Building wind farms

Gail Rajgor

Part one: the precarious construction phase of a wind farm development needs careful preparation.

Editor's note - this article is taken from the November/December issue of Renewable Energy Focus (REFocus) magazine. For a free subscription, click here. Part two will appear on 28 December.

Installing a turbine onto its foundation and completing final assembly can be done in a day, but the full job of constructing a wind farm involves a long list of civil engineering and electrical work. It can take anything from one to three years, and calls for expert project management skills.

Once planning approval and project finance is secured, careful management of a complex series of engineering, logistical and electrical processes is vital.

Whilst turbine suppliers busy themselves with getting the turbine of choice manufactured, pre-assembled and ready for shipping to site, the project developer needs to undertake extensive site preparation before the final build can even be contemplated:

“They build access roads and clear the areas where turbines will be erected,” explains The Canadian Wind Energy Association. “They then prepare the foundations and do the excavating, followed by installing the formworks and pouring concrete.”

Once all components have been received, final assembly and connection to the grid can take place:

“A crane is used to erect the tower and install the nacelle and rotor with its hub and blades. On the ground, the electrical collection network is installed and connected to the grid through the substation.” The entire construction phase can, for larger projects, take between one to three years depending on the size of the wind farm.

When explained in a nutshell like that, it all sounds pretty straightforward. Of course, in reality is anything but, especially when it comes to offshore wind - which has the same basic construction steps but the work involved is far more complex (see later in the article).

However, while planning concerns and market frameworks are major factors in determining whether a project can proceed or is economically viable, it's the construction phase where things are most likely to go wrong.

The slightest delay or technical hitch can send investment plans into a dive, and spark off heated battles with insurance firms (most wind policy insurance claims relate to the construction phase, most notably in relation to cable damage).

The right personnel

“Contractor experience is key,” says James Green from insurance firm JLT Group, who notes that for offshore wind, insurers are “very hot on anything to do with cables” in particular. He points out that 70% of all claims for renewables relate to cable damage, most of them for offshore projects. Companies need to better check whether they are “using the correct cable laying method for the geological conditions of the seabed, particularly when the cables come onshore”, he suggests.

But it is not just offshore where construction challenges are increasing. All projects, be they on land or at sea, face greater environmental scrutiny during the construction process, while onshore more and more wind farms are being built in extreme climatic conditions (affecting weather windows, logistics, basic ground conditions etc); adopting larger and heavier machines; or simply getting bigger in terms of the number of turbines planned for installation.

With wind technology becoming evermore advanced, projects are more ambitious in overall scope, and a flood of new entrants have entered the market in all parts of the supply chain. Companies like GCube, a specialist underwriter in the renewables sector, admits it has had to do “a lot more technical due diligence and risk assessment on projects, not only from a technology perspective, but also from a method perspective and supply chain perspective”, says the company's Fraser McLaughlin:

“We won't even look at the underwriting side until we get comfort that the technology is robust; and that the project management - which is critically important offshore - is robust, the design; and the method statements; and the weather windows; [are all under control].” And he stresses, “we like to sit down and meet the project teams. We like to see the whites of their eyes.”

GCube has invested “a significant amount of money” into what it calls its Knowledge Management System. “The criteria we started using was to build up a database of claims data, which we have from about 10 years, and then geographic data - where the projects are going to be sited. But just as important these days is who is actually building, designing and operating the projects. It's interesting just how much this all does come down to people.”

During the construction of a wind farm there are a multitude of activities that have to be done simultaneously, while other works depend upon the completion of another part before they can proceed. Having an overall project manager to oversee construction work - to ensure the build is coordinated from start to finish - is vital.

Many project developers would have already appointed a lead contractor under an Engineering, Procurement and Construction (EPC) contract from the outset. This entity would have designed the wind farm, and also overseen the main construction and commissioning activities too.

Increasingly, the turbine supplier is taking full responsibility for overseeing the installation and connection of the actual generators. The Balance of Plant (BOP) – civil engineering; electrics etc.; will be done by specialist contractors (often appointed by the EPC contractor).

