A photovoltaic array is environmentally friendly and a source of unlimited energy generation.However,it is presently a costlier energy generation system than other non-renewable energy sources.The main reasons are sea...A photovoltaic array is environmentally friendly and a source of unlimited energy generation.However,it is presently a costlier energy generation system than other non-renewable energy sources.The main reasons are seasonal variations and continuously changing weather conditions,which affect the amount of solar energy received by the solar panels.In addition,the non-linear characteristics of the voltage and current outputs along with the operating environment temperature and variation in the solar radiation decrease the energy conversion capability of the photovoltaic arrays.To address this problem,the global maxima of the PV arrays can be tracked using a maximum power point tracking algorithm(MPPT)and the operating point of the photovoltaic system can be forced to its optimum value.This technique increases the efficiency of the photovoltaic array and minimizes the cost of the system by reducing the number of solar modules required to obtain the desired power.However,the tracking algorithms are not equally effective in all areas of application.Therefore,selecting the correct MPPT is very critical.This paper presents a detailed review and comparison of the MPPT techniques for photovoltaic systems,with consideration of the following key parameters:photovoltaic array dependence,type of system(analog or digital),need for periodic tuning,convergence speed,complexity of the system,global maxima,implemented capacity,and sensed parameter(s).In addition,based on real meteorological data(irradiance and temperature at a site located in Addis Ababa,Ethiopia),a simulation is performed to evaluate the performance of tracking algorithms suitable for the application being studied.Finally,the study clearly validates the considerable energy saving achieved by using these algorithms.展开更多
Soil erosion/sedimentation is an immense problem threatening the live storage capacity of dam reservoirs in Ethiopia. This in turn reduces the power generation capacities of hydropower reservoirs. Therefore, studies w...Soil erosion/sedimentation is an immense problem threatening the live storage capacity of dam reservoirs in Ethiopia. This in turn reduces the power generation capacities of hydropower reservoirs. Therefore, studies which give insight into soil erosion/sedimentation mechanisms and mitigation methods is important. The high rate of soil erosion/sedimentation threats the lifespan of Gilgel Gibe-I hydropower reservoir, The problem of sedimentation in Gilgel Gibe-I will also affect Gilgel Gibe-2 which uses the water released from Gilgel Gibe-1. The sustainability of these hydropower plants needs catchment management practices that will reduce soil erosion. This paper presents the results of monthly and yearly sediment yield simulations experiments conducted for Gilgel Gibe-1 under different BMP （best management practice） scenarios. The scenarios applied in this paper are： （1） maintaining existing conditions; （2） introducing filter strips; （3） applying stone/soil bunds; （4） reforestation. The SWAT （soil and water assessment tool） was used to model soil erosion, identify soil erosion prone areas and assess the impact of BMPs on sediment reduction via simulations. The simulation results showed that applying filter strips, stone bunds and reforestation scenarios could reduce the current sediment yields at soil erosion prone areas and at the outlet of the catchment area which is the inlet to Gilgel Gibe-I reservoir.展开更多
Heterogeneous Networks(HetNets)and cell densification represent promising solutions for the surging data traffic demand in wireless networks.In dense HetNets,user traffic is steered toward the Low-Power Node(LPN)when ...Heterogeneous Networks(HetNets)and cell densification represent promising solutions for the surging data traffic demand in wireless networks.In dense HetNets,user traffic is steered toward the Low-Power Node(LPN)when possible to enhance the user throughput and system capacity by increasing the area spectral efficiency.However,because of the transmit power differences in different tiers of HetNets and irregular service demand,a load imbalance typically exists among different serving nodes.To offload more traffic to LPNs and coordinate the Inter-Cell Interference(ICI),Third-Generation Partnership Project(3GPP)has facilitated the development of the Cell Range Expansion(CRE),enhanced Inter-Cell Interference Coordination(eICIC)and Further enhanced ICIC(FeICIC).In this paper,we develop a cell clustering-based load-aware offsetting and an adaptive Low-Power Subframe(LPS)approach.Our solution allows the separation of User Association(UA)functions at the User Equipment(UE)and network server such that users can make a simple cell-selection decision similar to that in the maximum Received Signal Strength(max-RSS)based UA scheme,where the network server computes the load-aware offsetting and required LPS periods based on the load conditions of the system.The proposed solution is evaluated using system-level simulations wherein the results correspond to performance changes in different service regions.Results show that our method effectively solves the offloading and interference coordination problems in dense HetNets.展开更多
Vertical Axis Wind Turbines(VAWTs)offer several advantages over horizontal axis wind turbines(HAWTs),including quieter operation,ease of maintenance,and simplified construction.Surprisingly,despite the prevailing beli...Vertical Axis Wind Turbines(VAWTs)offer several advantages over horizontal axis wind turbines(HAWTs),including quieter operation,ease of maintenance,and simplified construction.Surprisingly,despite the prevailing belief that HAWTs outperform VAWTs as individual units,VAWTs demonstrate higher power density when arranged in clusters.This phenomenon arises from positive wake interactions downstream of VAWTs,potentially enhancing the overall wind farm performances.In contrast,wake interactions negatively impact HAWT farms,reducing their efficiency.This paper extensively reviews the potential of VAWT clusters to increase energy output and reduce wind energy costs.A precise terminology is introduced to clarify ambiguous terms researchers use to quantify cluster parameters.While examining commonly studied and proposed VAWT cluster configurations,several aspects are discussed such as aerodynamic interactions,wake characteristics,structural dynamics,and performance metrics.Additionally,the current state-of-the-art and research gaps are critically described.The review also covers computational modeling,optimization techniques,advanced control strategies,machine learning applications,economic considerations,and the influence of terrain and application locations.展开更多
This study looks into the resource assessment, technology economics and modeling of different energy alternatives and proposes a rechargeable battery storage-based large-scale wind/photovoltaic hybrid power system to ...This study looks into the resource assessment, technology economics and modeling of different energy alternatives and proposes a rechargeable battery storage-based large-scale wind/photovoltaic hybrid power system to meet an average electrical load demand of 2.4 MW and peak load of 2.9 MW for a remote rural district in Ethiopia called Geladin. The district is 682 km away from nearby grid. The site enjoys high solar and wind resources that can be harnessed for electric power generation to electrify the community. HOMER simulation software is used for optimal sizing and techno-economic analysis. The diesel generator is used as back up to fill the gaps in case both resources are out. Average monthly solar irradiation data of 6.2 kWh/m2 is determined from measured sunshine duration data by implementing a suitable specific model for the site. NASA satellite based estimated wind speed data of 10 years average at hub height of 50 m for the site in question is extracted from the SWERA (Solar and Wind Energy Resource Assessment) database (with annual average of 6.1 m/s) and its weigh-bull distribution parameter, k of 1.98 is estimated which indicates a fair wind speed distribution of the site to generate electric power using wind turbine. The proposed optimal system results electricity generation indicates that 92% from wind turbine, 3% from photovoltaic, 5% from diesel generator and managed to obtain a much lower cost of energy (COE = 0.11USD/kWh) than other alternatives investigated in this study such as grid extension and diesel generator.展开更多
