Lillgrund

Lillgrund is a compact offshore wind farm in the Öresund strait off Malmö, Sweden, and for its time represented Sweden’s largest operational offshore wind deployment. Developed and wholly owned by Vattenfall, the project was delivered as a pilot-scale, developer-led installation to gain operational experience with offshore grids, foundations and dense turbine layouts in shallow water. Its compact layout and central round offshore transformer platform made Lillgrund an early testbed for array electrical design and farm-scale wake management. Construction exposed practical lessons: geotechnical work identified localized boulders and required extra excavation for some foundations, and winter weather and a cable-lay vessel failure complicated the export and inter-array cable works. Post-award electrical studies and commissioning revealed design issues that required remediation — for example a main transformer insulation level that needed attention, the fitment of surge arresters on turbines, and transient phenomena on the onshore 130 kV breaker during energisation — lessons that informed later projects. The farm’s offshore substation and export cable were permanently integrated into the developer’s solution and tied into the onshore Bunkeflo substation, reflecting a conventional Swedish grid-connection model rather than a merchant/auction transfer. Since commissioning in the late-2007/early-2008 period Lillgrund has provided long-term operational data used in wake, control and ecological studies, and remains a reference project for early offshore experience in the Baltic/Öresund region.