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Small Wind Electric Systems
An Oregon
Consumer's Guide
U.S. Department of Energy
Small Wind Electric Systems
Cover photo: . This Southwest Air 403 wind turbine is one of two turbines in a grid-connected solar hybrid
system used for utility bill reduction for this home in Elgin, Oregon.
Photo credit: Charles Koch/PIX10973
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
sources of electricity.
Small wind electric systems can
make a significant contribution to
our nation's energy needs. Although
wind turbines large enough to pro-
vide a significant portion of the elec-
tricity needed by the average U.S.
home generally require one acre of
property or more, approximately
21 million U.S. homes are built on
Bergey Windpower/PIX01476
one-acre and larger sites, and 24%
of the U.S. population lives in rural
areas.
A small wind electric system will
work for you if: Homeowners, ranchers, and small businesses can use wind-
• There is enough wind where you generated electricity to reduce their utility bills. This grid-
connected system installed for a home in Norman, Oklahoma,
live reduces the homeowner's utility bill by $100 per month.
• Tall towers are allowed in your
neighborhood or rural area
• You have enough space Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
• You can determine how much
First, How Can I Make My Home More Energy Efficient? . . . .2
electricity you need or want to
produce Is Wind Energy Practical for Me? . . . . . . . . . . . . . . . . . . . . . .3
What Size Wind Turbine Do I Need? . . . . . . . . . . . . . . . . . . . .4
• It works for you economically.
What are the Basic Parts of a Small Wind Electric System? . .5
The purpose of this guide is to pro- What Do Wind Systems Cost? . . . . . . . . . . . . . . . . . . . . . . . .7
vide you with the basic information Where Can I Find Installation and Maintenance Support? . . . .8
about small wind electric systems to How Much Energy Will My System Generate? . . . . . . . . . . . .9
help you decide if wind energy will
Is There Enough Wind on My Site? . . . . . . . . . . . . . . . . . . . .11
work for you.
How Do I Choose the Best Site for My Wind Turbine? . . . . .14
Why Should I Choose Wind? Can I Connect My System to the Utility Grid? . . . . . . . . . . . .15
Wind energy systems are one of the Can I Go "Off-Grid"? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
most cost-effective home-based Glossary of Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
renewable energy systems. For More Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22
2 Small Wind Electric Systems
Depending on your wind resource, a Home Energy Use
small wind energy system can lower Based on national averages
your electricity bill by 50% to 90%,
help you avoid the high costs of Water
having utility power lines extended heating
to remote locations, prevent power 14%
interruptions, and it is nonpolluting. Heating and
Lighting, cooling
How Do Wind Turbines Work? cooking, 44%
and other
Wind is created by the unequal heat- appliances
ing of the Earth's surface by the sun. 33%
02979309m
Wind turbines convert the kinetic
energy in wind into mechanical
power that runs a generator to
Refrigerator 9%
produce clean electricity. Today's
turbines are versatile modular sources The largest portion of a utility bill for a typical
of electricity. Their blades are aerody- house is for heating and cooling.
namically designed to capture the
maximum energy from the wind. The proper insulation and
wind turns the blades, which spin a weatherization products.
shaft connected to a generator that • Save money and increase comfort
makes electricity. by properly maintaining and
upgrading your heating,
First, How Can I Make
ventilation, and air-conditioning
My Home More Energy systems.
Efficient?
• Install double-paned, gas-filled
Before choosing a wind system for
windows with low-emissivity
your home, you should consider
(low-e) coatings to reduce heat
reducing your energy consumption by
loss in cold climates and spectrally
making your home or business more
selective coatings to reduce heat
energy efficient. Reducing your
gain in warm climates.
energy consumption will significantly
lower your utility bills and will • Replace your lights in high-use
reduce the size of the home-based areas with fluorescents. Replacing
renewable energy system you need. 25% of your lights can save about
To achieve maximum energy effi- 50% of your lighting energy bill.
ciency, you should take a whole- • When shopping for appliances,
building approach. View your home look for the ENERGY STAR® label.
as an energy system with interrelated ENERGY STAR® appliances have
parts, all of which work synergisti- been identified by the U.S.
cally to contribute to the efficiency of Environmental Protection Agency
the system. From the insulation in and U.S. Department of Energy
your home's walls to the light bulbs in as being the most energy-efficient
its fixtures, there are many ways you products in their classes.
can make your home more efficient.