Ethiopia is the second largest flower exporter in Africa. However, finding effective solutions for flowers waste management that are economical, efficient and environmentally friendly is a very difficult task. In this...Ethiopia is the second largest flower exporter in Africa. However, finding effective solutions for flowers waste management that are economical, efficient and environmentally friendly is a very difficult task. In this paper, a novel technology to recover energy from flower waste with the objective of producing biochar from flower waste by using pyrolysis has been presented. The pyrolysis reactor has been designed, manufactured and tested. Characterization of the flower waste has also been done by estimating the ultimate and proximate analysis. Besides the energy content has been measured by using Bomb calorimeter. Detailed proximate analysis has been performed and the energy content of the biochar has also been measured. The result shows that 10 kg of biochar is produced by using 18 kg of flower waste with a conversion efficiency of 55.5% and approximately 310.8 kg of biochar can be generated daily. Based on the result, the measured value of lower heating value of the produced biochar is 26.54 MJ/kg and approximately 392.2 kg of firewood is replaced daily. Thus, by adopting this innovative technology and producing biochar, the amount of flower waste is reduced from going to the landfill, energy is recovered from flower waste, income is generated from the selling of the produced biochar and the energy problems of the society is solved and finally environmental impact of the flower waste is reduced.展开更多
Groundwater movement beneath watershed divide is one component of the hydrological cycle that is typically ignored due to difficulty in analysis. Numerical ground-water models, like TAGSAC, have been used extensively ...Groundwater movement beneath watershed divide is one component of the hydrological cycle that is typically ignored due to difficulty in analysis. Numerical ground-water models, like TAGSAC, have been used extensively for predicting aquifer responses to external stresses. In this paper TAGSAC code was developed to identify the inter-basin groundwater transfer (IBGWT) between upper Awash River basin (UARB) and upper rift valley lakes basin (URVLB) of Ethiopia. For the identification three steady state groundwater models (for UARB, URVLB and for the two combined basins) were first created and calibrated for the 926 inventoried wells. The first two models are conceptualized by considering the watershed divide between the two basins as no-flow. The third model avoids the surface water divide which justifies IBGWT. The calibration of these three models was made by changing the recharge and hydrogeologic parameters of the basins. The goodness of fit indicators (GoFIs) obtained was better for the combined model than the model that describes the URVLB. Furthermore, the hydraulic head distribution obtained from the combined model clearly indicates that there is a groundwater flow that doesn’t respect the surface water divide. The most obvious effect of IBGWT observed in these two basins is that it diminishes surface water discharge from URVLB, and enhances discharge in the UARB. Moreover, the result of this study indicates potential for internal and cross contamination of the two adjacent groundwater.展开更多
In designing a canal system, a major problem is to decide what conveyance parameter to apply in the calculations. Since basic knowledge on this subject is lacking, it is usually taken from literatures. Most of the irr...In designing a canal system, a major problem is to decide what conveyance parameter to apply in the calculations. Since basic knowledge on this subject is lacking, it is usually taken from literatures. Most of the irrigation projects in Ethiopia are found to work below their expectation. One of the main reasons is the conveyance parameters variation from the expected (design) value which ultimately affects the envisioned conveyance efficiency. To evaluate this variation, Fentale irrigation scheme was used as case study. The conveyance efficiency used at the design stage was 80%, which was within Food and Agricultural Organization of the united nations recommendations;while the field survey value was 17%. Such huge variation was due to the fact that the assigned conveyance parameter values (roughness coefficient, hydraulic radius and bed slope) no longer represent the current situation of the scheme. Such variation has resulted in increase in the depth and top width of the water surface which further resulted in 13% and 3% increase in wetted perimeter and top width of the canal, respectively. Thus this study suggests that conveyance parameters shall be derived from history of existing irrigation schemes in a country, rather than adopting it from standard literatures. As such construction quality, maintenance activities and technological transfer activities in a country shall be seen in deciding the conveyance parameters. The study also suggests that the ever increasing water shortage in an irrigation project could be managed by proper maintenance of the entire irrigation system.展开更多
This paper presents an effective means of analyzing the safety of a tunnel under dynamic loading in areas<span style="font-family:Verdana;"> </span><span style="font-family:Verdana;"...This paper presents an effective means of analyzing the safety of a tunnel under dynamic loading in areas<span style="font-family:Verdana;"> </span><span style="font-family:Verdana;">with seismic records. A particular case of the railway tunnel in the earthquake-prone regions of the escarpment seismic zone of Ethiopia was the specific focus area of the research. Probabilistic seismic hazard analysis (PSHA) and deaggregation have been conducted to determine the design earthquake required as an input for the dynamic analysis. The PSHA</span><span style="font-family:Verdana;"> </span><span style="font-family:Verdana;">performed by considering the operating design earthquake with conservative assumptions of the local geological features resulted in a peak ground acceleration of 0.36. Two pairs of design earthquake have been obtained from the deaggregation process, which were used to filter acceleration time histories for the selected design earthquake from the ground motion database of Pacific Earthquake Engineering Research Center. Finally, full dynamic analyses of the tunnel have been performed by applying the scaled acceleration time histories corresponding to the structure in the specific site. It was demonstrated how to prove the stability of the tunnel located in difficult ground conditions by performing plane strain analyses with the possible minimum computational efforts.</span>展开更多
