The Future of Transmission: Interconnectors, Offshore Grids, and System Planning

Introduction

The transmission system is the backbone of Great Britain’s electricity market, responsible for moving power from where it’s generated to where it’s needed, balancing supply and demand in real time, and underpinning security of supply. As the energy transition accelerates, the transmission network faces unprecedented challenges and opportunities: integrating vast new volumes of offshore wind, connecting with neighbouring markets via interconnectors, and adopting a whole-system approach to planning and operation. In this article, I’ll explore the evolving role of transmission, the policy and regulatory frameworks shaping its future, the technical and commercial challenges ahead, and the innovations that will define the next era of system operation.

1. The Transmission System: An Evolving Landscape

1.1. Traditional Role

Historically, the transmission system—operated by National Grid Electricity System Operator (ESO) and National Grid Electricity Transmission (NGET)—was designed for one-way flows from large, centralised power stations to demand centres. The network was planned and operated to ensure reliability, with redundancy and robust standards.

1.2. The New Reality

Today, the system is being transformed by:

Decarbonisation: Rapid growth of renewables, especially offshore wind, and the retirement of coal and nuclear.
Decentralisation: Increasing volumes of distributed generation and flexible demand at the grid edge.
Digitalisation: Real-time data, automation, and advanced analytics are reshaping system operation.
Market Integration: Growing interconnection with Europe and the emergence of pan-European markets.

2. Interconnectors: Linking GB to Europe

2.1. What Are Interconnectors?

Interconnectors are high-voltage cables that link the GB electricity system to neighbouring countries, enabling cross-border flows of power. They play a vital role in:

Security of Supply: Providing access to additional capacity during periods of stress.
Price Convergence: Smoothing price differences between markets and supporting efficient dispatch.
Renewables Integration: Allowing surplus renewable generation to be exported or imported as needed.

2.2. The Growth of Interconnection

As of 2022, GB has over 7 GW of operational interconnector capacity, with links to France (IFA, IFA2), Belgium (Nemo Link), the Netherlands (BritNed), Norway (North Sea Link), and Ireland (East-West, Moyle). By 2024, capacity is expected to exceed 10 GW, with new projects like Viking Link (to Denmark) and Greenlink (to Ireland) under construction (Ofgem: Interconnectors).

2.3. Market Coupling and Trading

GB participates in pan-European market coupling, enabling efficient cross-border trading and access to day-ahead, intraday, and balancing markets. The UK-EU Trade and Cooperation Agreement (TCA) sets the framework for ongoing cooperation post-Brexit.

2.4. Risks and Challenges

Reliance on Imports: During pan-European stress events (e.g., cold snaps), interconnector flows may be constrained.
Market Complexity: Navigating different market rules, codes, and regulatory regimes.
Physical Security: Interconnectors are critical infrastructure and must be protected from cyber and physical threats.

2.5. Case Study: North Sea Link

The North Sea Link, a 1.4 GW interconnector between GB and Norway, went live in 2021. It enables the exchange of renewable power—hydro from Norway, wind from GB—supporting decarbonisation and system balancing (National Grid: North Sea Link).

3. Offshore Grids: Integrating Offshore Wind at Scale

3.1. The Offshore Wind Ambition

The UK government’s target of 40 GW of offshore wind by 2030 (and up to 50 GW by 2035) is central to net zero. Integrating this capacity requires a step change in offshore transmission infrastructure.

3.2. The Current Model: Point-to-Point OFTOs

Today, each offshore wind farm is connected to shore via a dedicated cable, operated by an Offshore Transmission Owner (OFTO). While effective for early projects, this model is increasingly inefficient as offshore wind scales up.

3.3. The Case for Offshore Coordination

A more integrated offshore grid—linking multiple wind farms, sharing infrastructure, and connecting directly to interconnectors—can reduce costs, minimise environmental impacts, and enhance system resilience.

