By Ryan Jacobson, PE, Black & Veatch

Over the past decade, wind energy has moved from a small and novel technology to a major portion of new energy construction. The size and complexity of wind projects has increased and many companies previously focused on fossil generation have now shifted considerable attention to wind.

Proper engineering is key to a wind project’s cost, performance and lifespan. Photo courtesy Black & Veatch.Click here to enlarge image

Black & Veatch has observed that the maturity with which wind projects are designed and built has not always kept up with its place in mainstream energy generation. The most significant issues Black & Veatch has observed repeatedly in wind projects are discussed in this article. Each of these can be addressed with the level of planning, testing and integration common in the greater energy industry and without the addition of significant costs or schedule. By dealing with these issues, owners and contractors can enjoy even greater success in their wind energy projects.

One Integrated Project

While the engineering for a wind energy project is not nearly as complex as many other forms of power generation, it is still so vital to the project’s cost, performance and lifespan that it should be performed in a high-quality manner.

Unlike other power generation projects where project design is often the responsibility of one firm or is broken into large pieces of the project, it is still common in wind energy for the design to be given to many firms working independently. The primary drawback of such an approach is the difficulty in coordination of the design, a task often left to the general contractor.

Black & Veatch has seen numerous projects where designs that appeared valid independently did not integrate into a cohesive or efficient overall plan, costing the project time and money during construction. Recently observed examples include needlessly cutting newly built access roads to lay collection cables, turbine placements that are too close to land not within the project and conflicting drainage plans between project substations and the balance of plant. The best solution to avoid these risks is for owners to demand the design be done in an integrated fashion.

An integrated wind energy design should reference and incorporate the relevant portions of all design packages into all others. For example, site civil design packages should show exactly where the collection system will be routed, where existing critical boundaries and environmentally sensitive areas are, where the foundation structures will rest and where existing infrastructure is. By having all of this information together, contractors and owners can know how the designs integrate and where everything spatially and functionally interfaces. Well-developed packages can show this information together without hampering design reviews or approvals by licensed professional engineers or inspectors.

Foundation for Success

Soil exploration no longer encompasses only the design of wind project access roads or wind turbine foundations. Soil interaction with a project’s buried electrical collection system is a vital aspect of the project’s design but one often marginalized or misunderstood in a wind farm’s design. Wind conditions high above the ground determine how much energy can be produced by the wind turbines, but it is the soil conditions below ground that can enable or inhibit delivering this energy to customers.

Wind farms run their energy through underground medium-voltage cable systems to funnel captured electricity to the nearby grid. Underground networks tying turbines together electrically web back to common runs of larger cables more capable of transporting the combined energy of these wind turbines. More commonly known as “home runs,” these energy arteries can run as far as 15 miles underground before connecting to their destination. Over this distance, the soil encountered can vary immensely in composition, moisture content and density, all of which create specific thermal conductive or insulating environments. The surrounding soil’s capability to transfer heat enables energy to be moved through these cables without damage due to overheating.

Industry practice in designing these electrical networks or “collector systems” has at times shown extreme caution as well as gross negligence when considering the soil thermal environments. Although the phrase “cheaper is better” is becoming a thing of the past, disregarding these systems’ operating conditions has proven quite costly to many project owners that have had to replace failed cable due to thermal damage. Black & Veatch has seen partial or complete failure of a collection system far earlier than the design life due to no other reason than a poor understanding of soil conditions and how they determine cable heat dissipation.

Black & Veatch advocates developing a proper geotech investigation that extends beyond the typical sub-grade material analysis used to design roads and turbine foundations. Allowing geotech contractors to pull samples from overburden, or spoils, from unknown drill depths for thermal resistivity testing is simply not adequate. Nor is testing the soil at proctor densities based on optimum moisture content. It’s imperative that soils be collected in a manner that best represents both native and reinstated conditions of the soil that will be surrounding the buried electrical cables.

