Green Technology: Wind energy gets serial

The Engineer
April 30, 2012

Offshore options: there are four main types of wind turbine foundations — monopile, jacket, tripile and gravity base.

Solid foundations: onshore assembly could enable serial production of offshore wind turbines

When Germany announced that it was effectively turning its back on nuclear power by mothballing all of its reactors by 2022, there were more than a few surprised faces and some awkward questions.

How exactly did the country think it was going to meet its energy needs? Surely it would have to import considerable amounts from neighbouring France, thereby subscribing to nuclear by proxy.

The answer was perhaps even more surprising. On 1 January this year, the German parliament enshrined into law an act requiring that by 2020 35 per cent of all of its energy needs must be provided by renewable sources, followed by 50 per cent by 2030 and 80 per cent by 2050 — far more ambitious in scope and magnitude than the European Union’s target of 20 per cent by 2020.

Germany was already making good progress in the sector, particularly with offshore wind and geothermal energy. There are currently eight operational offshore wind farms, generating around 200MW. To meet the first set of 2020 targets, though, calls for upwards of 10GW.

Clearly there needs to be a complete step-change in production; a few parks going up here and there every decade or so simply won’t cut it.

Europe’s largest construction company, the Austro-German group Strabag, started dabbling in the offshore wind business around 10 years ago, focusing on its existing strengths of production, transport and installation. It also began experimenting with new designs for base foundations, believing that this was a key limiting factor the overall production chain in offshore wind.

Essentially there are around four main types of wind turbine foundations in use(image above). 

When turbines took their first tentative steps from land into the shallow waters just off the coast, they generally employed monopile foundations — a simple design in which the wind tower is supported by a steel pipe, either directly or through a transition piece.

Depending on the subsurface conditions, the pile is typically driven into the seabed by either large impact or vibratory hammers, or the piles are grounded into the sockets drilled into rock. They are reasonably cost effective but not suited to water depths of more than 15m and they struggle to hold turbines greater than 2-3MW.

To handle some of the latest generation of 5-10MW wind turbines, moored in greater water depths many miles off the shore, requires a bit more support. Jacket foundations consist of a frame construction similar to an electricity pylon. It is technology essentially borrowed straight from the oil industry.To read more click here...