• For more information on how to
• Reduce your heating and cooling make your home energy efficient,
needs by up to 30% by investing see Energy Savers, in the For More
just a few hundred dollars in Information section.
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 that does not have easy tive data. For example, the ambient
access to 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 potential sized wind turbine is no noisier than
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
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 to electricity you want to generate. For
100 kilowatts. The smaller or "micro" residential applications, you should
(20–500-watt) turbines are used in a establish an energy budget to help
variety of applications such as charg- define the size of turbine you will
ing batteries for recreational vehicles need. Because energy efficiency is
and sailboats. usually less expensive than energy
production, making your house more
One- to 10-kW turbines can be used in energy efficient first will probably be
applications such as pumping water. more cost effective and will reduce
Wind energy has been used for cen- the size of the wind turbine you need
turies to pump water and grind grain. (see How Can I Make My Home
Although mechanical windmills still More Energy Efficient?). Wind turbine
provide a sensible, low-cost option for manufacturers can help you size your
pumping water in low-wind areas, 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 9400 kilowatt-hours (kWh) of electric-
windmills must be placed directly ity per year (about 780 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 kilo-
systems can be placed where the wind watts (kW) would be required to
resource is the best and connected to make a significant contribution to this
the pump motor with an electric demand. A 1.5- kW wind turbine will
cable. meet the needs of a home requiring
300 kWh per month in a location with
This 1 kW Whisper a 14-mile-per-hour (6.26-meters-per-
turbine provides second) annual average wind speed.
direct AC power for
the water pump for The manufacturer can provide you
stock tanks on a with the expected annual energy out-
ranch in Wheeler, put of the turbine as a function of
Texas.
annual average wind speed. The
manufacturer will also provide infor-
mation on the maximum wind speed
at which the turbine is designed to
operate safely. Most turbines have
automatic overspeed-governing sys-
tems to keep the rotor from spinning
out of control in very high winds. This
information, along with your local
Elliott Bayly/PIX09681
wind speed and your energy budget,
will help you decide which size tur-
bine will best meet your electricity
needs.
Small Wind Electric Systems 5
What are the Basic Parts Basic Parts of a Small
of a Small Wind Electric Wind Electric System
System? Rotor
Home wind energy systems gener-
Generator/ Tail
ally comprise a rotor, a generator or alternator
alternator mounted on a frame, a tail
02979312m
(usually), a tower, wiring, and the
"balance of system" components:
controllers, inverters, and/or batter-
ies. Through the spinning blades, the Tower
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 power production. For instance, to
that have two or three blades, which raise a 10-kW generator from a 60-foot
are usually made of a composite mate- tower height to a 100-foot tower
rial such as fiberglass. involves a 10% increase in overall
system cost, but it can produce 25%
The amount of power a turbine will more power.
produce is determined primarily by
the diameter of its rotor. The diameter There are two basic types of towers:
of the rotor defines its "swept area," or self-supporting (free standing) and
the quantity of wind intercepted by guyed. Most home wind power sys-
the turbine. The turbine's frame is the tems use a guyed tower. Guyed tow-
structure onto which the rotor, genera- ers, which are the least expensive, can
tor, and tail are attached. The tail consist of lattice sections, pipe, or tub-
keeps the turbine facing into the ing depending on the design, and
wind. supporting guy wires. They are easier
to install than self-supporting towers.
