration kinetics of anchovy. Experimental drying kinetics was measured at four air temperatures (50, 60, 70 and 80 °C) and for a constant air flow of 300m3/h. The moisture desorption isotherms of the anchovy were determined at three temperatures (30, 40 and 50 °C), using the static gravimetric method to determine the optimum water activity for conservation of the nets anchovy. Experimental results showed that the drying kinetics of the anchovy was accelerated synchronously with the increase of the air temperature. The value of optimal water activity for conservation of anchovy is aw=0.30 and the desorption isotherms suggest a non spontaneous process. Nine drying models were adapted to the drying data; the Logaritmic model allowed better adaptation than the other models. The effective diffusion coefficient value Deff determined by Fick’s second law varied from 3.84 10-9 to 5.60 10-9 m2/s and the activation energy value was Ea=12.90 kJ/mol.

Feasible heating systems have been designed to increase the availability of open-air swimming pools in winter in subtropical climate regions. However, the approach to optimally size the main components of the system from multiple aspects is lacking. A techno-economic optimization method for swimming pool heating systems is proposed here. Minimizing the lifecycle cost of the system while ensuring the thermal comfort of the pool are considered as the optimization objectives. The volume of phase change material storage tank and the heating capacity of air-source heat pumps are selected as design variables. To improve computational efficiency, surrogate models are developed using the response surface approach, in which the dataset is generated from the simulation platform established using MATLAB and TRNSYS. Generic algorithm and non-dominated sorting genetic algorithm II are adopted to conduct single-objective and double-objective optimizations, respectively. Case studies indicate that optimal combinations for the size of main components can be identified using the proposed optimization approach. The energy and economic performance of the heating system are enhanced after optimization. The proposed techno-economic optimization method provides an instructive guideline for the optimal design of swimming pool heating systems.

Residues from management activities of fruit growing can be an important source of biomass for energy generation. The aim of this study was to determine the potential use of apple pruning residues for energy generation as process steam or power energy. To this end, branches from the pruning of commercial apple orchards have been evaluated in the Santa Catarina State, Brazil. To compare with the traditional biomass used for energetic purposes, particles of Pinus sp. from the industrial timber processing have also been analyzed. Homogeneous pellets of the two types of biomass were produced, and three more mixes containing the two raw materials were made. Pellets have been evaluated according to their physical and energetic properties. The results have been compared to the ISO 17225-2 Standard. Apple pruning residues have the potential for energy generation in boilers, that is, for the production of process steam and electric power. Their potential can vary from 12,649.54 MWh y-1 to 115,442.44 MWh y-1. The physical and energetic properties varied between the analysed residues, except the gross calorific value (19.69 MJ kg-1 for pine wood particles and 20.27MJ kg-1 for apple pruning). Comparing with the pine wood (87 kg.m-3), the apple pruning (141 kg.m-3) has a higher amount of biomass per unit volume processed for energy and less residence time in the burning systems (17.54% fixed carbon for apple pruning and 18.91% fixed carbon for pine wood). However, it generates more wastes (ashes) after burning (3.25% for apple pruning and 0.46% for pine wood). The pellets’ energy density increased by 3.35 times the energy density of the apple pruning particles after pelletizing. The homogeneous apple pruning pellets can only be applied to industrial use (I3), mainly because of its high ash content (2.27%). The pine wood with apple pruning mix used for pellet production reduces the ash content and increases the bulk density and energy density, which improves the quality of the pellets.

Methanolysis of biomass has attracted increasing attention due to it has some advantages, such as low critical points and strong hydrogen donation ability. In this paper, methanolysis of cellulose, cellobiose (sucrose), and monosaccharide (glucose) were performed to obtain methanol-soluble portions (MSPs). The relatively volatile or less polar species in the MSPs were analyzed with a gas chromatograph/mass spectrometer (GC/MS), and the polar species were identified with a negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometer (FTICRMS). According to analysis with GC/MS, the MSPs include ethers, esters, ketones, acids, sugars, phenols, and furans. The analysis with FTICRMS shows that the polar compounds in the MSPs are O1–O15 class species with 1–14 double bond equivalent (DBE) and 5–35 carbon atom number (CAN). The most abundant class species in MSPs from cellulose, sucrose, and glucose methanolysis are O5, O7, and O7, respectively. The species in MSPs from sucrose and glucose methanolysis center at higher DBE value and more CAN than those in MSP from cellulose methanolysis. Meanwhile, the oxygen atom number of O4–O10 class species in the MSPs were negatively correlated with the average DBE value. The results indicate that condensation intensively proceeded with the specific regularity during sucrose and glucose methanolysis.

