A techno-economic model for optimising component sizing and energy dispatch strategy for PV-diesel-battery hybrid power systems

This paper presents the development and application of a simple spreadsheet-based simulation model for sizing, energy performance evaluation and economic analysis of PV-diesel-battery power supply systems. The model is employed to generate a set of sizing curves that define the design space for hybrid systems using dimensionless generator component size variables, for a specified supply reliability and diesel energy dispatch strategy. The component size combination with the least unit cost of energy is selected among the many possible combinations satisfying a desired loss-of-load probability. Storage battery and diesel generator lifespan, as well as generator fuel efficiency, which depend on the operational loading stress of these components, are recognised as important variables in the economics of the system. The lifespan of the battery is premised to depend on the depth and rate of discharge of the operating cycles, while both the diesel generator lifespan and fuel efficiency are dependent on the degree and frequency of partial loading. The choice of diesel generator dispatch strategy was shown to be another important factor influencing the energy performance and economics of the system. The outputs of the model reveal several important sizing, operational and economic characteristics of the systems, and enables appraisal of comparative advantage of different types of designs and operational strategies. The merits of the hybrid concept are well demonstrated by the study results

Towards sustainable energy system options for improving energy access in Southern Africa

Access to modern energy services is one of the pre-requisites to improved livelihood, yet the poor, particularly in developing countries, remain tied to unhealthy and inefficient traditional fuels. Renewable energy technologies are increasingly popular energy supply alternatives to fossil-based fuels in many countries. This study presents sustainable energy system implementation options for increasing energy access in developing countries, with special emphasis on Sub-Saharan Africa. A feasibility case study and various implementation options are presented for possible deployment of these systems. Hybrid optimization of multiple energy resources software was used to simulate and validate the proposed hybrid system design and performance. The simulation results indicate that hybrid systems would be feasible options for distributed generation of electric power for remote locations and areas not connected to the electricity grid. Such a hybrid energy system, through providing modern energy services, gives promise to free-up rural communities to engage in productive activities. The opportunity to power or facilitate productive activities such as agro-processing, fabrication and services can potentially reduce poverty

Switched model predictive control for energy dispatching of a photovoltaic-diesel-battery hybrid power system

A new adaptive switched model predictive control (MPC) strategy is designed in this paper for energy dispatching of a photovoltaic-diesel-battery (PDB) hybrid power system, where the battery is unpermitted to charge and discharge simultaneously. The distinguishing feature of the proposed switchedMPC is that, new switched constraints are constructed to describe the different modes (charging and discharging) of the battery, such that the burden of using a switched multiple-input-multiple-output (MIMO) state-space model could be circumvented. Parameters of the battery are unknown constants, and are estimated online with an adaptive updating law. In the switched MPC algorithm, predictive horizon and control horizon vary according to the predefined switching schedule. Based on optimization with the switched constraints, receding horizon control is utilized to obtain the dispatching strategy for the hybrid power system. Performances of the closed-loop system with the proposed switched MPC are verified by simulation results.http://ieeexplore.ieee.org/xpl/RecentIssue.jsp?punumber=87hb201

Demand side management of photovoltaic-battery hybrid system

In the electricity market, customers have many choices to reduce electricity cost if they can economically schedule their power consumption. Renewable hybrid system, which can explore solar or wind sources at low cost, is a popular choice for this purpose nowadays. In this paper optimal energy management for a grid-connected photovoltaic-battery hybrid system is proposed to sufficiently explore solar energy and to benefit customers at demand side. The management of power flow aims to minimize electricity cost subject to a number of constraints, such as power balance, solar output and battery capacity. With respect to demand side management, an optimal control method (open loop) is developed to schedule the power flow of hybrid system over 24 h, and model predictive control is used as a closed-loop method to dispatch the power flow in real-time when uncertain disturbances occur. In these two kinds of applications, optimal energy management solutions can be obtained with great cost savings and robust control performance.http://www.elsevier.com/locate/apenergyhb201

Energy dispatch strategy for a photovoltaic-wind-diesel-battery hybrid power system

