Operating Voltage and Frequency Regime Validation of Grid Code Requirements in South Africa

Comprehensive review of the requirements of AC transmission grid codes and the role of FACTS devices in integrating renewable power plants

Large‐scale renewable energy (RE) integration in the power systems is displacing conventional sources of generation, thus reducing the system's inherent inertia and primary frequency response (PFR) capabilities. This reduced response may decline the system's ability to stabilise frequency after inevitable events such as loss of generation or load and thus requires additional PFR. To meet the PFR requirements, fast‐acting resources like energy storage systems (ESS) and demand response (DR) (transferrable and interruptible loads) need to be integrated within the system. In this regard, a novel stochastic security‐constrained unit commitment framework is proposed to assess the potential of ESS and DR to ensure additional PFR requirements and handle post contingency frequency dynamics. Moreover, the proposed methodology analyses the impact of uncertain RE integration on system frequency dynamics using Bayesian inference statistics. Case studies are carried out on 39 bus New England and 118 bus IEEE test systems, incorporating post fault frequency security parameters. Simulation results analyse the PFR contribution of ESS and DR and indicate a substantial reduction in system operating cost and RE curtailment with their integration. The proposed analysis would help system operators to maintain required PFR under high RE penetration, and handle unavoidable contingencies.

The introduction of renewable generation to South Africa's grid has introduced challenges to the management and regulation of power quality (PQ). These have been addressed by establishing PQ compliance criteria in line with local circumstances and by the introduction of a Power Quality Guideline for renewable power plants (RPPs). A key challenge to RPPs has been meeting emission limits for harmonics. This has been addressed in South Africa's RPP Guideline by the development and introduction of a Group Harmonic Distortion limit which provides some flexibility to RPPs in making individual harmonic emission limits. The use of 95th percentile harmonic impedance envelopes is discussed and recommendations for impedance envelopes are made for different voltage levels within the South African Grid, based on actual network data. A lesson learnt is that using international standards and guidelines provides a starting point for compliance rules when introducing renewable generation. Developing countries that share economic and electricity network characteristics with South Africa should tailor the PQ rules and guidelines for RPPs to meet local conditions.

The large-scale renewable energy power plants connected to a weak grid may cause bus voltage fluctuations in the renewable energy power plant and even power grid. Therefore, reactive power compensation is demanded to stabilize the bus voltage and reduce network loss. For this purpose, time-series characteristics of renewable energy power plants are firstly reflected using K-means++ clustering method. The time group behaviors of renewable energy power plants, spatial behaviors of renewable energy generation units, and a time-and-space grouping model of renewable energy power plants are thus established. Then, a mixed-integer optimization method for reactive power compensation in renewable energy power plants is developed based on the second-order cone programming (SOCP). Accordingly, power flow constraints can be simplified to achieve reactive power optimization more efficiently and quickly. Finally, the feasibility and economy for the proposed method are verified by actual renewable energy power plants.

To systematically analyze the impact of the DC frequency limit controller (FLC) configuration scheme on the frequency characteristics of asynchronous interconnected power grids with renewable energy integration, a comprehensive frequency analysis model for three-area asynchronous interconnected power grids including the FLC is proposed. The model is based on the SFR model considering renewable energy integration and includes a simplified model of the DC FLC. A rigorous validation of the rationality and stability of the model is achieved through detailed mathematical calculations and pole-zero analysis. Taking the local power grids as an example, the established model is used to study the difference between single- and double-sided configuration of the DC FLC, the relationship between the increase in the renewable energy penetration rate and the frequency characteristics of each regional power grid, and the influence of DC FLC configuration on the maximum acceptance ratio of renewable energy. Through data comparison and theoretical analysis, the influence of FLC configuration on the frequency characteristics of each region of the asynchronous power grid under renewable energy integration is obtained. The results show that the configuration of a bilateral FLC on the DC line has more advantages in alleviating the complementary power disturbance at both ends and obvious limitations on the non-complementary power disturbance at both ends. Compared with the configuration of the bilateral FLC, the configuration of a unilateral FLC on the weak grid has a larger proportion of renewable energy acceptance. When the DC FLC power transmission capacity is sufficient, the weak grid and the adjacent two asynchronous grid DC tie lines are configured with a single-sided FLC, and the weak grid is theoretically connected to the renewable energy penetration rate of up to 100%.