In Afghanistan, more than 60% of the population does not have access to a reliable source of electrical energy. A thermo-economic analysis is conducted to compare the performance of a Photovoltaic (PV), Central Tower Receiver (CTR) plant and a Parabolic Trough Collector (PTC) plant with and without storage for the city of Herat, in Afghanistan. The nominal capacity of both plants is 110 MWe. The PTC plant with energy storage has the highest efficiency of about 43% that is approximately 50% more than the PV plant, however, the PV plant has more uniform power production profile. The output power of PTC with energy storage is 25% more than output power of PTC without energy storage and output power of CTR plant is half of PTC plant with energy storage. The Levelized Cost of Electricity (LCOE) is 0.146 $/kWh for CTR plant, 0.063 $/kWh for PV plant, 0.1076 $/kWh for PTC plant with energy storage, 0.104 $/kWh for PTC plant without storage and 0.12 $/kWh for PTC plat without storage and without backup fossil fuel systems. Increase of incentive by 10% leads to decrease of LCOE by about 20% for PTC and 13% for PV and 12% for CTR power plants.

The main aim of this paper is to accelerate the drying process of black ginger in a forced convection mixed mode horizontal solar dryer (FCMHSD) by using two successive air mass flow rates. When the drying rate attains the falling rate period, air mass flow rate has minimal effect on drying rate. To diffuse bound moisture present in the product, air mass flow rate has to be reduced for raising the air temperature in the solar dryer. In this manuscript, two cases were considered for drying; Case – 1 with constant air mass flow rate of 0.062 kg/s and Case – 2 with two successive air mass flow rates of 0.062 kg/s during the initial period of drying and 0.018 kg/s during the falling rate period. The performance of FCMHSD was evaluated in terms of drying time, drying efficiency, specific energy consumption (SEC) and moisture diffusivity. The estimated SECs for Case – 1 and Case – 2 were 1.07 kWh/kg and 0.56 kWh/kg, respectively. A significant improvement in thermal performance and moisture diffusivity were observed when the FCMHSD operated under Case – 2 than under Case – 1. The use of two successive air mass flow rate is a new approach for accelerating the drying process.

Hurricanes induce multiple hazards including high wind speeds, large waves, and storm surge. The characteristics of these hazards have an important effect on the design of offshore structures and determine the suitability of simplifying assumptions for modeling, such as whether the maxima can be reasonably modeled as occurring simultaneously during the hurricane and whether N-year values of the hazards can be modeled separately and combined. Such assumptions are common in practice. Assessing the implications of these assumptions to better inform hazard modeling along the U.S. Atlantic coast is the central objective of this paper. To this end, the characteristics of wind speeds, waves, and storm surge, during hurricanes are evaluated for ten areas where development of offshore wind is proposed. The assumptions are evaluated for a model of an offshore wind turbine using time histories of hazards during intense hurricanes and using so-called environmental contours constructed through a novel implementation of the Inverse First Order Reliability Method. The results of this study show that these assumptions are reasonably accurate, especially for wind and wave in shallow waters and for wind and surge in deep waters. Hazard ratios are proposed as a suitable representation of the characteristics of hazard maxima.

The combined increase of energy demand and the amount of greenhouse gases (GHG) in the atmosphere force the power generation to ride by a sustainable path. Photovoltaic conversion is one of the emerging technologies pointing out as a potential source of energy for the coming years. The aim of this study is to propose a sustainable hydro-solar model to substitute the current model of power production in Brazil. The review of floating PV power plants has pointed very small participation of this technology despite the exceptional country's geophysical condition. The big land extension occupied by solar panels to generate significant amounts of energy suggests the use of open water surfaces for the installation of large PV plants. The expressive amount of flooded areas by Hydro-Electric Power Plant (HEPP) reservoirs was evaluated to identify the potential for the implementation of PV Floating Power Plants (PV-FPP) near the HEPP dams. As a result of this study, the authors had found that by using less than 10% of their surface the HEPP reservoirs in Brazil can accommodate PV-FPP supplying the electricity demand with solar energy during peak irradiation hours while balancing grids with hydro-power during low/no irradiation times, improving the operational flexibility.

