Hope Floats  

Renewable Energy World has a look at some developments in the world of floating offshore wind power - one of the final frontiers for renewable energy - "Floating offshore wind opens up the deep".

The development of floating offshore wind turbines presents a number of advantages over more conventional foundations, not least of which is the opportunity to exploit wind resources far offshore in deep water.

Until recently a typical state-of-the-art solution for securing offshore wind turbines was to place them on special foundations, which are either lowered onto a permanent position on the sea floor or rammed into the seabed. However, in addition to improving existing offshore foundation solutions and introducing new permanent foundation concepts, several innovative solutions are under development that are based on floating wind turbine foundation systems.

Advocates of floating wind turbine concepts point to a series of disadvantages with conventional offshore wind installations that feature a permanent seabed foundation, which do not affect their more mobile counterparts. These include demanding commissioning, service and repair, and retrofit operations that all have to be carried out offshore. These can be vulnerable to bad weather in conditions characterized by poor installation accessibility. Working offshore also implies high costs for installation upkeep, not least due to demanding sea travel and open sea transfers.

Another key issue is the substantial risk of extended installation downtime during high winds. Under these conditions dynamic turbine loads are at maximum, yields most favourable, and simultaneously the implications of a breakdown most severe due to difficult turbine access. ...

A joint co-operation agreement between power engineering giant Siemens Wind Power and energy company Hydro of Norway aims to develop a floating wind turbine. Based on Hydro’s Hywind concept the partners envisage a floating demonstration turbine offshore in 2009 near Karmøy, an island off the south-west coast of Norway for which Hydro has a licence. Siemens is to deliver the wind turbine for the proposed demonstration unit. while Hydro will apply its offshore platform expertise.

Hydro expects to apply the technology in future on sites located 90–180 km offshore and in water depths of up to 700 metres. Hydro’s design concept is similar to its technology used in oil rigs, which comprises a long, submerged floating concrete cylinder that is ballasted. However, this prominent feature makes the design unsuitable for shallower waters.

Marine engineering consultancy firm Sea of Solutions BV is based in the Netherlands and was founded in 2001. Key activities are the development of dedicated projects and products for operators, contractors and ship owners in the fields of marine exploration, construction and maritime transport. One of its latest products is a new offshore wind turbine foundation concept named the Floating to Fixed Wind Energy Concept (F2F). During the design stage, Sea of Solutions limited itself to a common North Sea water depth of about 25 metres for the initial market focus, but the design, best described as a ‘hybrid type foundation’ can be extended to deeper waters. ...

WindSea

Norwegian engineering consultancy company Force Technology has over three decades experience in the design and maintenance of offshore structures and has gained extensive additional know-how in related fields like wind and sea wave topics and marine corrosion protection. Now, the company has developed a new patent-pending offshore wind technology. Known as the WindSea, this unmanned floating structure is self-orientating towards the wind and, the company says, has been designed with a dual focus on excellent dynamic response to wave and wind, along with safety and reliability.

The initial structure is calculated to accommodate three wind turbines of 3.2 MW each, but the WindSea concept is scaleable to 5 MW and substantially bigger in future, says company spokesperson Hans Jørgen Mikkelsen. ‘The WindSea lattice-type welded steel foundation structure features a 23 metre draught and towers founded on a structure 17 metres above sea level. One very important design criterion with regards to minimizing the materials fatigue of structural components due to cyclic loading, was stability. The WindSea deflection under normal operational conditions could be limited to one degree only. But even under a 100-year storm extreme load situation, the maximum deflection is less than 4.5o, and this is a condition when the turbines will be shut off anyway,’ says Mikkelsen. ...

Blue H Technology

Netherlands-based industry newcomer Blue H Technology has developed a floating turbine system that, from a conceptual point of view, is rather different from existing solutions. In early February the company’s Chief Executive Neal Bastick said: ‘Blue H is now in the process of installing the world’s first deep-water floating prototype wind turbine. The test location is at 19.6 km off the southern Italian cost at a so-called Tricase site near Puglia, where the water depth is 108 metres.’

The prototype was built in Italy at a shipyard in the city of Brindisi. It is equipped with an 80 kW two-blade variable-speed WES18 mk1 wind turbine, supplied by Wind Energy Solutions (WES) of the Netherlands. Founded in 2003, WES specializes in small to medium-sized variable speed turbines rated from 2.5–250 kW, wind technology it acquired from the bankrupt former Lagerwey.