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Small Wind Electric Systems
                       A U.S.
                  Consumer’s Guide
Small Wind Electric Systems

                              Location—A home in Charlotte, Vermont
Small Wind Electric Systems                                     1

  Small Wind Electric Systems
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                small wind energy system can lower                      Home Energy Use
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Is Wind Energy Practical                  structures p...
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                      What Size Wind Turbine                                        Turb...
Small Wind Electric Systems               5

What are the Basic Parts
of a Small Wind Electric
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                           Tilt-down towers can also be low-         application, th...
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Small wind turbines generate direct                           ...
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some annual maintenance. Bolts             wind speed results in a large i...
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                          Air Density Change with Elevation                ...
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Is There Enough Wind                         particular location. Airport...
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     Flagging, the effect
     of strong winds on               ��������            ...
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               Obstruction of the Wind by a Building
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     A grid-connected                                Grid-connected Systems
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If your wind turbine is connected to        provider. In the case of private (i...
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                 utilities from imposing any insurance                                fa...
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                                 Hybrid Power Systems                 ...
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                   expensive extension. The cost of                                 • Yo...
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Glossary of Terms                         kWh—Kilowatt-hour, a measure
Airfoil—The shape...
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                 Swept area—The area swept by the          Wind Energy Basics
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Government Agencies                     Videos
U.S. Department of Energy’s Energy      A...
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                 2002 Farm Bill — Wind                           The amount of the payme...
Small Wind Electric Systems

U.S. Department of Energy Regional Offices
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Small Wind Guide

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Small Wind Guide

  1. 1. Small Wind Electric Systems A U.S. Consumer’s Guide
  2. 2. Small Wind Electric Systems Location—A home in Charlotte, Vermont Capacity—10 kilowatts Turbine manufacturer—Bergey Windpower Company Photo credit—Trudy Forsyth, NREL/PIX09123 Location — Wales Wind Energy Project, Wales, Alaska Capacity — 0.1 MW Turbine manufacturer — Atlantic Orient Corporation Developer — Kotzebue Electric Association Photo credit — Steve Drouilhet, NREL/PIX09674 Capacity—10 kilowatts Turbine manufacturer—Bergey Windpower Company Photo credit—Bergey Windpower Company, NREL/PIX02102 Location—A ranch near Wheeler, Texas Capacity—1 kilowatt Turbine manufacturer—Southwest WindPower Photo Credit—Elliott Bayly/PIX07169 Location — A farm in western Kansas Capacity — 10 kilowatts Turbine manufacturer — Bergey Windpower Company Photo credit — Warren Gretz, NREL/PIX09618 Location—A cabin in South Park, Colorado Capacity—600 watt Turbine manufacturer—Southwest WindPower Photo credit—E. McKenna, NREL/PIX04712
  3. 3. Small Wind Electric Systems 1 Small Wind Electric Systems A U.S. Consumer’s Guide Introduction Can I use wind energy to power my home? This question is being asked across the country as more people look for affordable and reliable sourc- es of electricity. Small wind electric systems can make a significant contribution to our nation’s energy needs. Although wind turbines large enough to provide a significant portion of the electricity needed by the average U.S. home gen- erally require one acre of property or more, approximately 21 million U.S. homes are built on one-acre and larger Bergey Windpower/PIX01476 sites, and 24% of the U.S. population lives in rural areas. A small wind electric system will work for you if: • There is enough wind where you Homeowners, ranchers, and small businesses can use wind- generated electricity to reduce their utility bills. This grid- live connected system installed for a home in Norman, Oklahoma, • Tall towers are allowed in your reduces the homeowner’s utility bill by $100 per month. neighborhood or rural area • You have enough space Contents • You can determine how much Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 electricity you need or want to First, How Can I Make My Home More Energy Efficient? . . . . 2 produce Is Wind Energy Practical for Me? . . . . . . . . . . . . . . . . . . . . . . 3 • It works for you economically. What Size Wind Turbine Do I Need? . . . . . . . . . . . . . . . . . . . 4 The purpose of this guide is to pro- What are the Basic Parts of a Small Wind Electric System? . . 5 vide you with the basic information What Do Wind Systems Cost? . . . . . . . . . . . . . . . . . . . . . . . . 7 about small wind electric systems to Where Can I Find Installation and Maintenance Support? . . . 8 help you decide if wind energy will How Much Energy Will My System Generate? . . . . . . . . . . . . 9 work for you. Is There Enough Wind on My Site? . . . . . . . . . . . . . . . . . . . 11 Why Should I Choose Wind? How Do I Choose the Best Site for My Wind Turbine? . . . . . 14 Wind energy systems are one Can I Connect My System to the Utility Grid? . . . . . . . . . . . 15 of the most cost-effective home- Can I Go “Off-Grid”? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 based renewable energy systems. Glossary of Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Depending on your wind resource, a For More Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
  4. 4. 2 Small Wind Electric Systems small wind energy system can lower Home Energy Use your electricity bill by 50% to 90%, Based on national averages help you avoid the high costs of extending utility power lines to Water remote locations, prevent power heating interruptions, and it is nonpolluting. 14% Heating and How Do Wind Turbines Work? Lighting, cooling Wind is created by the unequal heat- cooking, 44% and other ing of the Earth’s surface by the sun. appliances Wind turbines convert the kinetic 33% 02979309m energy in wind into mechanical power that runs a generator to produce clean electricity. Today’s turbines are versatile modular sources Refrigerator 9% of electricity. Their blades are aero- The largest portion of a utility bill for a typical dynamically designed to capture the house is for heating and cooling. maximum energy from the wind. The wind turns the blades, which spin a • Save money and increase shaft connected to a generator that comfort by properly maintaining makes electricity. and upgrading your heating, ventilation, and air-conditioning First, How Can I Make systems. My Home More Energy Efficient? • Install double-paned, gas-filled windows with low-emissivity Before choosing a wind system for (low-e) coatings to reduce heat your home, you should consider loss in cold climates and spectrally reducing your energy consumption by selective coatings to reduce heat making your home or business more gain in warm climates. energy efficient. Reducing your energy consumption will signifi- • Replace your lights in high-use cantly lower your utility bills and will areas with fluorescents. Replacing reduce the size of the home-based 25% of your lights can save about renewable energy system you need. 50% of your lighting energy bill. To achieve maximum energy effi- • When shopping for appliances, ciency, you should take a whole- look for the ENERGY STAR® label. building approach. View your home ENERGY STAR® appliances have as an energy system with interrelated been identified by the U.S. parts, all of which work synergisti- Environmental Protection Agency cally to contribute to the efficiency and U.S. Department of Energy of the system. From the insulation in as being the most energy-efficient your home’s walls to the light bulbs products in their classes. in its fixtures, there are many ways to • For more information on how to make your home more efficient. make your home energy efficient, • Reduce your heating and see Energy Savers in the For More cooling needs by up to 30% by Information section. investing just a few hundred dollars in proper insulation and weatherization products.
