Showing papers by "Kanzumba Kusakana published in 2018"

Optimal power dispatch of a grid-interactive micro-hydrokinetic-pumped hydro storage system

Abstract: Developing nations around the world are facing energy deficit crisis due to an increasing energy demand and slow exploitation of renewable energy (RE) technologies. Among different RE technologies, hydrokinetic is a promising technology that has proved to generate electricity cheaper than solar and wind technologies. Among different energy storage devices, pumped hydro storage (PHS) has proved to be the most cost-effective option. Due to rising electricity price, domestic farm-houses situated in close proximity to the flowing water resource can make use of a hydrokinetic-PHS system to reduce the electricity cost and to sell excess energy into the grid through feed-in tariff (FIT) scheme. This paper introduces an optimal energy management model for power dispatching within a grid-interactive micro-hydrokinetic pumped hydro storage (MHK-PHS) system. The aim is to minimize the grid consumption costs and to maximize the energy sales revenue by considering the weekdays and weekend time-of-use (TOU) tariffs. The simulation results have shown the effectiveness of the model since it allows most of the load power demand to be met by the RE systems during expensive peak-period as a means of minimizing the grid consumption costs. Most of the energy sales took place during standard and expensive peak periods as a means of maximizing the energy sales revenue. Additionally, the simulation results have shown that an energy saving potential of 100.1% and 104.23% can be achieved during high demand and low demand seasons, respectively.

Optimal operation scheduling of grid-connected PV with ground pumped hydro storage system for cost reduction in small farming activities

Abstract: A model of electricity cost minimization is proposed which can be implemented in small farming activities where boreholes are present for water supply. In this case, a hybrid system composed of solar photovoltaic and pico hydro supplied by a pumped storage system are used minimize the electricity cost in a dynamic electricity pricing environment. The varying price of electricity, the load demand, the reservoir state of water stored as well as the solar resource at any instant determine the optimal power flow from the different power sources to the load; these are the control variables to be optimised with the aim of reducing the power consumed from the grid. The optimization problem can be solved using linear programming. The simulation results can be used to investigate the impact and benefit of the proposed model on the electricity cost reduction of small loads in the South African farming sector.

Hybrid DG-PV with groundwater pumped hydro storage for sustainable energy supply in arid areas

Abstract: This paper discusses the development of a model for the optimal operation of a hybrid diesel-photovoltaic pumping system using, groundwater in a pumped hydro storage scheme which can be used to minimize the daily electricity cost of a farm. The developed model can minimize the power produced from the diesel generator, while optimally managing the generated power flow from the PV and the groundwater pumped hydro storage given the variable load demand as well as the availability of solar resource. As a case study, the model has been used to simulate a small farming activity in South Africa, with the aim of evaluating the potential energy cost saving achievable using the proposed system when compared to exclusive power production using a diesel generator. The simulation results show that a potential 71.3% of energy cost saving can be achieved using the proposed hybrid system with the optimal control model rather, than supplying the load demand by the diesel generator exclusively.

Scheduling and economic analysis of hybrid solar water heating system based on timer and optimal control

Abstract: In this paper, an optimal control approach is modelled and applied to a hybrid solar electric water heater. The hot water consumption profile of a medium density household is considered. Real historic exogenous data obtained from a weather station in the region is used as input for the developed model. The aim is to assess the cost saving potential the system can achieve under time-based pricing structure enforced by the electricity supplier in the region, while maintaining the desired temperature level of the hot water user. As a baseline, the operation of a timer-based thermostatically controlled scheme, the most commonly used method of control to minimize the energy usage and in turn the costs, is simulated. Comparisons between the operation of the HSWH with timer-based control and the optimally controlled HSWH presented a cost saving of 84.39% in the winter and 15.50% during summer period. Annual cost savings of 32.86% were noted. Additionally, the energy usage periods of the system are shifted to low demand regions of residential load profiles, decreasing the strain on the national electricity grid.

Energy Management of a Grid-Intergrated Hybrid Peer-to-Peer Renewable Charging Station for Electric Vehicles

Abstract: Electric vehicles are fast becoming a popular site in the world. Their technologies have been widely developed over the years. However, their charging infrastructure is still a subject of interest, as most of the electric vehicle charging requirements were previously met by an AC grid. However, over the year's research has been conducted on the implementation of renewable energies in the charging station. Most of the research studies focus on the management, optimal control, charging schemes and charging strategies. There is no research done on a charging station that combines the grid integrated hybrid renewable energy system such as Wind and PV comprising of a central battery bank with a peer to peer energy trading model. The aim of this research study is to develop a well-coordinated charging scheme of Electric vehicles in a charging station whilst optimally managing the charging and discharging of the central battery bank (used for energy storage) as well as the power dispatch of the grid and Wind and PV charging station. The proposed model will maximize electric vehicle user satisfaction that meets all the charging requirements of the charging station whilst offering cost effective charging scheme such as peer-to-peer energy sharing model.

