• Energy Research

Abstract One of the challenges of utilizing solar PV in residential buildings is the management of load in accordance to the intermittent nature of solar resource. In this paper, Mixed Integer Linear Programming (MILP) is proposed to effectively plan and allocate load for consumption in such a way that the user defined priority of loads are conserved. In this way, the loads are made to follow the battery state of charge in accordance to the intermittent nature of solar resource without adversely affecting the quality of life of the user. In doing this, energy audit of a typical 4-bedroom residential building belonging to a medium-income family is carried out and classified into controllable and non-controllable loads. The energy audit is also used to size the PV system and the battery bank taking into consideration the financial status of the user (i.e. adequately sized and under-sized PV system based on financial status of the user). A load manager based on MILP with solar resource load following capability is thereafter developed and implemented in a computational program to manage the load based on user’s priority. Six scenarios are created to gain insights into the effectiveness of the proposed load manager. The results reveal that the proposed technique is effective in allocating loads based on the available solar resource in such a way that the user priority is maintained.

In this paper, critical review of various work done in the areas of wind energy resource, modelling of wind energy conversion system (WECS) and issues regarding wind power integration into the grid are presented with the aim of examining the development, progress, achievements and direction of research. Some of the findings show that every site is unique; therefore, no generic conclusion can be drawn with regards to wind characteristics and the wind power potential of locations. The study also reveals that there is no single model of WECS. The model to be adopted will depend on the problem to be solved. This paper is useful in providing background details for wind turbine designers, researchers and practical engineers who are new in the field of wind energy.

The availability of reasonably accurate global solar radiation data is vital for the success of any solar project. However, only a few meteorological stations around the world capture these data as a result of the high cost of measuring equipment and the lack of technical capability in calibrating them. In an attempt to resolve this challenge, engineers and researchers have developed various alternatives to generate the data. In this paper, we surveyed the methods used in generating synthetic global solar radiation with a view to classifying them and bringing out the advantages and the challenges of each. This could motivate the development of a new set of robust prediction techniques that combines the strengths of different existing models for prediction purposes. The various prediction techniques can be generally classified into four categories: the regression techniques, the artificial intelligence methods, the statistical approaches, and the satellite imagery techniques. It is shown from the review that the regression techniques are widely used for the prediction of global solar radiation because of their simplicity. However, their accuracy depends on the completeness of the meteorological data employed in predicting global solar radiation. The statistical methods are based on the assumption that data have an internal linear structure that can be identified and used for prediction purposes. However, it is observed in the literature that the techniques, especially the time series techniques, are generally not good for short time prediction as the error in the prediction of the next value in a series is usually large. Satellite imagery is desirable if surface data for location does not exist. Generally, the use of surface measurements together with a cloud index based on satellite imagery is encouraged to increase the accuracy of prediction. Artificial intelligence methods have been generally favoured for their capability to handle complex relationships between the global solar radiation and the other meteorological data, and as well provide better accuracy and efficiency. This paper is important to engineers and researchers who are interested in the global solar radiation prediction methods.

In this paper, comparative assessments of four earthing grid system configurations (the triangular shape, the rectangular shape, the T-shape and the L-shape) are performed with the aim of determining the best earthing grid configuration in terms of earthing grid resistance, Ground Potential Rise (GPR), touch voltage and step voltage for a typical food and beverages industry in Nigeria. The IEEE earthing technique and the Finite Element Method (FEM) are employed to simulate the earthing grid system configurations using commercially available software (Electrical Transient Analyser Program, ETAP 12.0). The results revealed that L-shape is the most preferred earthing configuration in terms of grid resistance, GPR and step voltage with the IEEE values of 0.292Ω, 1610.9 V and 436.5 V, respectively and FEM values of 0.195Ω, 1077.1 V and 186.6 V, respectively. Meanwhile, the rectangular shape gives the best result for designed touch voltage with the value of 284.5 V for the IEEE method and 286 V for the FEM method followed by the L-shape with the values of 340.8 V for the IEEE technique and 294.8 V for the FEM. Both the IEEE method and the FEM return the same trend of result for all grids. However, IEEE method is much better in terms of computational speed. Keywords: Earthing grid system, Earthing Configurations Electrical Transient Analyser Program (ETAP), Finite Element Method (FEM), IEEE earthing technique

Abstract In this paper, probability distribution of clearness index is proposed for the prediction of global solar radiation. First, the clearness index is obtained from the past data of global solar radiation, then, the parameters of the appropriate distribution that best fit the clearness index are determined. The global solar radiation is thereafter predicted from the clearness index using inverse transformation of the cumulative distribution function. To validate the proposed method, eight years global solar radiation data (2000–2007) of Ibadan, Nigeria are used to determine the parameters of appropriate probability distribution for clearness index. The calculated parameters are then used to predict the future monthly average global solar radiation for the following year (2008). The predicted values are compared with the measured values using four statistical tests: the Root Mean Square Error (RMSE), MAE (Mean Absolute Error), MAPE (Mean Absolute Percentage Error) and the coefficient of determination (R2). The proposed method is also compared to the existing regression models. The results show that logistic distribution provides the best fit for clearness index of Ibadan and the proposed method is effective in predicting the monthly average global solar radiation with overall RMSE of 0.383 MJ/m2/day, MAE of 0.295 MJ/m2/day, MAPE of 2% and R2 of 0.967.