  5. 5. Small Wind Electric Systems 3 Is Wind Energy Practical structures permitted in residentially for Me? zoned areas, although variances are A small wind energy system can often obtainable. Most zoning ordi- provide you with a practical and nances have a height limit of 35 feet. economical source of electricity if: You can find out about the zoning restrictions in your area by calling • your property has a good wind the local building inspector, board of resource supervisors, or planning board. They • your home or business is located on can tell you if you will need to obtain at least one acre of land in a rural a building permit and provide you area with a list of requirements. • your local zoning codes or In addition to zoning issues, your covenants allow wind turbines neighbors might object to a wind machine that blocks their view, or • your average electricity bills are they might be concerned about noise. $150 per month or more Most zoning and aesthetic concerns • your property is in a remote can be addressed by supplying objec- location without easy access to tive data. For example, the ambient utility lines noise level of most modern residential • you are comfortable with long-term wind turbines is around 52 to 55 deci- investments. bels. This means that while the sound of the wind turbine can be picked out Zoning Issues of surrounding noise if a conscious Before you invest in a wind energy effort is made to hear it, a residential- system, you should research poten- sized wind turbine is no noisier than tial obstacles. Some jurisdictions, for your average refrigerator. example, restrict the height of the In Clover Valley, Minnesota, this 3-kW Whisper H175 turbine on a 50-foot tower is connected to the utility grid to offset the farm’s utility- supplied electricity. World Power Technology/PIX07168
  6. 6. 4 Small Wind Electric Systems What Size Wind Turbine Turbines used in residential applica- Do I Need? tions can range in size from 400 watts The size of the wind turbine you need to 100 kW (100 kW for very large depends on your application. Small loads), depending on the amount of turbines range in size from 20 watts electricity you want to generate. For to 100 kilowatts (kW). The smaller or residential applications, you should “micro” (20- to 500-watt) turbines are establish an energy budget to help used in a variety of applications such define the turbine size you will need. as charging batteries for recreational Because energy efficiency is usually vehicles and sailboats. less expensive than energy produc- tion, making your house more energy One- to 10-kW turbines can be used in efficient first will probably be more applications such as pumping water. cost effective and will reduce the size Wind energy has been used for centu- of the wind turbine you need (see ries to pump water and grind grain. How Can I Make My Home More Although mechanical windmills still Energy Efficient?). Wind turbine provide a sensible, low-cost option manufacturers can help you size for pumping water in low-wind areas, your system based on your electricity farmers and ranchers are finding that needs and the specifics of local wind wind-electric pumping is a little more patterns. versatile and they can pump twice the volume for the same initial A typical home uses approximately investment. In addition, mechanical 10,000 kilowatt-hours (kWh) of elec- windmills must be placed directly tricity per year (about 830 kWh per above the well, which may not take month). Depending on the average the best advantage of available wind wind speed in the area, a wind tur- resources. Wind-electric pumping bine rated in the range of 5 to 15 kW systems can be placed where the wind would be required to make a signifi- resource is the best and connected to cant contribution to this demand. A the pump motor with an electric cable. 1.5- kW wind turbine will meet the needs of a home requiring 300 kWh per month in a location with a 14- This 1-kW Whisper mile-per-hour (6.26-meters-per-sec- turbine provides ond) annual average wind speed. The direct AC power for manufacturer can provide you with the water pump for stock tanks on a the expected annual energy output ranch in Wheeler, of the turbine as a function of annual Texas. average wind speed. The manufac- turer will also provide information on the maximum wind speed at which the turbine is designed to operate safely. Most turbines have automatic overspeed-governing systems to keep the rotor from spinning out of control in very high winds. This information, along with your local wind speed and your energy budget, will help you Elliott Bayly/PIX09681 decide which size turbine will best meet your electricity needs.
  7. 7. Small Wind Electric Systems 5 What are the Basic Parts of a Small Wind Electric System? ����� Home wind energy systems gener- ally comprise a rotor, a generator or ����������� ���� alternator mounted on a frame, a tail ���������� ��������� (usually), a tower, wiring, and the “balance of system” components: controllers, inverters, and/or batter- ies. Through the spinning blades, the ����� rotor captures the kinetic energy of the wind and converts it into rotary motion to drive the generator. Wind Turbine Most turbines manufactured today are horizontal axis upwind machines generator from a 60-foot tower height with two or three blades, which are to a 100-foot tower involves a 10% usually made of a composite material increase in overall system cost, but it such as fiberglass. can produce 29% more power. The amount of power a turbine will There are two basic types of tow- produce is determined primarily by ers: self-supporting (free standing) the diameter of its rotor. The diameter and guyed. Most home wind power of the rotor defines its “swept area,” systems use a guyed tower. Guyed or the quantity of wind intercepted by towers, which are the least expensive, the turbine. The turbine’s frame is the can consist of lattice sections, pipe, or structure onto which the rotor, genera- tubing (depending on the design), and tor, and tail are attached. The tail supporting guy wires. They are easier keeps the turbine facing into the wind. to install than self-supporting tow- ers. However, because the guy radius Tower must be one-half to three-quarters Because wind speeds increase with of the tower height, guyed towers height, the turbine is mounted on require enough space to accommodate a tower. In general, the higher the them. Although tilt-down towers are tower, the more power the wind more expensive, they offer the con- system can produce. The tower also sumer an easy way to perform Tilt-down towers raises the turbine above the air maintenance on smaller light-weight provide easy turbulence that can exist close to turbines, usually 5 kW or less. maintenance for the ground because of obstructions turbines. such as hills, buildings, and trees. A Tilt-Down Tower general rule of thumb is to install a ������������� wind turbine on a tower with the bot- ������������� tom of the rotor blades at least 30 feet ���������� ��������������������� �������� (9 meters) above any obstacle that �������������������� is within 300 feet (90 meters) of the ��������������� ���������� tower. Relatively small investments in increased tower height can yield very high rates of return in power produc- tion. For instance, to raise a 10-kW ���������
