Simplified CFD modelling of tidal turbines for exploring arrays of devices

The status of marine current tidal energy technology is currently in the research and development phase, with a few deployments and tests of prototypes under-way in some countries. There is a huge pressure for tidal farms to be of Gigawatt scale in order to have a real, economically viable impact on renewable energy utilization targets outlined for 2020. A route to achieving this is the large scale energy farm philosophy, similar to wind farms, based on very large numbers of unit current tidal stream devices. However, this emerging technology development raises different research questions which lead to further problems in the practical implementation of tidal stream devices. Thus, the aim of this study was: (i) to develop a new, computationally cheap computational fluid dynamics (CFD) based model of the Momentum-Reversal-Lift (MRL) tidal turbine, and (ii) to perform a detailed calculations of the flow field of single and multiple turbines using the developed model to investigate the flow features such as, downstream wake structures, dynamics of the free surface, wake recovery, and the influence of wake interactions on the performance of individual devices. A new CFD based Immersed Body Force (IBF) model has been developed to represent the MRL turbine. The IBF model was developed based on the concept of actuator disc methodology by incorporating additional geometric features that induce energy absorption from the flow which also lead to a downstream wake structure intended to reflect more closely those of the real turbines than simple momentum sink zone models. This turbine model was thoroughly used to investigate the performance of the MRL turbine and the associated flow characteristics and proved its capability in analysing several issues relating to this design of tidal turbines. Several calculations have been carried out and a full range of operating points of the MRL turbine was formulated. A maximum power coefficient of, Cp = 0.665, was obtained with a blockage ratio of, B = 0.016. However, the performance of the turbine was improved at a higher blockage ratio both in a single and tidal stream farm investigations. The power coefficient of a single turbine was improved by about 3% when simulated with a blockage ratio of, B = 0.029, and even a higher value was obtained in a tidal stream farm containing three turbines configured in the spanwise direction which reached up to, CP = 0.761, with a global blockage ratio of, B = 0.027. These power coefficients are higher than the Lanchester-Betz limit of CP = 0.593 obtained at B = 0, which is mainly due to the tidal turbine operating in a constrained environment, high blockage ratio, that increases the thrust force on the device. The power coefficient of the IBF model showed consistently higher values compared to experiments and a detailed CFD model results. This indicates that the power coefficient calculated using the IBF model includes some other losses within the turbine region, such as losses due to viscous, shear etc. Investigations on the influence of closely packed clusters of turbines in a tidal streamfarm showed that a laterally close configuration of turbines improved the performance of individual turbines due to the blockage effect, which is created by the array of turbines in the span-wise direction. In contrast, a small longitudinal spacing between turbines inflicted a massive energy shadowing that affects the performance of downstream turbines. However, a tidal stream farm with a staggered turbine layout can reduce the longitudinal spacing by about 50% with a minimum of 6D lateral spacing compared with a regular turbine layout due to the advantage of using an accelerated bypass flows.University of Exete

COVID-19 and energy access: An opportunity or a challenge for the African continent?

As the COVID-19 pandemic gains ground in the African continent, it will create havoc and unprecedented health and economic crisis. The crisis has exposed the robustness and resilience of the economies and services such as health systems around the world and it is disaster in the making while the pandemic is spreading fast to the African continent. This is alarming mainly because the continent has weak health system compounded by low access to modern and reliable electricity. It is also anticipated that the crisis will be brought ample opportunities and the African governments and the people should make coordinated and concerted effort in developing conducive business environment and exploit the opportunities presented to facilitate energy access focusing on clean and renewable energy technologies. This is a big test for the continent and thus it will either brought prosperity through facilitating universal energy access by effectively utilizing the opportunities brought by the crisis or the lack of energy access will continue affecting communities the ability to improve their livelihoods

Comparative assessment of the challenges faced by the solar energy industry in Ethiopia before and during the COVID-19 pandemic.

