OFFSHORE WIND Ӏ RENEWABLES
FLOATING FARMS Mediterranean tides are much less problematic than North Sea ones. They average only around half-a-metre, one-eighth of the range at Nigg, which means that on-loading windfarm components by SPTM remains a sensible option. Provence Grand Large offshore windfarm, off the coast of Marseille, is France’s first pilot floating wind farm. Southern France has a very
narrow continental shelf, which limits the potential for farms on the seabed. Instead, Provence Grand Large will have three 8.4 MW wind turbines from Siemens Gamesa erected on innovative pyramid- shaped floating foundations; they are anchored by tensioned mooring lines which do not disturb the seabed or its ecology. Their footprint on the maritime domain is reduced to a few dozen metres compared with several hundred for existing technologies. The first phase of the project, the onshore lifting of components for assembly, has been completed; the second phase, the weighing and load-out of the three floating foundations onto the outgoing barge, began in March this year (2023) by Sarens. Each floating foundation weighed around 2800 tonnes and was 45m high and 70m
The load stabilising system from Huisman and Siemens Gamesa; the small red tuggers on the boom are preventing horizontal rotation
wide. Each had to be weighed then transported to, and positioned on, a semi-submersible barge. For the weighing Sarens used nine 500 tonne load cells, the same number of hydraulic jacks, three hydraulic power packs, and a weighing interface.
The load-out took place in June
and involved two trains of K24ST SPMTs; six powerpacks – four in use, two as spares; two six-axle SPMTs for auxiliary works; and four 30-metre MB1500x1000 modular beams. The foundations were
transported by the two SPMT trains a distance of 50 to 150 metres to the quay wall. Crews worked in two shifts to keep up with the vessel float-off operation and finally loaded out the floating foundations onto the barge. Provence Grand Large is a pilot
project intended to demonstrate that offshore floating windfarms can become economically viable and is France’s first ‘pre- commercial’ floating offshore wind farm. It is scheduled to begin producing power at the end of this year.
PRECISION ALIGNMENT Construction of windfarms is not complete when the towers and nacelles are erected. The blades
still need to be attached and this can be one of the most delicate and difficult parts of the operation. It has to be done on-site – which is generally windy and blades, of course, are of a shape that is designed specifically to catch the wind. Controlling these monsters – they can be 100m long and more – at great height, and aligning them with absolute precision so that the fastening bolts can be secured, is no task for the fainthearted. Huisman and Siemens Gamesa
have combined their expertise to develop a solution. It is especially intended for blades but can also be used for nacelles and tower segments. Its Travelling Load Stabilising system can be applied universally, it claims, on heavy lifting cranes to stabilise wind turbine components during installation. It consists of a combination of
two pairs of tuggers working in unison to control the load. One pair, fitted to independent trolleys, can travel along integrated rails – with one set on each side of the crane’s stiff boom. The trolleys are thus separated by the width of the boom. Lines from them run to separate positions on the load and keep it from rotating in the horizontal plane. They automatically follow the crane’s main block to stay level with the load.
The second pair of tugger lines is
deployed from the crane tip – again one from either side of it, so again separated by the width of the boom. Their tugger lines provide a vertical force, perpendicular to the first pair of tuggers, and keep the load steady in that plane. By approaching the load from two different directions the system provides significantly more control than a conventional single pair of tuggers. The tuggers are always at the optimal elevation and the boom
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