This paper presents a scheme of distance protection for a renewable energy plant in electric power distribution systems. In many developing countries where renewable energy power plants are typically located in rural remote areas, they must be connected to weak power distribution systems inevitably. Although over-current relays are used to protect feeders at substations, fuses are only available elsewhere along feeder lines. To secure the system operation, distance protection is assigned to protect feeders. In this paper, distance relays are placed in the feeder along with over-current relays and fuses. Design of the distance protection of multi-source systems is described. This study considered the system consisting of a renewable energy plant. The power plant was a 6-MW unit of firmed power generation. The test feeder was simplified to be an equivalent four-bus test feeder for relaying purpose. Fault analysis in this paper was performed by using PowerWorld™ software. Obtained fault currents were used to establish protective zones of distance relays. In addition, this paper also compared the result of using distance protection with those of using directional over-current protection. As a result, protection of the power feeder with renewable power plants by using distance relaying can reduce complication in relay setting due to the impedance-based setting of the distance relay.

Environmental Taxation and Subsidization in an Oligopolistic Wholesale Market of Electricity with Intermittent Renewable Energy Sources

Integration of large-scale renewable energy (RE) sources in particular, wind and solar energy into the grid introduces current and voltage harmonics due to power electronics devices as well as inverter connected into the RE sources. Ensuring adequate harmonics in the line currents of RE integrated power system is one of the biggest challenges today. Therefore, this study investigates the potential impacts in particular current and voltage harmonics causes due to large-scale integration of RE into the Berserker Street Feeder, Frenchville Substation under Rockhampton distribution network (DN), Central Queensland, Australia. From the model analyses, it has clearly evident that harmonics across the network increases with the increase of RE integration and causes uncertainties in the feeder as well as in the DN. This study also explores possible mitigation measures and it has seen that optimized STATCOM effectively reducing the adverse harmonic impacts of integrating large-scale RE into the DN.

Over the past 10 years, in most countries of Europe, North America and China, renewable energy grid integration technical standards are mostly developed by some electricity association or power grid companies. However, with the increasing scale of renewable energy generation and gradually intensified impact on the power grid, more countries confirm the legitimacy of renewable energy grid integration provisions through the legislation in national level. Due to the difference in the power source structure, load characteristics, power grid situation, and other specific circumstances in different countries or regions, grid code of renewable energy integration in different countries are not identical. However, these technical standards have some common focuses. They all stressed that the renewable energy power plants must have a certain active power control, reactive power / voltage control and fault ride through capability as well as the ability to withstand the power system voltage and frequency deviation. Some of the standards require the renewable energy power plants to provide model information, operating parameters and grid integration performance testing reports. This paper provides an introduction about common focus on technical standards of renewable energy grid integration, and tries to explore potential challenge caused by RE grid integration.

This paper assesses the possibility of sustainable agriculture in South Africa in the context of recent policy initiatives. The new environmental strategy for agriculture represents a significant break with policy initiatives developed during apartheid. The likelihood of sustainable farming practices being adopted in South Africa will, however, face at least three obstacles. These are the integrated structure of industrial farming, the concern over yields, and current political and economic changes in South African agriculture. It is argued that sustainable techniques are unlikely to develop in the large scale farming sector in the near future. If the considerable research and extension resources of the state are reoriented quickly enough, sustainable farming methods can be embraced by an emerging class of black commercial farmers.

The importance of adopting modern technology in agriculture, especially in a changing climate, cannot be underestimated in Africa. The aim of this review was to highlight the past and the status quo with regard to the adoption of current farming practices in relation to climate-smart agriculture (CSA) by communal livestock farmers in South Africa. The impact of animal agriculture on climate change was also deliberated. Different internet search engines and databases, like Google Scholar, EBSCO Host, Science Direct, etc., and peer-reviewed articles, books, and government and academic reports were employed to provide information to adequately address the aim. Keywords like “the impact of climate smart agriculture on communal livestock farmers”, “communal livestock in South Africa”, “communal farming and technology adoption”, etc. were used for the search. Various issues pertaining to the impact of animal agriculture on climate change, greenhouse gas (GHG) emissions, and implementing CSA in livestock farming were extensively discussed. The findings indicated that there is limited research on the adoption of CSA by communal livestock farmers in South Africa. The review concluded that strategies to adopt modern technology in communal areas should address the issues to enhance knowledge of farmers and all stakeholders, through increasing awareness, trainings, and skills programs. The government should build local capacity in innovative and affordable water and agricultural solutions, and reliable financial mechanisms should be in place to implement innovative sound technologies in communal areas.