The wave energy can be a critical solution for growing international renewable energy demand. The present study demonstrates the wave potential of the southern side of the Caspian Sea. In this regard, the mathematical equation of the wave energy was presented. Moreover, the wave energy simulation was performed using the wind data from ECMWF within 2011–2015 by implementing the MIKE software. For this reason, nine nominated stations were presented and the wave height characteristics and the maximum wave potential were evaluated in order to validate the results of the simulation, Amirabad and Neka stations were selected and the results were compared and good agreement was observed. Moreover, a mesh structure was presented to demonstrate the depth variation of the Caspian Sea. The results of the simulation were achieved for nine stations and the wave height and peak wave period was demonstrated. The wave power contours were revealed for every station. The result showed that the May (0.9 kW per meter) and December (3.6 kW per meter) have the lowest and highest wave energy potential for selected stations.

The proposed framework produces wind resource maps and estimates the energy production in complex terrain by combining computational fluid dynamics (CFD) with observations from an arbitrary number of masts. It provides a fast and comprehensive solution to the research gap that is to obtain accurate CFD inflow conditions and to mitigate the modeling error by incorporating observations to produce a wind resource map and estimate energy yield. Wind data are processed by direction bins both to initialize simulations and to combine with the latter. The wind resource map is then obtained by superposing the power density maps from each sector. Ultimately, a database containing different turbine models and hub heights is used to filter the best performing cases. Validation at two complex terrain sites reveals that the wind flow model is sufficiently accurate using the proper parameters, and that reasonable inflow conditions and assimilated wind speed fields are achieved. The framework was tested at a complex site in Brazil and was more sensitive to the number of simulated wind directions than to grid refinement. This research provides a comprehensive contribution toward wind resource mapping in complex terrain because it is computationally fast and flexible in the number of masts.

A precessing vortex core in the draft tube of Francis turbine is considered as unstable flow conditions and the cause of many undesirable system instabilities for hydraulic power stations. The feature of vortex rope, pressure fluctuations and runner outlet velocity at part-load conditions are investigated experimentally and numerically in this paper. An obvious vortex rope could be observed at 0.88Q11BEP point and produces the most intensive periodic pressure fluctuation at the vortex rotation frequency fv along the whole passage of Francis turbine. At other conditions away from this point, the vortex rope becomes unobvious or even invisible, and the associated pressure fluctuation amplitude also reduces. This trend could be well represented by the new parameters G and Vs, which could be used to determine the strength of helical vortex field based on the gradient of time-averaged velocity on horizontal section of the draft tube cone. Transient simulations using VLES turbulence model could obtain satisfying results by comparing with experimental data, especially in terms of the time-averaged axial velocity profile resolution. Therefore, this new method enables the designers to evaluate vortex strength in engineering applications.

Because of the clearance and pressure difference between the pressure side (PS) and the suction side (SS), the tip leakage flow developed and evolved into tip leakage vortex (TLV). The relationship between the swirling strength of TLV and the pressure difference between the PS and the SS was analyzed. The velocity distribution in the tip clearance was also investigated in a multiphase pump. The reliability of numerical method was verified using high-speed photography. The trajectory of TLV was found to be distributed in a wavy shape and the swirling strength of TLV was positively correlated with the pressure difference between the PS and the SS. The tip separated vortex was formed when the tip leakage flow entered the tip clearance, and the TLV was formed when tip leakage flow moved out of the tip clearance. The low-pressure region in the tip clearance consisted of two parts. The part near the PS was caused by the tip separated vortex, and the other part near the SS was caused by the TLV. In addition, the flow separation phenomenon occurred at the radial coefficient of 0.97 and led to the increase of the turbulent energy loss of the pump.