  8. 8. 6 Small Wind Electric Systems Tilt-down towers can also be low- application, the balance of system ered to the ground during hazard- parts may include a controller, storage ous weather such as hurricanes. batteries, a power conditioning unit Aluminum towers are prone to (inverter), and wiring. Some wind cracking and should be avoided. turbine controllers, inverters, or other Most turbine manufacturers provide electrical devices may be stamped wind energy system packages that by a recognized testing agency, like include towers. Underwriters Laboratories. Mounting turbines on rooftops is not Stand-Alone Systems recommended. All wind turbines Stand-alone systems (systems not vibrate and transmit the vibration connected to the utility grid) require to the structure on which they are batteries to store excess power gener- mounted. This can lead to noise and ated for use when the wind is calm. structural problems with the building, They also need a charge controller to and the rooftop can cause excessive keep the batteries from overcharging. turbulence that can shorten the life of Deep-cycle batteries, such as those the turbine. used for golf carts, can discharge Balance of System and recharge 80% of their capacity The parts that you need in addition hundreds of times, which makes them to the turbine and the tower, or the a good option for remote renewable balance of system parts, will depend energy systems. Automotive batteries on your application. Most manufac- are shallow-cycle batteries and should turers can provide you with a system not be used in renewable energy package that includes all the parts you systems because of their short life need for your application. For exam- in deep-cycling operations. ple, the parts required for a water pumping system will be much differ- ent than what you need for a residen- tial application. The balance of system required will also depend on whether the system is grid-connected, stand- alone, or part of a hybrid system. For a residential grid-connected A Bergey XL.10, 10-kW wind turbine is part of a grid-connected wind/photovoltaic hybrid system that reduces the utility power used by this home in Vermont. Trudy Forsyth, NREL/PIX09122 and PIX09123 The balance of system (upper right) includes from left to right, a Trace inverter for the PV system, a breaker box, and a Powersync inverter for the wind system.
  9. 9. Small Wind Electric Systems 7 Small wind turbines generate direct A Southwest current (DC) electricity. In very small Windpower Air 303, 300-watt systems, DC appliances operate turbine is the sole directly off the batteries. If you want to source of electricity use standard appliances that use con- for this remote home in northern ventional household alternating cur- Arizona. rent (AC), you must install an inverter to convert DC electricity from the batteries to AC. Although the inverter slightly lowers the overall efficiency of the system, it allows the home to be wired for AC, a definite plus with lenders, electrical code officials, and future homebuyers. Southwest Windpower/PIX09156 For safety, batteries should be iso- lated from living areas and electron- ics because they contain corrosive and explosive substances. Lead-acid batteries also require protection from temperature extremes. increases. Although small turbines Grid-Connected Systems cost less in initial outlay, they are In grid-connected systems, the only proportionally more expensive. The additional equipment required is a cost of an installed residential wind power conditioning unit (inverter) energy system with an 80-foot tower, that makes the turbine output electri- batteries, and inverter typically cally compatible with the utility grid. ranges from $15,000 to $50,000 for Usually, batteries are not needed. a 3- to 10-kW wind turbine. Although wind energy systems What Do Wind Systems involve a significant initial invest- Cost? ment, they can be competitive with Installation costs vary greatly depend- conventional energy sources when ing on local zoning, permitting, and you account for a lifetime of reduced utility interconnection costs. A small or avoided utility costs. The length turbine can cost anywhere from $3,000 of the payback period—the time to $50,000 installed, depending on before the savings resulting from your size, application, and service agree- system equal the cost of the system ments with the manufacturer. (The itself—depends on the system you American Wind Energy Association choose, the wind resource on your [AWEA] says a typical home wind site, electricity costs in your area, and system costs approximately $32,000 how you use your wind system. For (10 kW); a comparable photovoltaic example, if you live in California and [PV] solar system would cost over have received the 50% buydown of $80,000.) your small wind system, have net A general rule of thumb for estimat- metering, and an average annual ing the cost of a residential turbine is wind speed of 15 miles per hour $1,000 to $5,000 per kilowatt. Wind (mph) (6.7 meters per second [m/ energy becomes more cost effective s]), your simple payback would be as the size of the turbine’s rotor approximately 6 years.
  10. 10. 8 Small Wind Electric Systems references of past customers with installations similar to the one you are considering. Ask the system owners about performance, reliability, and maintenance and repair requirements, and whether the system is meeting their expectations. Also, find out how long the warranty lasts and what it includes. Where Can I Find Installation and Maintenance Support? The manufacturer/dealer should be able to help you install your machine. Many people elect to install the machines themselves. Before attempt- ing to install your wind turbine, ask Warren Gretz, NREL/PIX09615 yourself the following questions: • Can I pour a proper cement foundation? • Do I have access to a lift or a way of erecting the tower safely? Small wind turbines like this Things to Consider When • Do I know the difference between 10-kW Bergey Purchasing a Wind Turbine AC and DC wiring? XL.10 provide electricity for Once you determine you can install • Do I know enough about electricity home, farm, and a wind energy system in compliance ranch applications. to safely wire my turbine? with local land use requirements, you can begin pricing systems and compo- • Do I know how to safely handle nents. Comparatively shop for a wind and install batteries? system as you would any major pur- If you answered no to any of the chase. Obtain and review the product above questions, you should probably literature from several manufacturers. choose to have your system installed As mentioned earlier, lists of manu- by a system integrator or installer. facturers are available from AWEA, Contact the manufacturer for help (see For More Information), but not or call your state energy office and all small turbine manufacturers are local utility for a list of local system members of AWEA. Check the yellow installers. You can also check the yel- pages for wind energy system dealers low pages for wind energy system in your area. service providers. A credible installer Once you have narrowed the field, will provide many services such as research a few companies to be sure permitting. Find out if the installer is a they are recognized wind energy licensed electrician. Ask for references businesses and that parts and service and check them out. You may also will be available when you need them. want to check with the Better Business You may wish to contact the Better Bureau. Business Bureau to check on Although small wind turbines are the company’s integrity and ask for very sturdy machines, they do require
