Browsing by Author "Assefa, Abebayehu (PhD)"

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    Adopting Building Integrated Photovoltaics (BIPV) for Harnessing Green Economy in Ethiopia: A Study on the Design, Modeling and Economic Analysis of Grid-Tied BIPV
    (Addis Ababa University, 2015-01) Berhanu, Tsion; Assefa, Abebayehu (PhD)
    Contrary to add-on Photovoltaics (PV), Building-integrated PV (BIPV) refers to the application of PV arrays where they are integral parts of the building envelope having the function of producing electricity as well. Ethiopia, as a country having average daily solar radiation of 5.2kWh/m2, can make use of this technology as a means of achieving the country’s goal of expanding electric power generation and green growth strategy. In addition, by producing power close to the point of use, the technology shall contribute to the reduction of the current 23% transmission and distribution losses encountered in the power system of the country. To this end, the opportunities of meeting some of the country’s electricity demand by introducing grid-tied BIPV in commercial and residential buildings of urban Ethiopia were investigated by taking the new Zemen Bank Headquarter 30-storey Building as a case study. A detailed design, simulation and economic analysis of a grid-tied BIPV system were conducted for four different scenarios of the building using PVsyst software. The results of the simulation showed that with an optimal design a significant amount of energy, 897,000kWh/year, which covers 69.54% of the estimated demand of the building can be generated. This can save up to 26,910USD per year based on the current electricity tariff of Ethiopia. The simulations of the four scenarios revealed that best results can be achieved by considering the system starting from the initial architectural design of the building rather than retrofitting an existing one. On the other hand, the economic evaluation resulted in an energy cost of US$0.11/kWh for the optimal design which is much higher than the prevailing electricity retail price of Ethiopia, US$0.03/kWh. From this it was concluded that grid-parity shall be achieved in the long run since the costs of PV modules is dropping while their efficiency is rising.
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    Design and Development of Fast Pyrolysis Fluidized Bed Reactor for Bio-oil Production
    (Addis Ababa University, 2011-12) Abrha, Tigabu; Assefa, Abebayehu (PhD)
    Fast pyrolysis of biomass is the most promising technology of converting solid biomass to liquid bio-oil as a renewable substitution of fossil resources in fuel and chemical feed stocks applications. Ethiopia with abundant biomass resources especially from coffee processing industry has the potential to provide an ideal platform for the development of this thermal conversion technology. This thesis was aimed of developing a 145 mm reactor diameter pilot scale fast pyrolysis system with coffee husk as the main feedstock. For detail analysis of the fast pyrolysis system a two-stage fluidized bed reactor was designed based on the fluidization technology with silica sand as the heat carrier to achieve rapid heat transfer required for the reaction. The amount of silica sand required was determined from the hydrodynamics and heat transfer performances. The assembly of the system consists of five main sections. These are the feed hopper, reactor subsystems (reaction chamber, gas-preheating chamber, plenum, and gas distributor plate), cyclone separator and condensation system. Smooth process and substantial bio-oil yields could be achieved for the experiments carried out with the reaction temperature within 300 to500 . But due to lack of appropriate fluidizing medium (lack of continuous gas supply compressor) the maximum gas temperature in the reaction chamber achieved was only 100 . Key Words: Biomass, Fast pyrolysis, Bio-oil
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    Design and Simulation of Grid-Tied Photovoltaic, Thermal and Biogas Energy Generating Systems to Power Universities in Ethiopia :A Case of Addis Ababa University , Collage of Natural and Computational Science.
    (Addis Ababa University, 2015-12) Abiti, Gezahegn; Assefa, Abebayehu (PhD)
    This paper confers with a study and unfold to systematic know how on how to furnish Ethiopian universities with power using their own abundantly available renewable energy resources and to establish a project for the same purpose. In pursuance of that, it was conducted by collecting and analyzing relevant and required data like electrical energy consumption, weather and site of the targeted universities while also rendering comprehensive attention to other design standards as well as specifications of machineries. The worst case design is thoroughly regarded herein the design section for it is more convincing with respect factor of safety in the event solar radiation falls below the annual average and when there is a minimum amount of biogas resource. The simulation, optimization and sensitivity analysis of the project is dealt by renewable energy tools of HOMER software. Foundation of the hybrid energy generating system is surfaced and actualized by making estimation of solar and biogas resource at a given site. The source data for AAUCNCSc revealed that a mean incident solar radiation of 3.66 kWh/m2/day and a potential of about 24 tons of biogas resource per a day can be collected considering safety factor for the variation as per day to day and month to month basis. The data collected for this study further showed that the electrical energy demand of the site was 104,870 kWh in the design year (July 2012) in which a combination of the two systems are going to offset the necessity. The assessment conducted revealed that out of the total of 104,870 kWh energy needed close to 81% is furnished by and fulfilled with biogas energy generating system while the remaining 19% of it is contributed by PV/T system and yet 0.00492kWh/yr (0.00%) is found to be excess which ought to be sold to the national grid . Pursuant to the financial analysis of HOMER, given to designed HPV/TBS and within an optimum cost of electricity (COE) of 0.263 $/kWh, renewable fraction (RF) of 1 can be obtained. Generally, if and when the total cost of PV/T modules, the Biogas generators and the converter are US$ 535,750.00, US$ 50,000.00 and US$ 8,000.00 respectively. The software further showed that in the emission analysis 4,172,041kg/yr of CO2, 18,099 kg/yr SO2 and 7,935 NO can be removed if this renewable design of the hybrid system is to be implanted instead of non renewable equivalent.