Clearing the path to site

Transporting turbine components to site is an art in itself - requiring specialist skills, vehicles, and logistical genius in designing the routes to be travelled from manufacturing facilities to final destination. Much of this is done in the pre-construction phase during general development, site selection, and planning application phases - then would be further refined when it comes to finalising the deals with equipment suppliers:

“Good traffic management is vital to a successful wind farm construction project, particularly in light of the intensity of public highway usage at key periods during the construction phase, and the presence of abnormal loads on the roads,” according to Good Practice During Windfarm Construction, a joint report from Scottish Renewables, Scottish Natural Heritage, the Scottish Environment Protection Agency, and the Forestry Commission Scotland.

Often, due to the inhospitable location of many wind farms, roads/access tracks need to be strengthened or even built from scratch (and the ground made good again) to cope with the heavy loads associated with wind farm development. This forms a key part of the civil engineering/BOP phase.

Indeed, on the engineering side, BOP contractors take responsibility for roads; drainage; crane pads; turbine foundation; meteorological mast foundations; and buildings for electrical switch gear, SCADA equipment, control centres, and maintenance/spare part stores.

On the electrical side, work focuses on the infrastructure requirements necessary for the turbines to feed electricity to the grid - such as point of connection equipment; underground cable networks; and overhead transmission lines.

Electrical BOP operations also involve the installation of electrical switch gear to protect and/or disconnect turbines or other equipment from the system; transformers and switches for individual turbines (where not built into the turbines); grounding and connections for control rooms, maintenance facilities, and any other buildings onsite. And all of this work has to be done while paying heed to environmental legislation. Often, an environmental/ecological consultant or clerk of works will be involved every step of the way.

“We employed specialist environmental consultants to assist us in the creation and implementation of an environmental action plan,” notes Jones Bros, the BOP contractor for GE's 58.5MW Cefn Croes windfarm in Aberystwyth, Wales (operational since 2005). “Considerable effort was put into measures preventing any damage to peat and marsh habitats where the construction changed any natural drainage routes.”

Jones Bros conducted the construction of the access roads, the turbine bases for the 39 GE 1.5 MW machines, the crane bases and the 33kV cabling for the project (which remains the UK's largest onshore development to date). The firm was also responsible for the safety of the heavy lifting operations of the tower, turbine and blade erections, and for the complex energy requirements of the 33kV systems.

“We've amassed a great deal of experience in managing the complex logistics of working over large expanses in remote areas, and our team understands the special requirements of projects involving the construction of access roads to accommodate abnormal loads, turbine foundations, substation buildings and electrical infrastructure,” the company states.

Scheduling factors

Ensuring timetables are adhered to or reducing installation times has always been vital, but is becoming increasingly important in today's tough economic climate. For Cefn Croes, John Bros' on-site batching plant ensured maximum flexibility and saved on countless heavy vehicle journeys: “This entire contract was successfully completed within schedule, despite delays caused by the worst winter in half a century.”

Some companies, like Gamesa – with its Wind Farm Palletisation Project – have standardised procedures to ensure efficient construction and turbine assembly. Each step in the Gamesa process – installing the base, erecting the tower, installing nacelles, assembling blades, control equipment, cabling, and grid connection – is clearly defined, and parts are palletised and delivered to site sequentially in line with the assembly process.

Meantime, the weather plays a major role when it comes to construction timetables and work conditions for a number of reasons. As well as the simple practical issue of being able to carry out physical work, “it is important to consider the time of year and scheduling of wind farm construction, to minimise impacts on the surrounding environment,” stresses the Good Practice During Windfarm Construction guide. “Careful scheduling and an awareness of the different issues likely to arise at different times of year will be beneficial, particularly in the context of planning for drainage and the impact of flooding events.”

A construction method statement (CMS), covering the construction timetable and seasonal considerations should be clearly outlined and followed, it adds. This should include details about what measures will be put in place to deal with weather-related events (flash floods, peat slide, snow melt, dust etc.) and how construction will be scheduled around key site constraints (such as the breeding bird season); and where scheduling is not practical, what other mitigation will be put in place.

Part two will look at how the construction process for offshore wind projects differs.

About the author:
Gail Rajgor is a writer working across the energy & environment sector. She is the former publisher of Sustainable Energy Developments magazine.



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Anumakonda said

25 December 2011
Excellent guidelines on how to build wind farms.

Dr.A.Jagadeesh Nellore(AP),India
Wind Energy Expert
E-mail: anumakonda.jagadeesh@gmail.com

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