  11. 11. Small Wind Electric Systems 9 some annual maintenance. Bolts wind speed results in a large increase and electrical connections should be in power. That is why a taller tower checked and tightened if necessary. will increase the productivity of any The machines should be checked for wind turbine by giving it access to corrosion and the guy wires for higher wind speeds as shown in the proper tension. In addition, you Wind Speeds Increase with Height should check for and replace any graph. The formula for calculating worn leading edge tape on the blades, the power from a wind turbine is: if appropriate. After 10 years, the Power = k Cp 1/2 ρ A V3 blades or bearings may need to be replaced, but with proper installation Where: and maintenance, the machine should P = Power output, kilowatts last up to 20 years or longer. Cp = Maximum power coefficient, If you do not have the expertise to ranging from 0.25 to 0.45, maintain the machine, your installer dimension less (theoretical maximum = 0.59) may provide a service and mainte- nance program. ρ = Air density, lb/ft3 A = Rotor swept area, ft2 or How Much Energy Will My π D2/4 (D is the rotor System Generate? diameter in ft, π = 3.1416) Most U.S. manufacturers rate their V = Wind speed, mph turbines by the amount of power they k = 0.000133 A constant to yield can safely produce at a particular power in kilowatts. (Multiplying wind speed, usually chosen between the above kilowatt answer by 24 mph (10.5 m/s) and 36 mph (16 m/ 1.340 converts it to horse- s). The following formula power [i.e., 1 kW = 1.340 illustrates factors that are important horsepower]). to the performance of a wind turbine. The rotor swept area, A, is important Notice that the wind speed, V, has an because the rotor is the part of the exponent of 3 applied to it. This turbine that captures the wind energy. means that even a small increase in Relative Size of Small Wind Turbines 40 8 30 Swept area, m2 7 7m 6 20 6m Rotor Diameter, m 5 10 5m 4 0 4m 1 2 3 4 5 6 7 Rotor Diameter, m 3 3m 2 2m 02979303m 1 1m 0 Source: Paul Gipe, Wind Energy Basics
  12. 12. 10 Small Wind Electric Systems Air Density Change with Elevation height of the tower that you plan to 10,000 use, and the frequency distribution of 9,000 the wind–an estimate of the number 8,000 of hours that the wind will blow at 7,000 each speed during an average year. Elevation, ft 6,000 They should also adjust this calcula- 5,000 tion for the elevation of your site. 4,000 Contact a wind turbine manufacturer 3,000 or dealer for assistance with this 2,000 calculation. 02979302m 1,000 To get a preliminary estimate of the 0 70 75 80 85 90 95 100 performance of a particular wind tur- Density change compared to sea level, % bine, use the formula below. AEO = 0.01328 D2 V3 So, the larger the rotor, the more Where: energy it can capture. The air density, AEO = Annual energy output, ρ, changes slightly with air tempera- kWh/year ture and with elevation. The ratings D = Rotor diameter, feet for wind turbines are based on standard conditions of 59° F (15° C) V = Annual average wind speed, at sea level. A density correction mph should be made for higher elevations The Wind Energy Payback Period as shown in the Air Density Change Workbook found at www.nrel.gov/ with Elevation graph. A correction for wind/docs/spread_sheet_Final.xls is temperature is typically not needed a spreadsheet tool that can help you for predicting the long-term perfor- analyze the economics of a small wind electric system and decide whether mance of a wind turbine. wind energy will work for you. The Although the calculation of wind spreadsheet can be opened using power illustrates important features Microsoft Excel 95 software. It asks about wind turbines, the best mea- you to provide information about how sure of wind turbine performance is you’re going to finance the system, annual energy output. The difference the characteristics of your site, and the properties of the system you’re between power and energy is that considering. It then provides you with power (kilowatts [kW]) is the rate at a simple payback estimation in years. which electricity is consumed, while If it takes too long to regain your capi- energy (kilowatt-hours [kWh]) is the tal investment—the number of years quantity consumed. An estimate of comes too close or is greater than the the annual energy output from your life of the system—wind energy will wind turbine, kWh/year, is the best not be practical for you. way to determine whether a particular wind turbine and tower will produce enough electricity to meet your needs. A wind turbine manufacturer can help you estimate the energy production you can expect. They will use a cal- culation based on the particular wind turbine power curve, the average annual wind speed at your site, the
  13. 13. Small Wind Electric Systems 11 Is There Enough Wind particular location. Airport wind data on My Site? are generally measured at heights Does the wind blow hard and con- about 20–33 ft (6–10 m) above ground. sistently enough at my site to make a Average wind speeds increase with small wind turbine system economi- height and may be 15%–25% greater cally worthwhile? That is a key ques- at a typical wind turbine hub-height tion and not always easily answered. of 80 ft (24 m) than those measured The wind resource can vary signifi- at airport anemometer heights. The cantly over an area of just a few miles National Climatic Data Center collects because of local terrain influences data from airports in the United States on the wind flow. Yet, there are steps and makes wind data summaries you can take that will go a long way available for purchase. Summaries towards answering the above of wind data from almost 1000 U.S. question. airports are also included in the Wind Energy Resource Atlas of the United As a first step, wind resource maps States (see For More Information). like the one on pages 12 and 13 can be used to estimate the wind resource Another useful indirect measurement in your region. The highest average of the wind resource is the observa- wind speeds in the United States are tion of an area’s vegetation. Trees, generally found along seacoasts, on especially conifers or evergreens, can ridgelines, and on the Great Plains; be permanently deformed by strong however, many areas have wind winds. This deformity, known as resources strong enough to power a “flagging,” has been used to estimate small wind turbine economically. The the average wind speed for an area. wind resource estimates on this map For more information on the use of generally apply to terrain features that flagging, you may want to obtain are well exposed to the wind, such as plains, hilltops, and ridge crests. Local Wind Speeds Increase with Height terrain features may cause the wind ��������� resource at a specific site to differ con- ��� siderably from these estimates. More detailed wind resource information, including the Wind Energy Resource ��� Atlas of United States, published by the U.S. Department of Energy (DOE), can be found at the National ���������������� Wind Technology Center Web site at �� www.nrel.gov/wind/ and the DOE Wind Powering America Web site at www.windpoweringamerica.gov. �� Another way to indirectly quantify the wind resource is to obtain average wind speed information from a �� nearby airport. However, caution should be used because local terrain influences and other factors may cause the wind speed recorded at � � �� �� ��� ��� an airport to be different from your �������������������������
  14. 14. 12 Small Wind Electric Systems Small Wind Electric Systems 13
