Techno-economic analysis of an off-grid micro-hydrokinetic river system as a remote rural electrification option

Thesis (M. Tech. (Electrical Engineering )) - Central University of Technology, Free State, 2014Remote rural electrification via grid-extension is a challenging solution due to high connection costs and low electricity consumption rate. As a result, it is difficult to recover the initial investment costs. Therefore, electrification is made possible by means of the commonly used off-grid approaches such as solar, wind, diesel generator and conventional micro-hydro. However, owing to non-continuous availability of sunlight and wind, high cost of diesel fuel, and requirements for construction of diversion weirs, these off-grid approaches might not offer a cost-effective and reliable solution to low income rural residents. There are many rural communities throughout the world without access to grid electricity and with access to flowing water. An off-grid micro-hydrokinetic river (MHR) system is one of the promising technologies to be used in remote rural areas with flowing water. It can bring sustainable improvement to their quality of life due to its high energy density and minimal environmental impact. This technology is still in the development stage and there is a lack of application, especially in rural areas. Hence, this study investigates the current status of MHR technology in rural applications. To demonstrate the economic feasibility of an off-grid MHR system, a rural site with multiple energy sources within South Africa has been used. The economic benefit offered by this proposed system at the selected site is compared to the economic benefits offered by other commonly used standalone systems such a solar, wind and diesel generator (DG). This economic comparison has been performed by making use of a Hybrid Optimization Model for Electric Renewable (HOMER) simulation tool. Grid extension has also been used as a comparison method for obtaining an economical distance between grid lines and the remote rural site. The results highlighted the acceptable economic performance of the MHR system. Finally, most of the available modelling and simulation tools for mechanical and electrical systems are not equipped with hydrokinetic modules. Hence, an MHR system model has been developed in MATLAB/Simulink in order to study its dynamic performance as submitted to variable water resource. Its performance has then been compared to the performance of a wind system counterpart for generating the same amount of electrical power. This proved/verified that the proposed system can generate electricity markedly cheaper than a wind system even in areas with adequate wind resource within South Africa

Optimal Energy Management Modelling Of A Grid-Connection Micro-Hydrokinetic With Pumped Hydro Storage

ThesisThe pressure on greenhouse gases (GHGs) emission reduction and energy deficit crisis are of global concern. The ever increasing energy demand due to population growth as well as industrial and commercial business developments, leads to energy deficit crisis for electric utility operators around the globe. This generates an increased probability of grid instability and blackout challenges. Hence, this promotes the requirement for the additional fossil fuel power plants, leading to electricity price increase for consumers, due to high investment cost and the rising fossil fuels prices. The exploitation of an onsite grid-connected renewable energy (RE) system may mitigate all of the above-mentioned challenges. However, the intermittent nature of RE resources (such as solar, wind, hydro, geothermal and marine) leads to a challenge of high uncertainty output power. Hence, power demand cannot be reliably met, due to daily or seasonal weather changes. Therefore, a stand-alone RE system should comprise of an energy storage system (ESS), to store surplus energy for later use when the power demand is more than the generated output power. Additionally, a grid-interactive RE system should also comprise of the ESS, due to the variable tariff rates imposed by utility companies around the globe. The aim is to store excess energy during low-priced off-peak periods, for later use during high-priced peak periods. Hence, minimal electricity bill may be achieved by the consumers. The utility grid operator may also reap a benefit of a reduced blackout probability, especially during peak demanding periods. Among various RE technologies, hydrokinetic is a promising RE solution to be exploited in areas with flowing water resources, such as rivers, tidal current or artificial water channels. It is easily predictable and has proved to generate electricity at flowing water speeds, ranging from 0.5 m/s and above. It has proved to generate electricity markedly better and affordable than solar and wind energy systems. Furthermore, it has proved to operate cost-effectively, if it comprises of a pumped-hydro storage (PHS) system instead of a battery-based storage system. Rural consumers, such a farms, industries and mines situated in close proximity to flowing water resources, may make use of a grid-connected micro-hydrokinetic-pumped-hydro-storage (MHK-PHS) system to reduce electricity bills and sell the excess energy to the grid. However, a grid-connected MHK-PHS system requires a complex optimal energy management system, instead of expecting a consumer to respond to a change in real-time electricity price. The system should allow for optimal energy storage and sales, while ensuring that the consumer load demand is met at all times, by considering variable time-of-use (TOU) tariffs and load demand uncertainties that might take place in real-time context. This work deals with optimal energy management of a grid-connected MHK-PHS system, under different demand seasons for different load demand sectors, through the consideration of variable TOU tariffs. The aim is to minimize the customer electricity bills if the proposed system is approved to be non-interactive or interactive with the utility grid. Additionally, the alternative aim is to maximize the energy sales into the grid, if the system is grid-interactive. The results have proved that the developed optimization-based model is capable of minimizing the grid-cost, particularly during expensive peak-periods. Furthermore, the energy sales revenue has been maximized during peak-periods. Sundays have proved to lead to the largest amount of grid-power storage into the storage system, as compared to other days of the week. The industrial load profile led to the low net income, since most energy sales take place during the evening peak hours, instead of morning peak hours. However, if the load demand uncertainty constraint is considered, the above-mentioned open-loop optimization-based model has been unable to optimize the power flow. This led to the unmet load demand difficulty, as well as the excessive supply of power. Hence, an additional control model has been developed to assist the open-loop optimization-based model, to handle the load demand uncertainty disturbance in real-time context. The control model proved to mitigate the issue of both unmet load demand and excessive supply of power through the application of a rule-based algorithm. Additionally, a higher energy savings was achieved through the successful reduction of the excessively supplied power