The COVID-19 pandemic is having an unprecedented impact on social, economic, and political situations of all countries around the world with no sight to its end. Business sectors such as solar distributors, which have been instrumental in supporting the governments' ambitious universal electrification programs, have been negatively affected by the pandemic. The main aim of this paper is therefore to explore and conduct a comparative assessment before and during the COVID-19 pandemic of the key challenges of solar-based businesses in Ethiopia focusing on the distributors and installers and to provide policy recommendations. Qualitative and quantitative assessments were employed during this study. The results show that before the pandemic, finding a skilled workforce, gaining a technical knowledge of the technology, competing in the market, and lack of consumer awareness and initial investment were the key challenges. The importation of solar technologies has been halted by the arrival of the COVID-19 exacerbating existing challenges and threatening the very existence of the businesses. The impact of the pandemic on income levels of end-users of solar technologies, together with the lack of sufficient supply of technologies to the businesses, most of the businesses are forced to lay off their employees deepening the unemployment rate and, in some cases, forcing businesses to be closed. These circumstances affect economic development and dents the progress made so far in facilitating energy access to remote communities. To protect these vulnerable but very essential small businesses, necessary interventions are recommended. This article is categorized under:Photovoltaics > Economics and Policy

CFD Simulations for Sensitivity Analysis of Different Parameters to the Wake Characteristics of Tidal Turbine

articleThis paper investigates the sensitivity of width proximity and mesh grid size to the wake characteristics of Momentum Reversal Lift (MRL) turbine using a new computational fluid dynamics (CFD) based Immersed Body Force (IBF) model. This model has been added as a source term into the large eddy simulation (LES), which is developed for solving two phase fluids. The open source CFD code OpenFOAM was used for the simulations. The simulation results showed that the grid size and width proximity have had massive impact on the flow characteristics and the computational cost of the tidal turbine. A fine grid size and large width inflicted longer computational time. In contrast, a coarse grid size and small width reduced the computational time but showed poor description of the flow features. In addition, a close proximity of the domain’s wall boundary to the turbine affected the free surface, the air body, and the flow characteristics at the interface between the two phases. These results showed that careful investigation of a suitable grid size and spacing between the wall boundary and the turbine is important to minimise the effect of these parameters on the simulation results.University of Exete

The role of community energy systems to facilitate energy transitions in Ethiopia and Mozambique

Policymakers and academics are focusing on energy transition to provide affordable, sustainable, and green energy for everyone. This is being driven by a combination of the lack of electricity access to millions of people particularly in the African continent and the requirement for the reduction of environmental impact through the use of greener energy resources and systems. This paper summarizes an interdisciplinary research program investigating community energy systems in Ethiopia and Mozambique to facilitate energy transitions. Specifically, it compares community energy landscapes, progress made, and existing challenges and opportunities. To determine the status of community energy development in the two countries, recent publications and official policies were reviewed, and community energy managers were interviewed. The review showed that renewable energy sources are the dominant focus for community energy developments, which is key to achieving a cleaner energy future. However, progress in community energy development has been slow in these countries. There are several reasons that hinder community energy systems from driving the necessary energy transition to a cleaner, modern, and affordable energy. Some of these reasons are the absence of favorable regulatory frameworks, incentive package, knowledge on business models, weak commitments from stakeholders, and insufficient community involvement. These issues vary in degree between the two countries

Sustainability challenges of hydropower and its implication on Ethiopia’s economy

Ethiopia has the potential to be 100% renewable. Its renewables are capable to solve its energy poverty and energy shortage in East Africa. The country’s climate resilient green economy strategy considers energy as key enabler for vibrant economy. The objective of this paper is to identify key challenges of the energy sector by studying 12 years of electricity generation data, 2012 to 2023, and to analyze the sector’s performance with a special emphasis on hydropower. In this study, both quantitative and qualitative methods were employed to draw performances indicators. The quantitative results showed that the country achieved 30% of its energy development plan with a deteriorating performance from 94% to 40%. This performance works for hydropower too, which dominants the electricity development and supply. The declining performance comes from government’s monopoly in the sector, financial deficit due to ongoing internal crises and technical unavailability of power plants. This performance has greatly influenced expansion of industries, access to electricity, unemployment, and other economic activities. The authors advise the government, stakeholders, and development partners to consider the recommendations given in this paper to boost the energy sector development and keep the country in healthy economic pace by all measures

