Wind1

Differential solar heating of the atmosphere causes wind. Wind energy increases as the cube of velocity and is extracted vertically. The power extraction footprint is governed by the height of the tower. The landscape footprint consists of the base of the tower and the downrange disruption in airflow. Extraction efficiencies for wind systems are high. Therefore the energy concentration per square foot is greater than for solar radiation. The principal disadvantages are that not many folks wish to live in areas of high wind, consequently transmission costs and/or storage is a factor, and there are a certain amount of visual and noise aesthetic impacts.

Vindeby wind farm. Baltic Coast. 11 Bonus 450kW stall turbines.

According to an editorial in the Seattle Times "Wind energy has long been the great Green hope. One consequence of this winter's [Seattle-2000/2001] power crisis is that it is being taken seriously in the Pacific Northwest for the first time.

The Stateline Wind Farm, under construction near Walla Walla by an affiliate of Florida Power & Light, will have 450 windmills generating 300 megawatts of electricity. By powerplant standards, it's only middling: the proposed natural gas plant at Sumas would produce more than twice as much power. But 300 megawatts is still substantial, and it can be brought on line in less than a year.

What made wind energy practical is the modern windmill. Mounted on a high, slender tower, it has three thin blades, pitch-controlled by computer. At a broad range of wind it generates a steady current. As windmills have improved, the cost per megawatt-hour has fallen. In 1991, the raw generating cost was about $100. It is now down to $35 to $40. A federal tax credit lops off another $5. To make it reliable, it must be helped by turning on other power when the windmill stops. It also has to be delivered. That raises its cost to about $60. That's more than power from a natural-gas plant, but is still only about one-sixth the recent price of power in wholesale markets.

Wind also hedges the region's risk from low rainfall, world energy crises or weird legislation in California. The Bonneville Power Administration, which has 7,000 megawatts of hydro power, now plans to buy 1,000 megawatts of wind. One-eighth may not sound like much, but it is. It is a very big deal."2

Advances in blade and turbine design over the past two decades have increased the efficiency and reliability of wind turbines, yet the basic idea remains the same. The kinetic energy of wind moves the turbine blades, which are connected to a driveshaft. The spinning driveshaft turns a generator. This alternating current (AC) electricity runs through conduit to a control center where the electricity is either fed into the grid or converted to direct current (DC) and stored in a battery. Many turbines spin at variable speeds, and the "wild" or variable frequency current they make is processed to 60 Hertz AC for the grid. Some turbines use an induction generator and make AC at the same frequency as the grid.

The swifter the wind, the more power you get from the wind machine. Because power is proportional to the cube of the wind speed, even a small increase in average wind speed can make a large difference in output. A turbine operating at 20 mph would generate eight times the power of a turbine operating at 10 mph. At 12 mph, a turbine generates 44 percent more power than at 10 mph. Power output is also related to the swept area of a turbine. When the rotor diameter is doubled, the output of the turbine is quadrupled.

Unlike a pinwheel, which will turn in the slightest breeze, wind turbines are designed to start turning, or "cut in," when the wind reaches a minimum speed, somewhere between four and 10 mph, depending on the model. They are also designed to protect themselves from high winds so that the generator does not burn out. They do this by changing rotor angle or blade pitch.

If you want to get maximum power from your turbine, you need a high, well-exposed site. Buildings, trees, even cornfields, can slow and divert your power source. As a general rule, the bottom of a turbine blade should be located at least 30 feet higher than any obstruction within 500 feet.

The current generation of wind turbines has been very reliable, usually spinning away for years with only annual bolt tightening and bearing grease jobs. Commercial wind farms employ technicians who perform regular maintenance, conduct tests on the turbines and their controls, and make repairs. In the case of smaller scale systems, this job gets added onto the duties of some height-loving, mechanically savvy staffer who gains the title of windsmith after going through training in system maintenance.

Commercial scale turbines range from about 50 kilowatts (kW) to more than 1.5 megawatts (MW) of rated power. Wind farms are arrays of these large wind turbines, often covering an area of many acres. Like producing oil and gas fields, most wind farmland remains available for farming, ranching, and other uses. To develop a wind farm you will need adequate wind power, at least 11 to 13 mph at the site, preferably more. A one to two-year anemometer study, coupled with local weather information, will help.

It costs approximately $1 million per megawatt of installed capacity to build a wind farm. To take advantage of economies of scale, windfarms generally must have a capacity of over 20 MW. Most new windfarms tend to be larger, from 50 to 200 MW in size, further improving economies of scale. For comparison, a typical coal-fired or nuclear power plant has a capacity of approximately 1,000 MW.