Optimal energy management modelling of a grid-connected micro-hydrokinetic with pumped hydro storage

Thesis (Doctor of Engineering in Electrical Engineering) -- Central University of Technology, Free State, 2018The pressure on greenhouse gases (GHGs) emission reduction and energy deficit crisis are of global concern. The ever increasing energy demand due to population growth as well as industrial and commercial business developments, leads to energy deficit crisis for electric utility operators around the globe. This generates an increased probability of grid instability and blackout challenges. Hence, this promotes the requirement for the additional fossil fuel power plants, leading to electricity price increase for consumers, due to high investment cost and the rising fossil fuels prices. The exploitation of an onsite grid-connected renewable energy (RE) system may mitigate all of the above-mentioned challenges. However, the intermittent nature of RE resources (such as solar, wind, hydro, geothermal and marine) leads to a challenge of high uncertainty output power. Hence, power demand cannot be reliably met, due to daily or seasonal weather changes. Therefore, a stand-alone RE system should comprise of an energy storage system (ESS), to store surplus energy for later use when the power demand is more than the generated output power. Additionally, a grid-interactive RE system should also comprise of the ESS, due to the variable tariff rates imposed by utility companies around the globe. The aim is to store excess energy during low-priced off-peak periods, for later use during high-priced peak periods. Hence, minimal electricity bill may be achieved by the consumers. The utility grid operator may also reap a benefit of a reduced blackout probability, especially during peak demanding periods. Among various RE technologies, hydrokinetic is a promising RE solution to be exploited in areas with flowing water resources, such as rivers, tidal current or artificial water channels. It is easily predictable and has proved to generate electricity at flowing water speeds, ranging from 0.5 m/s and above. It has proved to generate electricity markedly better and affordable than solar and wind energy systems. Furthermore, it has proved to operate cost-effectively, if it comprises of a pumped-hydro storage (PHS) system instead of a battery-based storage system. Rural consumers, such a farms, industries and mines situated in close proximity to flowing water resources, may make use of a grid-connected micro-hydrokinetic-pumped-hydro-storage (MHK-PHS) system to reduce electricity bills and sell the excess energy to the grid. However, a grid-connected MHK-PHS system requires a complex optimal energy management system, instead of expecting a consumer to respond to a change in real-time electricity price. The system should allow for optimal energy storage and sales, while ensuring that the consumer load demand is met at all times, by considering variable time-of-use (TOU) tariffs and load demand uncertainties that might take place in real-time context. This work deals with optimal energy management of a grid-connected MHK-PHS system, under different demand seasons for different load demand sectors, through the consideration of variable TOU tariffs. The aim is to minimize the customer electricity bills if the proposed system is approved to be non-interactive or interactive with the utility grid. Additionally, the alternative aim is to maximize the energy sales into the grid, if the system is grid-interactive. The results have proved that the developed optimization-based model is capable of minimizing the grid-cost, particularly during expensive peak-periods. Furthermore, the energy sales revenue has been maximized during peak-periods. Sundays have proved to lead to the largest amount of grid-power storage into the storage system, as compared to other days of the week. The industrial load profile led to the low net income, since most energy sales take place during the evening peak hours, instead of morning peak hours. However, if the load demand uncertainty constraint is considered, the above-mentioned open-loop optimization-based model has been unable to optimize the power flow. This led to the unmet load demand difficulty, as well as the excessive supply of power. Hence, an additional control model has been developed to assist the open-loop optimization-based model, to handle the load demand uncertainty disturbance in real-time context. The control model proved to mitigate the issue of both unmet load demand and excessive supply of power through the application of a rule-based algorithm. Additionally, a higher energy savings was achieved through the successful reduction of the excessively supplied power

Micro-hydrokinetic river system modelling and analysis as comparedto wind system for remote rural electrification

Published ArticleMicro-hydrokinetic river (MHR) system is one of the promising technologies to be used for remote ruralelectrification. In rural areas with access to both wind and flowing water resources, wind generationis selected as a first electrification priority. The potential benefit of generating electricity using flowingwater resource is unnoticed. Hence, this paper presents the modelling and performance analysis of a MHRsystem as compared to wind generation system using MATLAB/Simulink software. These performancesare compared to generate the same amount of electrical power. A permanent magnet synchronous gener-ator (PMSG) has been chosen or used to investigate the behaviour of each system under variable speeds.The developed model includes horizontal turbine model, drive train model and PMSG model. The simu-lation results illustrate the ability of a hydrokinetic turbine driven PMSG to generate electricity markedlybetter and cheaper than a wind driven PMSG within South Africa. Hence, the MHR system presents acheap electrification opportunity for poor rural households