By Douglas J. Smith IEng, Senior Editor
Harnessing the wind is nothing new. As far back as 200 BC China used simple windmills to pump water, and by the 17th century the Dutch were using wind power to reclaim thousands of acres of land by draining the Rhine River delta. Here in the U.S., wind energy was used in the late 1800s by farmers to pump water. It was also used to generate electricity for homes and industry. Nonetheless, as industrialization took root in the U.S., the use of wind energy started to decline.
Today, we are seeing a resurgence of wind to generate electricity in the U.S. According to the American Wind Energy Association (AWEA), from 1999 through 2003, U.S. wind generating capacity expanded at an annual average rate of 28%. As of December 2003 the total wind power capacity in the U.S. was 6,374 MW, Figure 1. Utility scale wind turbines are reported to be in operation in 30 states. With advances in aerodynamics and composite materials, 3.6 MW capacity wind turbines are now available.
In 2003, the U.S. added 1,687 MW of wind capacity, the second highest yearly capacity in history. Oklahoma, Illinois and Ohio installed their first utility scale wind turbines and Minnesota added the most new wind power, 226 MW. GE Energy’s wind operations emerged as the leading provider of wind turbines in 2003, supplying more than 50% of the capacity added.
If the wind power industry can maintain an annual growth rate of 18%, AWEA estimates that wind could supply 6% of U.S. electricity by 2020. Unfortunately, with the expiration of the federal wind energy production tax credit in December 2003, there is concern that the market in 2004 for new wind power will be drastically reduced.
Before considering anything else, the first task in developing a wind project is to determine the wind resource. Monitoring of a site to determine the energy potential can take up to a year or more. This will determine where the best sites are located and how much energy can be extracted from the wind at that particular site. At the same time, an environmental review to determine what wildlife is in the area is also carried out. According to Todd Presson, project manager for enXco’s Hoosac Wind project, environmental studies can also include assessing the project’s impact on flora, fauna and wetland resources.
The U.S. has one of the largest wind energy resources in the world, and in theory, the amount of energy available is as much as 40 times the country’s current energy consumption. Realistically, however, only a small fraction of this is practical due to poor efficiency of energy extraction, siting issues and steep, rocky and/or inaccessible terrain. Even so, the National Wind Coordinating Committee (NWCC) says that the wind still has the potential to supply from 10-40% of the U.S. electricity needs.
Wind energy resources, Figure 2, are distributed unevenly around the country. The areas of the country where large wind turbines are being used are where wind speeds of Class 5 and above are present. Although Class 3 and 4 wind speed areas are not actively being developed, wind turbines that will run efficiently at these lower speeds are under development, says the NWCC. Most of the Class 4 winds and higher, are found near the east and west coasts, along ridges in the Rocky and Appalachian mountains and in a wide belt stretching across the Great Plains.
Although a site’s wind characteristics are essential for choosing a site, its proximity to existing transmission lines is also important. Interconnecting with the electric grid is essential for large wind farms. If a site’s transmission infrastructure costs are high, it can make the project uneconomical. Just because a site is windy does not mean that it is suitable for the development of a wind turbine farm.
According to Robert H. Gates, GE Energy’s senior manager for wind turbine sales in the Americas, the economics of the power sales agreement and the permitting process can be the biggest challenges in developing a wind power project. It is essential that a study be conducted to determine the interconnect requirements and see if the economics of the project will accommodate the costs, says Gates.
Walter Hornaday, president, Cielo Wind Power, states that their biggest challenge in developing a wind project is finding a buyer for the power. Although electric utilities are very experienced in buying capacity and energy together, many utilities are cautious about procuring energy only from wind production.
Many other issues need to be considered before developing a wind project, according to the AWEA. Is there high raptor activity in the area? Are endangered or protected species in the area that could be jeopardized by the presence of the facility? Will aesthetics and noise be an issue for the local community? Will the wind turbines obstruct the flight path of local air traffic? Are the rights of landowners being protected? In most cases, these issues can be addressed successfully, but developers need to be prepared to evaluate a given issue, formulate a response, and defend the chosen position.
Although permitting is essential before a wind project can be constructed, securing access to the site, financing the project and finding a market for the electric power are equally important and must be pursued in parallel. Before a wind project can be financed, the developer must have a sound business plan that includes wind resource data, interconnection requirements and approval, and a long-term power purchase agreement. According to Presson, although financing a well-designed wind power project can be straightforward, the financing typically depends on the availability of federal tax credits.
The three most important factors that Hornaday looks for when scouting for potential wind energy sites are the wind resource, the proximity to transmission lines and permitting risks. Once a site is deemed tohave the potential for developinga wind project, Cielo Wind Power conducts a survey of the site and installs meteorological towers.
Because greenfield sites occasionally have no access roads, Cielo Wind Power has twice had to resort to the use of helicopters or mules to transport the equipment for the meteorological towers and wind measuring equipment. Data on the wind quality is collected over a period of months or several years in some instances, says Hornaday.
After locating a suitable site, negotiations with the landowners commence. Getting landowners approval to conduct environmental and wind resource studies must be done before the permitting process can be started. The landowners, public or private, will want some form of compensation for any wind turbine project constructed on their land. Invariably the agreement with the owners is for the payment of a royalty, a percentage of the proceeds from the sale of electricity, or a lease agreement where the landowner is paid a fixed amount per year per turbine. It is important that the owners of the land be informed upfront on the need for constructing roads, transmission equipment and the need to access the site with heavy equipment. Road construction may also require the cooperation of the local community.
