Evaluating HVAC Submarine Cables for Offshore Energy Transmission

The offshore energy sector is scaling fast, and every infrastructure decision carries weight. Developers, transmission system operators, and grid planners face one foundational question on each cable project: HVAC or HVDC? With the submarine power cable market worth roughly USD 20.79 billion in 2026, a misaligned choice carries serious financial and operational consequences.

HVDC dominates the headlines. The 580 km NordLink cable runs on HVDC, and the Xlinks Morocco–UK project required it across 1,400 km of seabed. For long-distance, high-capacity transmission, that choice is well established.

But most offshore projects do not operate at that scale. HVAC accounts for over 60% of the submarine power cable market by current type, a figure that reflects deliberate engineering logic. This article examines when HVAC is the correct choice for a submarine power cable project and where teams get the decision wrong.

Why HVAC Works—and Where It Starts to Fail

Technology selection begins with one physical constraint.

HVAC cables carry three-phase alternating current. They generate substantial capacitive reactive power that circulates without doing useful work. On land, engineers install compensation devices at intervals along the route. Offshore, that option disappears. Compensation can sit only at the cable ends, and its effect weakens as length increases.

Beyond roughly 50 km, reactive power consumes a growing share of the cable's rated capacity. By 80–100 km, utility-scale HVAC becomes hard to justify.

HVDC carries no reactive power. Every ampere of capacity delivers real, usable power at any distance. That single distinction drives the technology split for long-distance transmission.

Where HVAC Remains the Right Default

Within roughly 50 km of shore, HVAC is not a fallback. Where HVDC converter costs never pay back, it is often the stronger decision, for four reasons:

Lower converter costs. HVAC substations cost far less than HVDC converter stations. Below a certain power threshold, that difference never returns.
Technical maturity. The industry understands HVAC systems across the full lifecycle. The supply chain is proven at scale.
Grid compatibility. When both cable ends sit on the same AC grid, HVAC avoids the conversion losses HVDC introduces.
Established contractor base. HVAC installation draws on a broad, experienced pool of marine contractors.

The Crete–Peloponnese interconnection illustrates the point. Two parallel HVAC cables link Crete to mainland Greece across roughly 174 km. At moderate power volumes, lower converter costs justified the transmission losses.

The Factors That Should Drive the Decision

Distance is the first filter, not the only one. Teams that apply a single distance threshold miss factors that shift the crossover point.

Power Volume

A 50–100 MW island link at 30 km is a different decision from a 500 MW export cable at the same distance. HVDC converter costs are largely fixed, so smaller projects carry higher costs per megawatt. That often shifts the economics toward HVAC.

Grid Architecture at Both Ends

When the receiving grid already runs on AC, HVAC removes the need for conversion. Where the grids run at different frequencies, HVDC becomes necessary regardless of distance.

Reactive Power Compensation

Research at the EERA DeepWind Conference 2025 confirmed that mid-cable shunt reactors can extend the viable range of HVAC systems beyond 50 km. Routes that permit offshore compensation platforms improve power delivery over longer distances.

Installation Environment

HVAC offshore power cable designs carry greater mechanical stress in deepwater or high-current seabeds. In shallow coastal waters, teams manage this well. In complex deepwater routes, HVDC's lighter single-core construction offers real handling advantages.

Where the Industry Gets This Wrong

Two errors recur in project planning.

The first is defaulting to HVDC for reputational reasons. Some developers treat the specification as a signal of ambition, but that is not an engineering rationale. Below the thresholds where HVDC transmission pays back, it adds cost, lead time, and complexity for no benefit.

The second error runs the other way. Teams extend HVAC into lengths where reactive losses cut delivered capacity, then compensate at the ends alone. That has limited effect over longer routes, and the performance loss is foreseeable at design stage.

Both errors share one cause: the decision enters too late, after routing and procurement terms are locked. Reversing those assumptions costs time and capital. The technology choice must happen before corridor planning.

What Project Owners Should Be Asking

For any offshore project in early development, these questions determine the right technology:

What is the route distance from the offshore asset to the onshore connection point?
Does the total power justify HVDC converter cost recovery over the project lifetime?
Do both grid termination points sit on the same synchronous AC system?
How do seabed conditions constrain submarine power cable design and installation?

No single threshold resolves all of these. The decision is a system-level one, best made with teams who have run the same analysis on comparable projects.

Where This Conversation Is Happening in 2026

These questions do not get resolved in technical papers alone. Project teams, TSOs, manufacturers, and regulators work through them together at dedicated submarine event.

Leadvent Group's 6th Annual Submarine Power Cable and Interconnection Forum takes place on 18–19 November 2026 in London, United Kingdom. This submarine event gathers 150+ senior practitioners from the subsea cable sector. Confirmed speakers represent National Grid Interconnectors, TenneT, EirGrid, Baltic Cable, Elia, Equinor, and DNV Netherlands. The agenda covers HVDC transmission expansion, offshore wind integration, cross-border interconnectors, and the decisions behind every submarine power cable project.

This forum is where those conversations happen at senior level. If your work covers transmission decisions, cable routes, or offshore power cable asset management, it belongs in your calendar. Reserve your delegate pass now and join 150+ subsea cable professionals shaping offshore transmission's next phase.

Frequently Asked Questions

At what distance does HVAC become unsuitable for submarine power cable projects?

The practical limit for utility-scale transmission sits at roughly 50–70 km. Beyond 80 km, reactive power losses make HVAC uneconomical without mid-cable compensation. For lower power volumes it has operated further, such as the Crete–Peloponnese interconnection at roughly 174 km.

Why does HVAC hold the majority share of the submarine power cable market?

Most offshore connections fall within the distance and power range where HVAC delivers better cost and performance, including nearshore wind export cables and island interconnections. HVDC leads at the long-distance end, but most projects globally do not reach that threshold.

What are the risks of specifying HVDC for a project that does not need it?

The main risk is capital spent on converter stations that never pay back at shorter distances. Teams also face longer lead times, greater maintenance complexity, and reduced contractor flexibility. Below 50 km at moderate power, HVDC often adds cost and risk with no benefit.

How is mid-cable reactive compensation changing the HVAC distance limit?

Mid-cable shunt reactors sit at intervals along the route rather than only at the ends. This extends the viable range of HVAC systems beyond the conventional 50 km threshold, delivering better active power over longer submarine power cable distances. The approach is an active area of development in 2026.

Previous Next