Optimal switching control of PV/T systems with energy storage using forced water circulation: Case of South Africa

Abstract: In this paper, the optimal switching control of flow in hybrid PV/T systems with forced water circulation is presented. Actual historic exogenous data obtained from a weather station in the considered area is used as input for the established model. The aim was based on developing an optimal control model to maximize the energy output of the PV module using water circulation to collect the heat and persevering in maintaining the surface temperature as minimal as achievable. Comparisons between the baseline and the proposed model yields an output power improvement of 2.65% during summer, whereas a 5.90% deterioration during winter. Therefore, the simulation results further demonstrate the proposed model yields a daily heat gain of 9.37 × 107 J, 26.03 kWh inside the water storage tank during the selected summer day and 2.61 × 107 J, 7.25 kWh during the selected winter day. A true payback period (PBP) analysis is presented, where the project lifetime is chosen to be 30 years. The PBP analysis shows it takes up to 4 years and 2 years for the investor to generate profit from the standard PV system and the optimal switching control model, respectively. However, when looking at both systems over their predicted lifetime, the optimal switching control strategy generates a higher profit of 92.41%.

Operation cost and energy usage minimization of a hybrid solar/electrical water heating system

Abstract: Approximately 40% to 60 % of the total energy consumed by a traditional household in South Africa can be allocated to the heating of water. Furthermore, most of water heating takes place during peak electricity consumption periods, where electricity costs are highest. In this paper, the optimal energy management of a hybrid solar electric water heater (HSWH) is presented. The hybrid system consists of an indirect flat plate collector coupled to an electric storage tank water heater (ESTWH). The electric resistive element inside the storage tank water heater serves only as an auxiliary heater when solar irradiance is insufficient. A typical medium density household within the Mangaung municipality area in the city of Bloemfontein, South Africa is considered. The aim is to evaluate if an optimal control approach can be used to effectively shift the energy usage profile of the system under the residential Time-of-Use (TOU) tariff enforced by the electricity supplier, while maintaining a comfortable thermal level of the hot water user. The secondary aim is to reduce the energy required to increase the thermal level of the water compared to a baseline water heater. The proposed water heating system with optimal control is modelled and simulated using Matlab OPTI-Toolbox. The control variable was successfully solved with switching taking place during off-peak periods while maintaining the desired temperature of the hot water consumer.

Review of Optimal Energy Management Applied on Ice Thermal Energy Storage for an Air Conditioning System in Commercial Buildings

Abstract: This paper investigates the cost saving potentials of energy for cooling loads in the commercial buildings using a realtime optimization control strategy capable of efficiently managing an operation of the (ITES) Ice Thermal Energy Storage for building's HVAC (Heating, Ventilation and Air Conditioning) system. The ITES is a Thermal Energy Storage (TES) system, which reduces the cost of energy in HVAC systems. Reduction in the cost of energy is achieved by shifting the cooling load from the peak and standard periods to the off-peak periods, with the aid of stored ice, which is produced when the energy cost is affordable and discharging when the cooling demand is high, particularly at expensive tariff rates. The challenge is that, most of the existing ITES systems, particularly in South Africa, are not optimal in operation. The conventional system should be optimally controlled to a higher accuracy. Based on investigations, a preferred accuracy could be achieved, with some comparisons and validations of results, by utilization of real-time control and optimisation tools, such as Fuzzy logic, Neural network, Closed-loop and Model Predictive Control (MPC). Effective utilization of ITES allows a further advantage in the management of the off-peak tariffs and consumers' demands, in accordance with the Time of Use (TOU) and maximum demand. Climate changes, installation, payback costs and other objective functions are required as additional options to the improved utilisation and design of the ITES system. The findings from the review and analysis of technologies and approaches to optimisation should benefit improvisation of the ITES in future applications.