  15. 15. 14 Small Wind Electric Systems Flagging, the effect of strong winds on �������� � � area vegetation, �� �������� can help determine ��������������� ��������� ���������� area wind speeds. �������� �� ��� �� ������ �������� �������� �������� �������� �������� � �� ��� ������� �������� ��������� �������� �������� ��������� � �������������������������������������������� ������ �� ��� ���� ��� �� ��� ��� ��������� ���� ����� ������ ������ ������ ������ ��� ���������� ���� ���� ���� ���� ���� ���� �� A Siting Handbook for Small Wind How Do I Choose the Best Energy Conversion Systems (see For Site for My Wind Turbine? More Information). You can have varied wind resources Direct monitoring by a wind resource within the same property. In addition measurement system at a site pro- to measuring or finding out about vides the clearest picture of the avail- the annual wind speeds, you need to able resource. A good overall guide know about the prevailing directions on this subject is the Wind Resource of the wind at your site. If you live in Assessment Handbook (see For More complex terrain, take care in selecting Information). Wind measurement the installation site. If you site your systems are available for costs as low wind turbine on the top of or on the as $600 to $1200. This expense may or windy side of a hill, for example, you may not be hard to justify depending will have more access to prevailing on the exact nature of the proposed winds than in a gully or on the lee- small wind turbine system. The mea- ward (sheltered) side of a hill on the surement equipment must be set high same property. In addition to geologic enough to avoid turbulence created formations, you need to consider by trees, buildings, and other obstruc- existing obstacles such as trees, tions. The most useful readings are houses, and sheds, and you need to those taken at hub-height, the eleva- plan for future obstructions such as tion at the top of the tower where the new buildings or trees that have not wind turbine is going to be installed. reached their full height. Your turbine If there is a small wind turbine sys- needs to be sited upwind of build- tem in your area, you may be able to ings and trees, and it needs to be 30 obtain information on the annual feet above anything within 300 feet. output of the system and also wind You also need enough room to raise speed data if available. and lower the tower for maintenance,
  16. 16. Small Wind Electric Systems 15 Obstruction of the Wind by a Building or Tree of Height (H) ������ ��������� 02979307m ��� ��������� � ���� 2H 20 H The farther you place your wind and if your tower is guyed, you must requires, the excess is sent or sold to turbine from allow room for the guy wires. the utility. obstacles such as buildings or Whether the system is stand-alone Grid-connected systems can be practi- trees, the less or grid-connected, you will also need cal if the following conditions exist: turbulence you will encounter. to take the length of the wire run • You live in an area with average between the turbine and the load annual wind speed of at least (house, batteries, water pumps, etc.) 10 mph (4.5 m/s) into consideration. A substantial amount of electricity can be lost as a • Utility-supplied electricity is result of the wire resistance—the lon- expensive in your area (about 10 to ger the wire run, the more electric- 15 cents per kilowatt-hour) ity is lost. Using more or larger wire • The utility’s requirements for will also increase your installation connecting your system to its grid cost. Your wire run losses are greater are not prohibitively expensive when you have direct current (DC) • There are good incentives for the instead of alternating current (AC). sale of excess electricity or for the So, if you have a long wire run, it is purchase of wind turbines. advisable to invert DC to AC. Federal regulations (specifically, the Can I Connect My System Public Utility Regulatory Policies Act to the Utility Grid? of 1978, or PURPA) require utilities Small wind energy systems can be to connect with and purchase power connected to the electricity distribu- from small wind energy systems. tion system and are called grid- However, you should contact your connected systems. A grid-connected utility before connecting to their dis- wind turbine can reduce your con- tribution lines to address any power sumption of utility-supplied electric- quality and safety concerns. Your ity for lighting, appliances, and utility can provide you with a list of electric heat. If the turbine cannot requirements for connecting your sys- deliver the amount of energy you tem to the grid. The American Wind need, the utility makes up the differ- Energy Association is another good ence. When the wind system produces source for information on utility more electricity than the household interconnection requirements. The
  17. 17. 16 Small Wind Electric Systems A grid-connected Grid-connected Systems wind turbine can reduce your consumption of ����� utility-supplied electricity. �� �������� ���� ���� ������� 02979301m following information about util- Most of North America gets more ity grid connection requirements wind in the winter than in the sum- was taken from AWEA’s Web site. mer. For people using wind energy to For more detailed information, visit displace a large load in the summer www.awea.org/ or contact AWEA like air-conditioning or irrigation (see For More Information). water pumping, having an annual NEG credit allows them to produce Net Metering NEG in the winter and be credited in The concept of net metering programs the summer. is to allow the electric meters of cus- tomers with generating facilities to Safety Requirements turn backwards when their generators Whether or not your wind turbine are producing more energy than the is connected to the utility grid, the customers’ demand. Net metering installation and operation of the wind allows customers to use their genera- turbine is probably subject to the tion to offset their consumption over electrical codes that your local gov- the entire billing period, not just ernment (city or county), or in some instantaneously. This offset would instances your state government, has enable customers with generating in place. The government’s principal facilities to receive retail prices for concern is with the safety of the more of the electricity they generate. facility, so these code requirements Net metering varies by state and emphasize proper wiring and installa- by utility company, depending on tion and the use of components whether net metering was legis- that have been certified for fire and lated or directed by the Public Utility electrical safety by approved testing Commission. Net metering programs laboratories, such as Underwriters all specify a way to handle the net Laboratories. Most local electrical excess generation (NEG) in terms of codes requirements are based on payment for electricity and/or length the National Electrical Code (NEC), of time allowed for NEG credit. If which is published by the National the net metering requirements define Fire Protection Association. As of NEG on a monthly basis, the consum- 1999, the latest version of the NEC did er can only get credit for their excess not have any sections specific to the that month. But if the net metering installation of wind energy facilities’ rules allow for annual NEG, the NEG consequently wind energy installa- credit can be carried for up to a year. tions are governed by the generic provisions of the NEC.