In this paper, an energy dispatch model that satisfies the load demand, taking into account the intermittent nature of the solar and wind energy sources and variations in demand, is presented for a solar photovoltaic–wind–diesel–battery hybrid power supply system. Model predictive control techniques are applied in the management and control of such a power supply system. The emphasis in this work is on the co-ordinated management of energy flow from the battery, wind, photovoltaic and diesel generators when the system is subject to disturbances. The results show that the advantages of the approach become apparent in its capability to attenuate and its robustness against uncertainties and external disturbances. When compared with the open loop model, the closed-loop model is shown to be more superior owing to its ability to predict future system behavior and compute appropriate corrective control actions required to meet variations in demand and radiation. Diesel consumption is generally shown to be more in winter than in summer. This work thus presents a more practical solution to the energy dispatch problem.National Research Foundation of South Africa and the Energy Efficiency and Demand Side Management Hub.http://www.elsevier.com/locate/solener2015-10-31hb201

The adoption of energy efficiency and a policy framework for Zimbabwe

Recent policy discussions on energy use in Zimbabwe sparked interest in the economic case for energy efficiency, suggesting the need to investigate the relevant costs and benefits. This paper investigated the potential of energy efficiency in manufacturing industries in Zimbabwe. Data collection was done using questionnaires, walk-through audits and semi-structured interviews. The data set was then analysed using regression analysis. The results show that there would be significant potential energy saving in Zimbabwe through adopting various energy efficiency programmes. The main energy efficiency barriers identified were: poorly structured electricity tariffs; risk of production disruption; resistance of operational staff to a changed working style; lack of coordination between company divisions; lack of information on energy efficiency programmes; and lack of support from senior management on issues that relate to energy efficiency. A straightforward energy efficiency policy framework is proposed, and three main players identified, namely government, energy regulator, and research institutions

Optimal control of a fuel cell/wind/PV/grid hybrid system with thermal heat pump load

This paper presents an optimal energy management strategy for a grid-tied photovoltaic–wind-fuel cell hybrid power supply system. The hybrid system meets the load demand consisting of an electrical load and a heat pump water heater supplying thermal load. The objective is to minimize energy cost and maximize fuel cell output, taking into account the time-of-use electricity tariff. The optimal control problem is solved using a mixed binary and real linear programming. The supply switch to the heat pump water heater and the power from the grid, power to/from the inverter, electrolyzer hydrogen power and fuel cell power are the control variables. The temperature inside the water storage tank and the hydrogen in the storage tank are the state variables. The performance of the proposed control strategy is tested by simulating different operating scenarios, with and without renewable energy feed-in or rather export to the grid, and the results confirm its effectiveness, as it increases the supply reliability of the system.The National Research Foundation (NRF) Grant No. 99766 South Africa, the University of Zambia, Council for Scientific and Industrial Research South Africa and the National Hub for Energy Efficiency and Demand Side Management.http://www.elsevier.com/locate/solener2017-10-31hb2017Electrical, Electronic and Computer Engineerin

A Bibliometric Analysis of Solar Energy Forecasting Studies in Africa

Solar energy forecasting is considered an essential scientific aspect in supporting efforts to integrate solar energy into power grids. Moreover, solar energy forecasting plays an essential role in mitigating greenhouse gas emissions and conserving energy for future use. This study conducted a bibliometric analysis to assess solar energy forecasting research studies evolution at the continental (Africa) and southern Africa levels. Key aspects of analysis included (i) scientific research trends, (ii) nature of collaboration networks, (iii) co-occurrence of keywords and (iv) emerging themes in solar energy forecasting over the last two decades, between the years 2000–2021. The results indicate that solar energy forecasting research has, on average, expanded by 6.4% and 3.3% in Africa and southern Africa, respectively. Based on the study context, solar energy forecasting research only gained momentum in 2015, peaking in 2019, but it is generally still subtle. The scientific mapping illustrated that only South Africa ranks among the leading countries that have produced high numbers of published documents and also leads in contributions to the research area in both Africa and southern Africa. Three emerging topics were identified from the thematic map analysis—namely, “solar irradiance”, “artificial intelligence” and “clear sky”, which implies that researchers are paying attention to solar irradiance, using modelling techniques that incorporate machine learning techniques. Overall, this study contributes to scientific information on the potential bankability of renewable energy projects that could assist power utilities, governments and policymakers in Africa to enforce the green economy through accelerated decarbonisation of the energy systems and building relationships with developed countries for support and better transitioning to solar energy. From a Water–Energy–Food nexus perspective, the results of this work could assist the scientific community in Africa to take advantage of the inherent interconnectedness of water, energy and food resources, whilst also advancing the use of integrated solutions to shape the focus of solar energy research into a more systems thinking and transdisciplinary approach involving the interconnected primary resources and stakeholders pursuit of the Sustainable Development Goals