Sugarcane is one of the important irrigated crops in Ethiopia and its production is highly linked with its energy and water use. In this paper, identifications and quantifications of input and output, direct and indir...Sugarcane is one of the important irrigated crops in Ethiopia and its production is highly linked with its energy and water use. In this paper, identifications and quantifications of input and output, direct and indirect energy sources, and energy use of farm operations were carried out on 11 irrigation schemes of Awash River Basin. In order to grow 91.8 to 167.6 tons of cane, 47.9 to 143.4 GJ/ha of total energy was used. Average total input energies of gravity, pump surface and sprinkler scheme categories to grow 109.8, 112.7 and 136.3 ton/ha were 53.6, 68.9 and 129.2 GJ/ha, respectively. Around 90% and 74% total energies of gravity surface and sprinkler schemes were consumed as direct and indirect energies, respectively. Irrigation found to be the most energy consuming operation constituting more than 50% input energy of all scheme categories. Energy efficiency of gravity schemes was 152% and 300% higher than pump driven surface and sprinkler schemes. Energy sequestrated in cane straws burned during harvesting found to be higher than fertilizer and pumping energy demands. Use of cane straws as manure and energy sources have the potential to substitute demands which in turn needs further investigations and analysis.展开更多
Instabilities in grid-connected inverters can arise from a number of sources, including mismatched parameters, grid impedance, faults, and feedback delays. Park’s transformation provides accurate control over reactiv...Instabilities in grid-connected inverters can arise from a number of sources, including mismatched parameters, grid impedance, faults, and feedback delays. Park’s transformation provides accurate control over reactive and active (real) power. This enhances the overall efficiency of the system by enabling operators to control reactive power compensation and optimize energy flow. In dynamic settings, this guarantees greater system stability and faster response times. The current paper aims to improve the grid system by utilizing the dq0 controller. The current work focuses on the analysis based on simulations and theory, where the state space equation serves as the basis for dq-axis current decoupling. A MATLAB platform was used to simulate the complete system. TDH values of 2.45%, or less than 5%, in the given results are acceptable. The suggested controller was hence appropriate for grid system applications.展开更多
Expansive soils undergo high volume change due to cyclic swelling and shrinkage behavior during the wet and dry seasons.Thus,such problematic soils should be completely avoided or properly treated when encountered as ...Expansive soils undergo high volume change due to cyclic swelling and shrinkage behavior during the wet and dry seasons.Thus,such problematic soils should be completely avoided or properly treated when encountered as subgrade materials.In the present study,the biomedical waste incinerator ash and lime combination was proposed to stabilize expansive soil.Particle size analysis,Atterberg limits,free-swell,compaction,unconfined compression strength,and California bearing ratio tests were conducted on the natural soil and blended with 3%,5%,7%,9%,and 11%biomedical waste incinerator ash(BWIA).The optimum content of BWIA was determined based on the free-swell test results.To further investigate the relative effectiveness of the stabilizer,2%and 3%lime were also added to the optimum soil-BWIA mixture and UCS and CBR tests were also conducted.In addition,scanning electron microscopy(SEM)tests for representative stabilized samples were also conducted to examine the changes in microfabrics and structural arrangements due to bonding.The addition of BWIA has a promising effect on the index properties and strength of the expansive soil.The strength of the expansive soil significantly increased when it was blended with the optimum content of BWIA amended by 2%and 3%lime.展开更多
Lead(Pb)is a toxic metal found in wastewater,posing significant health risks to both humans and the environment.This study aimed to develop a novel adsorbent for lead removal from aqueous solutions.This adsorbent,a co...Lead(Pb)is a toxic metal found in wastewater,posing significant health risks to both humans and the environment.This study aimed to develop a novel adsorbent for lead removal from aqueous solutions.This adsorbent,a coffee husk extract-capped magnetite with pumice silica nanocomposite(CHE-capped M/PU/Si-NC),was synthesized using a completely green approach.The novelty of this study lies in the green synthesis of silica nanoparticles(SiO_(2)-NPs)throughout the process.Coffee husk extract(CHE)served as both a stabilizing and capping agent for the SiO_(2)-NPs,which were synthesized from sodium silicate(Na_(2)SiO_(3))extracted from bagasse ash(BA).Subsequently,the CHE-capped silica was co-precipitated with phyto-fabricated magnetite and integrated into a pumice matrix to produce the final CHE-capped M/PU/Si-NC adsorbent.The CHE-capped M/PU/Si-NC was characterized using SEM,XRF,FTIR,BET,XRD,TGA,and zeta potential analysis.The surface area of the CHE-capped M/PU/Si-NC was determined to be 313 m^(2)·g^(-1),and TGA results indicated good thermal stability up to 690℃.The zeta potential was measured at-37.7 mV.XRD analysis of CHE-capped M/PU/Si-NC confirmed the formation of magnetite and revealed its crystal structure.The maximum adsorption performance of this material was observed to be 95%at an adsorbent dosage of 2 g·L^(-1) and an initial Pb^(2+)concentration of 100 g·L^(-1).The adsorption kinetics were best described by the pseudo-second-order kinetic model.The Langmuir isotherm provided a good fit with a maximum adsorption capacity of 150 mg·g^(-1)(R^(2)=0.99).Regeneration studies demonstrated that the adsorbent maintained its high Pb^(2+) uptake capacity for up to five cycles.Overall,these findings suggest that this adsorbent is a promising candidate for the removal of Pb^(2+) from water and wastewater.展开更多
The direct conversion of carbon dioxide(CO_(2))and propylene oxide(PO)into propylene carbonate(PC)offers a green way to utilize anthropogenic CO_(2).However,this reaction is limited by low conversion of PO and harsh r...The direct conversion of carbon dioxide(CO_(2))and propylene oxide(PO)into propylene carbonate(PC)offers a green way to utilize anthropogenic CO_(2).However,this reaction is limited by low conversion of PO and harsh reaction conditions.In this study,we solve this problem using ionic liquids(ILs)/metal oxide composites(ILs@MAO).The catalytic activity of MAO-500(500?annealing temperature)is poor evidenced by its low conversion of PO(24.94%).However,ILs@MAO-500 has a high conversion of PO(97.54%)under similar reaction conditions(2 h at 1.5 MPa CO_(2) pressure,90℃,and 0.85 g catalyst).The ILs consist of imidazolium cation with weak coordinated[NTf_(2)]^(-)anion leading to outward movement of anion resulting in the formation of“heterodinuclear complex”.This complex generates an amorphous-crystalline intermediate with balanced acidbase sites that activate PO and stabilize the catalytic intermediate.In large part,the high PO conversion is theorized to be primarily due to the abundant reactive sites in the ILs that are covalently immobilized on the MAO-500 carrier.Furthermore,even after multiple recycling,ILs@MAO-500 remains stable and exhibits high yield and selectivity.The proposed solvent-free catalytic system is mild,kinetically fast,and naturally safe for coupling CO_(2) and PO into PC synthesis.展开更多