Abstract Hydrogen gas when produced from renewable energy sources and fed into fuel cells has the potential to produce energy in a sustainable manner. This present work estimates the electricity generation and environmental potentials of hydrogen produced from biogas. The biogas is produced in an anaerobic digester using the food component of the municipal solid waste collected from the selected cities in the South-Western Nigeria. The amount of hydrogen produced is determined using the stoichiometric chemical equations of biogas steam reforming process with water-gas shift reaction. The environmental benefit is estimated by considering ecological analysis of the system. The amount of fossil fuel that could be replaced by using the generated hydrogen gas for electricity production and the associated greenhouse gas emission that could be prevented are also evaluated. The results reveal that Lagos has the highest hydrogen generation potential of about 285 million kg (0.285 million tons) per year followed by Ibadan with 93 million kg (0.093 million tons) per year while the least production occurred in Osogbo. About 411 million kg (0.411 million tons) is produced from the reforming process in all the locations over the timeframe of 20 years (i.e., 2017–2036). This hydrogen production is equivalent to about 1.02% of the global hydrogen production in 2011 put at around 40.5 million tons. The total amount of hydrogen gas produced could generate about 19.46 million kWh of electricity per annum. An encouraging value of ecological efficiency of about 94.33% was achieved using hydrogen as source of energy. The results also show that a total of 7.446 million litres of diesel fuel could be replaced by hydrogen gas in the selected cities which is equivalent to 1.489 Billion Naira. The total amount of carbon dioxide and carbon monoxide emissions that could be avoided is about 16.031 million kg and 45.477 thousand kg. The sensitivity analysis showed that steam reforming efficiency and waste collection rate have positive correlation to hydrogen yield and electricity generation potential.

In this paper, detailed and comprehensive analysis of the technical, environmental and economic benefits of providing adequate water supply using solar PV system for three selected abattoirs (Bodija, Akinyele and Iyana church abattoirs) in Ibadan are presented. First, an estimate of average daily water requirement for slaughtering and cleaning cattle is obtained for each of the abattoir. This was achieved through oral interviews conducted at the different abattoirs to arrive at a reliable estimate. Thereafter, the total water requirement, the water storage capacity and the electrical load requirement necessary for the sizing of solar PV system that will enhance the smooth operation of the abattoir are determined. Some of the key results revealed that the water requirements of the abattoirs are 208,780, 91,632 and 78,590 l/week, respectively. The most suitable submersible pump for the three abattoirs is 60GS50 (5hp, 60gallon/min Goulds series). The cost of pumping water and providing lighting for smooth operation of the abattoirs are $0.23, $0.21 and $0.19, respectively. The results also show that 16,300, 15,200 and 14,600 kg/yr of carbon dioxide as well as 46.37, 43.36 and 41.45 kg/yr of carbon monoxide could be avoided, respectively with the implementation of the project.

Abstract In this paper, the effectiveness of an hybrid grid-photovoltaic (PV) power supply for an urban household is investigated. Two parameters are used for the evaluation: (1) the cost of buying electricity and (2) the environmental benefits. Yearly energy utilisation of a household and solar irradiation are collected and used in this study. A model of a hybrid grid-PV system is developed in HOMER software to investigate the efficacy of the system in the selected site. The results show that almost 26% of operating costs could be saved yearly by implementing the hybrid supply. The emission of greenhouse gasses in service to the particular site is also reduced by 26%. The sensitivity analysis results show that the grid-PV system can be more favourable as the price of energy increases. That is, the energy purchased from the grid declines as the cost of energy purchased increases. This is also observed with the increment of both price of energy and its utilisation. A reduction of cost of energy is also observed.

The energy sector in South Africa is highly driven by coal, making the country one of the highest greenhouse gas (GHG) emitters in the world. As one of the signatories to the UN Framework Convention on Climate Change, the country is determined to reduce its carbon footprint. In this paper, the role of green hydrogen produced from renewable energy sources to the South African energy sector is presented with the objective of increasing the share of renewable energy in the country's energy mix. First, an overview of the South African energy sector is presented with the aim of pointing out the energy inputs and the usage patterns. Thereafter, the potential of renewable energy resources that could support green hydrogen production is highlighted. Some of the key findings show that 67% of total primary energy sources in South Africa is coal. Industrial and residential sectors account for the bulk of energy usage with 53% and 19%, respectively. It is also revealed that industrial and transportation sectors account for 51% and 38%, respectively, of GHG emission with the residential sector contributing only 2%. The renewable energy resources in South Africa are encouraging for green hydrogen production. Solar has an average 2500 h of sunshine per year with daily total solar irradiation between 4 and 6.5 kWh/m2 day. The annual average wind speed ranges from 5.6 to 8.7 m/s with power density between 218 and 693 W/m2 at 10 m anemometer height in the coastal region of the country. The biomass potential is estimated as 83.91 Teragram per annum with hydropotential of 4.851 GW. This paper is important as it will serve as a firsthand scientific information for optimal development and investment in green hydrogen production in South Africa.