A critical issue is power transmission. High voltage distribution and transmission lines can cost tens or hundreds of thousands of dollars per mile, and transformers add additional costs. If your site is far from transmission lines, you will have to make up for the added transmission cost in greater wind speeds or some other economic advantage. Even if a turbine is set near transmission lines, the regional transmission organization may not immediately carry all of the electricity you expect to produce.

Another major issue is finding a buyer. While the cost of wind electricity is comparable to the costs of other electricity sources in the nation, it may be higher than the cost of electricity in your state or region. If you find a consumer utility several states away, you will also need to find transmission utilities willing to provide carrying capacity to your customer. These sales have been made easier through the advent of green power companies. Some states, local governments, and corporations have developed renewable energy portfolio standards; these standards require a certain percentage of their energy supply to be derived from renewable sources. Tribes may further market their electricity as Native American green energy, thereby potentially gaining a marketing advantage over other green power producers.

The economics of off-the-grid sites are very different from grid-intertied systems. For remote sites, the power must be less expensive than the alternative, which would be the cost of buying and transporting diesel fuel or running a utility line at the cost of approximately ten to thirty dollars per lineal foot. For grid-intertied systems, the average costs over the turbine's lifetime must be comparable to or less than the utility cost. For either type of application, it is important to invest some time in wind power analysis.3 Description of the wind energy resources for the United States as well as information on assessment of wind site potential is available from the National Renewable Energy Laboratory (NREL) wind energy resource atlas.4

The NREL wind energy resource atlas shows that areas potentially suitable for wind energy applications are dispersed throughout much of the United States. Estimates of the wind resource in this atlas are expressed in wind power classes ranging from Class 1 to Class 7, with each Class representing a range of mean wind power density or equivalent mean speed at specified heights above the ground (Table 1). Areas designated Class 4 or greater are suitable with advanced wind turbine technology under development today. Power Class 3 areas may be suitable for future generation technology (year 2000 and beyond). Class 2 areas are marginal and Class 1 areas unsuitable for wind energy development.

Table 1. Classes of Wind Power Density

According to the atlas, the San Juan Islands are Class 2 to Class 3, the Mount Baker foothills Class 3 to Class 4, and Class 5 are the higher Cascade peaks such as Mount Baker.

Recording wind anemometer stations have been established adjacent to the Lummi Seapond Aquaculture facility at Sandy Point, the Stommish Grounds, and the Tosco oil refinery. Wind speed and directions recorded are used to derive seasonal power potentials. Unlike local airport data, wind speed values above 29 knots are not lumped as "high," but are included in average figures.

Annual Wind Energy Potential of Rotor Area at the Tosco Site

A summation of hourly energy values shows annual wind energy potential of 210 Kilowatt-hours per square meter of rotor area at the Tosco site.

Based upon instantaneous hourly readings, the average annual wind speed at the Tosco oil refinery was 5 mph (2.2 m/s) out of the southeast. No wind speeds were recorded that exceeded 39 mph (17.4 m/s). However, this is a ground station. Actual wind speed 30 feet above this station is projected to be 1.5 times ground wind speed.5 This would almost make wind energy feasible at this site as cut-in speed for most wind generators is in this 7 mph (3.1 m/s) range. Additionally, it is incorrect to compute power potential from average speed in a medium where power increases as the cube of speed. This is so because wind speed tends to assume a skewed bell-shaped curve. A frequency distribution of energy based upon hourly speed values shows that in spite of decreasing frequency as speed increases, substantial energy is available at wind speeds above the mean.

If we re-calculate wind power for a hypothetical 3.2 KW wind machine on a 44 foot tower (wind speed 1.5 times ground) at the Intalco site including cut-in (6 knot = 3.09 m/s), cut-out (27 knot = 13.9 m/s) and efficiency (25 percent), we arrive at an estimated daily output of 1135 Whr/m2/day (1,657,492 Whr/m2/yr divided by 365 days times .25 efficiency = 1135 Whr/m2/day). For a 16.3 m2 rotor, this equals 18,504 Whr/day (Table 2).

Table 2. Hypothetical Wind Power Scenario

References Cited

1. Northwest Indian College National Indian Center for Marine and Environmental Research and Education. Feasibility Studies for Potential Application of Renewable Energy Technologies at Tribal Colleges and Universities Supplemental Announcement 07. Volume III - Draft Phase 1 Final Report. Submitted: June 30,2001. <http://nwic-research.org/DOE%20PhaseII%20Vol3.htm>

2. Seattle Times. February 25, 2001. Editorial: Time to Ride the Wind.

3. Indian Sustainable Energy News. Vol 2. No 1. Winter 2000. Lawrence Berkeley National Laboratory. Berkeley, CA.

4. National Renewable Energy Laboratories. Wind Energy Resource of U.S. <http://www.nrel.gov/wind/pubs/atlas> LINK IS NO LONGER AVAILABLE

5. Solar Electric Catalog. Wind Power. <http://www.solarelectric.com>

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