  18. 18. Small Wind Electric Systems 17 If your wind turbine is connected to provider. In the case of private (inves- the local utility grid so that any of the tor-owned) utilities, the terms and power produced by your wind tur- conditions in these agreements must bine is delivered to the grid, then your be reviewed and approved by state utility also has legitimate concerns regulatory authorities. about safety and power quality that Insurance need to be addressed. The utility’s principal concern is that your wind Some utilities require small wind turbine automatically stops deliver- turbine owners to maintain liability ing any electricity to its power lines insurance in amounts of $1 million or during a power outage. Otherwise more. Utilities consider these require- line workers and the public, thinking ments necessary to protect them from that the line is “dead,” might not take liability for facilities they do not own normal precautions and might be and have no control over. Others hurt or even killed by the power from consider the insurance requirements your turbine. Another concern among excessive and unduly burdensome, utilities is whether the power from making wind energy uneconomic. In your facility synchronizes properly the 21 years since utilities have been with the utility grid and it matches the required to allow small wind systems utility’s own power in terms of volt- to interconnect with the grid, there This grid- age, frequency, and power quality. has never been a liability claim, let connected, alone a monetary award, relating to 10-kW Bergey A few years ago, some state govern- electrical safety. wind turbine ments started developing new offsets standardized interconnection require- In seven states (California, Georgia, electrical power Maryland, Nevada, Oklahoma, consumption for ments for small renewable energy a small business generating facilities (including wind Oregon, and Washington), laws in Norman, turbines). In most cases, the new or regulatory authorities prohibit Oklahoma. requirements are based on consen- sus-based standards and testing pro- cedures developed by independent third-party authorities, such as the Institute of Electrical and Electronic Engineers and Underwriters Laboratories. Interconnection Requirements Most utilities and other electricity providers require you to enter into a formal agreement with them before you interconnect your wind turbine with the utility grid. In states that have retail competition for electricity service (e.g., your utility operates the local wires, but you have a choice of electricity provider) Bergey Windpower/PIX07166 you may have to sign a separate agreement with each company. Usually these agreements are writ- ten by the utility or the electricity
  19. 19. 18 Small Wind Electric Systems utilities from imposing any insurance facility. Although the basic principle requirements on small wind sys- is sound—utilities should not be tems that qualify for “net metering.” held responsible for property dam- In at least two other states (Idaho, age or personal injury attributable Virginia), regulatory authorities have to someone else—indemnity provi- allowed utilities to impose insurance sions should not favor the utility but requirements but have reduced the should be fair to both parties. Look for required coverage amounts to levels language that says, “each party shall consistent with conventional residen- indemnify the other . . .” rather than tial or commercial insurance policies “the customer shall indemnify the (e.g., $100,000 to $300,000). If your utility . . .” insurance amounts seem excessive, Customer Charges you can ask for a reconsideration from regulatory authorities (in the case of Customer charges can take a variety private investor-owned utilities) or of forms, including interconnection the utility’s governing board (in the charges, metering charges, and case of publicly owned utilities). standby charges. You should not hesitate to question any charges that Indemnification seem inappropriate to you. Federal An indemnity is an agreement law (Public Utility Regulatory Policies between two parties in which one Act of 1978, or PURPA, Section 210) agrees to secure the other against loss prohibits utilities from assessing dis- or damage arising from some act or criminatory charges to customers who some assumed responsibility. In the have their own generation facilities. context of customer-owned generat- ing facilities, utilities often want customers to indemnify them for any potential liability arising from the operation of the customer’s generating Connecting to the Utility Grid: A Success Story This 10-kW Bergey wind turbine, installed on a farm in Southwestern Kansas in 1983, pro- duces an average 1700–1800 kilowatt-hours per month, reducing the user’s monthly utility bills by approximately 50%. The turbine cost about $20,000 when it was installed. Since then, the cost for operation and maintenance has been about $50 per year. The only unscheduled main- tenance activity over the years was repair to the turbine required as a result of a lightning strike. Insurance covered all but $500 of the $9000 cost of damages. The basic system parts include: Warren Gretz, NREL/PIX09634 Bergey XL.10 wind turbine 100-foot free-standing lattice tower Inverter
  20. 20. Small Wind Electric Systems 19 Hybrid Power Systems A hybrid system Combine multiple sources to deliver non-intermittent electric power that combines a wind system with a solar and/or diesel generator can provide reliable off- grid power around the clock. ���������� ��������� ������ ���� �������������� �� ���������� 02979301m ���� ������� ������������ Can I Go “Off-Grid”? For the times when neither the wind turbine nor the PV modules are pro- Hybrid Systems ducing, most hybrid systems provide Hybrid wind energy systems can power through batteries and/or an provide reliable off-grid power for engine-generator powered by conven- homes, farms, or even entire com- tional fuels such as diesel. If the bat- munities (a co-housing project, for teries run low, the engine-generator example) that are far from the near- can provide power and recharge est utility lines. According to many the batteries. Adding an engine- renewable energy experts, a “hybrid” generator makes the system more system that combines wind and complex, but modern electronic photovoltaic (PV) technologies offers controllers can operate these systems several advantages over either single automatically. An engine-generator system. In much of the United States, can also reduce the size of the other wind speeds are low in the summer components needed for the system. when the sun shines brightest and Keep in mind that the storage capac- longest. The wind is strong in the ity must be large enough to supply winter when less sunlight is available. electrical needs during non-charging Because the peak operating times periods. Battery banks are typically for wind and PV occur at different sized to supply the electric load for times of the day and year, hybrid one to three days. systems are more likely to produce power when you need it. (For more An off-grid hybrid system may be information on solar electric or PV practical for you if: systems, contact the Energy Efficiency • You live in an area with average and Renewable Energy Information annual wind speed of at least Portal—see For More Information.) 9 mph (4.0 m/s) • A grid connection is not available or can only be made through an
  21. 21. 20 Small Wind Electric Systems expensive extension. The cost of • You would like to gain energy running a power line to a remote independence from the utility site to connect with the utility grid • You would like to generate clean can be prohibitive, ranging from power. $15,000 to more than $50,000 per mile, depending on terrain. Living Off-Grid: A Success Story This home, built near Ward, Colorado (at an elevation of 9000 feet), has been off-grid since it was built in 1972. When the house was built, the nearest util- ity was over a mile away, and it would have cost between $60K–$70K (based on 1985 rates) to connect to the utility lines. The owners decided to install a hybrid electric system powered by wind, solar, and a generator for a cost of about $19,700. The parts of the system include: Bergey 1.5-kW wind turbine, 10-ft (3-m) diameter rotor, 70-ft. (21-m) tower Solarex PV panels, 480 watts 24 DC battery bank, 375 ampere-hours Trace sine wave inverter, 120 AC, 1 phase, 4 kW Onan propane-fueled generator, 6.5 kW rated (3 kW derated for altitude) Electric appliances in the home include television, stereo, two computers, toaster, blender, vacuum cleaner, and hair dryer. The largest electric loads are created by a well pump and washing machine. The generator runs about 20% of the time, par- ticularly when the washing machine is in use. Propane serves the other major loads in the home: range, refrigerator, hot Jim Green, NREL/PIX02796 water, and space heat. Solar collectors on the roof provide pre-heating for the hot water.