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    Design ond Simulation of Fluidized Bed Gasifier to Improve the Quality of Synthesis Gas
    (Addis Ababa University, 2011-10) Genzeb, Abywork; Assefa, Abebayehu (PhD)
    Biomass has emerged as one of the promising candidates for the future, in the renewable energy area. Biomass has been a major source of fuel for human from the existence of mankind. Rapid urbanization and widespread use of fossil fuels in the industrial world has related it to the status of a minor source of energy. The innovation, however, started with increasing concerns over reducing carbon footprints and also due to strong causative connections between non-renewable fossil fuels and “global warming”. Alternative energy production through biomass gasification (a thermo-chemical process of converting biomass into the producer gas or syngas) produces combustible gases, such as carbon monoxide, hydrogen, and methane. These gases can be used for generation of direct heat, electricity, or liquid fuels through the Fischer Tropsch process. However, a major limitation of the overall process is the purity of the generated synthesis gas. The tars and particulates generated in the gasification process constitute a major impediment to the commercial use of this technology because they may condense on valves, fittings, and therefore, hinder the smooth running of an engine. This research was aimed at developing a gas characterization and better understanding of the effect of various parameters on the syngas composition, and the removal of tars and particulates in the synthesis gas generated from a bubbling fluidized bed biomass gasifier. The study is primarily design of the different components of the gasifier and supplemented by the mathematical modeling that explains various steps in terms of existing scientific principles. The study compares the experimental results sited from different literatures with the equilibrium model results and also identifies the optimum operating parameters and design criteria for better quality syngas production. Using the proposed model, the optimum compositions of carbon monoxide, methane and hydrogen with the respective values of the operating temperature, moisture content and equivalence ratio was obtained.
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    Design, Simulation of Fluid Flow and Optimization of Operational Parameters in Tesla Multiple-Disk Turbine
    (Addis Ababa University, 2014-04) Shimeles, Surafel; Assefa, Abebayehu (PhD)
    Tesla turbine, an unconventional co-axial multiple-disk turbine utilizing a blend of friction and boundary layer effect for power production, has been a topic of many academic and experimental works for a century. Decades after its first patent in 1913 by Serbian genius -Nikola Tesla, the turbine has seen subject of many fluid investigators that sought to explain mainly the fluid dynamics behind the flow between its narrow inter-disk spaces for purpose of maximizing utility for practical applications. Among the available literature, there is a plethora of research in analytical and experimental spheres while on the other hand, there are limited published works regarding numerical investigation of the turbine. Between the different numerical genera, negligibly no numerical work has been performed in studying the turbulent regime of flow. In the current work, a background discussion introducing the Tesla turbine theory, merits, demerits and previously done works is presented. A modified two-dimensional Cuoto etal. turbine design procedure is used to construct 2D and 3D geometrical models for CFD analysis. Two principal models have been prepared, each of which having their inherent strengths and weaknesses. The effect of certain operational parameters such as rotor angular speed and flow on selected performance figure of merits has been quantitatively analyzed. By keeping flow input variables, the number of nozzles has been varied as an added geometrical design parameter to see performance disparity between different combinations. The results revealed peculiar flow characteristics belonging to the disk gaps and the strong variances of the selected figures of merits with controlling parameters. In some cases, operational limitation thresholds were established due to the strong correlations of these performance variables with turbine output quantities.
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    Experimental Analysis of Drying of Agricultural Product
    (Addis Ababa University, 2004-09) Hagos, Berhane; Assefa, Abebayehu (PhD)
    An experimental system set up has been developed to investigate the drying rate of the selected material, the drying air temperature and relative humidity and moisture content profiles developed with the food materials during forced convective air drying. The moisture content profile was determined by employing the technique of oven drying method. Embedded thermocouples were used to sense temperature at different locations, and the embedded digital relative humidity measuring instruments were used to sense the relative humidity and recording the values manually at different locations of the drying chamber. A data logger and a computer front end were implemented for data acquisition. Temperature, relative humidity, moisture and drying rate profiles are presented as function of the drying time. All profiles described the drying phenomena inside each trays of the drying chamber. The close relations of overall drying rate and profiles of moisture content, drying air temperature and relative humidity are discussed. Finally correlations are formulated from the experimental data to relate the drying parameters; drying air temperature, relative humidity, velocity, initial moisture content of material to be dried and drying time that predict the moisture content on wet basis.