When sampled and tested correctly, soil properties can provide the key component to understanding how the electrical cables will perform under load over the project’s lifespan. Additionally, selecting the right geotech firm that understands how soils and cables coexist thermally is just as important for testing and determining the soils’ thermal characteristics. Through proper planning and execution of this part of the geotech investigation, project owners can benefit both financially and with peace of mind that their electrical systems were designed with a high level of certainty and avoided unnecessary margins or underestimated conditions.

Safety

Safe project construction is the goal of every contractor, just as safe operation is for every operator. While some safety concerns for wind energy are unique to the industry, others are exacerbated by a wind project’s size and remote location. Complicating this is the lack of a cohesive industry standard for wind project safety, a process only recently begun by an ANSI A10 subcommittee made up of wind industry experts and safety professionals and chaired by Black & Veatch.

As with any construction project, the key to wind farm safety is training and planning. Well-executed safety plans consider all safety issues ahead of time and determine the training, equipment, communications and planning needed to avoid incidents or deal with them when they occur. Some important issues that need to be considered are:

• On-site rescue. Wind projects are remote, often with local emergency medical services not close by or not equipped with the tools or skills needed to accomplish complicated rescues from high structures such as wind turbines. Personnel on a wind project site need to be able to rescue injured workers and get them to the ground where local emergency personnel can take over.
• Weather planning. Wind energy projects are often located in harsh environments. High winds can be made harsher by cold or hot temperatures, plus additional factors like ice, dust or rain. While turbine erection work is commonly planned for periods of expected calm weather, other aspects of project construction can be hampered by the elements. Planning needs to be done so workers have the appropriate protective equipment and training on how to work in poor weather and how to recognize when the weather exceeds safe conditions.
• Multiple contractors. Wind farms are built by multiple specialty contractors. Often, several contractors need to work in close proximity. It is vital for safety that each contractor knows what the other is doing and what hazards are part of that work. Communication is key to safety.

Logistics

Black & Veatch has found the difference between well-executed wind energy project construction and chaos is often based on the level of logistical planning. With such an enormous and spread out project site, multiple contractors and a tight schedule, it is vital that detailed logistical planning be done.

The most critical piece of logistical planning is a project schedule. While every contractor will develop a general schedule at the start of a project, good planners will develop a highly detailed schedule that tracks each work crew and every significant site activity.

Furthermore, while each subcontractor needs to plan its work sufficiently, it will not be effective if it is not brought into a common schedule by a general contactor that is able to look at all aspects together. Failure to do this will lead to contractors interfering with each other, probable delays in schedule and possible safety incidents.

Some safety concerns are exacerbated by a project’s size and location. Photo courtesy Black & Veatch.Click here to enlarge image

It is still common among some contractors to avoid detailed scheduling, with an attitude of “we know what we are doing, trust us.” Black & Veatch has never seen a wind energy project done effectively that didn’t have such scheduling performed. Every project observed that had the “trust us” attitude ended in delays and quality problems.

One aspect of wind energy logistics that deserves special attention is wind turbine deliveries. Wind projects have more heavy and complex loads being delivered during construction than just about any other form of energy construction. There are too many deliveries for site construction to be paused to allow for them, so work must be planned to accommodate deliveries. As such, the turbine suppliers and/or delivery companies must also be part of project planning and scheduling.

As with any construction, things happen during even well-planned wind projects that can cause delays. As a result, project planning must be an on-going activity. Someone on-site must be empowered with scheduling responsibility. This person can update the schedule as needed and watch for possible conflicts between work crews and component deliveries. Otherwise, owners and crews alike may be left with outdated plans that are worthless.

As wind energy has matured from a small, niche activity to mainstream power generation, project design and construction are maturing as well. Following these main themes will allow owners and contractors to create wind projects that are the high quality and reliable facilities needed to support the future of our industry.

Author: Ryan Jacobson, PE, is manager of wind energy services at Black & Veatch. Contributing to this article were J. Anderson York, lead electrical engineer; Robert Nasset, lead civil engineer; and Sean Tilley, lead wind resource specialist. All are part of Black & Veatch’s Wind Energy Services group and are based in Denver, Colo.