Deep water foundations for the next round of offshore wind farms must rely on tried and tested solutions from the oil and gas industry, engineers warned this week.
Geotechnical engineers said that attempts by the Carbon Trust to promote the use of innovative solutions would prove too risky to developers.
Concerns were raised following a report by Mott MacDonald for the Department of Energy and Climate Change showed the cost of offshore wind farms to be far more expensive than other mainstream energy sources.
The Carbon Trust’s offshore £30M accelerator programme is looking at reducing the cost of offshore foundations in up to 80m of water.
It is trialling solutions such as gravity foundations, tripods
and floating structures as alternatives to jacket structures used regularly in the oil and
Jacket structures work by supporting the turbine on a braced steel structure with four legs, each attached to a piled foundation.
Ramboll technology director for offshore wind Henrik Carstens said the Carbon Trust’s cheaper foundations would not deliver enough savings to justify the increased risk from using unproven technology.
Carstens said that while jacket structures are more expensive, they are a proven technology and minimise project risks.
“Wind farms require enormous investment, and the foundations are just 20% to 25% of the costs,” he said.
“Even if you are able to develop a new system that can shave 10% off foundation costs, this is just 2% to 2.5% of the overall project costs.
“But you would not want to risk the project for a 2.5% saving. Companies do not want to take risks and will go for a proven path.”
“You would not want to risk the project for a 2.5% saving. Companies do not want to take risks and will go for a proven path”
Henrik Carstens, Ramboll
Royal Haskoning geotechnical advisory group director Philip Smith agreed risk and innovation had to be balanced.
“A number of consultants are giving detailed thought to what the options are. There is a move for designs [of offshore foundations] to be innovative but where there is innovation, there is also risk. It’s a matter of balancing the two.
“Adapting an oil and gas platform is one way forward but there is a worry that the costs will be too large.”
Carstens acknowledged that the cost of jacket structures used regularly in the oil and gas industry for offshore drilling platforms had to come down. They cost in the region of £5/kg to produce.
The Carbon Trust said Carstens had underestimated the proportional cost of foundations for deep water wind farms.
“We think installation costs for turbines 50km to 200km offshore could be 30% to 45% of the total cost, and that includes the costs of the foundation,” said Carbon Trust senior technology acceleration manger Ben Sykes. “We are hoping to make savings of some 20% here.”
“We absolutely need oil and gas expertise, but we do not need the oil and gas mindset,” he said. “In oil and gas you are not optimised for cost, but for other things.”
The return on investment on an oil or gas platform is so high that construction costs are less important than reliability.
There is also no mass production in oil and gas.
“Consequently the risk profile is different,” said Sykes. “And there has not been any serial fabrication at scale.”
Grontmij chief consultant for wind energy Per Vølund agreed that there was much to learn from the oil and gas industry but that it was impossible to predict which technologies would win through.Grontmij is project managing the Carbon Trust’s offshore acceleration scheme.
Mott MacDonald’s UK Electricity Generation Costs Update report highlighted the huge costs for offshore wind.
It said that at £157-£186/MWh it was “much more expensive” than onshore wind costs, which was among the cheapest and comparable to nuclear.
While offshore is projected to see a large reduction in costs, compared with onshore wind,
it will still face much higher costs at £110-£125/MWh for projects commissioned from 2020,” said the report. Gas plants cost as little as £80/MWh.
The first large-scale pilot scheme for the third round of offshore wind is underway at the Ormonde wind farm 10km off Barrow-In-Furness in the Irish Sea.
Burntisland Fabrications has constructed 30 jacket structures for offshore wind turbines to produce 150MW of power.
“We are looking at how to reduce costs for capex - looking to reduce costs and make fabrication more straight forward,” said Burntisland Fabrications MD John Robertson.
Burntisland has also announced that it has set up a joint venture with consultant Atkins to drive down the cost of fabrication.