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    Experimental Investigation on Performance Characteristics and Efficiency of Electric Injera Baking Pans „(Mitad)‟
    (Addis Ababa University, 2011-11) Tafere, Awash; Assefa, Abebayehu (PhD)
    Enjera baking is the most energy intensive activity in Ethiopia; and preparation of enjera is rather a long process relative to other Ethiopian food. The aim of this thesis work is to investigate the performance characteristics and efficiency of the electric baking pan („mitad‟) experimentally and to prove the efficiency of improved „mitad‟ is best. Experimentation and processing of data were performed to study the energy consumption cost and ways to increase the performance of the baking pan. Thermo-physical properties were determined quasi experimentally before, during, and after baking processes of the product („Enjera‟). Initial heating up and cyclic enjera baking time with its power consumption and heat loss analysis of the system were presented for performance comparison of the baking pans. Experiments were conducted to measure temperature profile during initial heating up and cyclic baking of the pans. Maximum energy losses are occurred at the bottom of conventional and improved baking pans with the efficiency of 52% and 75% respectively. Even though the efficiency of improved electric „mitad‟ was higher than the conventional one, still there was high energy loss due to poor insulation material. Performance improvement options of each baking pans can be made by increasing the number of cycles and density of the batter. This alternative can be increase the efficiency by 5-10% of the baking pans. Economic result illustrates that improved baking pan has higher initial capital investment than the conventional one; but they have lower operating costs. Then overall present worth of improved baking pan has lower cost than conventional baking pan. Finally, based on the points outlined above, improved electric „mitad‟ have an advantage over conventional electric „mitad‟ and our recommendation is to install improved baking pans in the kitchens of the Ethiopian house hold. Key words: Experimental investigation, Thermophysical Property, Heat Transfer Analysis
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    Feasibility Study and Performance Evaluation (Simulation) of Solar Dryer for Akaki Spare Part and Hand Tools Share Company Moulding Sand Drying Mechanism
    (Addis Ababa University, 2011-11) Tadesse, Aschenaki; Assefa, Abebayehu (PhD)
    ilica sand is sand that is used for molding processes. When a catalyst is added to it, it develops the bonding characteristics of the raisin, which binds the silica sand together. Its moisture content (17.24% initial and 0.5% final moisture content) is extremely critical sand additive that can be greatly impact casting quality. In this study flat plate solar collector was used because, it is the most important type of solar collector and it is simple in design, has no moving parts and requires little maintenance. The analysis of heat transfer coefficient (losses) through flat plate collector was discussed and the techniques that used to reduce these losses also mentioned (by using insulation). Mathematical modeling of solar dryer and drying chamber was described. This paper presents designs and performance evaluation of solar dryer for silica sand with its cost estimation. In the dryer, the heated air from a separate solar collector is passed through a tray, and at the same time, vertical blackened wall of the drying chamber, which is exposed to solar radiation. The results obtained during the test period revealed that the temperatures, moisture removed, drying rate and drying efficiency through dying chamber were decreasing during its upraise path. Initial cost of model solar dryer was estimated (2805 ETB). The number of dryer required is eleven so the total cost is equal to 30855ETB
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    Feasibility Study for Replacement of Diesel Water Pumping System with PV Water Pumping System (A case of Borana Zone Water Supply, Ethiopia)
    (Addis Ababa University, 2013-06) Bonsa, Muleta; Assefa, Abebayehu (PhD)
    This study assess the economic viability of solar PV systems for water pumping project in Borana zone, where groundwater is the main source of water for the population, and compare it with the conventional option of using decentralized Diesel-powered generators to supply electricity to pump water from bore hole. Life cycle cost analysis for both systems have been done by accounting for the higher initial cost of PV system and compared it with Diesel system. However, the high running costs for the Diesel system could still encourage the selection of PV system considering its reliability, the longer life as well as the lower maintenance and operation costs. AC submersible water pumps have been investigated to analyze the feasibility of the system because of the unavailability of DC submersible pumps that can operate at higher depth and discharge. There are 13 wells on this site and all of them are designed to operate with a diesel generator of 75 kW. The investigation is done on three wells with AC pumps of 22 kW, 25 kW, 30 kW, and discharge of 7.5 l/s, and total head of 165 m and 170 m to analyze the amount energy saved in each case and the total area required for PV installation. The rest of the wells have similar discharge, head and aquifer with the selected wells because the distance between each well is 500 m only. The comparison between both systems was extended to cover the environmental impacts. Environmental impacts have been identified and discussed because there is a higher concern worldwide regarding environmental issues including greenhouses gases emissions. The result obtained indicates that the project will start generating profit in the fourth year of operation, the unit water cost for all cases of PV system are less than that of unit cost of DG systems and important financial parameters such as IRR, equity pay-back and NPV show solar energy is the viable alternative source of energy for water pumping systems in the study area. The economic analyses were done using RETScreen-4 software to investigate the financial feasibility and cash flows for water pumping system.