Enset fiber is a promising feedstock for biofuel production with the potential to reduce carbon emissions and improve the sustainability of the energy system.This study aimed to maximize hydrogen and butanol productio...Enset fiber is a promising feedstock for biofuel production with the potential to reduce carbon emissions and improve the sustainability of the energy system.This study aimed to maximize hydrogen and butanol production from Enset fiber through simultaneous saccharification and fermentation(SSF)process in bottles as well as in bioreactor.The SSF process in bottles resulted in a higher butanol concentration of 11.36 g/L with a yield of 0.23 g/g and a productivity of 0.16 g/(L h)at the optimal process parameters of 5%(w/v)substrate loading,16 FPU/g cellulase loading,and 100 rpm agitation speed from pretreated Enset fiber.Moreover,a comparable result to the bottle experiment was observed in the bioreactor with pH-uncontrolled SSF process,although with a decreased in butanol productivity to 0.095 g/(L h).However,using the pre-hydrolysis simultaneous saccharification and fermentation(PSSF)process in the bioreactor with a 7%(w/v)substrate loading led to the highest butanol concentration of 12.84 g/L with a productivity of 0.104 g/(L h).Furthermore,optimizing the SSF process parameters to favor hydrogen resulted in an increased hydrogen yield of 198.27 mL/g-Enset fiber at atmospheric pressure,an initial pH of 8.0,and 37°C.In general,stirring the SSF process to shift the product ratio to either hydrogen or butanol was possible by adjusting temperature and pressure.At 37°C and atmospheric pressure,the process resulted in an e-mol yield of 12%for hydrogen and 38%for butanol.Alternatively,at 30°C and 0.55 bar overpressure,the process achieved a yield of 6%e-mol of hydrogen and 48%e-mol of butanol.This is the first study to produce hydrogen and butanol from Enset fiber using the SSF process and contributes to the development of a circular bioeconomy.展开更多
The Ethiopian water policy strictly follows water allocation as a principle in setting out water consumption problems and demand projection. Hydroelectric power plants supply the larger share (88%) of the electricity ...The Ethiopian water policy strictly follows water allocation as a principle in setting out water consumption problems and demand projection. Hydroelectric power plants supply the larger share (88%) of the electricity in Ethiopia. 86% of Ethiopia’s plan to 2020 energy supply is expected to be from hydropower. This paper defines water consumption in hydropower production as the quantity of water that leaves the analyzed projects (reservoir regulated hydropower projects) through evaporation. Water consumed by hydropower development has never been studied at a country scale. Thus, in attempting to understand water consumption by the hydropower development, this study will be the first to acknowledge the water consumption by all storage regulated hydropower plants developed in Ethiopia. While studying and designing reservoir regulated hydropower production, the overall effect of water consumption by the projects is assumed to be minimal;thus ignoring water allocation to hydropower projects is a common procedure in Ethiopia. In this study, for multipurpose projects, to identify the water consumption by hydropower against the other purpose (irrigation) consumption, water consumption factors based on economic benefits were used. The study has shown that the 14 existing and under construction reservoir regulated hydropower projects will consume 1.881 billion m3 of water annually. This will make hydropower the second most water consuming water resource development next to Irrigation in the country. Together with the 22 upcoming projects the water consumption will be 3.756 billion m3/year. The results also show that hydropower consumption in the country will take an average of 2.41% of the total water stored in a reservoir. This value is in the range of nearly zero for power projects that use natural lakes as their reservoir (Tana Beles, Tis Abay I & II) and GERD to 10.64%. The total reservoir volume that will be created in the country after completion of the 22 planned projects is larger than 233 BCM, which is greater than the surface water volume the country possesses. This indicates that the future water consumption by hydropower plants shall be revised in accordance with changes made in the final design of each planned projects. Nonetheless, this research provides scientific support for the argument that the production of hydroelectricity by reservoir regulated hydropower schemes, in countries like Ethiopia, is a water consumer. Thus, water allocation shall not ignore its demand.展开更多
For many decades, Ethiopia had been using a meter gauge railway from Addis Ababa to the red sea port of Djibouti. Currently, the century old railway is completely replaced by a brand new standard gauge electrified rai...For many decades, Ethiopia had been using a meter gauge railway from Addis Ababa to the red sea port of Djibouti. Currently, the century old railway is completely replaced by a brand new standard gauge electrified railway line aiming to connect the country to the global market by guaranteeing a unified access to different regions of the country. In order to meet modern railway standards, a 1 x 25 kV catenary system is adopted in Ethio-Djibouti railway line corridor. In this paper, an alternative and a more superior 2 x 25 kV traction power supply system is presented. The modeling and analysis of the 2 x 25 kV traction supply system including the traction load, the substation power transformer, the autotransformer(AT), the catenary line impedance, etc., are performed. In addition, in order to validate the benefits of the proposed system, a comparative analysis of the two types of traction power supply arrangement has been conducted using MATLAB simulation. The analysis focuses on evaluating the voltage profiles of both power supply configurations on the basis of BS EN 50163:2004 international standard.展开更多
This paper introduces a novel hybrid optimization algorithm,Adaptive Hybrid PSO-Embedded GA(AHPEGA),which dynamically adapts to optimization performance by integrating Particle Swarm Optimization(PSO)and Genetic Algor...This paper introduces a novel hybrid optimization algorithm,Adaptive Hybrid PSO-Embedded GA(AHPEGA),which dynamically adapts to optimization performance by integrating Particle Swarm Optimization(PSO)and Genetic Algorithms(GA).The primary objective is to enhance the neuroevolutionary training of multilayer perceptron-based controllers(MLPCs)through the joint optimization of model parameters and structural hyperparameters.Traditional training methods frequently encounter issues such as premature convergence and limited generalization.AHPEGA addresses these limitations through an adaptive training strategy that dynamically adjusts parameters during the evolutionary process,thereby improving convergence speed and solution quality.By effectively reducing entrapment in local minima and balancing exploration and exploitation,AHPEGA improves the quality of neural controller design.The algorithm’s performance is evaluated against conventional optimization methods,demonstrating significant improvements in accuracy,convergence speed,and consistency across multiple runs.The practical applicability of the proposed method is demonstrated through simulation in the context of a VSC-based islanded microgrid(MG),where ensuring reliable and effective control under variable operating conditions is critical.This highlights AHPEGA’s capability to optimize intelligent control strategies in MG systems,particularly under dynamic and uncertain conditions,reinforcing its practical value in real-world energy environments.展开更多
基金supported by the following project of the Addis Ababa Institute of Technology,African Railway Center of Excellence,and World Bank group:“A research on integration of renewable and Alternative Energy Sources into Ethiopian Railway System.”(AAITRS-GSR-7767-18).