Tower However, because the guy radius
Because wind speeds increase with must be one-half to three-quarters
height, the turbine is mounted on of the tower height, guyed towers
a tower. In general, the higher the require enough space to accommodate
tower, the more power the wind them. While tilt-down towers are
Tilt-down towers
system can produce. The tower also more expensive they offer the con- provide easy
raises the turbine above the air sumer an easy way to perform maintenance for
turbulence that can exist close to turbines.
the ground because of obstructions
Tilt-Down Tower
such as hills, buildings, and trees. A
Tilt-up tower
general rule of thumb is to install a in the normal
wind turbine on a tower with the operating
Tilt-up tower in the position
bottom of the rotor blades at least lowered position for
30 feet (9 meters) above any obstacle maintenance or
hurricanes
that is within 300 feet (90 meters) of
the tower. Relatively small invest-
ments in increased tower height can
yield very high rates of return in 02979311m
6 Small Wind Electric Systems
maintenance on smaller light-weight a residential grid-connected applica-
turbines, usually 5 kW or less. Tilt- tion, the balance of system parts may
down towers can also be lowered to include a controller, storage batteries,
the ground during hazardous weather a power conditioning unit (inverter),
such as hurricanes. Aluminum towers and wiring. Some wind turbine
are prone to cracking and should be controllers, inverters, or other electri-
avoided. Most turbine manufacturers cal devices may be stamped by a
provide wind energy system packages recognized testing agency, like
that include towers. Underwriters Laboratories.
Mounting turbines on rooftops is not Stand-Alone Systems
recommended. All wind turbines Stand-alone systems (systems not con-
vibrate and transmit the vibration nected to the utility grid) require bat-
to the structure on which they are teries to store excess power generated
mounted. This can lead to noise and for use when the wind is calm. They
structural problems with the building, also need a charge controller to keep
and the rooftop can cause excessive 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 and
Balance of System recharge 80% of their capacity hun-
The parts that you need in addition to dreds of times, which makes them a
the turbine and the tower, or the bal- good option for remote renewable
ance of system parts, will depend on energy systems. Automotive batteries
your application. Most manufacturers are shallow-cycle batteries and should
can provide you with a system pack- not be used in renewable energy sys-
age that includes all the parts you tems because of their short life in
need for your application. For exam- 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 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
Trudy Forsyth, NREL/PIX09122 and PIX09123
home in Vermont.
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.
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 source of electricity
to use standard appliances that use for this remote
home in northern
conventional household alternating Arizona.
current (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, electri-
cal code officials, and future
Southwest Windpower/PIX09156
homebuyers.
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.
proportionally more expensive. The
Grid-Connected Systems cost of an installed residential wind
In grid-connected systems, the only energy system that comes with an
additional equipment required is a 80-foot tower, batteries, and inverter,
power conditioning unit (inverter) typically ranges from $13,000 to
that makes the turbine output electri- $40,000 for a 3 to 10 kW wind turbine.
cally compatible with the utility grid. Although wind energy systems
Usually, batteries are not needed. involve a significant initial invest-
ment, they can be competitive with
What Do Wind Systems conventional energy sources when
Cost? you account for a lifetime of reduced
A small turbine can cost anywhere or avoided utility costs. The length of
from $3,000 to $35,000 installed, the payback period—the time before
depending on size, application, and the savings resulting from your sys-
service agreements with the manufac- tem equal the cost of the system
turer. (The American Wind Energy itself—depends on the system you
Association [AWEA] says a typical choose, the wind resource on your
home wind system costs approxi- site, electricity costs in your area, and
mately $32,000 (10 kW); a comparable how you use your wind system. For
photovoltaic [PV] solar system would example, if you live in California and
cost over $80,000.) have received the 50% buydown of
A general rule of thumb for estimating your small wind system, have net
the cost of a residential turbine is metering, and an average annual
$1,000 to $3,000 per kilowatt. Wind wind speed of 15 miles per hour
energy becomes more cost effective (mph) (6.7 meters per second [m/s]),
as the size of the turbine’s rotor your simple payback would be
increases. Although small turbines approximately 6 years.
cost less in initial outlay, they are
8 Small Wind Electric Systems
the company's integrity and ask for
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
Warren Gretz, NREL/PIX09615
able to help you install your machine.
Many people elect to install the
machines themselves. Before attempt-
ing to install your wind turbine, ask
yourself the following questions:
• Can I pour a proper cement
foundation?