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    Integration of Solar Thermal System for Improved Energy Consumption in Low Temperature Industrial Processes, Case: Harar Brewery.
    (Addis Ababa University, 2016-05) G/Hawariat, Ashenafi; Assefa, Abebayehu (PhD)
    The objectives of this paper are to analyze thermal energy production of heat pipe evacuated tubes solar collector and investigate the integration of solar thermal system with conventional system in low-temperature industrial processes in Harar Brewery Factory. In this study, Matlab program and RET Screen software were implemented to identify technical and financial feasibility of the system. Six low temperature processes, such as feed water pre-heating, kegging, CIP, Mashing at 780C, bottle cleaning and mashing at 520C were selected in the industry for integration of solar thermal system. The total annual conventional thermal energy consumption of the selected processes is 11,176.18MWthr. This covers 54.15% of the annual total thermal energy consumption in the industry from the chemical energy of fuel (20638.23MWthr). The solar thermal system of a single heat pipe evacuated tubes solar collector was analyzed. The maximum outlet water temperature is 800C for mass flow rate of 47.52 kg/hr through the manifold. However, the maximum outlet water temperature is 520C in mashing process for the mass flow rate of 75.60kg/hr. and, the maximum outlet water temperature for bottle cleaning at 650C. It should have a mass flow rate of 66.6kg/hr. The maximum instantaneous efficiency is during sun shine and sun set hours. And, the minimum instantaneous efficiency is 84.96% on March 31 at 11:00 in the morning for the mass flow rate of 47.52kg/hr. However, the minimum instantaneous efficiency is 83.02% when the mass flow rate is 66.6kg/hr. And, the minimum instantaneous efficiency of the system is 62.19% when the mass flow rate of water is 75.60kg/hr. The maximum solar thermal energy harvested form a single collector at a mass flow rate of 47.52kg/hr is 3.19KWt on March 31 at 11:00 in the morning. However, the highest daily solar thermal energy produced on March 12 is 22.01KWthr and the lowest daily solar thermal energy produced on July 19 is 3.66KWthr. The appropriate location of solar collectors is identified to harness the maximum possible solar energy. The optimal number of collectors needed for partial supply of thermal energy to the industry are 368 (30 for mashing at 520C, 62 for mashing at 780C, 59 for bottle cleaning, 22 for feed water pre heating, 168 for CIP and 27 for kegging ). The Annual solar thermal energy production was analyzed for all processes. Those are 127.03MWhr, 333.47Mwhr and 1613.98MWhr for mashing at 520C, bottle cleaning and other thermal processes at 78-800C respectively. The total annual solar thermal energy harvested for all selected processes is 2074.48MWhr. vi Due to the integration of solar thermal system in low temperature industrial processes, the consumption of conventional thermal energy for the selected processes are reduced to 9101.70MWhr/year. Which means 18.56% of thermal energy consumption for selected processes in the industry could be saved. However, the total annual thermal energy consumption of the industry is reduced to 18147.76MWthr. This means 12.07% (10.05% from selected processes, 2.01% from overall heat loss and 0.01% from pre heating of fuel) of the fuel consumption in the industry is saved. In other way, 205,840.65 liter of furnace oil is saved every year. The total initial investment cost of the project is $440,864 (50% is project equity and the remaining is project debt). This project saves $165,813 of the annual cost of the industry for thermal energy application and reduces 729.54 tons of carbon dioxide (CO2) emission per year. The project equity is returned back with 1.6 years.
