Congestion Hotspot Mapping in Grid Systems

1. Introduction

Congestion hotspot mapping is the process of identifying parts of an electricity grid where transmission or distribution networks are likely to become overloaded or constrained. A congestion hotspot may occur when electricity flowing through a transmission line, transformer, substation, or other network element reaches or exceeds its safe operating limit.

Modern electricity systems are becoming more complex because of renewable energy, distributed generation, electric vehicles, battery storage, wheeling arrangements and changing electricity demand. Therefore, identifying congestion hotspots is important for reliable and efficient grid management.

Congestion mapping normally uses information about electricity demand, generation patterns, network capacity, weather, planned projects, historical outages and power-flow conditions. The objective is not merely to identify existing congestion but also to predict future congestion.

2. Meaning of Congestion Hotspots

A congestion hotspot is a geographical or network location where the available transmission or distribution capacity is insufficient to accommodate expected electricity flows.

For example, a region may have large solar generation but insufficient transmission capacity to transport electricity to major demand centres. The transmission corridor connecting the renewable-energy region to the demand centre can therefore become a congestion hotspot.

Hotspots may occur because of:

insufficient transmission capacity;

overloaded transformers;

limited substation capacity;

rapid renewable-energy development;

concentrated electricity demand;

transmission-line outages;

inadequate network expansion;

reverse power flows from distributed generation; and

extreme weather conditions.

3. Mapping Methodology

Congestion hotspot mapping generally involves several stages.

First, data collection is undertaken. The system operator collects information about generation, demand, network topology, transmission limits and historical network events.

Second, power-flow analysis is conducted. Engineers examine how electricity will move through the network under different operating conditions.

Third, contingency analysis examines situations such as the failure of a transmission line or transformer. This is important because a grid may operate normally under ordinary conditions but become congested after a major component fails.

Fourth, geographical mapping identifies locations where congestion is concentrated.

Finally, forecasting can identify future hotspots created by new renewable-energy projects, industrial development, electric vehicles or changes in electricity consumption.

Artificial intelligence and digital-twin technologies can increasingly assist this process, but their decisions must remain subject to technical standards and regulatory oversight.

4. South African Legal Framework

In South Africa, congestion hotspot mapping must be understood within the Electricity Regulation Act 4 of 2006 (ERA), the National Energy Regulator Act 40 of 2004, electricity licences and the applicable Grid Codes.

The ERA regulates generation, transmission, distribution and trading of electricity. NERSA has regulatory authority over the electricity sector. The Grid Code provides technical rules concerning the operation and reliability of the electricity system.

The importance of system reliability was recognised in Eskom Holdings SOC Ltd v Sonae Arauco (Pty) Ltd (2024). The Supreme Court of Appeal explained that the Grid Code requires the system operator to take prompt remedial action where an abnormal condition threatens reliable operation of the grid.

This principle is directly relevant to congestion mapping because hotspot identification can provide an early-warning mechanism for abnormal or potentially dangerous network conditions.

5. Case Law

Eskom Holdings SOC Ltd v Sonae Arauco (2024)

This case concerned load-shedding and protection of the national electricity grid. The SCA recognised the system operator's responsibility to protect reliable grid operation under the Grid Code.

Although the case did not directly concern “congestion hotspot mapping”, it is relevant by analogy because congestion analysis is one method through which network risks can be identified before they threaten system integrity.

Eskom Holdings SOC Ltd v Lekwa Ratepayers Association (2022)

The SCA confirmed that electricity generation, transmission and distribution are regulated under the ERA and that NERSA has an important regulatory role.

For congestion mapping, this demonstrates that technical decisions affecting transmission and distribution infrastructure operate within a statutory regulatory framework rather than being purely private engineering decisions.

Sibanye Gold v Eskom (2026)

In Sibanye Gold (Pty) Ltd v Eskom Holdings SOC Ltd and Others, the High Court considered a proposed 50 MW solar PV facility and a power line crossing Eskom's 132 kV transmission lines. The court examined technical risks, network infrastructure, regulatory requirements and Eskom's reasons for refusing a wayleave.

The case is particularly useful for congestion mapping because it shows the importance of technically supported reasons when decisions affect access to electricity infrastructure. The court found Eskom's refusal unlawful and constitutionally invalid and set it aside.

United Democratic Movement v Eskom (2023)

The High Court considered the consequences of load-shedding and recognised that protecting the integrity of the national electricity grid involves significant constitutional interests.

This illustrates why congestion-management decisions must consider both technical reliability and their effects on electricity users.

6. Legal Issues in Hotspot Mapping

Several legal questions arise when congestion maps are used by regulators and system operators.

First is accuracy and accountability. If a project is rejected because a particular network area is classified as congested, the underlying technical evidence should be reliable.

Second is transparency. Developers may need information about available network capacity when deciding where to construct renewable-energy projects.

Third is procedural fairness. Regulatory or administrative decisions based on congestion information may be reviewable where they are irrational, unlawful or procedurally unfair.

Fourth is equal access. Congestion management should not be used arbitrarily to favour one market participant over another.

Finally, congestion maps may contain commercially sensitive information. Rules concerning confidentiality and access to information may therefore become relevant.

7. Importance for Future Energy Governance

Congestion hotspot mapping can support better transmission planning, renewable-energy integration, connection decisions, storage deployment and investment planning. It can also help regulators identify areas requiring network reinforcement.

However, the map should be treated as a decision-support instrument, not as an automatic legal decision-maker. Technical models should be independently verifiable, regularly updated and capable of explaining the assumptions behind their conclusions.

Conclusion

Congestion hotspot mapping provides an important connection between electricity engineering and energy law. It identifies areas where network capacity may become insufficient and allows system operators and regulators to take preventive measures.

South African case law, particularly Sonae Arauco, Lekwa Ratepayers Association, and Sibanye Gold, demonstrates the importance of reliable grid operation, statutory regulation, technical justification and lawful decision-making. Although South African courts have not yet developed a dedicated doctrine of “congestion hotspot mapping”, existing electricity-law principles provide a foundation for its responsible use in future grid governance.