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NEW GENERATION JACK-UPVESSEL makes installing offshore wind farms more efficientAs interest in windpower as a future source of energy grows, attention is turning to investments in offshore wind farms. Wärtsilä and Aker Solutions have combined their expertise to develop an offshore wind farm installation vessel which offers unique technical features and maximum levels of cost efficiency. The result of the cooperation is the High Performance Turbine Installation Vessel (HPTIV).

TEXT: HARRIET ÖSTER ILLUSTRATION: WÄRTSILÄ

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The High Performance Turbine Installation Ves-

sel (HPTIV) is a customised design which offers a

highly efficient route to the construction of offshore

windpower facilities. Equipped with jack-up legs,

HPTIVs are designed to carry out installation work in waters

of shallow to medium depth. Their construction allows them

to withstand the rough environments which often occur in the

seas of northern Europe.

Wärtsilä will be providing the HPTIV with vessel design,

electrical power generation equipment, propulsion machin-

ery and high-end automation. Aker Solutions, an international

oil and gas services company, is supplying a hydraulic jacking

system which incorporates the company's own novel techni-

cal solution.

The new vessel concept fulfils industry requirements for a

large deck space, adequate crane capacity, all-year-round and

all-weather operational capabilities and cost-efficient operat-

ing systems. As the three 6-cylinder in-line Wärtsilä 34DF and

two 9-cylinder in-line Wärtsilä 20DF dual-fuel engines which

provide the vessel’s main and auxiliary power operate on lique-

fied natural gas (LNG) with low levels of emissions, the HPTIV

will be capable of operating in IMO emission control areas.

HPTIVs will be marketed as a complete package. Wärt-

silä and Aker Solutions will also offer 24/7 global support for

repairs, maintenance and component supply.

WÄRTSILÄ AND AKER SOLUTIONS ARE WELL-KNOWN IN THE NORTH SEA

"Combining Wärtsilä's vessel design expertise and Aker Solu-

tions’ unique jacking system has resulted in an environmentally

sound concept for a complete vessel solution with new features

that are not on offer elsewhere," says Henning von Wedel, Sen-

ior Mechanical Engineer, Wärtsilä Ship Design in Germany.

In recent years, Wärtsilä has developed two different designs

for offshore wind farm installation vessels, and vessels of these

types are under construction at shipyards in Poland and South

Korea. The new HPTIV co-operative venture with Aker Solu-

tions which was announced at the end of March 2011 has

attracted considerable attention.

"We are already engaged in intensive dialogue with some

potential customers for this new generation of installation ves-

sels,” says von Wedel. “The HPTIV concept has been much wel-

comed, especially by oil and gas companies who have an inter-

est in offshore wind farms and operations in the North Sea.

Both Aker Solutions and Wärtsilä are well known as reliable

suppliers who provide extensive, in-depth support at all levels."

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Its design allows the HPTIV to withstand the rough environments which often occur in the seas of northern Europe. [Below]

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ROBUST CONSTRUCTION FOR ROUGH SEA CONDITIONSOffshore wind farms located in northern Europe tend to be built in water that is 50 metres deep or less. The HPTIV will be able to operate in water depths ranging from 4.5 to 50 metres.

The new vessel is designed to withstand the rough conditions in the North Sea at all times of the year. Both the leg design and the jacking system are strong and robust. Jacking can be performed when the significant wave height is 2.5 metres. Installation work using the crane can be performed in wind speeds of up to 15 metres/sec and when the significant wave height is 5 metres.

During pre-positioning and jacking operations, tidal currents can be up to 3.5 knots. The heavy lift machinery functions in wind speeds of up to 18 metres/sec. Really rough weather can force operations to be suspended, but the jack-up vessel can survive gale-force winds of up to 36 metres/sec and seas with a significant wave height of up to 10 metres.

In spite of its robust construction, the HPTIV is a relatively lightweight unit with a distributed load, i.e. it has an optimised strength/weight ratio. The payload is 5150 tonnes. The 3300 m² of deck space equals that available on a much larger vessel, and as the crane moves along rails, the whole of the deck area can be used for cargo.

EFFICIENT AND ENERGY-SAVING ONBOARD SYSTEMS

The HPTIV is equipped with integrated power management and automation functions, allowing crew numbers - and the time required to complete operational tasks - to be minimised. As well as reducing operational costs, this makes installation operations safer and more efficient.

Regulations regarding emissions in the North Sea, the Baltic Sea and the English Channel are becoming stricter. As the HPTIV uses Wärtsilä's duel-fuel engines to generate both its main and auxiliary power, liquefied natural gas (LNG) can be used as fuel, minimising associated emissions.