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    Modeling and Simulation of Solar Chimney Power Plant with and without the Effect of Thermal Energy Storage Systems
    (Addis Ababa University, 2011-09) Daba, Robera; Assefa, Abebayehu (PhD)
    A solar updraft tower power plant – sometimes also called 'solar chimney' or just ‘solar tower’ – is a solar thermal power plant utilizing a combination of solar air collector and central updraft tube to generate a solar induced convective flow which drives pressure staged turbines to generate electricity. Several technologies exist that can convert solar energy into electrical energy. The solar chimney is part of the solar thermal groups of solar conversion technologies. Of these technologies the solar dish has the highest energy efficiency (the current record is a conversion efficiency of 30% of solar energy). Solar trough plants have been built with efficiencies of about 20%. The solar chimney has an efficiency of less than 2%. However, due to its greater scale and simplicity, the solar chimney may have an economic efficiency approaching or exceeding that of the other methods. To improve efficiency of the plant thermal storage system is used. Thermal storage system improves the power output by re-shaping the profile of the power output. The most commonly suggested method for creating energy storage is to place extra thermal mass under the collector in the form of black containers of water. In this paper both the solar chimney power plants: the plant with and without thermal storage system are simulated for the case of Afar region using Fluent and the effect of turbine position is also analyzed. The cost of the power output per kilowatt-hour is reduced while using the thermal storage system. It also regulates the power output. The power output increases as the turbine is positioned at higher position but the cost of the chimney so the plants cost increases very much. Solar chimneys are very suitable for use in remote communities where there is high solar energy capacity; such as Afar and Somalia, as a power source for both residential and industrial use, based on reliability, cost, and operational factors. They can provide a suitable energy source in many remote areas of Ethiopia, including areas that are not currently supplied by conventional means.
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    Modeling, Simulation and Performance Evaluation of Central Receiver System Power Plant with Thermal Storage
    (Addis Ababa University, 2010-09) Bedru, Muaz; Assefa, Abebayehu (PhD)
    Solar Central Tower systems have a single receiver placed on top of a tower surrounded by hundreds of mirrors (heliostats) which follow the apparent motion of the sun in the sky and which re-direct and focus the sunlight onto the receiver. The key elements of a solar tower system are the heliostats:- provided with a two-axis tracking system, the receiver, the steam generation system and the storage system. A fluid circulates through the receiver, collecting thermal energy at high temperatures, and flows to an insulated storage tank. Steam for the 10 MW turbines is made as needed by pumping the hot fluid to a heat exchanger. The receiver and energy storage fluid is a commercial molten potassium and sodium nitrate mixture. The number of heliostats will vary according to the particular receiver‟s thermal cycle and the heliostat design. The power plant analyzed in this paper has a capacity of generating 10MW electric power. The power cycle was modeled using EES to obtain the state point variables such as conductances of the heat exchangers, mass flow rates of steam and HTF, enthalpies, temperatures, pressures etc… at specified state points for steady state operation of the plant. These state point variables are used as reference inputs and/or parameters during system simulation using TRNSYS. The CRS was modeled in TRNSYS simulation studio using existing TRNSYS 16.0 components most of which are from STEC library release 3.0 packages. The CRS financial and economic analysis as well as different system component size and number was optimized using SAM. Without the incorporation of thermal storage, 788 heliostats with 97m2 area satisfies the power demand specified for this research but the addition of thermal storage increases the number of heliostats to 1200 with significant increase in initial system cost and decrease in levelized energy cost. A six hour capacity two tank thermal storage is incorporated with the power plant in order to avoid power transient during low and high DNI, to have power when there is no sunlight, to increase the capacity factor and to minimize the levelized cost of energy. The addition of a thermal storage extends the power plant operation to 16 hours with 13 hours of constant 10MW net electrical power output for a clear sunny day. The SAM analysis reveals that the ii addition of thermal storage in the system significantly increase the investment cost from $58,072,837.73 to $76,781,394.61 with minimizing effect of LCOE from 33.02 to 26.79 cents/kWh and increasing capacity factor from 17.3 to 30.0%
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    Modeling; Simulation and Performance Evaluation of Parabolic Trough Solar Collector Power Generation System
    (Addis Ababa University, 2009-09) Mesfin, Mekuannint; Assefa, Abebayehu (PhD)
    Parabolic troughs are one of the low cost solar electric power options available today and have significant potential for further cost reduction. Parabolic trough power plants use concentrated sunlight, in place of fossil fuels, to provide the thermal energy required to drive a conventional power plant. These plants use a large field of parabolic trough collectors which track the sun during the day and concentrate the solar radiation on a receiver tube located at the focus of the parabolic shaped mirrors. A heat transfer fluid passes through the receiver and is heated to temperatures required to generate steam and drive a conventional Rankine cycle steam power plant. In this thesis paper model of a parabolic trough power plant, taking into consideration the different losses associated with collection of the solar irradiance and other thermal losses is presented. MATLAB software is used to model the power plant at reference state and TRNSYS software is used to simulate the performance of the model at off design weather conditions. MATLAB modeling of the power plant is used to find the different reference values which are used as inputs for the TRNSYS modeling and simulation of the power plant. The reference values include the solar field area, the heat transfer fluid (HTF) and steam/water mass flow rates, overall heat transfer coefficients of the different heat exchangers, etc. The TRNSYS modeling and simulation are used to determine the net power, initial steam temperature, the inlet and outlet heat transfer fluid temperatures out of the solar field and steam and HTF mass flow rates in hourly basis for representative days of year 2001. The cost and financial analysis is made for the power plant. Solar Advisor Model is used to make this analysis under Addis Ababa weather condition. This analysis is used to determine the different costs associated with the power plant. The cash flow for the 30 years of operation of the power plant is also shown.
