'Hardening risk' as lenders and insurers fret over floating wind's dynamic cables

The floating wind industry must fill important technology gaps associated with dynamic umbilical cables if it is to mitigate the risks now pushing up financing and insurance costs, according to a study by the World Forum Offshore Wind (WFO).

In one of its periodic appraisals of issues that could slow commercial scale deployment of floating wind, WFO's floating wind committee (FOWC), published a White Paper covering design and risk assessment for dynamic cables on floating wind projects.

The report noted growing levels of lender and insurer scrutiny toward a category of hardware seen as critical for sustaining revenue and asset value, with dynamic cable failure and resulting downtime seen as a potential cause of expensive claims.

The White Paper identified design optimisation of dynamic inter-array and export cables for floating offshore wind as areas where technology advancements are needed, alongside another parallel call for achieving higher voltages of inter-array and export cables.

'Demystifying' dynamics

The WFOC’s sub-committee for cables and substations was tasked with researching design and risk assessment and ‘demystifying’ issues from design to installation.

Its report said the sector must also demonstrate effective risk mitigation in the design, manufacture and installation of subsea cables, even where standards “may not yet include higher voltage brackets and floating wind specifications”.

“Insurers are particularly concerned with the technology readiness of cable systems given the consequence of cable failure, as well as a history of issues at various bottom-fixed wind farms,” the White Paper stated.

"These consequences can easily stretch to millions of euros in damage repairs for a single cable in addition to the lost revenue caused by wind farm’s unavailability.”

FWO said the impacts in coverage costs are already being felt on floating wind technologies, including the dynamic sections of export inter-array cables, which are facing exclusion of coverage for defective parts, known in the insurance industry, as LEG 1, because they are treated as not fully qualified.

The London Engineering Group (LEG), a traditional consultative body for insurance classes, produces coverage clauses which vary in their exclusions with respect to engineering risks, ranging from the lowest coverage for loss or damage due to design defects (LEG 1) to higher and highest (LEG 2&3).

"This means that costs for losses due to defect. including the related loss of revenue will remain with the project. As such, it is recommended to developers that they request a cable/accessory/connector design which is suitable for a cost-efficient and fast repair or replacement," the report stated.

Daisy chains

Another aspect of floating wind farm design under growing scrutiny is the prevailing daisy chain configuration linking turbines along a cable and ending with a connection to the grid, usually via a substation and/or an export cable.

"Failures at the inter-array cable on the end of the daisy chain that is adjacent to the export cable, the export cable itself or the substation, have higher impacts on business interruption," the White Paper warned.

“This layout implies operational risk; a fault at one FOWT can affect the whole array, causing significant downtime and putting the other FOWTs at risk depending on the return path and sizing,” it continued.

The report also highlights incremental risks posed by a tow-to-port repair strategy that could require cables to be stored either on the seabed or on a temporary buoy.

Insurers' submissions for the study called for more redundancy and easy replaceability of the systems, for example, if possible by using multiple, smaller cables.

This is especially important if substations are being used as singular connection points for multiple renewable energy projects (such as wind, wave and tidal), the White Paper argued.

Fixed and hanging

The FOWC pointed out that a short section of cable at the exit of a fixed-bottom turbine or substation is exposed to the water column and subject to loads.

This portion is customarily equipped with a multi-component cable protection system (CPS) to provide protection against the forces that can lead to mechanical overbending, but the FOWC noted that in the last couple of years, CPS issues affected up to ten fixed offshore wind farms, contributing to a hardening insurance market.

As things stand, they argue that floating wind standards could further reflect the criticality of these parts by requiring certain technology readiness levels or designating higher consequence classes in these categories.

“The downtime risk to the other FOWTs is high. An onsite repair concept could reduce the necessity of a quick connection-disconnection system,” the White Paper explained.

The FOWC study suggested that other types of global cable layouts such as fishbone and star could provide more redundancy and flexibility, and reduce the number of cables, but noted that the technology for subsea hubs and connectors is still being developed.

“The industry is currently estimating where subsea connectors make sense for floating wind given their current cost and early technology development status,” the report stated.

FOWC also referred to a UK study by the ORE Catapult innovation and research centre for offshore renewable energy, which concluded that cable failures already make up 75-80% of offshore wind insurance claims in that country, while only making up 5-10% of the original project cost, even before the promised growth in floating wind.

In the UK, the study found that the average downtime for a bottom-fixed wind farm inter-array cable repair is approximately 40 days and for an export cable approximately 60 days.

'Lazy wave'

In floating offshore wind, however, the dynamic sections of the cables are longer and they hang in the water column from the floater or floating substation, typically in a 'lazy wave' shape.

Ancillaries help maintain the cable shape in the water column and protect the connection points from overload and fatigue. Such equipment consists of bend stiffeners, buoyancy and ballast modules, tether and anchor systems, touch down and abrasion protection and bend restrictors.

Although such technologies are fully mature in the oil and gas industry, a perceived gap in for floating wind already seems to be pushing up costs, FOWC said, with “developers now facing a hardening market with a tightening of terms and conditions, limitations of cover, shrinking capacity for challenging placements and increasing rates for floating offshore wind”.

Reviewing floating wind cable specifications, along with risks and mitigation measures, the FOWC homed in on dynamic export cable standards and wet connector technology as two areas of technology in need of development, and advocated a holistic approach to engineering and integrity management.

The White Paper advocated a holistic engineering approach that integrates designs of topsides, station-keeping and mooring systems with overall dynamic cable design and maintenance solutions.

It added that the industry "would greatly benefit from specific dynamic cable standards and load classes for offshore wind" and added that this should include requirements to test at higher temperatures than already recommended to know how insulation systems are affected, as well as additional studies to evaluate the feasibility of scaling existing products to larger cross-sections, ensuring that the metallic barriers can experience bending without fatigue or breakage.

More rigorous standards and testing for ancillaries was also recommended, with a note on adapting equipment to shallower waters, where the there may no longer needs to accommodate the strain caused by the internal pressure of flexible pipes.

This logic was also applied to the location of floating wind hulls in much shallower water than is the case in the oil industry, producing a response to waves that affects a larger percentage of the cable’s length than is the case in much deeper water.

"Other issues surrounding mid- to deep-water environments will be uncovered as the technology matures and new projects get built in deeper sites," the report noted.

"The need for longer cable lengths, withstanding pressure, the influence of sagging and more complex installation processes are some of the foreseeable challenges."