Optimal Sizing of a Micro-Hydrokinetic Pumped-Hydro-Storage Hybrid System for Different Demand Sectors

Abstract: Due to high investment costs of renewable energy systems, optimal sizing of hybrid renewable energy system is critical to adequately meet the load demand at low cost. Studies based on optimal sizing of the hydrokinetic hybrid systems used the hybrid optimization model for electric renewable (HOMER) software as a simulation tool. The HOMER Legacy Version that was used in these studies does not have a built-in hydrokinetic module in its library. As a result, the authors used a wind turbine module to model a hydrokinetic turbine. In this study, the optimal size of a river-based micro-hydrokinetic pumped-hydro-storage (MHK-PHS) hybrid system is determined using HOMER Pro Version 3.6.1 since it has a built-in hydrokinetic module in its library. The results obtained using HOMER Pro Version 3.6.1 will be compared to the results obtained using the methodology adopted by previous researchers (using HOMER Legacy Version). The objective is to validate the best economical approach for sizing a hydrokinetic hybrid system. The second objective of the study is to investigate the effect brought by different demand sectors such as residential, commercial, and industrial load on sizing and operation of the proposed MHK-PHS hybrid system. The results have shown that the methodology applied in HOMER Legacy Version leads to oversizing of the storage system. This resulted into higher initial capital cost, net present cost (NPC), levelized cost of energy (COE), and operating cost. The results also proved that for the same daily energy consumption, a type of a demand sector does not affect the size of a hydrokinetic turbine and annual excess energy. Instead, it affects the size of the storage capacity as well as the size of the hydro-turbine. The commercial load profile proved to lead to the lowest state of charge (SOC) of the storage reservoir.

Practical Implementation of Hybrid Energy Systems for Small Loads in Rural South Africa

Abstract: Hybrid renewable energy systems are economical off-grid methods of generating power to remote rural areas, where power lines are prohibited due to costs. However, South Africa's policies and regulations are not making it any easier for these systems to be more exposed and accessible in real time. Most of the research studies on renewable hybrid systems or microgrids in South Africa focused mainly on the optimal sizing and optimal control of different systems by making use of renewable energy simulation software's, but there is no research done on the implementation of these hybrid systems in real time. The aim of the study is to come up with the methodology to design, implement and control a hybrid system in South Africa conditions for small rural loads. However, further comprehensive research work have to be done on the study.

Usage of Battery Energy Storage Systems to Defer Substation Upgrades

Abstract: Electricity is generated and distributed instantaneously. In electricity utilities, this is occasionally an enormous amount of wasted capacity. Illegal connections may contribute to overloads and trips, as the network is carrying more users than what it was designed for. Before substation upgrades may take place, new and existing consumers who need additional electricity are rejected, due to capacity constraints in existing substations. The installation of large scale battery energy storage systems may support the long-term carbon mitigation strategy of South Africa, to transition to a low carbon economy. The aim of this paper is to propose a Battery Energy Storage System (BESS) design that may lead to costly network upgrade deferral and reduced demand charges.

Smart System for Impressed Current Cathodic Protection Running on Hybrid Renewable Energy

Abstract: The primary objective of this paper is to propose a system for Impressed Current Cathodic Protection running on renewable energy. Generally additional corrosion prevention based on sacrificial anodes, Impressed Current Cathodic Protection and Alternating Current mitigation are installed into underground/ buried pipelines to provide protection against accelerated corrosion to the part of the pipeline that becomes unprotected by a result of degraded coating and stray currents. In this research, studies to determine the amount of power required to shift the potential level of the buried pipeline will be outlined, this will clearly show the load profile of the structure to be protected and from there a hybrid system shall be designed and modelled. This document outlines the reason for hybrid powered Impressed Current Cathodic Protection, objectives of the research and how they will be achieved.

Techno-economic Comparison of Timer and Optimal Switching Control applied to Hybrid Solar Electric Water Heaters

Abstract: In this paper, an optimal energy control model is used to evaluate the potential energy cost saving of a hybrid solar water heater. The aim is to maximize energy cost savings under time-based pricing while maintaining the desired water temperature of the hot water user. The optimally controlled system is compared to traditional timer based controlled system with the same layout as the proposed system. The hybrid water heating system is modelled and simulated using Matlab. From the formulated objective function and the case study in this work, the results present that using an optimally controlled hybrid heater will have an approximate annual cost saving of 20.8%.