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    Prediction of Performance Parameters and Determination of Aerodynamic Characteristics of Wind Turbine Airfoil Using CFD Modeling:
    (Addis Ababa University, 2014-08) Merid, Million; Assefa, Abebayehu (PhD)
    In the current situation of global energy crisis, generation of energy derived from renewable energy resource has grown a significant attention. Wind energy is a very interesting due to the fact that fuel is free of cost. The most important aspect of wind energy technology is the wind turbine and its aerodynamic characteristics of the airfoil forming the blade. Thus predicting the performance parameters and determining aerodynamic characteristics of airfoil section are important. However, this requires continued experimental wind tunnel test and validation tools such as computational fluid dynamics (CFD). The primary objective of this study was learning the CFD software and its applications. Secondly, this study was focused on predicting aerodynamic characteristics of an airfoil for varying angles of attack (AOAs). Simulation was done to deduce aerodynamic parameters (lift, drag, lift to drag ratio, contour plot of velocity and pressure distribution over the airfoil section). This can reduce dependence on wind tunnel testing. The simulation was done on airflow over a two – dimensional NACA 63-415 airfoil using FLUENT (version 6.3.26) at various angles of attack varied from -50 to 200 using two turbulence models (S-A and SST k- ω) with the aim of selecting the most suitable model. Domain discretization was carried out using structured quadrilateral grid generated with GAMBIT (version 2.3.16), the fluent pre-processing tool. Comparisons and validation were made with available experimental data for NACA 63-415 airfoil with numerical results. Accordingly, it was found that the two turbulence models achieved a reasonable and a good agreement in predicting the coefficients especially for angle of attacks prior to stall. Among the model, studied the most appropriate turbulence model for the simulations were the SST k- ω two equation models, which had good agreement with the experimental data than S-A one equation model. As a result, it was decided to use the SST k- ω turbulence model for the main analysis with acceptable deviations in results (9.028% for lift and 12.203 % for drag coefficients). This study concluded that CFD simulation provides sufficiently accurate results for a majority of AOAs. The discrepancy in calculating the lift and drag values comes from limitations in the turbulence model behavior. However, the majority of the lift and drag curves match the experimental data. Finally, this study includes simulation results of Adama I wind turbine airfoil section and predicted results was complied.
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    Simulation and Optimization of Wind Turbine, Solar PV, Storage Battery and Diesel Generator Hybrid Power System for a Cluster of Micro and Small Enterprises Working on Wood and Metal Products at Welenchity Site
    (Addis Ababa University, 2013-02) Jima, Terefe; Assefa, Abebayehu (PhD)
    This thesis presents the design of a hybrid electric power generation system utilizing both wind and solar energy for supplying a cluster of three micro and small enterprises (MSEs) working on wood and metal products at the Welenchity site. The work was begun by investigating wind and solar energy potentials of the desired site, compiling data from different sources and analyzing them using software. The wind speed and solar irradiation data for the site understudy are collected from the National Metrological Agency (NMA) and analyzed using the software tool HOMER. The results related to wind energy potential are given in terms of the monthly average wind speed, the wind speed PDF, the wind speed CDF, the wind speed DC, and power density plot for the site. Whereas the solar energy potential, has been given in the form of solar radiation plots for the site. According to the results obtained through the analysis, the site has abundant solar energy potential and the wind energy potential is unquestionably high enough to be exploited for generating electric energy using wind turbines with low cut-in wind speed. The design of a standalone PV-wind hybrid power generating system has proceeded based on the promising findings of these two renewable energy resource potentials, wind and solar. The simulations and design has been carried out using the HOMER software. By running the software the simulation results which are lists of power supply systems have been generated and arranged in ascending order according to their net present cost (NPC). Sensitivity variables, such as range of wind speed, solar radiation and diesel price have been defined as inputs into the software and the optimization process has been carried out repeatedly for the sensitivity variables and the results have been refined accordingly. The model developed is fairly general and may be adequate for preliminary results for energy consumption cost for MSEs willing to adopt renewable energy sources. Therefore the most economical scenario is using wind-PV –Diesel Generator-Battery hybrid system as stated before. Keywords: hybrid renewable energy system, wind energy, photovoltaic, HOMER, PV-wind hybrid, cluster of micro and small enterprises
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    Simulation of Modern Steam Power Plant
    (Addis Ababa University, 2005-06) Hailu, Alemayehu; Assefa, Abebayehu (PhD)
    The thesis describes a steam power plant simulator which has been developed using the MATLAB code. The simulation is important to study the behavior of the steam power plant system by means of a model, and the results obtained allow us to consider many different design possibilities as well as varieties operating conditions. Therefore, different designs may be evaluated so that an acceptable design can be chosen and safe levels may be established for the operating conditions. These results are also used for optimization of the plant. The basic considerations in the development of a mathematical model are first presented in the thesis, followed by a discussion of simulation of a steam power plant. Conservation equations and characteristic curves are used to model the component of the steam power plant. From these mathematical model equations, the component modules are developed using MATLAB code. Output parameters are obtained from input data to the component modules. The STEAM_POWER_PLANT_SIMULATION program is used to simulate the power plant system. In the program there are two main solvers. These are: the turbine-heater solver and boiler solver. The turbine-heater solver consists of the turbine and feed water heaters including the pumps and the condenser. The boiler solver has its own residue generator function and Jacobean generator function and then Newton-Raphson technique is used to solve a set of nonlinear algebraic equations.