Other environmentally sound solutions used onboard include using heat obtained from the engine cooling system to distil drinking water, heat onboard accommodation and generate hot water for use by crew members. Waste-heat-recovery absorption chillers will provide air conditioning during the summer months.

HYDRAULIC JACKING SYSTEM OFFERS FLEXIBILITY

According to von Wedel, the unique features of the HPTIV

design are focused in two overall solutions: the jacking system

and efficient use of the vessel’s main deck.

Conventional jack-up vessels are equipped with either mas-

sive tubular or square-section legs. When vessels reach a cer-

tain size – and also when the strength requirements are high –

triangular truss legs have to be employed: At each installation

site, the vessel’s legs are lowered onto the seabed and it is then

jacked up until it is at the required operational height. Vessels

of this type have only previously been used by the offshore oil

and gas industry.

"Offshore drilling vessels are jacked up maybe once a year,”

says von Wedel. “But when you’re installing wind turbines, this

operation could be performed every other day. And the weather

can be really bad in the middle of the North Sea, so both the

vessel and its truss legs have to be able to cope with it."

"Traditionally, jack-up vessels with truss legs use a rack and

pinion system to carry out the jacking-up operation,” he con-

tinues. “The HPTIV required technology that is both more flex-

ible and robust. The solution was to replace rack and pinion

mechanisms with a continuous hydraulic jacking system which

allows smooth and reliable operation even when the weather

is bad. The truss legs also provide a robust form of construc-

tion for operation in harsh environments.”

MOVABLE GANTRY CRANE MAKES OPERATION MORE EFFICIENTThe large open deck of the HPTIV has been optimised for wind

turbine installation operations. "A large area is more valuable

if the whole of it can be reached by the crane,” says von Wedel.

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OFFSHORE WINDPOWER IS GROWING FASTExpectations regarding rapid growth in energy production from windpower resources are high, especially in Europe. The EU’s goal is that renewable energy should provide 20% of the electrical power consumed in Europe in 2020, and 33% by 2030. In 2010, this figure was just 5.3%. The contribution of offshore wind farms to this form of energy generation is expected to grow particularly fast.

As the number of wind farms on land increases, obstacles such as competition for the use of space and complaints about noise and visual impact grow. Wind farms located at sea avoid these obstacles.

Offshore wind farms can cover very large areas and also allow the size of the wind turbines employed to be larger, which means more power can be generated at a lower unit cost. Good wind conditions at sea can also improve levels of turbine efficiency by 50% or more.

OFFSHORE GENERATION EXPECTED TO REACH 17% BY 2020

On the other hand, wind farms located at sea face additional challenges such as expensive foundations that are difficult to construct, lengthy - and therefore expensive - grid connections, and the fact that both construction work and access is only possible when weather conditions are favourable. Delays in either construction or maintenance can lead to costly downtime.

According to the European Wind Initiative (EWI), only 2% of the EU’s total amount of installed wind generating capacity was located offshore in 2008 (EWI, 2010). This proportion is expected to grow to 17% by 2020 and to 38% by 2030.

Targets of the EWI’s development programme include making land-based wind energy a competitive energy source by 2020 and making offshore wind energy competitive by 2030. EWI, national programmes and other financial sources are supporting research and development in windpower technology with some EUR 6 billion of funding in the 2010–2020 period.

In its forecasts of EU energy trends to 2030, the European Commission has indicated that national plans for renewable sources of energy will result in windpower delivering 14-18% of the EU's total demand for electricity by 2020. Offshore windpower resources will be concentrated in the North Sea and the Baltic Sea.

“The unique approach we employed is to have

a gantry crane running on rails. As the crane is

movable, it can be used to access the whole of the

vessel’s working deck."

The HPTIV can carry three windmill founda-

tions or five complete 5 MW wind turbine assem-

blies on deck. Compared to traditional construc-

tions, the 1000-ton offshore-type gantry crane

results in a significant improvement in installa-

tion efficiency.

"As the crane is centrally located between the

vessel’s four legs, its weight is evenly distributed

and none of the legs is exposed to stress that is

OFFSHORE WIND FARMS CAN COVER VERY LARGE AREAS AND ALLOW THE SIZE OF THE WIND TURBINES EMPLOYED TO BE LARGER.

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too high,” says von Wedel. “And the

HPTIV can therefore be jacked up in

places where its legs would otherwise

sink into the mud on the sea floor.”

“Wind-farm installation operations

in offshore locations have to be effi-

cient,” he continues. ”Making offshore

wind energy competitive means min-

imising the cost of each megawatt of

installed generating capacity."