Offshore wind export cable
The high voltage cable that links the offshore substation to the onshore grid. A single point of failure for the farm, it accounts by market estimates for most of the cost of offshore wind losses.
October 15, 2020, 4:54 pm, Irish Sea. Export circuit SSEC3 at Gwynt y Môr, a 576 MW farm off the coast of Wales, trips; testing places a single fault about 11 km from shore. The circuit carries 25% of the farm's transmission capacity, and the three other cables hold. The repair replaces kilometers of cable; the circuit comes back on March 7, 2021, sixteen days after the target date, then runs capped at 52.8% of its capacity until summer 2022 so as not to fail a second time. Ofgem later agrees to treat the outage as an event adjusting the transmission owner's revenue, by 9.17 million pounds for 2020-2021 before a 3 million deduction. The export cable is the cheapest item per megawatt and the most expensive in losses. Market estimates converge: DNV cites a figure of around 80% of offshore wind financial losses and claims tied to cables, and portfolios published by the market range from about half to three quarters of loss cost, depending on whether one counts claims or dollars. By count, turbines dominate. By cost, the cable wins, because it is a single point of failure: a farm with one export cable loses its entire output at the first break. Riffgat, in the German North Sea, stayed offline from November 2015 to spring 2016 after a short circuit on its cable. Causes split between installation (excess tension, bending radius, protection poorly fitted at the foundation entry), insufficient burial that leaves the cable exposed to anchors and trawlers, and manufacturing defects in joints. Repair time makes the loss: locate the fault, mobilize a cable ship, find spare cable and joints, wait for a weather window. Expect anything from a few weeks, when spares are in stock, to four or five months in winter. Business interruption is written with a deductible in days, and underwriters look first at whether a spares inventory and a pre-agreed repair contract exist.
Textbook case, in numbers. A 600 MW farm exports through two 300 MW cables. One breaks and stays out for 100 days. Lost output: 300 MW × 24 h × 100 days × 40% capacity factor = 288,000 MWh, at 90 euros/MWh, or 25.92 million euros. The business interruption policy has a 60-day deductible: it pays 40/100 × 25.92 = 10.368 million. The repair costs 15 million, physical damage deductible 1 million: 14 million. With a single 600 MW cable, the loss doubles to 51.84 million and the BI payment to 20.736 million.
export cable, subsea export cable, offshore export circuit, HV export cable
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