Modelling and analysis of smart localised energy system for a sustainable future power network

Combating the increasing effect of climate change and averting future energy crisis resulting partly due to our continued dependence on conventional energy sources requires exploring aggressively more sustainable means of generating and utilising energy. Currently, most developed countries are transitioning slowly from a fossil fuel dominated energy system to a sustainable and renewable energy based system. However, for the results of these transitions to be impactful and reduce the global temperature rise to the expected 1.5oC, the approach must be wholistic and encompassing. Although there are a lot of ongoing research in the areas of renewable energy integration into the grid, however, there seems to be a dearth of such studies in some specific aspect of the power system application. Consequently, this thesis models and performs several analyses on a smart localised energy system with the aim of decarbonising some aspects of the future power network. The study investigated the dynamics of residential power demand in Nigeria and modelled the residential energy consumption profile. An excel-based algorithm was developed and applied to the developed model. The results of the residential energy consumption was based on the appliance energy end use methodology. This was used to develop a load profile indicative of a typical urban residential energy demand in Nigeria and employed to predict the effects of residential loads on the power system. Following the frequent use of diesel generators by municipal councils to power street lighting, several case studies demonstrating how to optimise street lighting energy consumption and improve energy efficiency were carried out using simple economic analysis indices such as Life Cycle Cost (LCC), Annualized Life Cycle Cost (ALCC), Net Present Cost (NPC), Cost of Energy (COE), and Return on Investment (ROI). The solar photovoltaic (SPV) system had the lowest LCC and ALCC, thus making it the most economically viable option. The response of the power system to Distributed Energy Resources (DERs) integration was also investigated. Data from a real low voltage (LV) distribution network in Nigeria was obtained and used in modelling the network using PSCAD/EMTDC software package. Different impact studies considering addition of distributed generation sources and increase in the load were performed. Volt-VAr optimisation (VVO) was performed to enable the inverter-based PV systems participate actively in voltage regulation by the provision of flexible reactive power support. A net total of 1.359 MVAr and 1.301 MVAr respectively are utilised from the inverter to regulate voltage within the acceptable limits, hence reducing the substation reactive power by 19.8% and 18.9% respectively during the controlled case study. Also, the total active power loss did reduce from 0.437 MW to 0.172 MW while the deviation of consumer voltages from the nominal system voltage was reduced by 33.4% during the controlled case studies. Overall, the VVO did enhance power quality and reliability by improving the feeder voltage profile and reducing the active power losses in the network. Lastly, to decarbonise some operation of the power system and improve the system resilience, DERs integrated black start restoration (BSR) strategy was implemented. The formulated BSR problem was implemented as a dynamic optimisation problem and the simulation was performed on the Nigerian 330 kV 48-bus system. The mixed-integer linear programming (MILP) technique was adopted and modelled to suit the nature of the BSR method developed. The black start power restoration sequence and the development of a viable restoration strategy were actualised. The simulation of the MILP model was achieved in MATLAB® using the IBM CPLEXTM solver. For the Nigerian 330 kV 48-bus system analysed, it was observed that most loads were optimally restored before the 30th time step for a black start operation. Both the experimental and numerical methodology were adopted in the validation of energy storage system (ESS) adopted for the proposed BSR simulated study. The optimal battery power availability for participating in restoration was reached in less than 50 minutes, with ESS optimally contributing to power restoration achieving 4.3% & 18.1% for Kaduna and Jos respectively

Dynamic modeling of energy consumption pattern of a typical Nigerian average urban and rural household for microgrid PV design

The knowledge of consumer electricity consumption is essential for the design of smart grid integration strategies and distributed generation. In recent times, the total energy consumption in the residential sector has continued to increase resulting from economic expansions, population and floor area growth which is an indication of a consistently increasing demand. Energy independence as part of the solution to energy efficiency has become a pressing issue for today's society. Using AutoCAD software alongside with an Excel spreadsheet, the average-demand, load factor, demand-factor and unit power density of the designed building were computed for an average urban and rural household. The hourly load profile of the building and percentage energy usage across both locations for the various seasons were determined. Lastly, a comparative performance of LED and Incandescent Lighting schemes were examined. It is hoped that the results of this study would help the decisions of the residential energy users

Volt-VAr optimization of a low voltage

Volt-VAr optimization (VVO) is important in a distribution system as the performance of the entire network depends on the voltage profile to a very large extent. The deployment of renewable energy sources, particularly photovoltaic (PV) systems, is usually achieved at the medium voltage (MV) and low voltage (LV) levels of distribution feeders and may exacerbate the challenges associated with maintaining the voltage profile within the pre-defined limits. For such a PV-rich system, VVO can be carried out such that the inverter-based PV systems can actively participate in voltage regulation and optimization by providing flexible reactive power support. This paper addresses the voltage concerns associated with high PV penetration by implementing a distribution grid optimal power flow (DOPF) problem on a realistic LV distribution network in Kano, Nigeria. The current injection-based I-V DOPF formulation is used to model the grid and the VVO utilizes the reactive power of the PV inverter to minimize the active power losses in the network. The results demonstrate the ability of the VVO to perform voltage regulation and can serve as a viable technique for mitigating voltage violation issues in the Nigerian grid

