Early involvement and good access to developers will be essential to help concrete providers tackle the UK offshore wind sector’s engineering challenges. NCE reports.
Last September the UK Energy Research Centre highlighted significant gaps in the Britain’s offshore wind energy supply chain (see box).
It revealed an over-reliance on overseas products and services that threaten to increase the capital costs of UK offshore wind farms to more than £3M/MW.
Turbine foundations represent a quarter of all project delivery costs. As part of the Round 3 of offshore wind projects, the UK is expected to install around 8,000 offshore wind turbines in the next decade. It is estimated that 2,700 turbines will require foundations at depths greater than 45m. While construction of these projects is not expected to start until around 2014, it is critical that the evolving UK industry starts to understand how it can construct and transport foundations while driving down costs, prioritising safety and ensuring installation and maintenance is made easier.
Many industry commentators suggest that steel monopile foundations will fail to meet the requirements for Round 3 because they will need to support larger and heavier turbines that are located in deeper water than previously developed sites. Concrete foundations are considered to offer a solution because they can provide a design life of over 50 years with minimal maintenance.
Some tier one contractors have already pledged a commitment to concrete gravity base foundations, which would be precast and mass-produced in large-scale portside facilities.
“Contractors should utilise existing proven concretes that have already been developed for challenging marine environments”
Jim Troy, Tarmac
Costain has teamed up with Hochtief and Arup and is currently assessing suitable sites for portside facilities (NCE 2 September 2010). It expects to make flask-shaped gravity base foundations 30m to 40m in diameter and 60m to 70m tall.
Concrete gravity bases offer a solution to the challenges of deepwater installations because they require minimum seabed preparation. This technology would also allow the foundation to be refloated following decommissioning so that no material is left on the seabed.
“With technology continually evolving, it doesn’t make sense for contractors to focus on specifying costly, ‘groundbreaking’ new concrete mixes for offshore wind foundations designed to last centuries,” suggests Tarmac director of concrete and mortar technologies Jim Troy.
Keeping up with designs
“Offshore wind turbines designed and installed in 2014 will have been technologically leapfrogged by the time it comes to replacing them, and retrofitting the existing foundations to keep up with the new turbine designs will be a difficult and expensive process.
“Instead, contractors should utilise existing proven concretes that have already been developed for challenging marine environments”, says Troy. “For those concerned about its longevity, the durability of such concretes means that they are able withstand harsh underwater conditions and will perform well as a foundation beyond the lifetime of the wind turbine - which usually requires replacement after a period of 25 years. Some of the offshore oil and gas platforms have had their concrete bases in place since the 1970s and have not experienced any problems,” he says.
Transporting heavy concrete foundations out to sea and manoeuvring them into position on the seabed is a big challenge for developers, but many Round 3 teams are already devising innovative logistical solutions to combat this.
Security of supply
Troy stresses that ensuring the security of supply of concrete should be the next important consideration for developers. “Contractors will need to work very closely with concrete suppliers early to plan logistics in detail and guarantee a steady supply of high-quality concrete,” he says.
Geoff Fawkes, from Tarmac’s National Accounts team, suggests that concrete suppliers must be engaged early and firmly embedded in the supply chain because they can also add value to design decisions and proposed construction methods. “There are two viable options for constructing concrete foundations. You either opt for an insitu concrete pour or manufacture precast units in portside facilities.
“While the latter is currently being favoured, coordinating a continuous supply of concrete for a single foundation weighing around 6,000t will require meticulous planning over a two to three year lead time given the number of turbines that are planned to be installed as part of Round 3 offshore wind farms.”
Fawkes adds: “Setting up a network of portside facilities is acknowledged as key to the success of delivering Round 3, and gaining the planning consents necessary for large-scale concrete plants will be a big element of this. However, providing security of supply goes beyond building state-of-the-art facilities.
Concrete suppliers need sufficient time to look at the logistics of sustainable aggregate and cement reserves as well as time to liaise with their own supply chain partners such as admixture providers and other engineering and property requirements, as well as plant and equipment manufacturers.
“Contractors have, for many years, banged the drum for early involvement, but to deliver the scale of Round 3 projects there is a real need for concrete suppliers to have a place around the table discussing with the contractor, the operator/client and the designer,” he concludes.
UKERC report: at a glance
The UKERC’s report ‘Great expectations: The cost of offshore wind in UK waters’ states that while the UK has big ambitions to maintain its position as a world-leading player in offshore wind, it is today importing 80% of equipment and services from abroad.
When offshore wind technology was first deployed in UK waters 10 years ago, capital and generation costs were expected to fall substantially over time. Since then, producing electricity has become generally more expensive, but the rise in offshore wind costs has been particularly dramatic.
Costs went up in part because of currency and commodity price movements but also because of supply chain shortages and bottlenecks. Planning delays also added to developers’ budgets and undermined supplier confidence.