Small wind • Do I have access to a lift or a way of
turbines like this Things to Consider When erecting the tower safely?
10 kW Bergey Purchasing a Wind Turbine
XL.10 provide • Do I know the difference between
electricity for Once you determine you can install a AC and DC wiring?
home, farm, and
ranch applications.
wind energy system in compliance • Do I know enough about electricity
with local land use requirements, you to safely wire my turbine?
can begin pricing systems and compo-
nents. Comparatively shop for a wind • Do I know how to safely handle
system as you would any major pur- and install batteries?
chase. Obtain and review the product If you answered no to any of the
literature from several manufacturers. above questions, you should probably
As mentioned earlier, lists of manu- choose to have your system installed
facturers are available from AWEA, by a system integrator or installer.
(see For More Information), but not Contact the manufacturer for help
all small turbine manufacturers are or call your state energy office and
members of AWEA. Check the yellow local utility for a list of local system
pages for wind energy system dealers installers. You can also check the yel-
in your area. low pages for wind energy system
Once you have narrowed the field, service providers. A credible installer
research a few companies to be sure will provide many services such as
they are recognized wind energy permitting. Find out if the installer is
businesses and that parts and service a licensed electrician. Ask for refer-
will be available when you need ences and check them out. You may
them. You may wish to contact the also want to check with the Better
Better Business Bureau to check on Business Bureau.
Small Wind Electric Systems 9
Although small wind turbines are that the wind speed, V, has an
very sturdy machines, they do require exponent of 3 applied to it. This
some annual maintenance. Bolts and means that even a small increase in
electrical connections should be wind speed results in a large increase
checked and tightened if necessary. in power. That is why a taller tower
The machines should be checked for will increase the productivity of any
corrosion and the guy wires for wind turbine by giving it access to
proper tension. In addition, you higher wind speeds as shown in the
should check for and replace any Wind Speeds Increase with Height
worn leading edge tape on the blades, graph. The formula for calculating
if appropriate. After 10 years, the the power from a wind turbine is:
blades or bearings may need to be Power = Cp 1/2 ρ A V3
replaced, but with proper installation
and maintenance, the machine should Where:
last up to 20 years or longer. Cp = Power coefficient, ranging
If you do not have the expertise to from 0.2–0.4, dimensionless
maintain the machine, your installer (theoretical max = 0.59)
may provide a service and mainte- ρ = Air density, lb/ft3
nance program.
A = Rotor swept area, or π D2/4
How Much Energy Will My (D is the rotor diameter in ft,
π = 3.1416)
System Generate?
Most U.S. manufacturers rate their V = Wind speed, mph
turbines by the amount of power they The rotor swept area, A, is important
can safely produce at a particular because the rotor is the part of the
wind speed, usually chosen between turbine that captures the wind energy.
24 mph (10.5 m/s) and 36 mph So, the larger the rotor, the more
(16 m/s). This formula illustrates energy it can capture. The air density,
factors that are important to the per- ρ, changes slightly with air tempera-
formance of a wind turbine. Notice ture and with elevation. The ratings
Relative Size of Small Wind Turbines
40
8
Swept area, m2
30
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
10 Small Wind Electric Systems
Air Density Change with Elevation the wind–an estimate of the number
10,000 of hours that the wind will blow at
9,000 each speed during an average year.
8,000 They should also adjust this calcula-
7,000 tion for the elevation of your site.
Elevation, ft
6,000 Contact a wind turbine manufacturer
5,000 or dealer for assistance with this
4,000 calculation.
3,000 To get a preliminary estimate of the
performance of a particular wind tur-
02979302m
2,000
1,000 bine, use the formula below.