The intensification of the use of different renewable energy sources is essential for the fulfillment of the Paris Agreement or for achieving the goals of sustainable development. The environmental impacts of various renewable energy sources have been engaging environmental professionals since their inception. The aim of this work is to collect the most important sizing variables and environmental impacts of hydropower, wind energy, geothermal energy, solar energy and biomass, which have been discussed in the literature.By using the tools of network science, it is possible to jointly manage the environmental impacts and the sizing variables of renewable energy power plants, so the impact mitigation can be performed efficiently already in the design phase. From the sizing variables and the environmental impacts, a multi-layered network is formed, based on which the relationships between the impacts can be explored and more efficient mitigation solutions can be implemented.The results show that the impacts of wind turbines on flying animals are outstanding, hydropower plants can be mostly described by changing the flow conditions, the noise and hydrothermal disturbance of geothermal power plants are outstanding, the visual and soil effects of solar power plants are most significant, while the biomass plants impacts related the harvest are most pronounced.This work helps to understand the environmental impacts of the increased utilization of renewable energy sources better and provides a framework for practitioners to enforce environmental considerations in design processes more easily.

The stochastic nature of renewable energy sources creates unpredictable variability making instantaneous demand and supply a big challenge. Demand response (DR) which is an intentional modification of consumer loads as per utility requirement can support the intermittent nature of renewable energy sources, helping grid operators to quickly respond to power variability. Smart grids provide an opportunity for consumers to produce energy and feed it into the grid as well as control their energy requirement which is one of the important aspects of DR implementation. This paper provides an overview of various aspects of DR programs available in the literature from point of view of challenges, benefits, and applications. Various opportunities and challenges for DR deployment on renewable energy integration and smart grids from the Indian context are discussed in the work. The objective of the paper is to suggest drivers that will motivate DR deployment with effective renewable energy integration in the country. One of the important aspects of DR implementation in the country is to assess DR potential available among the different categories of consumers. Consumer baseline gives reference consumption which is used to assess DR potential. A case study has been conducted on one of the industrial feeders in Goa state to estimate consumer baseline load (CBL) using different methods. Average, maximum value, adjustment, and regression-based CBL estimation methods used for analysis are compared based on evaluated performance metrics. From the analysis, it is found that the adjustment method is most accurate for CBL estimation.

Implementing an applicable demand response (DR) program enables the complete demand-side potentials and ensures a secure, more economic and greener operation of the power systems with the integration of renewable energy. Therefore, the present paper proposes a stochastic security-constraint scheduling approach for optimum operation of both supply and demand sides via well-designed pricing and incentive schemes. The DR programs are time-of-use and emergency DR programs. The study addresses the Independent System Operator (ISO)'s viewpoint, and it aims at finding the optimal DR strategy (from a set of DR programs) in a way that an efficient electricity market is obtained, ensuring the security and environmental constraints. To this end, a security constraint unit commitment (SCUC) problem considering DR and renewable energy resources is proposed. Different indices are considered through a multi-objective problem for evaluating the efficiency of the market, security of the system, reliability and air pollution. These indices include market prices, social welfare, load factor (peak-to-valley proportion), air pollution, and power security, among others. In order to find the best DR strategy, a multi-objective problem is solved to consider all the mentioned indices.

The integration of renewable energy sources into existing energy systems is imperative for enhancing climate resilience and mitigating the adverse impacts of climate change. This comprehensive review explores the multifaceted aspects of renewable energy integration for climate resilience, focusing on key challenges, strategies, and opportunities. By analyzing the latest research findings and case studies, this review offers insights into the diverse approaches to renewable energy integration and their implications for enhancing climate resilience at local, regional, and global scales. The review begins by examining the significance of renewable energy integration as a crucial component of climate resilience strategies. It delves into the interconnectedness between renewable energy deployment and climate adaptation, highlighting the potential of renewable energy systems to enhance energy security, reduce greenhouse gas emissions, and build community resilience to climate-related hazards. Subsequently, the review explores the challenges associated with renewable energy integration, including intermittency, grid stability, and socioeconomic considerations. It discusses innovative solutions and technological advancements aimed at overcoming these challenges, such as energy storage technologies, smart grid systems, and demand-side management strategies. Moreover, the review investigates the role of policy frameworks, regulatory mechanisms, and financial incentives in facilitating renewable energy integration for climate resilience. It assesses the effectiveness of various policy instruments and governance structures in promoting renewable energy deployment and fostering climate-resilient energy systems. Furthermore, the review highlights the importance of stakeholder engagement, community involvement, and capacity-building initiatives in ensuring the successful implementation of renewable energy projects. It emphasizes the need for inclusive and participatory approaches to renewable energy planning and decision-making, particularly in vulnerable and marginalized communities. Overall, this comprehensive review provides valuable insights into the complex dynamics of renewable energy integration for climate resilience. By synthesizing existing knowledge and identifying emerging trends, it informs policymakers, practitioners, and researchers about the opportunities and challenges associated with leveraging renewable energy as a key strategy for building climate resilience in a rapidly changing world. Keywords: Renewable Energy, Integration, Climate, Resilience, Policy.