文摘A photovoltaic array is environmentally friendly and a source of unlimited energy generation.However,it is presently a costlier energy generation system than other non-renewable energy sources.The main reasons are seasonal variations and continuously changing weather conditions,which affect the amount of solar energy received by the solar panels.In addition,the non-linear characteristics of the voltage and current outputs along with the operating environment temperature and variation in the solar radiation decrease the energy conversion capability of the photovoltaic arrays.To address this problem,the global maxima of the PV arrays can be tracked using a maximum power point tracking algorithm(MPPT)and the operating point of the photovoltaic system can be forced to its optimum value.This technique increases the efficiency of the photovoltaic array and minimizes the cost of the system by reducing the number of solar modules required to obtain the desired power.However,the tracking algorithms are not equally effective in all areas of application.Therefore,selecting the correct MPPT is very critical.This paper presents a detailed review and comparison of the MPPT techniques for photovoltaic systems,with consideration of the following key parameters:photovoltaic array dependence,type of system(analog or digital),need for periodic tuning,convergence speed,complexity of the system,global maxima,implemented capacity,and sensed parameter(s).In addition,based on real meteorological data(irradiance and temperature at a site located in Addis Ababa,Ethiopia),a simulation is performed to evaluate the performance of tracking algorithms suitable for the application being studied.Finally,the study clearly validates the considerable energy saving achieved by using these algorithms.
文摘Soil erosion/sedimentation is an immense problem threatening the live storage capacity of dam reservoirs in Ethiopia. This in turn reduces the power generation capacities of hydropower reservoirs. Therefore, studies which give insight into soil erosion/sedimentation mechanisms and mitigation methods is important. The high rate of soil erosion/sedimentation threats the lifespan of Gilgel Gibe-I hydropower reservoir, The problem of sedimentation in Gilgel Gibe-I will also affect Gilgel Gibe-2 which uses the water released from Gilgel Gibe-1. The sustainability of these hydropower plants needs catchment management practices that will reduce soil erosion. This paper presents the results of monthly and yearly sediment yield simulations experiments conducted for Gilgel Gibe-1 under different BMP （best management practice） scenarios. The scenarios applied in this paper are： （1） maintaining existing conditions; （2） introducing filter strips; （3） applying stone/soil bunds; （4） reforestation. The SWAT （soil and water assessment tool） was used to model soil erosion, identify soil erosion prone areas and assess the impact of BMPs on sediment reduction via simulations. The simulation results showed that applying filter strips, stone bunds and reforestation scenarios could reduce the current sediment yields at soil erosion prone areas and at the outlet of the catchment area which is the inlet to Gilgel Gibe-I reservoir.
文摘Heterogeneous Networks(HetNets)and cell densification represent promising solutions for the surging data traffic demand in wireless networks.In dense HetNets,user traffic is steered toward the Low-Power Node(LPN)when possible to enhance the user throughput and system capacity by increasing the area spectral efficiency.However,because of the transmit power differences in different tiers of HetNets and irregular service demand,a load imbalance typically exists among different serving nodes.To offload more traffic to LPNs and coordinate the Inter-Cell Interference(ICI),Third-Generation Partnership Project(3GPP)has facilitated the development of the Cell Range Expansion(CRE),enhanced Inter-Cell Interference Coordination(eICIC)and Further enhanced ICIC(FeICIC).In this paper,we develop a cell clustering-based load-aware offsetting and an adaptive Low-Power Subframe(LPS)approach.Our solution allows the separation of User Association(UA)functions at the User Equipment(UE)and network server such that users can make a simple cell-selection decision similar to that in the maximum Received Signal Strength(max-RSS)based UA scheme,where the network server computes the load-aware offsetting and required LPS periods based on the load conditions of the system.The proposed solution is evaluated using system-level simulations wherein the results correspond to performance changes in different service regions.Results show that our method effectively solves the offloading and interference coordination problems in dense HetNets.
文摘Vertical Axis Wind Turbines(VAWTs)offer several advantages over horizontal axis wind turbines(HAWTs),including quieter operation,ease of maintenance,and simplified construction.Surprisingly,despite the prevailing belief that HAWTs outperform VAWTs as individual units,VAWTs demonstrate higher power density when arranged in clusters.This phenomenon arises from positive wake interactions downstream of VAWTs,potentially enhancing the overall wind farm performances.In contrast,wake interactions negatively impact HAWT farms,reducing their efficiency.This paper extensively reviews the potential of VAWT clusters to increase energy output and reduce wind energy costs.A precise terminology is introduced to clarify ambiguous terms researchers use to quantify cluster parameters.While examining commonly studied and proposed VAWT cluster configurations,several aspects are discussed such as aerodynamic interactions,wake characteristics,structural dynamics,and performance metrics.Additionally,the current state-of-the-art and research gaps are critically described.The review also covers computational modeling,optimization techniques,advanced control strategies,machine learning applications,economic considerations,and the influence of terrain and application locations.