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    Simulation of Parabolic Trough Concentrating Solar Power Generation System
    (Addis Ababa University, 2014-04) Tesfu, Seblewongel; Assefa, Abebayehu (PhD)
    Climate change has drastically increased causing global warming due to emission of greenhouse gas with the provision of energy services that community of the world uses. In order to work against this trend, varieties of researches are necessary to avoid the negative impacts of global warming. Among the various forms, of utilizing energy mechanisms that curtails the emission of greenhouse gases is solar energy electricity production. In this work, theoretical performance of concentrated solar power system (CSPS) using parabolic trough collectors (PTC) is investigated. The software TRNSYS and the Solar Thermal Electric Components (STEC) library are used to model the power system design and simulations. This model was constructed using data from an existing 30 MW Solar Electric Generating System (SEGS VI) using PTC’s in Karmer Junction, California. Input data and results of the simulation of the already existing SEGS VI plant were used for validating the current model. The validated model is used for building a 10 MW system using TRNSYS. The reference state point properties which are used as inputs in the 10 MW TRNSYS model are determined using MATLAB software. A MATLAB code is used to find the initial pressure after giving first guess for the initial pressure and checking the error. This initial pressure is found to be P (1) = 100 [bar]. This pressure is found for initial steam temperature of 371 OC. Then, hourly simulations of electrical power and direct normal irradiance (DNI) are determined for selected days of year 2001 (for which complete data are available), for Adigala, Ethiopia. Different kinds of criteria for land use, annual irradiation and infrastructure are discussed in order to properly locate the CSP plants. Depending on the data gathered and on the criteria set for the CSP installation, north eastern Ethiopia is a suitable site since it has a flat land topology and high solar insolation. As the cost of power generation by CSP technologies is of great importance for the promotion of the technology to be proven as competitive alternative to the conventional oil or gas fired power plants. This thesis work tackles the economic aspect by investigating the cost of electricity generation of the modeled parabolic trough power plant using simulation tool SAM (System Advisor Model).
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    Simulation of Solar Cereal Dryer Using Trnsys
    (Addis Ababa University, 2007-01) Tkubet, Habtamu; Assefa, Abebayehu (PhD)
    In many countries of the world, the use of solar thermal systems in the agricultural area to conserve vegetables, fruits, coffee and other crops has shown to be practical, economical and responsible approach environmentally. Solar heating systems to dry food and other crops can improve the quality of the product, while reducing wastes produce and traditional fuels - thus improving the quality of life. However the availability of good information is lacking in many of the countries where solar food processing systems are most needed. This work presents the performance of several individual, medium and large-scale food processing systems, which incorporate solar drying. A general purpose of solar crop dryer for drying of various agricultural products such as coffee, fruits, Vegetables, cereals, etc, is simulated. The simulated solar dyer consists of the solar air heater ( solar collector) which uses low emissivity glass cover, weather data, and an integrated dryer chamber attached to the collector where the products to be dried are placed. A thermal solar collector model is developed to determine the available useful energy for heating the ambient air with the available solar radiation. Basic heat transfer equations for single-plate and double glass glazing are drived and techniques for the solution of these questions are presented. A computer program is written to predict the collector outlet temperature, mass flow rate and other engineering variables from the input of the meteorological data and collector parameters and also done for the dryer chamber by using the input from the collector out put and the properties like initial moisture content, initial temperature of cereals and other engineering properties. Results of the system simulation are presented in graphical form suitable for system performance determination. From the incident flux, ambient air temperature and solar collector parameters, the useful energy, collector output temperatures of the out put air are determined. Simulation of Solar Cereal Dryer Using TRNSYS i x The output properties of the collector are the input parameters for the drying chamber. These parameters are used to determine the moisture content, the relative humidity, the mass of water vapor and the output temperature of the air at the out put of the drying chamber.