Landowners need to know the length of the lease agreement. Is the payment lump sum or based on revenue generated? Who is responsible for the cost of access roads? Another concern, will the developer provide insurance coverage to protect the landowner from lawsuits involving the operation and access to the wind turbines/farm?
Preparing to attach rotor to nacelle. Photo courtesy of Cielo Wind Power LLC.
Once all the permits and a satisfactory land lease agreement have been obtained, the next priority is the construction of access roads. Presson states that the access roads must be deigned to support the weight of the equipment during construction. At this point conventional earth moving equipment—excavators, bulldozers, graders and dump trucks—are moved onsite to begin the construction of the roads and the wind turbine pads. During this phase equipment lay-down areas are prepared and water, power and other services are installed.
When developing a 75 MW wind farm in Texas, Cielo Wind Energy determined that the best site for locating the wind turbines was on a mesa. Unfortunately, to get the equipment to the mesa required the construction of a permanent land bridge between the mesa and the edge of another mesa. The total length of the bridge was approximately 300 ft.
While the access road(s) are under construction, the contractor starts to install the low voltage electric cables and conduit underground between the turbine pads. Power from the wind turbines is carried from the base of the wind turbine tower to its own transformer. From the transformer the electric cables are connected to a substation prior to being connected to the grid. Sometimes the cables from the transformers are carried overhead to the substation on wooden poles.
Once the electric cables have been buried the concrete pads for the turbines are ready to be constructed. Although the overall site can be rugged, with access roads constructed to each turbine, it is still essential that the concrete pads be flat. This allows the turbine tower to be installed plum without any further leveling. The spacing of the turbines will depend on the site’s wind characteristics and the size and type of the wind turbines.
Assembling blades to hub. Photo courtesy of GE Wind.
Delivery of the wind turbine components to the site is a major challenge and can involve many tractor-trailers. Because of the size of the components, project staff must coordinate the deliveries with state and local highway authorities to determine if any permits are required or if there are other restrictions.
Because of the blades’ length (250 feet or more) and the weight of the nacelle (50 tons), any routes chosen for delivering them to the site should have adequate turning radius for the long loads. There should also be no axle load or bridge weight restrictions.
A 1.5 MW wind turbine requires a 300-ton conventional crane to lift the components in place. The turbine components include the hub, nacelle and the rotor blades. During construction each wind turbine is individually oriented to take maximum advantage of the wind resource.
After completing construction, the turbines are ready for commissioning. This involves operating the turbines with the wind blowing and testing of the electric collection and interconnecting systems. However, because the turbine blades are balanced prior to being shipped to the site, no on-site balancing is required. Because a wind project consists of a number of independent wind turbines, each one must be individually commissioned. Commissioning consists of following a manufacturer’s checklist for testing all key components of the turbine.
According to Hornaday, there are advantages and disadvantages to the assembly line nature of constructing a large wind farm. The disadvantage is if there is a major problem with the wind turbine, the problem is generally generic and will be present on the other turbines. On the other hand, if a smarter, more efficient method is found for the construction and commissioning of the wind turbine, this can be utilized for the other turbines. As a result, Hornaday says there is the potential to reduce costs substantially.
According to Gates, the major critical path items before construction can begin are the power purchase agreement and permitting. Once construction starts, the critical path items are the equipment delivery and the completion of the utility interconnect. Although the physical construction of a wind farm in general is less than one year, the power purchase agreement negotiations and permitting can take several years, says Gates.
Because Cielo Wind Power’s projects are primarily in Texas, the company has been able to develop and construct a project in 18 months on average. The critical path for most Cielo projects is the long lead-time for the wind turbines and the installation of the high voltage cabling and equipment.
Hornaday states that site preparation—roads, foundations and getting a head start of the electric infrastructure—takes them about two months. The turbines are installed at the rate of approximately 40 MW/month, he says.
Sitting Wind Projects
Because of its environmental benefits, one would think that siting a wind farm would be no problem. Wrong. As with any electric generating plant project, before construction and operation can proceed, a proposed wind project has to go through a siting review process in order to acquire the permits and approvals.
Opposition to wind projects is growing in certain areas. Six years ago, the Finnish government stated that after economics the visual impact on the landscape is the most significant obstacle to wind development in their country. Bob Strauss, one of Germany’s foremost playwrights, recently stated “No phase of industrialization has caused such a brutal destruction of the landscape as wind power.” In the U.S. some communities are against the siting of wind turbines because of what they perceive as visual pollution.
Supporters of renewable energy, including wind power, are also having reservations about the construction of offshore wind farms in their own backyard. It’s somewhat ironic that Sen. Edward Kennedy, D-Mass, an advocate for renewable energy, is not keen on the proposed offshore wind farm project in Nantucket Sound.
Because of the sudden increase in wind farms, the U.S. Congress is considering a stricter approval process for permitting these projects. The NIMBY syndrome (not in my back yard) and BANANA syndrome (build absolutely nothing anywhere near anything) are still alive and are a worry for developers of wind turbine projects. According to Gates, permitting a site that is near urban areas and/or known environmentally sensitive areas can be very challenging.
In Canada, after almost 18 months, the J.D. Irving Company is still no nearer receiving a permit for its proposed Canadian wind project. The company wants to construct 20 wind turbines, 400 ft high with blade diameters of 250 ft, near Malpeque and Prince Edward Island National Park. A major reason for the surrounding communities not wanting the project is it would aesthetically ruin the area for tourism. The developers of this project are still fighting to get a permit.