Hywind floating wind turbine

Deep water wind turbines

A new floating wind turbine promises to slash industry costs.

In 2008, the world saw its first floating wind turbine. Rated at a modest 80kW, the two-bladed turbine, developed by Blue H of The Netherlands, was moored in 113m-deep water some 21km off the coast of Italy.

A year later, Hywind was towed 10km off the coast of Norway, into the North Sea. Standing in 220m-deep waters, the 2.3MW turbine, constructed by energy giant Siemens and owned by Norwegian oil and gas business Statoil, is still generating electricity for the Norwegian grid. But while such structures have demonstrated this technology to be viable, at what cost?

'Right now the industry is into proving that floating wind turbines are possible, but for me that's not enough,' says Dominique Roddier, chief technology officer at US-based renewable energy developer Principle Power. 'Hywind was the first project and it cost $75m. If we prove it's possible at this price have we helped or hurt the industry?'

The company is one of several developing floating foundations for wind turbines to be sited in water depths of more than 50m. These structures, typically based on oil and gas platform designs, are tethered to the seabed, rather than fixed like the pile-driven monopile or concrete and steel base foundations used in shallower water turbines.

Principle Power's WindFloat is a three-legged floating foundation designed to accommodate any 5MW, or larger, turbine. Currently being built in collaboration with electricity operator Energias de Portugal, the platform prototype should be afloat off Portugese shores by the end of summer 2012.

Roddier is certain a transition to deeper waters is inevitable for offshore wind generation, mainly because the potential energy resource is huge. Calculations from the UK-based Public Interest Research Centre, a government and industrial collaboration including The Department for Energy and Climate Change, E.ON, Dong Energy and other businesses, indicate the maximum practical UK offshore renewable resource to be 2,131TWh. A phenomenal 1,533TWh could come from floating offshore wind.

What's more, floating wind turbines could open up offshore wind energy resources to nations that don't have the shallow water seabed conditions crucial to conventional, fixed offshore wind generation. Japan, for one, has a large number of coastal cities with high electricity demand, but deep-water seabeds make conventional offshore wind generation difficult. And as Roddier points out, France has very few shallow water sites, Portugal has none, and US sites tend to be too close for comfort for onshore residents.

'These [nations] have no options other than floating technology,' he says. 'But businesses really do have to think about costs. When we move from the demonstration stage to the pre-commercial stage, the banks will look very carefully at what we are doing. If [a project] is too expensive the entire industry suffers.'

With WindFloat, Roddier and colleagues are adapting a strategy akin to past oil and gas platform designs, that is, to minimise costs across the whole life of the project. As a result, the Portugal project should cost between $20 to $30m, less than half the cost of HyWind.

Floating wind costs

According to Roddier, the first cost-cutting step has been to design WindFloat as small as possible, while ensuring the platform will keep a turbine tower vertical and survive in bad weather. To this end, a horizontal plate at the foot of each column enhances stability. Meanwhile, a 'fail-safe trim optimisation system' pumps small volumes of water from one column to the next, depending on wind direction, in effect counter-balancing the platform. The mooring system will use between four and six conventional chain and polyester lines, again to keep costs down.

As well as minimising costs, industry issues, from steel shortages to inadequate manufacturing facilities, must be addressed. While many in the offshore wind industry are confident that manufacturers will be swift to respond to market opportunities, importantly, Roddier believes the floating wind industry is ready to innovate.

For example, in the case of WindFloat, floating turbine fabrication can take place at the quayside, avoiding the huge costs of placing the tower and turbine onto a floating platform in open water. As Roddier points out, today's offshore wind projects have to use installation vessels, which cost around £150,000 a day, to drive foundation piles into the sea. Because his floating turbine has been designed for quayside assembly, the platforms can be fully-tested before leaving the harbour, reducing operations and costs.

Roddier is also confident the quay-side manufacturing infrastructure exists. 'Shipyards are all over the world. You have to adapt your floating turbine design to the location where you are going to build, which means you must have an idea of where you are going to fabricate,' he says. 'It's a question of being flexible... but we also have a lot of room for innovation.'

Future of turbines

And once commercial viability has been demonstrated, the innovation will only continue. According to Roddier, while the first floating wind farm will have three-bladed turbines, future installations may have more novel configurations.

'Banks don't want to take any risks with relatively new technologies. You know, someone with a two-bladed turbine is going to have a difficult time raising money,' he explains. 'But once banks are convinced it is economical, then you can start looking at innovations that will reduce cost. It will make sense to bring in two-bladed or vertical-axis turbines as they are cheaper and more economic.'

In this vein, Roddier and his team have also been working on adapting the WindFloat platform to accommodate wave energy generation. Outlandish, yes, but as Roddier points out, the project has already received $750,000 from the US Department of Energy and could prove economical, given the wave generator would share electrical cabling and mooring with existing floating wind turbines.

'We've been looking at several wave devices that we could fit to increase the power generated [at a platform],' he explains. 'Our funders have said yes, it's a great idea if you can do it. However, it is very adventurous at this point and not ready for commercial use. Would I try to sell it to an investor today? Absolutely not.'

But while add-on wave generators may be a little too adventurous for your careful lender, recent developments indicate investors are buying into floating wind turbines. After successfully decommissioning its first floating turbine, Blue H now plans to build a 90MW floating wind farm at the same location, and Statoil is in discussions with the governor of Maine, US, and Scottish Development International to site wind farms in US and Scottish waters.

Given WindFloat is expected to plug into the grid by summer 2012, with a handful of other projects following by 2014, will we see the first floating wind farm soon? 'Yes, you will probably see the first farm by 2016,' predicts Roddier. 'Floating wind turbines are not going to go away.'

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