文摘This study looks into the resource assessment, technology economics and modeling of different energy alternatives and proposes a rechargeable battery storage-based large-scale wind/photovoltaic hybrid power system to meet an average electrical load demand of 2.4 MW and peak load of 2.9 MW for a remote rural district in Ethiopia called Geladin. The district is 682 km away from nearby grid. The site enjoys high solar and wind resources that can be harnessed for electric power generation to electrify the community. HOMER simulation software is used for optimal sizing and techno-economic analysis. The diesel generator is used as back up to fill the gaps in case both resources are out. Average monthly solar irradiation data of 6.2 kWh/m2 is determined from measured sunshine duration data by implementing a suitable specific model for the site. NASA satellite based estimated wind speed data of 10 years average at hub height of 50 m for the site in question is extracted from the SWERA (Solar and Wind Energy Resource Assessment) database (with annual average of 6.1 m/s) and its weigh-bull distribution parameter, k of 1.98 is estimated which indicates a fair wind speed distribution of the site to generate electric power using wind turbine. The proposed optimal system results electricity generation indicates that 92% from wind turbine, 3% from photovoltaic, 5% from diesel generator and managed to obtain a much lower cost of energy (COE = 0.11USD/kWh) than other alternatives investigated in this study such as grid extension and diesel generator.
文摘Ethiopia is the second largest flower exporter in Africa. However, finding effective solutions for flowers waste management that are economical, efficient and environmentally friendly is a very difficult task. In this paper, a novel technology to recover energy from flower waste with the objective of producing biochar from flower waste by using pyrolysis has been presented. The pyrolysis reactor has been designed, manufactured and tested. Characterization of the flower waste has also been done by estimating the ultimate and proximate analysis. Besides the energy content has been measured by using Bomb calorimeter. Detailed proximate analysis has been performed and the energy content of the biochar has also been measured. The result shows that 10 kg of biochar is produced by using 18 kg of flower waste with a conversion efficiency of 55.5% and approximately 310.8 kg of biochar can be generated daily. Based on the result, the measured value of lower heating value of the produced biochar is 26.54 MJ/kg and approximately 392.2 kg of firewood is replaced daily. Thus, by adopting this innovative technology and producing biochar, the amount of flower waste is reduced from going to the landfill, energy is recovered from flower waste, income is generated from the selling of the produced biochar and the energy problems of the society is solved and finally environmental impact of the flower waste is reduced.
文摘Groundwater movement beneath watershed divide is one component of the hydrological cycle that is typically ignored due to difficulty in analysis. Numerical ground-water models, like TAGSAC, have been used extensively for predicting aquifer responses to external stresses. In this paper TAGSAC code was developed to identify the inter-basin groundwater transfer (IBGWT) between upper Awash River basin (UARB) and upper rift valley lakes basin (URVLB) of Ethiopia. For the identification three steady state groundwater models (for UARB, URVLB and for the two combined basins) were first created and calibrated for the 926 inventoried wells. The first two models are conceptualized by considering the watershed divide between the two basins as no-flow. The third model avoids the surface water divide which justifies IBGWT. The calibration of these three models was made by changing the recharge and hydrogeologic parameters of the basins. The goodness of fit indicators (GoFIs) obtained was better for the combined model than the model that describes the URVLB. Furthermore, the hydraulic head distribution obtained from the combined model clearly indicates that there is a groundwater flow that doesn’t respect the surface water divide. The most obvious effect of IBGWT observed in these two basins is that it diminishes surface water discharge from URVLB, and enhances discharge in the UARB. Moreover, the result of this study indicates potential for internal and cross contamination of the two adjacent groundwater.
文摘In designing a canal system, a major problem is to decide what conveyance parameter to apply in the calculations. Since basic knowledge on this subject is lacking, it is usually taken from literatures. Most of the irrigation projects in Ethiopia are found to work below their expectation. One of the main reasons is the conveyance parameters variation from the expected (design) value which ultimately affects the envisioned conveyance efficiency. To evaluate this variation, Fentale irrigation scheme was used as case study. The conveyance efficiency used at the design stage was 80%, which was within Food and Agricultural Organization of the united nations recommendations;while the field survey value was 17%. Such huge variation was due to the fact that the assigned conveyance parameter values (roughness coefficient, hydraulic radius and bed slope) no longer represent the current situation of the scheme. Such variation has resulted in increase in the depth and top width of the water surface which further resulted in 13% and 3% increase in wetted perimeter and top width of the canal, respectively. Thus this study suggests that conveyance parameters shall be derived from history of existing irrigation schemes in a country, rather than adopting it from standard literatures. As such construction quality, maintenance activities and technological transfer activities in a country shall be seen in deciding the conveyance parameters. The study also suggests that the ever increasing water shortage in an irrigation project could be managed by proper maintenance of the entire irrigation system.
