6 research outputs found

    Optimal control of conventional hydropower plant retrofitted with a cascaded pumpback system powered by an on-site hydrokinetic system

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    This paper presents an optimal control strategy for a hydropower plant retrofitted with a hydrokineticpowered cascaded pumpback system in dry season. Pumpback operation aims at recycling a part of the down-stream discharge back to the main dam to maintain a high water level to optimise the energy value of the available water. The problem is formulated as a multi-objective optimisation problem to simultaneously minimise the grid pumping energy demand, minimise the wear and tear associated with the switching frequency of the pumps, maximise the restoration of the volume of the dam through pumpback operation and maximise the use of on-site generated hydrokinetic power for pumping operation. The performance of the proposed cascaded model is compared with the classical single pump pumped storage model. Simulation results based on a practical case study shows that the cascaded pumpback model can reduce the pumping energy demand by up to 48.18% and increase the energy yield of the resultant system by up to 47.10% in dry season.The authors would like to thank the MasterCard Foundation, the National Hub for Energy Efficiency and Demand Side Management South Africa and the University of Zambia-Zambia for financial and other support towards this research.http://www.elsevier.com/locate/enconman2018-01-31hb2017Electrical, Electronic and Computer Engineerin

    Optimal energy mix of a microhydro-wind-grid system powering a dairy farm in Western Cape, South Africa

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    This paper presents an optimal control strategy of a grid-tied microhydro-wind power system for a rural dairy farm in South Africa. The problem is formulated as a multi-objective optimisation programme in discrete time domain to minimise grid imported energy cost under Time of Use Tariff (TOU) while at the same time maximising revenue generated from the sale of surplus renewable energy to the grid at a specified renewable energy feed-in tariff. The application of the proposed model to a practical case study shows the potential of the model to save the farmer the grid energy cost up to 75.07% in summer and 70.69% in the winter with a discounted repayment period of 3 years and 7 months.The MasterCard Foundation and the National Hub for Energy Efficiency and Demand Side Management.http://www.elsevier.com/locate/procediaam2018Electrical, Electronic and Computer Engineerin

    Sustainable Energy Access and Irrigation Planning in Sub Saharan Africa

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    Sub-Saharan Africa (SSA) is the least developed and most vulnerable region to climate change globally, with electricity access and irrigation rates at 45% and 5%, respectively. The region\u27s high reliance on rain-fed farming results in significant yield gaps, increasing dependence on food imports and aid. Projected declines in rainfed agricultural productivity due to climate-induced rainfall variability, coupled with a rapid population growth rate of 2.8% per year, will likely exacerbate food insufficiency. SSA is largely rural, with an urbanization rate of 42%. Much of its population lives in sparsely populated settlements characterized by low electricity demand, which poses a significant barrier to electrification. Integrating irrigation energy demand into electrification planning can mitigate this low-electricity demand barrier, making rural electrification economically viable from a system perspective. Additionally, providing low-cost electricity for irrigation has potential to enhance agricultural productivity and the economic well-being of farmers. This dissertation addresses the challenge of sustainable energy access and food production in SSA through three distinct yet interrelated studies. The first study develops an integrated modeling framework—coupling a crop model, a hydrologic model, and a techno-economic model—to assess solar irrigation potential in the current rainfed croplands of SSA based on commonly grown food crops. The second study assesses and quantifies irrigation energy requirements for mid-century (2045-2055) and end-century (2085-2095) periods, using 2010-2020 as the baseline, under varying climate and socioeconomic scenarios. This study relies on future irrigation water withdrawal projections from the Global Change Assessment Model (GCAM). The third study develops an integrated modeling framework, coupling a microgrid model and a crop model to assess and quantify the symbiotic benefits of co-planning minigrid-driven rural electrification and smallholder irrigation farming in SSA

    Optimal control of a conventional hydropower system with hydrokinetic/wind powered pumpback operation

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    The need to ease pressure from the depleting fossil fuel reserves coupled with the rising global energy demand has seen a drastic increase in research and uptake of renewable energy sources in recent decades. Of the commonly exploited renewable energy resources, hydropower is currently the most popular resource accounting for 17% of the world's total energy generation, a portion which translates to 85% of the renewable energy share. However, despite the huge potential, hydropower is dependent on the availability of water resource, which is affected by climate change. During wet seasons, hydropower system operators are faced with a deluge of floods which results in excess power generation and spillage. The situation reverses in dry seasons where system operators are compelled to curtail power generation because of low water levels in the hydro reservoirs. The later situation is more pronounced in drought prone regions such as Southern Africa where some hydropower plants are completely shut down in dry seasons due to water shortage. This dissertation focuses on the application of optimal control to hydropower plants with pumpback retrofits powered by on-site hydrokinetic and wind power systems. The first section of this work develops an optimal operation strategy for a high head hydropower plant retrofitted with hydrokinetic-powered cascaded pumpback system in dry season. The objective of pumpback operation is to recycle a part of the downstream discharged water back to the main dam to maintain a high water level required for optimal power generation. The problem is formulated as a discrete optimisation problem to simultaneously minimise the grid pumping energy demand, minimise the wear and tear associated with the switching frequency of the two pumps in cascade, maximise restoration of the reservoir volume through pumpback operation and maximise the use of on-site generated hydrokinetic power for pumping operation. Simulation results based on a practical case study show the pumping energy saving advantages of the cascaded pumping system as compared to a classical pumped storage (PS) system. The second section of this work develops an optimal control system for assessing the effects of ecological flow constraints to the operation of a hydropower plant with a hydrokinetic-wind powered pumpback retrofit. The aim of the control law in this case is to use the allocated water to optimally meet the contractual obligations of the power plant. The problem is formulated as a discrete optimisation problem to maximise the energy output of the reservoir subject to some defined technical and hydrological constraints. In this system, pumping power is met primarily by the wind power generator output supplemented by the on-site generated hydrokinetic power. The excess hydrokinetic power is exported to the grid to meet the committed demand. Three different optimisation scenarios are developed: The first scenario is the baseline operation of the hydropower plant without any intervention. The second scenario incorporates the hydrokinetic-wind-powered pumpback operation in the optimal control policy. The third scenario includes the downstream flow constraint to the optimal control policy of the second optimisation scenario. Simulation results based on a practical case study show that ecological flow constraints have negative effects to the economic performance of a hydropower plant.Dissertation (MEng)--University of Pretoria, 2017.MasterCard Foundation Scholars ProgramCentre of New Energy SystemsUniversity of PretoriaElectrical, Electronic and Computer EngineeringMEngUnrestricte
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