Interview by Rikki Stancich

A group of Texan oil rig engineers have come together to develop a novel offshore wind turbine foundation solution, the Titan Wind Turbine Platform, designed for mid-depth waters. The idea is straightforward: a three-legged jack-up foundation that floats to site with the turbine pre-installed at the harbour.

The Y-shaped hull is designed to provide sufficient righting arm for stability, allowing it to be transported in high seas. Flotation compartments at each leg of the hull provide stability during transportation to site. Trusses near the center of the platform connect the buoyancy compartments and support the wind turbine.

After transporting the platform to the desired location, the footings are flooded and the legs are lowered to the sea floor. The platform is then raised a few feet above the water surface and the preload tanks are filled with water.

Preloading the footings provides a vertical force greater than any load generated by wind on the platform and wind turbine, waves and current. The footings are spread apart to stabilize the platform and keep it from overturning during high wind, wave, and current episodes.

When the footings have been preloaded, ‘fins’ on the bottom of the footings are immersed into the sea floor to prevent the platform from moving laterally. Having preloaded the footings, the platform is raised, elevating the bottom of the hull above wave height.

A key advantage of the Titan Wind Turbine Platform is that it is transportable. If the wind turbine requires major repairs, the legs of the platform are raised and the platform towed to a dock or repair yard, eliminating the need for costly crane barges to carry out repairs at sea.

Wind Energy Update speaks to Colin Hardy, Offshore Wind Power Systems of Texas, to learn why he thinks the Titan Wind Turbine Platform is the only viable solution for Round 3 wind farms.

Wind Energy Update: Titan has developed a new gravity-base /jack-up rig foundation for offshore turbines. What are the major advantages of using a jack-up style foundation?

Colin Hardy: If you want to put a 5MW turbine in and sleep at night, a jack-up is the way forward, nothing beats a jack-up.  With jack-up barges you can control the height, and they are jacked up above the waves, so the waves are not beating against the tower.

As far as the oil industry is concerned, ‘monopile’ doesn’t come into their vocabulary - they would just never use them. The oil industry knows that putting in a fixed platform of any type is a big headache. Monopiles need to be perpendicular, so if they go ‘off beam’, you’ve got a big, expensive problem. Fatigue from current and waves sets in pretty quickly and a lot of monopiles are already breaking up due to problems with the grout and tilting.

The great thing about jack-ups is that if there is a huge storm you can get them back up on the perpendicular again pretty quickly, or you can just tow them back into port for repair and redeployment. Jack-up rigs can also go into just about any ocean floor.

The Titan 200 is a variation of a jack-up barge, designed to go 250 feet, which covers a big percentage of Round 3 water depths. It has been designed by engineers who have worked on these systems offshore for years.  

An important point is that the oil industry never does anything offshore – everything is done on land and then floated out when you get the weather window.

Wind Energy Update: The turbine is floated to site on the platform of the foundation, which is designed as a hull. What design features enable the stability required to float the upright turbine to site?

Colin Hardy: It has been designed to American Bureau of Shipping (ABS) requirements. The engineers that designed the Titan 200 have been building spars and platform buoys and the likes for years. They have won OTC (Offshore Technology Conference) awards for their patents and ideas. Our team of engineers is comprised of some of the best in the [offshore oil and gas] industry.

The floating hull-shape was designed for the maximum strength of the turbine. It acts like a barge, and is towed by tugboat to the area where it will be installed. The platform is like an individual ship – it can be positioned accurately before the legs go in. The technology is proven  - there are already hundreds of these jack-ups in the Gulf of Mexico and the North Sea.

This is a great opportunity for technology transfer from the offshore oil and gas industry to the offshore wind industry.  

Wind Energy Update: A key advantage is that the platforms are designed to be mobile to facilitate O&M and repairs, which eliminates the need for expensive crane barges. What other cost advantages does it offer?

Colin Hardy: There are so many advantages, as you are dealing with individual mobile units, not ship dependent, that can be optimally installed in just about any sea bed, without any prior sea bed preparations, not requiring a flat sea bed, working just as well on uneven sea beds, (a big headache for any offshore fixed platform installation, needing large piles and expensive/extensive ROV work ).

Another key benefit is that the decomissioning costs after 25 years are minimal compared to other methods, and the systems do no damage to the sea bed at all, because large amounts of concrete and piling are not needed.

Additionally, the economics are a lot better because you don’t have the heavy lift vessel hire costs, and their cost escalation due to delays and weather problems etc. You know up-front what the units will cost, which is a major advantage in view of all the cost-overruns we are seeing on offshore wind farms at present.

Each turbine foundation platform is an individual unit, with steel legs and a steel hull, forming the strongest foundation available. The commodities used for the foundation platforms themselves will come from low-cost producers (given that US and European steel prices are so high), but the assembly of the foundation platforms would take place locally. So the parts ‘kits’ would be manufactured in a lower cost country and shipped to location for onsite assembly and array deployment.

The transport vessel would offload the hulls and the platforms would then be assembled with the legs, towers and turbine. You’re assembling onshore in perfect conditions, so everything can be done to the highest standard.

Wind Energy Update: Have you identified any UK port locations that have the requisite facilities? How many ports exist today that could handle this level of quayside assembly?

Colin Hardy: There are several options. We are looking at Dundee, Grimsby/Humberside and Leith, but ultimately it will depend on the developers that we work with. The industry is pushing hard to get upgrades to UK port facilities, so this shouldn’t be a problem.

Wind Energy Update: How long does it take to install a Titan 200 and what size turbines are they designed to support?

Colin Hardy: It takes two days to install, based on our experience with other rigs. The Titan 200 is designed for 3.6MW – 5MW turbines, but they can be designed for just about any size, the bigger the better in fact.

Wind Energy Update: How much does each unit cost?

Colin Hardy: The prototype will cost around US$10-12 million, so we are looking at around US$4-5million for the installation of mass-produced units. Which is very competitive compared to a monopile, especially when you add in the costs of ships, piling, concrete, divers, and constraints presented by uneven sea floors etc.

Wind Energy Update: Have any Titan 200 foundations been deployed to date? If not, are we likely to see any Titan foundations in UK waters any time soon?

Colin Hardy: We haven’t built one yet, but are planning do so with interested parties in Corpus Christi (Texas) and also in the Mediterranean. GDF Suez has shown an interest for the future in the Titan 200, as they move from shallow coastal water to deeper waters further from shore.

Our main focus now is in the UK’s Round 3, and we have ongoing discussions with a number of Developers/contractors there.

To respond to this article, please write to the editor:

Rikki Stancich: rstancich@gmail.com

Image courtesy of Offshore Wind Power Systems of Texas