Center for Energy Technology

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Browsing Center for Energy Technology 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 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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    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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    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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    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
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    Wind Resource Data Analysis for Mosoboharena Wind Farm
    (Addis Ababa University, 2015-10) Abdella, Mezid; Assefa, Abebayehu (PhD)
    Ethiopia has been relied much on hydroelectric plants for of its power demand. But Hydro power is exposed to the effects of climatic change. Problem of water level fluctuation is increasing continuously in most of the hydropower dams resulting from the climate change. As the demand for safe and clean electricity increases due to industrial development and population growth in the country, expanding wind energy industry is greatly helpful to Ethiopia to meet its growing massive energy demand and to promote sustainable development. The country has enormous potential to generate electricity from wind. This study investigates the wind energy resource potential for Mosobo-Harena using different statistical methods and software. MS-Excel and MATLAB programs were used to generate time-series graphs of wind speed and direction , frequency distributions of wind speeds (wind speed histogram) and a wind rose for 12 continuous months from January 1/2007 to December 31/ 2007. And WAsP (The Wind Atlas Analysis and Application Program) was used for predicting wind resources, wind atlas generation, develop site wind resource map, identify wind potential sites, sitting of wind turbines and estimating farm annual energy production (AEP). The analysis was conducted based on one year 10 minutes interval wind speed collected data from mast at Mosobo-Harena at heights of 10m and 40m above ground level. This site has an average wind speed of 5.47 m/s and annual wind power density is 161w/m2 at mast height of 10m. The digital map of the study area was prepared by digital map generating software called Global Mapper considering an area of 20km by 20 km. Grid resource map for the wind farm was generated at some standard heights of 10m, 40m, 60m, 80m and 100m. Then from these standard heights, the hub height of the turbine was decided to be 60m for this project. And thus wind turbine Vestas V60-850kw was selected from WAsP documentation catalogue. The proposed wind farm has 72 turbines. At the selected turbine hub height of 60m, the annual mean wind speed and wind power density of the farm are 6.79m/s and 316W/m2 respectively, this is categorized as IEC class-III wind resource at this height. And the farm installed capacity is 61.8 MW, the net farm AEP is estimated to be 201686.7 MWhr and the average capacity factor was calculated to be 37.6%.