Offshore Coordination Project: National Grid ESO, Ofgem, and BEIS are leading work to develop a coordinated offshore network (ESO: Offshore Coordination).
Holistic Network Design (HND): The ESO’s HND process is mapping optimal offshore and onshore network configurations to meet 2030 targets.

3.4. Technical and Regulatory Challenges

Grid Code and CUSC Changes: Integrating offshore grids requires updates to the Grid Code and Connection and Use of System Code (CUSC).
Investment and Delivery: Coordinated planning, timely investment, and supply chain capacity are critical.
Environmental and Social Impacts: Minimising impacts on coastal communities and marine environments.

3.5. Case Study: East Coast Cluster

The East Coast Cluster is a major offshore wind and carbon capture project, integrating multiple wind farms, hydrogen production, and CO₂ transport and storage. It exemplifies the complexity and opportunity of coordinated offshore infrastructure (East Coast Cluster).

4. Whole-System Planning and Operation

4.1. Network Options Assessment (NOA)

The ESO’s Network Options Assessment is an annual process that evaluates transmission investment needs based on Future Energy Scenarios (FES), system modelling, and stakeholder input.

4.2. Future Energy Scenarios (FES)

The FES explore different pathways to net zero, informing network planning, market design, and policy.

4.3. Whole-System Coordination

ESO-DSO Interface: Closer coordination between the ESO and DSOs is essential for optimising investment, flexibility, and system operation.
Cross-Vector Planning: Integrating electricity, gas, heat, and transport in planning and operation.

4.4. Digitalisation and Data

Digital Twins: Virtual models of the transmission system support scenario analysis, real-time operation, and resilience planning (ESO: Digital Twin).
Open Data: The ESO’s Data Portal provides open access to system data, supporting transparency and innovation.

5. Regulatory and Market Frameworks

5.1. Ofgem’s RIIO-T2 Price Control

RIIO-T2 (2021–2026) sets the framework for transmission investment, innovation, and performance. It incentivises timely, efficient delivery of new infrastructure and supports digitalisation and whole-system outcomes (Ofgem: RIIO-T2).

5.2. Industry Codes

Grid Code: Sets technical requirements for connection and operation.
CUSC: Governs connection and use of the transmission system.
BSC: Settlement and balancing arrangements, including for interconnectors and offshore assets.

5.3. Market Design Evolution

Capacity Market: Transmission adequacy is a key input to capacity market auctions and security of supply assessments.
Ancillary Services Reform: New products and markets for inertia, stability, and voltage support.

6. Challenges and Risks

6.1. Investment and Delivery

Supply Chain Constraints: Delivering major projects on time and budget is increasingly challenging.
Permitting and Consents: Securing planning permission and community support for new infrastructure.

6.2. System Security and Resilience

Black Start and Restoration: Ensuring the system can recover from major outages.
Cybersecurity: Protecting critical infrastructure from cyber threats.

6.3. Market and Regulatory Uncertainty

Brexit and EU Relations: Ongoing evolution of trading arrangements and regulatory alignment.
Code Complexity: Navigating multiple codes and regulatory processes.

7. Opportunities and the Road Ahead

7.1. Net Zero Delivery

The transmission system is central to delivering net zero—integrating renewables, enabling flexibility, and supporting electrification.

7.2. Innovation and Digitalisation

Advanced analytics, automation, and digital twins will enable more dynamic, efficient, and resilient system operation.

7.3. International Leadership

The UK’s experience with offshore wind, interconnection, and whole-system planning is informing global best practice.

8. Lessons Learned

Coordination is Key: Success depends on integrated planning across onshore, offshore, and cross-border assets.
Flexibility and Resilience: The system must be both flexible and robust to manage new risks and opportunities.
Regulation Must Evolve: Agile, forward-looking regulation is essential to support innovation and investment.

Conclusion

The future of transmission in Great Britain is interconnected, offshore, and whole-system. Delivering on the promise of net zero will require unprecedented coordination, investment, and innovation. The journey is complex, but the rewards—a secure, flexible, and sustainable energy system—are within reach.

References: