After the first drillings towards the Tata Steel site, contractor NRG turned the electric drilling machine in sculpture park ‘Een Zee van Staal’ 180 degrees for the drilling under the dunes. An electric drill has also been placed on the ‘sand castle’ on Velsen beach. In the coming weeks, both machines will drill towards each other at a depth of about 30 metres to connect the Hollandse Kust offshore wind farm (west Beta).
In recent months, contractor NRG has built a temporarily elevated working area on the beach of Velsen for the two drillings under the dunes.
“With this ‘sand castle’ we eliminate the height difference on either side of the dunes,” says project leader Johannes Becker on behalf of contractor NRG. “This way we prevent the drilling fluid, which we use to keep the boreholes open, from running out again at the lowest point. After we have drilled a hole, we pull an empty plastic casing pipe into the hole where TenneT’s electricity cables will soon be laid.”
This is not the first time NRG has performed this technical feat. Many people from Wijk aan Zee and Heemskerk undoubtedly remember the double-sized sand castle at the Noorderbad pavilion in Heemskerk. Drilling occurred four times under the dunes here to land the sea cables for the Hollandse Kust Noord and ‘West Alpha’ wind farms.
Becker: “This time only involves two drillings, so the sand castle is smaller in size.”
‘Socket at sea’
TenneT will install a ‘socket at sea’ next year 50 kilometres off the coast of Egmond aan Zee. The wind turbines that energy company RWE will have built at sea in 2025 will then be connected to this. To bring that power ashore at Velsen from 2026, contractor NBOS (combination Boskalis + Orient Cable) will install two electricity cables in the seabed next year. Behind the dunes, these sea cables are connected underground with ‘large crown stones’ in so-called socket pits to the cables on land.
Contractor NRG is making six boreholes to connect ‘west Beta’. Two under the dunes and four on land for the electricity cables that bring the power to the transformer station in Wijk aan Zee. From the transformer station, TenneT has had the cables for ‘west Beta’ laid at the same time as those for ‘north’ and ‘west Alpha’ in 2021/2022, up to the high-voltage substation along the A9 near Beverwijk. There, TenneT will eventually feed the power into the national electricity grid, making the power available to households, companies and industry.
NRG uses the intersect method for drilling under the dunes.
Becker: “To do this, we drill from the beach and the work site in the Sculpture Park towards each other in a GPS-controlled manner. The drill heads will, therefore, meet each other halfway at a depth of about thirty metres in the seabed. The advantage of intersect drilling is keeping the fluid pressure in the borehole as low as possible. From experience with previous drilling on the beach of Heemskerk, we know that the sand package in which we work provides good counter pressure.”
Companies, governments, social organisations, interest groups and people have worked together to build wind farms on the Dutch North Sea coast in recent years. We achieved our 2023 ambitions on time, within budget and almost without subsidy: more than 4.5 GW of offshore wind energy, so no subsidy is required anymore for the construction of the wind farms. The offshore wind farms provide 15.8% of the current electricity supply for companies and people at home. That is more than we agreed 10 years ago in the Dutch Energy Agreement. And that is a great achievement. Thanks to the successful approach to offshore wind, we can even accelerate in the coming years so that offshore wind energy can supply 16% of clean energy without subsidies in 2030.
Image source: Courtesy of TenneT
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