文摘This paper presents an effective means of analyzing the safety of a tunnel under dynamic loading in areas<span style="font-family:Verdana;"> </span><span style="font-family:Verdana;">with seismic records. A particular case of the railway tunnel in the earthquake-prone regions of the escarpment seismic zone of Ethiopia was the specific focus area of the research. Probabilistic seismic hazard analysis (PSHA) and deaggregation have been conducted to determine the design earthquake required as an input for the dynamic analysis. The PSHA</span><span style="font-family:Verdana;"> </span><span style="font-family:Verdana;">performed by considering the operating design earthquake with conservative assumptions of the local geological features resulted in a peak ground acceleration of 0.36. Two pairs of design earthquake have been obtained from the deaggregation process, which were used to filter acceleration time histories for the selected design earthquake from the ground motion database of Pacific Earthquake Engineering Research Center. Finally, full dynamic analyses of the tunnel have been performed by applying the scaled acceleration time histories corresponding to the structure in the specific site. It was demonstrated how to prove the stability of the tunnel located in difficult ground conditions by performing plane strain analyses with the possible minimum computational efforts.</span>
文摘Sugarcane is one of the important irrigated crops in Ethiopia and its production is highly linked with its energy and water use. In this paper, identifications and quantifications of input and output, direct and indirect energy sources, and energy use of farm operations were carried out on 11 irrigation schemes of Awash River Basin. In order to grow 91.8 to 167.6 tons of cane, 47.9 to 143.4 GJ/ha of total energy was used. Average total input energies of gravity, pump surface and sprinkler scheme categories to grow 109.8, 112.7 and 136.3 ton/ha were 53.6, 68.9 and 129.2 GJ/ha, respectively. Around 90% and 74% total energies of gravity surface and sprinkler schemes were consumed as direct and indirect energies, respectively. Irrigation found to be the most energy consuming operation constituting more than 50% input energy of all scheme categories. Energy efficiency of gravity schemes was 152% and 300% higher than pump driven surface and sprinkler schemes. Energy sequestrated in cane straws burned during harvesting found to be higher than fertilizer and pumping energy demands. Use of cane straws as manure and energy sources have the potential to substitute demands which in turn needs further investigations and analysis.
文摘Instabilities in grid-connected inverters can arise from a number of sources, including mismatched parameters, grid impedance, faults, and feedback delays. Park’s transformation provides accurate control over reactive and active (real) power. This enhances the overall efficiency of the system by enabling operators to control reactive power compensation and optimize energy flow. In dynamic settings, this guarantees greater system stability and faster response times. The current paper aims to improve the grid system by utilizing the dq0 controller. The current work focuses on the analysis based on simulations and theory, where the state space equation serves as the basis for dq-axis current decoupling. A MATLAB platform was used to simulate the complete system. TDH values of 2.45%, or less than 5%, in the given results are acceptable. The suggested controller was hence appropriate for grid system applications.
文摘Expansive soils undergo high volume change due to cyclic swelling and shrinkage behavior during the wet and dry seasons.Thus,such problematic soils should be completely avoided or properly treated when encountered as subgrade materials.In the present study,the biomedical waste incinerator ash and lime combination was proposed to stabilize expansive soil.Particle size analysis,Atterberg limits,free-swell,compaction,unconfined compression strength,and California bearing ratio tests were conducted on the natural soil and blended with 3%,5%,7%,9%,and 11%biomedical waste incinerator ash(BWIA).The optimum content of BWIA was determined based on the free-swell test results.To further investigate the relative effectiveness of the stabilizer,2%and 3%lime were also added to the optimum soil-BWIA mixture and UCS and CBR tests were also conducted.In addition,scanning electron microscopy(SEM)tests for representative stabilized samples were also conducted to examine the changes in microfabrics and structural arrangements due to bonding.The addition of BWIA has a promising effect on the index properties and strength of the expansive soil.The strength of the expansive soil significantly increased when it was blended with the optimum content of BWIA amended by 2%and 3%lime.
文摘Lead(Pb)is a toxic metal found in wastewater,posing significant health risks to both humans and the environment.This study aimed to develop a novel adsorbent for lead removal from aqueous solutions.This adsorbent,a coffee husk extract-capped magnetite with pumice silica nanocomposite(CHE-capped M/PU/Si-NC),was synthesized using a completely green approach.The novelty of this study lies in the green synthesis of silica nanoparticles(SiO_(2)-NPs)throughout the process.Coffee husk extract(CHE)served as both a stabilizing and capping agent for the SiO_(2)-NPs,which were synthesized from sodium silicate(Na_(2)SiO_(3))extracted from bagasse ash(BA).Subsequently,the CHE-capped silica was co-precipitated with phyto-fabricated magnetite and integrated into a pumice matrix to produce the final CHE-capped M/PU/Si-NC adsorbent.The CHE-capped M/PU/Si-NC was characterized using SEM,XRF,FTIR,BET,XRD,TGA,and zeta potential analysis.The surface area of the CHE-capped M/PU/Si-NC was determined to be 313 m^(2)·g^(-1),and TGA results indicated good thermal stability up to 690℃.The zeta potential was measured at-37.7 mV.XRD analysis of CHE-capped M/PU/Si-NC confirmed the formation of magnetite and revealed its crystal structure.The maximum adsorption performance of this material was observed to be 95%at an adsorbent dosage of 2 g·L^(-1) and an initial Pb^(2+)concentration of 100 g·L^(-1).The adsorption kinetics were best described by the pseudo-second-order kinetic model.The Langmuir isotherm provided a good fit with a maximum adsorption capacity of 150 mg·g^(-1)(R^(2)=0.99).Regeneration studies demonstrated that the adsorbent maintained its high Pb^(2+) uptake capacity for up to five cycles.Overall,these findings suggest that this adsorbent is a promising candidate for the removal of Pb^(2+) from water and wastewater.
基金supported by the National Research Foundation(NRF)grants funded by the Ministry of Education(2020R1A6A1A03038817),Republic of Korea.
文摘The direct conversion of carbon dioxide(CO_(2))and propylene oxide(PO)into propylene carbonate(PC)offers a green way to utilize anthropogenic CO_(2).However,this reaction is limited by low conversion of PO and harsh reaction conditions.In this study,we solve this problem using ionic liquids(ILs)/metal oxide composites(ILs@MAO).The catalytic activity of MAO-500(500?annealing temperature)is poor evidenced by its low conversion of PO(24.94%).However,ILs@MAO-500 has a high conversion of PO(97.54%)under similar reaction conditions(2 h at 1.5 MPa CO_(2) pressure,90℃,and 0.85 g catalyst).The ILs consist of imidazolium cation with weak coordinated[NTf_(2)]^(-)anion leading to outward movement of anion resulting in the formation of“heterodinuclear complex”.This complex generates an amorphous-crystalline intermediate with balanced acidbase sites that activate PO and stabilize the catalytic intermediate.In large part,the high PO conversion is theorized to be primarily due to the abundant reactive sites in the ILs that are covalently immobilized on the MAO-500 carrier.Furthermore,even after multiple recycling,ILs@MAO-500 remains stable and exhibits high yield and selectivity.The proposed solvent-free catalytic system is mild,kinetically fast,and naturally safe for coupling CO_(2) and PO into PC synthesis.
