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  • 1.
    Bekele, Getachew
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Study into the Potential and Feasibility of a Standalone Solar-Wind Hybrid Electric Energy Supply System2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The tendency to use renewable energy resources has grown continuouslyover the past few decades, be it due to fear over warnings of globalwarming or because of the depletion and short life of fossil fuels or evenas a result of the interest which has developed among researchers doingscientific research into it. This work can be considered as joining any ofthese groups with an objective of giving electric light to the poorpopulation living in one of the poorest nations in the world.The aim of the work is to investigate supplying electric energy fromsolar-wind hybrid resources to remotely located communities detachedfrom the main grid line in Ethiopia. The communities in mind are one oftwo types; the first is the majority of the poor population residing in thecountryside; and the other is people relocated by the Government fromthe over used and dry regions to relatively productive and fertile ones inline with the long-term poverty reduction plan.The work was begun by investigating wind energy and solar energypotentials at four geographically different locations in Ethiopia bycompiling data from different sources and analyzing it using a softwaretool. The locations are Addis Ababa (09:02N, 038:42E), Mekele (13:33N,39:30E), Nazret (08:32N, 039:22E), and Debrezeit (8:44N, 39:02E).The results related to wind energy potential are given in terms of themonthly Average wind speed, the wind speed probability densityfunction (PDF), the wind speed cumulative density function (CDF), thewind speed duration curve (DC), and power density plots for all fourselected sites. According to the results obtained through the analysis, thewind energy potential, even if it is not exceptional, is irrefutably highenough to be exploited for generating electric energy.The solar energy potential, based on sunshine duration data collectedover a period of 7 - 11 years and radiation data obtained from differentsources, has been calculated using regression coefficients specific to thesites in question. Based on the sunshine duration data, the monthlyaverage daily sunshine amount for each of the places has also beencomputed and given in a form of plot. Through additional work on theresults of the calculations, the solar energy potential has been given inthe form of solar radiation plots for each of the selected sites. Asexpected, the results indicated an abundance of solar energy potential.It is based on the promising findings of these two energy resourcepotentials, wind and solar, that the feasibility study for a standalonesolar-wind hybrid energy supply system has proceeded, targeting thecommunity mentioned earlier. The hybrid system consisted of Windturbine, Photovoltaic panel, diesel generator and a bank of batteries, witha power conditioning converter included in the system.The hybrid standalone supply system is intended to provide electricity toa model community of 200 families with five to six family members ineach. The community is equipped with a primary load, a deferrable load,a community school and a health post. An electric load which includeslighting, water pumping, a radio receiver, and some clinical equipmenthas been suggested. Hybrid Optimization Model for ElectricRenewables, HOMER, software has been used for the analysis. Theaverage wind speed and average solar radiation calculated from the datafor all of the selected sites has been used to input into the software.The hybrid system design is approached in three different ways. The firstapproach is to include within the hybrid system those components whichare locally available, without giving special attention to their efficienciesand proceed with the design work. The second approach is tothoroughly search the market for the best and most efficienttechnological products and to select the best components for theanalysis. A third approach considered in an attempt of cost minimizationis to see if a self-contained type of design can be a better solution. Whatthis means is every household will have its own supply system that mayconsist of any combination of PV and wind turbine including converter,battery and charge controller.After running the simulations, lists of power supply systems have beengenerated, sorted according to their net present cost. Sensitivity variables,such as range of wind speeds, range of radiation levels and diesel pricehave been defined as inputs into the software and the optimizationprocess has been carried out repeatedly for the sensitivity variables andthe results have been refined accordingly.

  • 2.
    Bekele, Getachew
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Feasibility study for a standalone solar–wind-based hybrid energy system for application in Ethiopia2010In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 87, no 2, p. 487-495Article in journal (Refereed)
    Abstract [en]

    The aim of this paper is to investigate the possibility of supplying electricity from a solar-wind hybrid system to a remotely located model community detached from the main electricity grid in Ethiopia. The wind energy potential of four typical locations has been assessed in a previous article. The solar potential has also been investigated and the results are presented in detail in an accompanying article awaiting publication. For one of the sites, Addis Ababa, the results of the investigation are given here in detail. For the other sites, the results are given as sensitivity diagrams only. Based on the findings of the studies into energy potential, a feasibility study has been carried out on how to supply electricity to a model community of 200 families, which comprises 1000 people in total. The community is equipped with a community school and a health post. The electric load consists of both primary and deferrable types and comprises lighting, water pumps, radio receivers, and some clinical equipment. A software tool, Hybrid Optimization Model for Electric Renewables (HOMER) is used for the analysis. The result of the analysis is a list of feasible power supply systems, sorted according to their net present cost. Furthermore, sensitivity diagrams, showing the influence of wind speeds, PV costs, and diesel prices on the optimum solutions are also provided.