Optimal Pump Scheduling in an Open Reservoir Water-Treatment Incorporating Evaporation and Seepage Effect

Abstract: Open reservoir systems pose a number of challenges, including sedimentation and flood control. The cost of electrical energy used for pumping water from the dam to the water treatment reservoirs is becoming considerably high. This may be attributed to poor management of the current pumping models, adding to the fact that water treatment systems do experience high level of evaporation and leakages. This study proposes an optimal energy management model to control the pumping scheduling of municipal water reservoir. The aim is to secure a continuous supply of potable water to the community, while minimizing both pumping and water costs.

Minimizing Diesel Running Cost Using PV with Groundwater Pumped Hydro Storage

Abstract: This paper discusses the development of a model for the optimal operation of a hybrid diesel-photovoltaic pumping system using groundwater in a pumped hydro storage scheme which can be used to minimize the daily electricity cost of farm The developed model can minimize the power produced from the diesel generator while optimally managing the generated power flow from the PV and the groundwater pumped hydro storage given the variable load demand as well as the availability of solar resource As a case study, the model has been used to simulate a small farming activity in South Africa with the aim of evaluating the potential energy cost saving achievable using the proposed system when compared to exclusive power production using a diesel generator The simulation results show that a potential 713% energy cost saving can be achieved using the proposed hybrid system with the optimal control model rather than supplying the load demand by the diesel generator exclusively

Performance of Solar-Thermal Organic Rankine Cycle (STORC) Power Plant with a Parabolic Trough System

Abstract: Modelling of the Organic Rankine Cycle (ORC) technology reduces the cost of testing and optimisation by providing tools for the evaluation and optimisation of existing and proposed ORC plants. This paper presents the thermodynamic potential for Solar-Thermal Organic Rankine Cycle (STORC) power plants by using Matlab Simulink® and Thermolib library software. The methodology was implemented based on existing plant designs in South Africa, which demonstrate opportunities for further optimisation of the available plants.

Optimal Energy Management and Economic Analysis of a Grid-Connected Hybrid Solar Water Heating System in Bloemfontein

Abstract: In this paper, an optimal energy management scheme is used to establish the potential operational cost saving that a hybrid solar water heater can attain compared to a baseline storage tank water heater. The two water heating systems are modelled and simulated using Matlab. From the case study undertaken, the simulation results demonstrate that using an optimally controlled hybrid solar water heater will have an approximate cost saving of 49% in a life cycle of 20 years. Moreover, a break-even point at 3.5 years was established between the baseline and proposed hybrid water heating system.

Prospective Implementation of Grid-Interactive Photovoltaic Systems in the South African Residential Sector

Abstract: The current increases in energy demand is in effecting renewable resources of energy an attractive option. The steady progress in renewable energy technologies is treating new opportunities for the utilization of renewable energy resources. Photovoltaic (PV) systems are among one of the most popular renewable energy sources that may be integrated with an electricity grid. With the new feed-in tariff scheme implemented by a few of the municipalities in South Africa, a new opportunity opened for residential consumers with the ability to generate energy. There is a list of regulations and policies that should be executed before the municipality should allow the consumer to connect the grid. However, apart from infrastructure, government policy and other techno-economical aspects, residential application of solar PV systems remain promising. This paper will review the relevant literature on photovoltaic technology, under the time of use (TOU) tariff and feed-in tariff scheme, applicable to residential consumers of energy in South Africa. Key elements such as operation, design, application and previous studies of PV systems used in residential application, will be discussed.

Demand Side Management of Grid- Tied Hybrid Photovoltaic-Diesel-Battery Energy System for a University Engineering Building

Abstract: The increasing electricity costs of the university engineering buildings has created a need for the review of the work done in the demand side management of grid-tied hybrid energy systems for commercial buildings. This paper proposes the architecture of an on-site grid-tied hybrid Photovoltaic/Diesel generator/Battery storage energy system for a university engineering building under time of use pricing considering maximum demand charge. The paper also identifies further research work.

Life Cycle Cost Comparison Between Motors Equipped with Variable Speed Drives and Dampers for Pumps and Fans

Abstract: Motor efficiency is important, but it is a small contributor to overall system efficiency. This paper will not review motor efficiency as a single important factor for energy saving, but the efficiency of the whole system. Meaning, the converted electrical energy into useful mechanical work for pumps and fans. This paper presents a review of relevant literature on life cycle cost (LCC) comparison between two different methods of motor flow control used for pump or fan systems. This study aims to provide an LCC mathematical model for new or existing pump or fan systems projects. The purpose of this study is to determine operating cost of the motor running at constant speed with dampers and compare them to variable speed drives (VSD) when utilised for the same application. The comparison will be carried under the same load demand and same cost of energy. The review will present an LCC mathematical model that will provide substantial financial guidance for pump or fan system projects.