The objective of this paper is to study the flow regime and hydrodynamic performance for a pitching Clark-Y hydrofoil. The aims are to (1) improve the understanding of the interplay between the hydrodynamic performance, unsteady flow structures and dynamic motion of the hydrofoil, (2) study the influence of the pitching rate on the transition of different flow regimes. The experimental investigations were conducted in the looped cavitation tunnel, and the dynamic moment measurement system was applied to obtain the hydrodynamic forces. The pitching hydrofoil is controlled to rotate from α+ = 10° to α+ = 15° firstly, then goes from α+ = 15° to α− = 5°, finally goes back to α+ = 10° from α− = 5°. The pitching rate is varying with the Reynolds number Re = 4.4 × 105. The numerical investigations were performed by solving the incompressible URANS equations using the coupled k-ω SST turbulence model and γ-Reθ transition model. The numerical results agree well with the experimental measurements. The pitching motion affects the turbulence kinetic energy distribution around the hydrofoil, leading to the delay or acceleration of the transition between different flow patterns. During the pitching process, higher level of turbulence kinetic energy distribution causes earlier transition from laminar to turbulence. Moreover, hysteresis effect of the hydrodynamic force is observed. For the upstroke stage, the higher pitching rate promotes the laminar separation slightly and intensifies the delay of turbulence separation. For the downstroke stage, the higher pitching rate promotes the turbulence separation extensively. The first leading edge vortex (LEV) and anticlockwise trailing edge vortex (TEV) are delayed with the increase of pitching rate, which is responsible to the delay of dynamic stall. The lower pitching rate shrinks the hysteresis loops and intensifies the fluctuation of the dynamic force.

To meet the future energy demand and avert any looming crises, efforts are being carried out to utilize sustainable and renewable energy resources. In this paper, the naturally occurring non-linearity and non-stationarity deficiencies within the climatological predictors to forecast solar radiation (Rdn) are resolved via a multivariate empirical mode decomposition method (MEMD). First, a set of antecedent weekly lags at timescale (t-1) of input datasets were collated and then were divided into training and testing subsets. The MEMD method is restricted to dissolve the training and testing climatic data independently into intrinsic modes functions (IMFs). As the numbers of total IMFs were very large, the singular value decomposition (SVD) algorithm is accustomed for dimensionality reduction simultaneously capturing the most relevant oscillatory features embedded within the IMFs. Finally, the random forest (RF) model is applied to forecast Rdn at selected solar-rich regions in Australia. The resulting hybrid MEMD-SVD-RF model was established as a consequence of the aforementioned modelling strategy. The results are benchmarked with other comparative models. The hybrid MEMD-SVD-RF model generates better and reliable forecasts having significant implications for renewable and sustainable energy applications and resources management.

In this paper, we focus on the variation of the transmittance of the receiver glass envelope as a function of the incidence angle and we measure its impact on the annual optical efficiency of a LFR plant using ray-tracing techniques. For this purpose, we draw up a detailed model of the LFR collector installed on the roof of the School of Engineering of the University of Seville, Spain. We also calculate the optical efficiency with and without a secondary reflector and with constant or variable transmittance receiver glass envelope properties. We run simulations using a clear-sky annual 1-min synthetic data set as input and calculate an average annual optical efficiency using efficiency matrices and Incidence Angle Modifiers (IAM) obtained from ray-tracing simulations. We find that the effect of the variation of the receiver glass envelope optical properties, as a function of the incidence angle, reduces the annual optical efficiency by 2.5%when the LFR plant has a basic secondary reflector and by 0.7% when there is no secondary reflector, according to the results obtained when using constant optical properties. We also evaluate the performance of the system with an optimised secondary reflector design.

The grid adjustment is seriously affected by the instability of Pumped Hydro Energy Storage plants (PHES), one of which is the phenomenon of Positive Slope (PS) in pump turbine. In this paper, two positive slopes were experimentally captured on one curve of the discharge-head performance in a pump turbine while only one positive slope is observed on one pump performance curve in general pumps. The similarities and differences of two positive slopes are demonstrated using data obtained with this pump turbine model. It is found that two positive slopes are caused by two different stalls, respectively. For the first positive slope, the stall with five stall cells in the vane-less domain (between impeller and wicket gates) is induced to play a key role. On each pump performance curve, with the smaller opening of guide vanes, the discharge of the first PS is less, until the first PS and the second PS becomes one PS. For the second positive slope, significant complex vortexes in the impeller inlet, the variations of cavitations and a lower signal of pressure fluctuation are observed. The discharges of the second positive slopes almost keep stable with the different wicket gates’ openings. For their common characteristics, hysteresis phenomena are observed in both PS and are influenced by cavitations.