  22. 22. Small Wind Electric Systems 21 Glossary of Terms kWh—Kilowatt-hour, a measure Airfoil—The shape of the blade cross- of energy equal to the use of one section, which for most modern hori- kilowatt in one hour. zontal axis wind turbines is designed MW—Megawatt, a measure of power to enhance the lift and improve tur- (1,000,000 watts). bine performance. Nacelle—The body of a propeller-type Ampere-hour—A unit for the quantity wind turbine, containing the gearbox, of electricity obtained by integrating generator, blade hub, and other parts. current flow in amperes over the time O&M costs—Operation and mainte- in hours for its flow; used as a mea- nance costs. sure of battery capacity. Power coefficient—The ratio of the Anemometer—A device to measure power extracted by a wind turbine the wind speed. to the power available in the wind Average wind speed—The mean wind stream. speed over a specified period of time. Power curve—A chart showing a Blades—The aerodynamic surface that wind turbine’s power output across catches the wind. a range of wind speeds. Brake—Various systems used to stop PUC—Public Utility Commission, a the rotor from turning. state agency which regulates utilities. Converter—See Inverter. In some areas known as Public Service Commission (PSC). Cut-in wind speed—The wind speed at which a wind turbine begins to PURPA—Public Utility Regulatory generate electricity. Policies Act (1978), 16 U.S.C. § 2601.18 CFR §292 that refers to small Cut-out wind speed—The wind speed generator utility connection rules. at which a wind turbine ceases to generate electricity. Rated output capacity—The output power of a wind machine operating Density—Mass per unit of volume. at the rated wind speed. Downwind—On the opposite side Rated wind speed—The lowest wind from the direction from which the speed at which the rated output wind blows. power of a wind turbine is produced. Furling—A passive protection for the Rotor—The rotating part of a wind turbine in which the rotor folds either turbine, including either the blades up or around the tail vane. and blade assembly or the rotating Grid—The utility distribution system. portion of a generator. The network that connects electricity Rotor diameter—The diameter of the generators to electricity users. circle swept by the rotor. HAWT—Horizontal axis wind turbine. Rotor speed—The revolutions per Inverter—A device that converts direct minute of the wind turbine rotor. current (DC) to alternating current Start-up wind speed—The wind speed (AC). at which a wind turbine rotor will kW—Kilowatt, a measure of power for begin to spin. See also Cut-in wind electrical current (1000 watts). speed.
  23. 23. 22 Small Wind Electric Systems Swept area—The area swept by the Wind Energy Basics turbine rotor, A = π R2, where R is the Paul Gipe radius of the rotor. ISBN 1-890132-07-01 Tip speed ratio—The speed at the tip A comprehensive guide to modern of the rotor blade as it moves through small wind technology. the air divided by the wind velocity. American Wind Energy Association This is typically a design requirement (202) 383-2500 for the turbine. www.awea.org or Turbulence—The changes in wind Chelsea Green Publishing Company speed and direction, frequently www.chelseagreen.com caused by obstacles. Wind Energy Resource Atlas of the Upwind—On the same side as the United States direction from which the wind is D. Elliott et al. blowing—windward. American Wind Energy Association VAWT—Vertical axis wind turbine. (202) 383-2500 www.awea.org Wind farm—A group of wind tur- rredc.nrel.gov/wind/pubs/atlas bines, often owned and maintained by one company. Also known as a wind Wind Power for Home, Farm, and power plant. Business: Renewable Energy for the New Millenium Yaw—The movement of the tower top Paul Gipe turbine that allows the turbine to stay ISBN-1-931498-14-8 into the wind. Completely revised and expanded For More Information edition of Wind Power for Home and Business Books Chelsea Green Publishing Company A Siting Handbook for Small Wind www.chelseagreen.com Energy Conversion Systems Wind Power Workshop H. Wegley, J. Ramsdell, M. Orgill and Hugh Piggott R. Drake Provides an overview on how to Report No. PNL-2521 Rev.1, 1980 design a home-built wind turbine. National Technical Information The Center for Alternative Service Technology 5285 Port Royal Rd. Machynlleth, Powys Springfield, VA 22151 SY20 9AZ, UK (800) 553-6847 Phone: 06154-702400 www.ntis.gov E-mail: help@catinfo.demon.co.uk Energy Savers Tips on Saving Energy www.foe.co.uk/CAT and Money at Home — A consumer’s guide for saving energy and reducing utility bills. www.eere.energy.gov/ consumerinfo/energy_savers
  24. 24. Small Wind Electric Systems 23 Government Agencies Videos U.S. Department of Energy’s Energy An Introduction to Residential Wind Efficiency and Renewable Energy Systems with Mick Sagrillo Information Portal A 63-minute video answering ques- www.eere.energy.gov tions most often asked by homeown- National Climatic Data Center ers as they consider purchasing and Federal Building, 151 Patton Avenue installing wind power systems Asheville, North Carolina, 28801-5001 American Wind Energy Association Phone: (828) 271-4800 Phone: (202) 383-2500 www.ncdc.noaa.gov www.awea.org U.S. Department of Commerce Web Sites National Technical Information Small Wind Systems Service Includes answers to frequently asked 5285 Port Royal Road questions and information on U.S. Springfield, Virginia 22161 manufacturers. (800) 553-6847 www.awea.org/smallwind.html www.ntis.gov Database of State Incentives for Non-Government Organizations Renewable Energy American Wind Energy Association www.dsireusa.org 1101 14th St., NW Green Power Network Net Metering 12th Floor Net metering programs are now avail- Washington, D.C. 20005 able in more than 35 states. Phone: (202) 383-2500 www.eere.energy.gov/greenpower/ www.awea.org markets Solar Energy International Small Wind “Talk” on the Web Short courses on renewable energy AWEA’s Home Energy Systems elec- and sustainable development tronic mailing list is a forum for the Phone: (970) 963-8855 discussion of small-scale energy sys- www.solarenergy.org tems that include wind. To subscribe, send a subscription request to awea- Periodicals wind-home-subscribe@egroups.com. Apples and Oranges Mick Sagrillo Wind Energy for Homeowners A comprehensive comparison of This Web page covers items you available small wind turbines avail- should consider before investing able on the Home Power Magazine in a small wind energy system and Web site: www.homepower.com provides basic information about the systems. Home Power Magazine www.nrel.gov/clean_energy/home_ The definitive bimonthly magazine wind.html for the homemade power enthusiast. Phone: (800)707-6586 Wind Resource Assessment www.homepower.com Handbook www.nrel.gov/docs/legosti/fy97/ 22223.pdf