Participation of load aggregator in grid frequency stabilization with consideration of renewable energy resources integration

Alterations in the proportion of conventional generation to that of renewable energy source could be a future challenge for electric energy networks. Conventional power plants are being replaced by wind and solar energy. Solar PV plants and wind turbines lower the system inertia constant, causing the grid frequency to shift. Renewable energy generation plants that are integrated into the energy system may cause problems with frequency stability if adequate frequency control techniques are not applied. In this study, a Load Frequency Control framework based on aggregators is developed to improve the frequency response of the power system. It was demonstrated that the aggregator is capable of forecasting available flexibility for the day ahead contributing to the frequency control process. The aggregator is contributing to the grid frequency stabilization considering the price signal for minimizing energy costs, with an effect on end user’s energy bills reduction. For assessing the aggregator’s flexibility availability, the aggregator calculates the contributed power after minimizing its energy costs. The results show that it is possible to use DR technology to stabilize the grid frequency. With the loss of generation of 50 MW, the aggregators contribute mainly for the morning event with a contribution of about 4 MW followed by the night event with the contribution of approximately 3.5 MW. The largest contribution was obtained between 06:00 and 8:00 for the examined area with three aggregators, and the smallest contribution was obtained between 22:00 and 24:00. By considering the whole power system, with the integrated renewable energy resources in different periods, the findings demonstrate that even though the frequency decreases, it quickly returns to the usual operating limit and stabilizes itself back to the normal operating limits of 50 Hz as a result of the aggregator participation in the process of grid frequency stabilization

Blackout and black start analysis for improved power system resilience: the African experience

The subtle but yet impactful effect of climate change has led to extreme weather conditions which has culminated to many natural disasters. Such events, depending on its severity would usually trigger a partial or complete power system blackout with significant impact on social, political and economic activities. Restoring the system back to normal is usually achieved either using the top-down or bottom-up approach which is described as black start. Emerging research has indicated that distributed energy resources (DERs) and remote controllable switches (RCSs) can be deployed for black start restoration (BSR) for distribution systems and microgrids. With these developments comes the opportunity to develop a restoration strategy which would further enhance the resilience of the power system. In view of this, an analysis of some recent power system blackout events in Africa was carried out with the aim of proposing robust black start restoration strategy that would enhance operational resilience. Besides this, the review of some of the blackout events in selected African countries aims to fill the missing knowledge gap in this area resulting from poor data management system which has made access to such information to be quite a daunting task

Nigerian distribution network feeder impact assessment with integration of electric vehicles

Electric Vehicle (EV) charging is classified into two major categories, depending on the type of chargers used. These are referred to as Alternating Current (AC) and Direct Current (DC) chargers. EVs' batteries are charged by an external source of electricity, such as the grid. Achieving the required charging voltage, charging current, and the charging power for the EV batteries requires power electronic interfaced technologies. AC charging requires an AC to DC converter, which is usually performed within the vehicle itself. DC charging, on the other hand, utilises an off-board converter to get DC power. The dynamic behaviour of power systems has changed drastically due to the increased usage of power electronic interfaced technologies. This paper presents different EV integration scenarios into a Nigerian distribution network feeder that serves both residential and commercial customers. The PSCADIEMTDC simulation software is used to investigate the impacts of different charger topologies from a grid perspective. The sizing of an appropriate filter is also proposed to help mitigate harmonic distortion introduced by various battery chargers in the network. The paper results bolster confidence in the ability of EVs and associated charging methods to be incorporated in different nations’ distribution network feeders via appropriate technologies while maintaining grid safety and reliability

Municipal street lighting systems energy cost and carbon footprint estimation in Uyo, Nigeria

This paper analyses the energy cost and carbon emission footprint of the current street lighting systems in Uyo Nigeria. Using a life cycle assessment approach, a comparative analysis of the carbon footprints of the diesel powered system alongside the two lighting schemes namely: the High Pressure Sodium (HPS) and Light Emitting Diodes (LED) systems were examined. The analysis shows that the LED systems although having an initial high replacement cost, are the most economically viable, offering the least energy cost per annum with very minimal carbon emission footprint as opposed to the diesel powered HPS system which has both high energy cost and carbon emission footprints. Besides this, LED lighting systems when compared with HPS offers a combination of improved nighttime visibility, reduced operations/maintenance cost and decrease in carbon emission. It is hoped that the results of this study would influence municipal authorities in their choice of lighting schemes