基金Open Access funding enabled and organized by Projekt DEALfunded by the DAAD-EECBP Homegrown Ph.D.Scholarship Program 2019,and the APC was funded by the Karlsruhe Institute of Technology(KIT)Publication Fund.
文摘Enset fiber is a promising feedstock for biofuel production with the potential to reduce carbon emissions and improve the sustainability of the energy system.This study aimed to maximize hydrogen and butanol production from Enset fiber through simultaneous saccharification and fermentation(SSF)process in bottles as well as in bioreactor.The SSF process in bottles resulted in a higher butanol concentration of 11.36 g/L with a yield of 0.23 g/g and a productivity of 0.16 g/(L h)at the optimal process parameters of 5%(w/v)substrate loading,16 FPU/g cellulase loading,and 100 rpm agitation speed from pretreated Enset fiber.Moreover,a comparable result to the bottle experiment was observed in the bioreactor with pH-uncontrolled SSF process,although with a decreased in butanol productivity to 0.095 g/(L h).However,using the pre-hydrolysis simultaneous saccharification and fermentation(PSSF)process in the bioreactor with a 7%(w/v)substrate loading led to the highest butanol concentration of 12.84 g/L with a productivity of 0.104 g/(L h).Furthermore,optimizing the SSF process parameters to favor hydrogen resulted in an increased hydrogen yield of 198.27 mL/g-Enset fiber at atmospheric pressure,an initial pH of 8.0,and 37°C.In general,stirring the SSF process to shift the product ratio to either hydrogen or butanol was possible by adjusting temperature and pressure.At 37°C and atmospheric pressure,the process resulted in an e-mol yield of 12%for hydrogen and 38%for butanol.Alternatively,at 30°C and 0.55 bar overpressure,the process achieved a yield of 6%e-mol of hydrogen and 48%e-mol of butanol.This is the first study to produce hydrogen and butanol from Enset fiber using the SSF process and contributes to the development of a circular bioeconomy.
文摘The Ethiopian water policy strictly follows water allocation as a principle in setting out water consumption problems and demand projection. Hydroelectric power plants supply the larger share (88%) of the electricity in Ethiopia. 86% of Ethiopia’s plan to 2020 energy supply is expected to be from hydropower. This paper defines water consumption in hydropower production as the quantity of water that leaves the analyzed projects (reservoir regulated hydropower projects) through evaporation. Water consumed by hydropower development has never been studied at a country scale. Thus, in attempting to understand water consumption by the hydropower development, this study will be the first to acknowledge the water consumption by all storage regulated hydropower plants developed in Ethiopia. While studying and designing reservoir regulated hydropower production, the overall effect of water consumption by the projects is assumed to be minimal;thus ignoring water allocation to hydropower projects is a common procedure in Ethiopia. In this study, for multipurpose projects, to identify the water consumption by hydropower against the other purpose (irrigation) consumption, water consumption factors based on economic benefits were used. The study has shown that the 14 existing and under construction reservoir regulated hydropower projects will consume 1.881 billion m3 of water annually. This will make hydropower the second most water consuming water resource development next to Irrigation in the country. Together with the 22 upcoming projects the water consumption will be 3.756 billion m3/year. The results also show that hydropower consumption in the country will take an average of 2.41% of the total water stored in a reservoir. This value is in the range of nearly zero for power projects that use natural lakes as their reservoir (Tana Beles, Tis Abay I & II) and GERD to 10.64%. The total reservoir volume that will be created in the country after completion of the 22 planned projects is larger than 233 BCM, which is greater than the surface water volume the country possesses. This indicates that the future water consumption by hydropower plants shall be revised in accordance with changes made in the final design of each planned projects. Nonetheless, this research provides scientific support for the argument that the production of hydroelectricity by reservoir regulated hydropower schemes, in countries like Ethiopia, is a water consumer. Thus, water allocation shall not ignore its demand.
文摘For many decades, Ethiopia had been using a meter gauge railway from Addis Ababa to the red sea port of Djibouti. Currently, the century old railway is completely replaced by a brand new standard gauge electrified railway line aiming to connect the country to the global market by guaranteeing a unified access to different regions of the country. In order to meet modern railway standards, a 1 x 25 kV catenary system is adopted in Ethio-Djibouti railway line corridor. In this paper, an alternative and a more superior 2 x 25 kV traction power supply system is presented. The modeling and analysis of the 2 x 25 kV traction supply system including the traction load, the substation power transformer, the autotransformer(AT), the catenary line impedance, etc., are performed. In addition, in order to validate the benefits of the proposed system, a comparative analysis of the two types of traction power supply arrangement has been conducted using MATLAB simulation. The analysis focuses on evaluating the voltage profiles of both power supply configurations on the basis of BS EN 50163:2004 international standard.
基金financial support from the Swedish International Development Cooperation Agency(SIDA)through the research capacity-building program between Addis Ababa University and Swedish universities.
文摘This paper introduces a novel hybrid optimization algorithm,Adaptive Hybrid PSO-Embedded GA(AHPEGA),which dynamically adapts to optimization performance by integrating Particle Swarm Optimization(PSO)and Genetic Algorithms(GA).The primary objective is to enhance the neuroevolutionary training of multilayer perceptron-based controllers(MLPCs)through the joint optimization of model parameters and structural hyperparameters.Traditional training methods frequently encounter issues such as premature convergence and limited generalization.AHPEGA addresses these limitations through an adaptive training strategy that dynamically adjusts parameters during the evolutionary process,thereby improving convergence speed and solution quality.By effectively reducing entrapment in local minima and balancing exploration and exploitation,AHPEGA improves the quality of neural controller design.The algorithm’s performance is evaluated against conventional optimization methods,demonstrating significant improvements in accuracy,convergence speed,and consistency across multiple runs.The practical applicability of the proposed method is demonstrated through simulation in the context of a VSC-based islanded microgrid(MG),where ensuring reliable and effective control under variable operating conditions is critical.This highlights AHPEGA’s capability to optimize intelligent control strategies in MG systems,particularly under dynamic and uncertain conditions,reinforcing its practical value in real-world energy environments.