  25. 25. 24 Small Wind Electric Systems 2002 Farm Bill — Wind The amount of the payments depends on the size of the wind installation, the pro- Energy Development duction of electricity by that system, and Provisions the length of the contract period. Mainstay offers 3-, 5-, and 10-year purchase con- Renewable Energy Systems and tracts. The longer contract periods provide Energy Efficiency Improvements greater incentive payments on a $/kWh Incentive Type: Low-interest loans, loan basis. Typical payments for wind, which guarantees, and grants are made quarterly, range from 0.2¢/kWh Eligible Technologies: Renewable energy to 1.5¢/kWh. systems (energy derived from wind, solar, biomass, geothermal, and hydro- There is a $100 certification fee to get gen derived from biomass or water started with Mainstay Rewards. However, using a renewable energy source) and the fee may be paid with future green tag energy efficiency improvements. sales, and is generally waived for partici- Applicable Sectors: Agriculture, rural pants who opt for 10-year contracts. small commercial The requirements are: Amount: Varies. The grant may not exceed 1. The system must be grid-connected; 25% of the cost of a project, and a com- 2. Net-metering by the utility does not bined grant and loan or guarantee may restrict the system owner from selling not exceed 50% of the cost of a project. the green tags; Terms: 2003 – 2007 3. The system owner must have title to the Date Enacted: 2002 green tags or renewable energy credits. Authority: Farm Bill, Title IX, Section 9006 They cannot have been sold Summary: This law allows direct financial or transferred to any other entity; assistance to farmers, ranchers, and rural 4. The system must be a new renewable, small businesses for the purchase of wind which, in most states, means pow- power and other renewable energy sys- ered up on or after 1/1/1999. See the tems and for energy efficiency improve- Mainstay Energy web site for ments. This program is authorized for exceptions; funding for up to $23,000,000 per year in 5. For any systems over 10 kW, the system 2003-2007, totaling up to $115 million. In generation must be metered separately. determining the amount of a grant or loan, For systems under 10 kW, separate USDA shall consider the type of renewable metering is not necessary. Payments energy system, the quantity of energy likely are made based on estimated to be generated, the expected environmen- production. tal benefits, the extent to which the system Contact: is replicable, and the amount of energy Mainstay Rewards Program savings from energy efficiency improve- Mainstay Energy ments and the likely payback period. 161 E. Chicago Ave. USDA Rural Development State Office Suite 41B contacts can be found at www.rurdev. Chicago, IL 60611-2624 usda.gov/rbs/farmbill/contacts.htm Phone: (877) 473-3682 Fax: (312) 896-1515 USDA Farm Bill Web site: www.rurdev. E-Mail: info@mainstayenergy.com usda.gov/rbs/farmbill/resourc.htm Web site: http://mainstayenergy.com Green Tag Purchase Program Mainstay Energy is a private company offering customers who install, or have installed, renewable energy systems the opportunity to sell the green tags (also known as renewable energy credits, or RECs) associated with the energy gener- ated by these systems. These green tags will be brought to market as Green-e* http://www.green-e.org or state certified products. Participating customers receive regular, recurring payments through the Mainstay Energy Rewards Program.
  26. 26. Small Wind Electric Systems Notes
  27. 27. U.S. Department of Energy Regional Offices www.eere.energy.gov/regions/ States in Region Southeast Regional Office 75 Spring Street, S.W., Suite 200 Alabama, Arkansas, Florida, Georgia, Atlanta, GA 30303 Kentucky, Mississippi, North Carolina, (404) 562-0555 South Carolina, Tennessee, Puerto Rico, www.eere.energy.gov/regions/southeast U.S. Virgin Islands Northeast Regional Office JFK Federal Building, Suite 675 Connecticut, Maine, Massachusetts, Boston, MA 02203 New Hampshire, New York, Rhode Island, (617) 565-9700 Vermont www.eere.energy.gov/regions/northeast Midwest Regional Office One South Wacker Drive, Suite 2380 Illinois, Indiana, Iowa, Michigan, Chicago, IL 60606-4616 Minnesota, Missouri, Ohio, Wisconsin (312) 353-6749 www.eere.energy.gov/regions/midwest Central Regional Office 1617 Cole Blvd. Colorado, Kansas, Louisiana, Montana, Golden, CO 80401 Nebraska, New Mexico, North Dakota, (303) 275-4826 Oklahoma, South Dakota, Texas, Utah, www.eere.energy.gov/regions/central Wyoming Mid-Atlantic Regional Office 1880 John F. Kennedy Boulevard, Suite 501 Delaware, Washington DC, Maryland, Philadelphia, PA 19103 New Jersey, Pennsylvania, Virginia, (215) 656-6950 West Virginia www.eere.energy.gov/regions/mid-atlantic Western Regional Office 800 Fifth Ave., Suite 3950 Alaska, Arizona, California, Hawaii, Idaho, Seattle, WA 98104-3122 Nevada, Oregon, Washington, American (206) 553-1132 Samoa, Guam, Palau, North Marianas www.eere.energy.gov/regions/western Wind Powering America www.windpoweringamerica.gov A Strong Energy Portfolio for a Strong America Energy efficiency and clean, renewable energy will mean a stronger economy, a cleaner environment, and greater energy independence for America. Working with a wide array of state, community, industry, and university partners, the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy invests in a diverse portfolio of energy technologies. Produced for the U.S. Department of Energy by the For more information contact: National Renewable Energy Laboratory, EERE Information Center a DOE national laboratory 1-877-EERE-INF (1-877-337-3463) www.eere.energy.gov DOE/GO-102005-2095 • March 2005 Printed with a renewable-source ink on paper containing at least 50% wastepaper, including 20% postconsumer waste.