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    Simulation of Wind Power Generation System and Clean Development Mechanism for Electrification in Nazareth Site
    (Addis Ababa University, 2011-07) Kebede, Dawit; Assefa, Abebayehu (PhD)
    In this thesis, the wind speed data measured by the GTZ TERNA program is used to assess the energy output for a hypothetical 51 MW installed capacity wind farm at Nazareth site. Using the RETScreen model, the energy output of the wind farm is presented in terms of gross energy production, renewable energy delivered, specific yield and wind farm capacity factor. The energy output analysis is done using four wind energy conversion systems of rated capacity 600, 800, 1000 and 1500 kW. The RETScreen model is used to perform the financial feasibility analysis of the wind farm at this site, likewise the sensitivity and risk analyses are performed. Furthermore, a Clean Development Mechanism (CDM) assessment is performed for this wind park. The net annual and total revenue generated from Certified Emission Reduction sales is calculated assuming Certified Emission Reduction prices of $6. The application of subsides on capital finance to the up-front and Clean Development Mechanism periodic cost are considered in order to evaluate the impacts of Certified Emission Reductions on project viability.
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    Wind Energy Resource Analysis: A Case Study of Aysha Wind Farm
    (Addis Ababa University, 2015-10) Wudu, Mengesha; Assefa, Abebayehu (PhD)
    Ethiopia satisfied 92 % of its energy demand using biomass sources while petroleum and electricity (hydropower) only contribute 7 % and 1 %, respectively, in 2009. Due to this limited electricity availability, among the total population only 23.3 % had access to electricity and among 82.7 % of Ethiopians living in rural areas only 2 % in 2011. In addition 99 % of the electricity production is from hydropower source which is highly vulnerable to fluctuations in energy supply due to varying water inflow to reservoirs. However, the country is well endowed with other renewable energy resources (solar, wind and geothermal) that can be used to develop electricity. Among these resources, harnessing Ethiopian wind energy potential (10,000 MW) is a promising solution as it offers better generation mix and seasonal complementarity to avoid vulnerabilities associated with hydropower. It also helps in improving the life of population who are unlikely to have access to electricity supply in foreseeable future. Accordingly, this study is conducted at Aysha Wind Farm with the aim to analyze its wind energy resource based on 10 minute mean data for the year 2008 G.C. Using different software and statistical model, the wind data has been analyzed to: select wind turbine class, power density & estimate farm AEP, develop site wind resource map and perform preliminary turbine micro-sitting. Based on the analysis and site survey, site roughness and wind shear exponent are also determined. Detail wind energy resource study is performed for the site using MS Excel, MATLAB and WAsP software. Analyzing a wind-mast data at a height of 10 m using MATLAB and MS Excel, mean wind speed of 8.455 m/s and average power density of 571 W/m2 have been found at the farm. To take the effect of the roughness of the site in to consideration, a wind resource map of 28.44 km x 36 km area is performed on the site. This is done based on two nominated wind turbines namely: Sany SE8220III 2 MW and Gamesa G80 2 MW at respective hub heights of 70 m and 67 m using WAsP software. Considering the nearby transmission line capacity i.e., 300 MW, 150 sets of each type of turbine has been put at the farm, analyzed and compared to each other. Accordingly, Gamesa G80 2 MW is selected for its least wind farm cost of 0.0193 USD per kWh. As per the preliminary analysis of the farm based on the selected turbine, total gross AEP of 1819.21 GWh and total net AEP of 1183.62 GWh (after considering total loss factor of 0.651 on the total gross AEP) have been found. In addition the average power density and CF at the wind farm are estimated at 1392.6 W/m2 and 44.92 %, respectively. Moreover the mean wind speed at hub height (67 m) is 11.83 m/s whereas the average Weibull shape factor (k) and scale factor (A) are estimated at 3.13 and 13.22 m/s, respectively. In conclusion, according to the wind power classes, Aysha wind farm is categorized as class 7 (excellent wind energy resource) which is promising to construct large wind farm. It is, therefore, recommended that Ethiopian government consider investing on Aysha wind farm as the farm has an excellent wind resource potential at a capacity of 300 MW. KEYWORDS: Wind Farm, Wind Climate, Energy Production, Wind Resource, Wind Shear Exponent, WAsP, Wind-Mast, Capacity Factor, Ethiopia, Power Density, Wind Turbines