Urban nexus and transformative pathways towards resilient cities: A case of the Gauteng City-Region, South Africa.

Challenges emanating from rapid urbanisation require innovative strategies to transform cities into global climate action and adaptation centres. We provide an analysis of the impacts of rapid urbanisation in the Gauteng City-Region, South Africa, highlighting major challenges related to (i) land use management, (ii) service delivery (water, energy, food, and waste and sanitation), and (iii) social cohesion. Geospatial techniques were used to assess spatio-temporal changes in the urban landscapes, including variations in land surface temperatures. Massive impervious surfaces, rising temperatures, flooding and heatwaves are exacerbating the challenges associated with rapid urbanisation. An outline of the response pathways towards sustainable and resilient cities is given as a lens to formulate informed and coherent adaptation urban planning strategies. The assessment facilitated developing a contextualised conceptual framework, focusing on demographic, climatic, and environmental changes, and the risks associated with rapid urbanisation. If not well managed in an integrated manner, rapid urbanisation poses a huge environmental and human health risk and could retard progress towards sustainable cities by 2030. Nexus planning provides the lens and basis to achieve urban resilience, by integrating complex, but interlinked sectors, by considering both ecological and built infrastructures, in a balanced manner, as key to resilience and adaptation strategies

Assessment of rural livelihoods, health and wellbeing in Vhembe District Municipality, South Africa and Narok County, Kenya: A water-energy-food nexus perspective

The Water-Energy-Food (WEF) nexus has become an integral component duly suited to enable sustainable development and an important tool to achieve and sustain various socioeconomic and environmental outcomes, including the 2030 Agenda for Sustainable Development Goals. The WEF nexus has become increasingly important in recent years as it can holistically address humankind's current triple challenges, including resource depletion, environmental degradation, and population growth. Socioeconomic factors such as increased population, economic development, and climate change patterns frequently induce unprecedented pressure on WEF resources. From the various climate change model simulations, the climate is likely to increase in the future, exacerbating the demand of the population to access the WEF resources and services. For effective resource planning and decision-making, the availability of WEF resources must be assessed under ongoing climate change. In this regard, this study assessed rural livelihoods, health, and wellbeing indicators within the WEF nexus framework in Vhembe District Municipality (VDM), South Africa, and Narok County, Kenya. The premise was to determine the drivers of livelihood changes by applying the analytic hierarchy process (AHP), a Multi-Criteria Decision-Making to understand the causal linkages between the WEF nexus resources and the sustainable livelihood indicators. Data collected from the literature review, questionnaire/group discussions, and field visit engagements were used to formulate and develop a matrix of indicators to assess livelihoods, health, and wellbeing. A correlation analysis based on the AHP was used to determine the linkages between WEF resources and sustainable livelihood indicators. The multivariate analysis used the correlation matrix to capture the pairwise degrees of relationship between WEF resources and sustainable livelihood indicators in the two study areas. The results show that the resources for sustainable livelihoods in VDM are more sustainable than those in Narok County. The Consistency Ratio values for Narok County and VDM were 0.046 and 0.067, respectively. The resulting composite index (0.143) classified both study sites under the lowly sustainable category. The results are important for informing policy formulation that guides timely interventions to balance socio-ecological systems