  • 3.
    Bekele, Getachew
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Solar energy potential assessment at four typical locations in EthiopiaIn: Energy for Sustainable Development, ISSN 0973-0826Article in journal (Other academic)
    Abstract [en]

    As a continuation of the study into wind energy potential previously completed, solar energy potential at the same four locations in Ethiopia has been investigated. These are Addis Ababa, 09” 02’N, 38” 42’E, 2408 m (AMSL); Mekele, 13” 33’N, 39” 30’E, 2130 m; Nazret 08:32N, 39:22E, 1690 m; and Debrezeit, 08”44’N, 39” 02’E 1850 m. As in the case of the wind data no radiation data has been properly recorded to evaluate the sola renergy potential of the country, except for in one single location, Addis Ababa. However, sunshine duration data has been collected over a relatively long period of time. Therefore, this study is based on sunshine duration data collected over more than 10 years at the specified locations and also on software and satellite interpolated data obtained from sources outside the country. A thorough literature survey has been carried out and different models by different authors have been investigated. After analyzing the data using well known equations taken from standard text books, the results obtained are given in the form of solar radiation plots for all locations. This study is the second stage in the assessment of the feasibility of a hybrid standalone electricity supply system to remotely located communities detached from the main grid.

  • 4.
    Bekele, Getachew
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Solar-wind-based village electrification in Ethiopia: a comparision of technologiesIn: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682Article in journal (Refereed)
    Abstract [en]

    The aim of this paper is to investigate the possibility of supplying electriclight and potable water from a solar-wind based hybrid system. The main target is a remotely resettled community in Ethiopia out of reach of the electric grid. The wind energy potential of the location has been assessed in a previous article. The solar potential has also been investigated in an accompanying article awaiting publication. Based on the findings of the potential, a feasibility study has been carried out on how to supply electricity to the community, modeled as having 200 families, comprising of approximately 1000 to 1200 people in total. A community school and a health post is also considered for the community. The electric load considered is of both primary and deferrable types consisting of lighting ,water pumps, radio receivers, and some clinical equipment. In theattempt of finding the most economical solution, a system with less energy efficient, and less expensive components have been compared to a more expensive system with the latest, most energy efficient ,technology on both the supply and load sides.

    A system solution on individual basis (solution per house hold) has also been considered and the net present cost (NPC) is compared against the aggregate solution. A software tool, Hybrid Optimization Model for Electric Renewables (HOMER) is used for the analysis. The result of the analysis is a list of feasible power supply systems, sorted according to their net present cost. Furthermore, sensitivity diagrams, showing the influence of wind speeds, PV costs, and diesel prices on the optimum solutions are also provided.

  • 5.
    Bekele, Getachew
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Wind energy potential assessment at four typical locations in Ethiopia2009In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 86, no 3, p. 388-396Article in journal (Refereed)
    Abstract [en]

    The wind energy potential at four different sites in Ethiopia - Addis Ababa (09:02N, 38:42E), Mekele (13:33N, 39:30E), Nazret (08:32N, 39:22E), and Debrezeit (8:44N, 39:02E) - has been investigated by compiling data from different sources and analyzing it using a software tool. The results relating to wind energy potential are given in terms of the monthly average wind speed, wind speed probability density function (PDF), wind speed cumulative density function (CDF), and wind speed duration curve (DC) for all four selected sites. in brief, for measurements taken at a height of 10 m, the results show that for three of the four locations the wind energy potential is reasonable, with average wind speeds of approximately 4 m/s. For the fourth site. the mean wind speed is less than 3 m/s. This study is the first stage in a longer project and will be followed by an analysis of solar energy potential and finally the design of a hybrid standalone electric energy supply system that includes a wind turbine, PV, diesel generator and battery.

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