R. Okou

Design and Analysis of an Electromechanical Battery for Rural Electrification in Sub-Saharan Africa

This paper presents the design and analysis of an electromechanical flywheel energy storage system to enhance rural electrification in sub-Saharan Africa. The system consists of a flywheel rotor, an electrical machine, control system, bearings, and a containment structure. With the exception of the power electronics and magnets, local materials were used for the manufacture of the flywheel system. The flywheel rotor is made from glass fiber-epoxy composite, designed using novel shape profiles and utilizes a stress based solution by introducing a central hole for shaft inclusion. The system was accelerated to 6000 r/min storing up to 227 kJ. Numerical stress analyses were performed during the design stage to ensure that the maximum tensile strength is not exceeded. A lumped parameter thermal model is used to estimate the temperature distribution to ensure safe operating conditions of the flywheel system and environment. A life cycle cost analysis performed found that by integrating a flywheel system into a Solar Home System implies a cost savings of 35% per kilowatthour when compared with lead-acid batteries.

A concept of dynamic pricing for rural hybrid electric power mini-grid systems for sub-Saharan Africa

This paper presents a dynamic pricing concept that can be applied to hybrid electric power mini-grid systems to enable affordability of energy in these systems setup for the supply of energy to rural consumers. A location was identified in Eastern Uganda, resource assessment done, and a proposed hybrid electric power mini-grid system designed to supply electricity to this rural location. A theoretical deterministic demand profile was generated, and with it different supply configurations of the system were simulated to meet the daily load. The fluctuations in the demand and supply triggered a change in the cost of generating energy, due to the variations in the contributing electricity generating sources. Through communication, an intelligently designed and operated time-varying pricing scheme can be an effective tool for influencing the actions of price-responsive end-users such as rural consumers. A software program was used to simulate the hourly demand, supply, and corresponding cost of energy variations. This pricing model could potentially contribute to the ongoing search for the provision of affordable rural energy services.

Control of a flywheel energy storage system for rural applications using a Split-Pi DC-DC converter

This paper presents a control strategy of a flywheel system to maximize the energy available on solar panels using a Split-Pi DC-DC converter for rural applications. This new topology is mainly used in electric vehicles. The control system was designed, prototyped and tested on a flywheel system with an Axial Flux PM machine (AFPM). It showed an improvement in the solar power delivered to the electrical machine. This was seen when the solar was supplying 66% of the load, and the flywheel was supplying 33%. Speed and current limiting were also found to be effective at the different limits and this was observed at different speeds. As the solar or loads changed, the control system automatically adjusted the flywheel power flow in the electrical machine to maintain the correct bus voltage. The protection systems designed was found to be effective as the equipment was protected from damage caused by careless or incorrect operation. The new control system was a huge improvement on the old one where as soon as there was insufficient solar power; the system switched over to the flywheel alone supplying the load.

High speed electromechanical flywheel design for rural electrification in Sub Saharan Africa

This paper presents the electromechanical flywheel energy storage system designed to enhance rural electrification in Sub-Saharan Africa. Most non-grid connected areas, mostly rural, are powered with solar home systems whose sustainability is limited by the short life span, low power density and low storage efficiency of the battery storage. The electromechanical flywheel rotor is made from glass fiber and epoxy composite and designed using novel shape profiles based on Berger, Porat and Stodolas design. Dr. Stodolas design utilizes a stress based solution by introducing a central hole for a shaft inclusion. An Axial flux brushless DC machine was considered because of the low cost, ease of construction and simple control. The system stores 1,080kJ and supplies 100W with an operating speed range of 8,000–25,000 rpm. Stress, modal and thermal analysis are performed on the flywheel system using finite elements and analytical methods. The brushless DC drive together with the DC-DC converter were constructed and tested. The various components were simulated, prototyped using locally available material and the results presented.

Analysis of an electromechanical battery for rural electrification in sub-Saharan Africa

This paper presents the thermal and structural analysis of an electromechanical battery energy storage system designed to enhance rural electrification in sub-Saharan Africa. The system consists of a flywheel rotor, an electrical machine, bearings and a containment structure. The flywheel rotor was constructed from E-glass fiber, the machine from imported NdFeB magnets and commercial energy efficient bearings. With the exception of the power electronics and magnets, local materials were used for the manufacture of the flywheel system. The system was designed to operate between 8,000 rpm to 25,000 rpm with a rated storage capacity of 300Wh. Numerical stress analysis was performed during the design stage to ensure that the maximum tensile strength is not exceeded. A lumped parameter thermal model was used to estimate the temperature distribution to ensure safe operating conditions of the flywheel system and environment. The results of both analyses are presented.

Test rig for high speed electromechanical flywheels in Sub Saharan Africa

This paper presents a test rig designed at the University of Cape Town to evaluate the performance of a high speed electromechanical flywheel for energy storage. The electromechanical flywheel is specifically designed to enhance rural electrification through improving the energy storage component in solar home systems. A safe, flexible and low vibration test rig has been designed. Modal analysis using an FE package ANSYS was used to validate the low vibrations at high speed rotation. Special attention was given to the alignment issues and this was done to avoid imbalance in the rig. The rig has the ability to test up to 40,000 rpm flywheel with maximum diameter of 0.55m as is. With changes in the bearings, much faster flywheels can be tested. In addition, the rig was built to ensure testing under various operating environments. A thermal model was developed for the rig and simulated with analytical and FE packages. Sensors are installed in the containment to monitor performance of flywheel system.

Considerations to electromechanical flywheel design to enhance rural energisation in Sub-Saharan Africa

The results of an electromechanical flywheel are presented to ascertain the considerations during the design stage. The design procedure is explained in brief. The considerations include, load profiling, mechanical and electrical aspects are discussed. This is essential in achieving the numerous advantages associated with the flywheel energy storage system. The results for low speed testing are presented with considerations to improving the system.

Thermal model of electromechanical flywheel with brushless DC machine

A thermal model of an electromechanical flywheel with a brushless DC machine is presented. Thermal analysis is particularly important during vacuum operation of the flywheel. Accurate prediction of temperature facilitates material selection, structural integrity and good performance. In addition, the choice of vacuum level, bearings, conductor sizes and system overload capability can be attributed to a good thermal model. A thermal model was developed and simulated on MATLAB Simulink. The simulation results were compared with experimental results and a good correlation was observed.