Investigation of the performance of a staggered configuration of tidal turbines using CFD

This paper investigates the influence of wake interaction and blockage on the performance of individual turbines in a staggered configuration in a tidal stream farm using the CFD based Immersed Body Force turbine modelling method. The inflow condition to each turbine is unknown in advance making it difficult to apply the correct loading to individual devices. In such cases, it is necessary to establish an appropriate range of operating points by varying the loading or body forces in order to understand the influence of wake interaction and blockage on the performance of the individual devices. The performance of the downstream turbines was heavily affected by the wake interaction from the upstream turbines, though there were accelerated regions within the farm which could be potentially used to increase the overall power extraction from the farm. Laterally closely packed turbines can improve the performance of those turbines due to the blockage effect, but this could also affect the performance of downstream turbines. Thus balancing both the effect of blockage and wake interaction continues to be a huge challenge for optimising the performance of devices in a tidal stream farm

Numerical simulation of a new type of cross flow tidal turbine using OpenFOAM - Part II: Investigation of turbine-to-turbine interaction

Copyright © 2013 Elsevier. NOTICE: this is the author’s version of a work that was accepted for publication in Renewable Energy. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Renewable Energy, Volume 50 (2013), DOI: 10.1016/j.renene.2012.08.064Prediction of turbine-to-turbine interaction represents a significant challenge in determining the optimized power output from a tidal stream farm, and this is an active research area. This paper presents a detailed work which examines the influence of surrounding turbines on the performance of a base case (isolated turbine). The study was conducted using a new CFD based, Immersed Body Force (IBF) model, which was validated in the first paper, and an open source CFD software package OpenFOAM was used for the simulations. The influence of the surrounding turbines was investigated using randomly chosen initial lateral and longitudinal spacing among the turbines. The initial spacing was then varied to obtain four configurations to examine the relative effect that positioning can have on the performance of the base turbine

Evidence-based energy conservation potentials and policy implications in the textile and garment industries of Ethiopia

Energy is one of the primary inputs in textile and garment processing industries and its cost share is reported between 5 and 10% of the total production cost in developed countries but is far higher in developing countries. The textile and garment sector is one of the fast growing economic sectors in developing nations like Ethiopia which have very limited scientific data particularly in the industries where there is no clear and concise information about the energy consumption pattern as well as the energy conservation practices. Thus, the main purpose of this study was to understand the energy usage pattern and conservation practices and to recommend evidence-based conservation measures and policy directions. The aim of this comprehensive study was therefore to conduct a detailed energy audit in the MAA garment and textile industry, in the town of Mekelle, at the northern part of Ethiopia, to analyze the major energy-consuming areas and implementation of evidence-based energy conservation solutions. This was achieved through primary and secondary data collected from the company. Accordingly, a total of 15 energy conservation recommendation was identified and proposed for possible implementation that have the potential to save a total cost of around $214,600 per year but requires nearly$98,300 investment leading to a payback period of 7 months. These recommendations include in the utilities of boiler, thermic fluid heater, air compressors, and lightings. In addition, key policy directions are recommended to support the sectors to reduce their energy consumption

Intelligent manufacturing eco-system: A post COVID-19 recovery and growth opportunity for manufacturing industry in Sub-Saharan countries

The lagging behind intelligent technologies and the COVID-19 pandemic together have impacted the emerging economy particularly the manufacturing sector in sub-Saharan countries. This paper systematically discusses intelligent manufacturing technologies with an aim to map out their importance and industrial applicability and to show their significance to contain COVID-19 pandemic. Intelligent Manufacturing Systems (IMS) is then adapted as a post COVID-19 recovery and growth opportunity to ensemble to production processes of manufacturing industry in the sub-Saharan countries. Proposition of a Triple Helix Collaboration Eco-system that delineate a recursive contribution of Government(s), academia, and industry accompanies the IMS adoption. The intention is to shape the existing industrial challenges through networking in the area of intelligence technologies. While proposing the Eco-system, a post COVID-19 recovery and growth opportunity and intra-Africa scientific collaborations are taken into account