Optimal Energy Control of a Rubber Tyre Gantry with Potential Energy Recovery

Abstract: The Rubber Tyre Gantry (RTG) cranes is a hoisting equipment usually used in port terminals to move shipping containers from one location to another. However, most of RTGs are operated inefficiently, hence a high energy cost is incurred. The reason of poor operation efficiency of RTG crane is that the equipment is operated at a constant speed during true vertical lift, no matter how the load and/or true vertical lift change, also during the lowering of a container, the regenerative breaking energy is usually dissipated through a resistor bank. This work therefore proposes an energy management model that would improve the energy efficiency of the RTG crane. First, we propose to optimally control the regenerative breaking energy to and from the battery bank taking into account the time-of-use tariff and maximum demand. Secondly, we propose to optimally control the hosting speed according to the variability of container weight and true vertical lift.

Economic analysis of photovoltaic/thermal systems with forced circulation under optimal switching control

Abstract: In this paper, an economic feasibility study is performed to evaluate the cost effectiveness of the optimal switching control model of flow in a 250 W PV/T system with forced water circulation by comparing it with a standard 250 W PV system without cooling, known as the baseline. There are economic performance indicators, such as simple payback period (SPP), internal rate of return (IRR), benefits-to-cost ratio (BCR), and lifecycle cost (LCC). The SPP method is easy to understand and to calculate. However, it doesn't factor in that money depreciates over time due to inflation and other factors. Also, the project lifetime is not taken into account with this method, where the investors will not be fully aware of the profitability of the project. Therefore, a True Payback period analysis based on a 30-year project lifetime is performed to calculate when each system will be paid back and thereafter generate profit. The analysis showed that the total capital cost of the standard PV system will be recovered after 10 years, which provides the investor 20 years to generate profit from their investment. However, the analysis showed it takes 14 years to regain the total capital investment for the optimal switching control strategy. The initial capital cost of the optimal switching control strategy is higher by a factor of 3 compared to the standard PV system, which seems repulsive to invest in the optimal switching control strategy. Nevertheless, when observing both these systems over their predicted lifetime, the optimal switching control strategy generates a much higher profit, regardless of its extortionate initial capital cost, and is therefore, the most efficient system.

Rule-based Control Strategy for a River-based Grid-connected Hydrokinetic System

Abstract: This paper presents an optimal control algorithm for improving the reliability of a river-based grid-interactive hydrokinetic system. The aim is to guarantee a reliable system operation during load demand uncertainties. The proposed system consists of a micro-hydrokinetic pumped-hydro storage (MHK-PHS) system, modelled to supply electricity to a commercial load profile. The open-loop optimization-based approach resulted in an unmet load demand and excessive energy supply, due to load demand uncertainty. Hence, a rule-based control algorithm is presented to ensure that the load demand is reliably met at all times. Thus, the results prove that the developed rule-based control algorithm, allowed the commercial load demand to be reliably met by solving both the unmet load demand and excessive energy supply challenges.

Flatness Based Control of a Variable Speed Micro Hydrokinetic Generation Systems

Abstract: In this paper, the concept of differential flatness is applied to a controller with the aim of producing constant voltage and frequency from a hydrokinetic with permanent synchronous generator submitted to variable water flow. The idea of this concept being to generate an imaginary trajectory that will take the system from an initial condition to a desired output generating power. The results show that, the generated output is dynamically adjusted during the voltage regulation process. The advantage of the proposed differential flatness based controller over the traditional proportional integral (PI) control is that decoupling is not necessary, as demonstrated by the modelling and simulation studies under different operating conditions, such as changes in water flow rate.

A Survey of Groundwater Pumping Technologies for Electricity Generation Through Hydropower

Abstract: Water is a universal need of every living organism, it is one of the leading elements of economic development through agricultural sector (farming). However, many South African farms have both challenges of water and electricity supply. The country runs its energy harness on both renewable and nonrenewable energy sources. This paper will review different groundwater pumping methods/ technologies looking at the South African context and find opportunities of using this set up to generate electricity. Therefore, different technologies will be analysed in terms of operation principle, cost, advantages, disadvantages and applicability. Furthermore, after the pumping infrastructure, different storage system as well as type equipment for the conversion of potential energy in water into electricity will be also presented.