0
70 75 80 85 90 95 100 AEO = 0.01328 D2 V3
Density change compared to sea level, %
Where:
AEO = Annual energy output,
for wind turbines are based on
kWh/year
standard conditions of 59° F (15° C)
at sea level. A density correction D = Rotor diameter, feet
should be made for higher elevations V = Annual average wind speed,
as shown in the Air Density Change mph
with Elevation graph. A correction for
temperature is typically not needed The Wind Energy Payback Period
for predicting the long-term perform- Workbook found at http://www.nrel.
ance of a wind turbine. gov/wind/ under consumer informa-
tion is a spreadsheet tool that can help
While the calculation of wind power you analyze the economics of a small
illustrates important features about wind electric system and decide
wind turbines, the best measure of whether wind energy will work for
wind turbine performance is annual you. The spreadsheet can be opened
energy output. The difference using Microsoft Excel 95 software.
between power and energy is that It asks you to provide information
power (kilowatts [kW]) is the rate at about how you're going to finance the
which electricity is consumed, while system, the characteristics of your
energy (kilowatt-hours [kWh]) is the site, and the properties of the system
quantity consumed. An estimate of you're considering. It then provides
the annual energy output from your you with a simple payback estimation
wind turbine, kWh/year, is the best in years. If it takes too long to regain
way to determine whether a particu- your capital investment—the number
lar wind turbine and tower will pro- of years comes too close or is greater
duce enough electricity to meet your than the life of the system—wind
needs. energy will not be practical for you.
A wind turbine manufacturer can help
you estimate the energy production
you can expect. They will use a calcu-
lation based on the particular wind
turbine power curve, the average
annual wind speed at your site, the
height of the tower that you plan to
use, and the frequency distribution of
Small Wind Electric Systems 11
Is There Enough Wind airport to be different from your par-
on My Site? ticular location. Airport wind data are
Does the wind blow hard and consis- generally measured at heights about
tently enough at my site to make a 20–33 ft (6–10 m) above ground.
small wind turbine system economi- Average wind speeds increase with
cally worthwhile? That is a key ques- height and may be 15%–25% greater
tion and not always easily answered. at a typical wind turbine hub-height
The wind resource can vary signifi- of 80 ft (24 m) than those measured
cantly over an area of just a few miles at airport anemometer heights. The
because of local terrain influences National Climatic Data Center collects
on the wind flow. Yet, there are steps data from airports in the United States
you can take that will go a long way and makes wind data summaries
towards answering the above available for purchase. Summaries of
question. wind data from almost 1000 U.S. air-
ports are also included in the Wind
As a first step, wind resource maps Energy Resource Atlas of the United
like the one on pages 12 and 13 can States (see For More Information).
be used to estimate the wind resource
in your region. The highest average Another useful indirect measurement
wind speeds in the United States are of the wind resource is the observa-
generally found along seacoasts, on tion of an area’s vegetation. Trees,
ridgelines, and on the Great Plains; especially conifers or evergreens, can
however, many areas have wind be permanently deformed by strong
resources strong enough to power a winds. This deformity, known as
small wind turbine economically. The "flagging," has been used to estimate
wind resource estimates on this map the average wind speed for an area.
generally apply to terrain features that For more information on the use of
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
02979308m
resource at a specific site to differ con- 150
siderably from these estimates. More
detailed wind resource information,
including the Wind Energy Resource
120
Atlas of United States, published by the
U.S. Department of Energy (DOE),
Tower height, ft
can be found at the National Wind
Technology Center web site at 90
http://www.nrel.gov/wind/ and the
DOE Windpowering America web
site at http://www.eren.doe.gov/ 60
windpoweringamerica/.
Another way to indirectly quantify
the wind resource is to obtain average
30
wind speed information from a
nearby airport. However, caution
should be used because local terrain
influences and other factors may 0
0 41 75 100 124
cause the wind speed recorded at an Increase in wind power, %
12 Small Wind Electric Systems Small Wind Electric Systems 13
14 Small Wind Electric Systems
Flagging, the effect
of strong winds on Flagging 0 I
area vegetation, No Brushing
can help determine Prevailing wind
deformity and slight
area wind speeds. flagging
II III IV
Slight Moderate Complete
flagging flagging flagging
V VI VII
Partial Complete Carpeting
throwing throwing
02979310m
Griggs-Putnam Index of Deformity
Index I II III IV V VI VII
Wind mph 7-9 9-11 11-13 13-16 15-18 16-21 22+
Speed m/s 3-4 4-5 5-6 6-7 7-8 8-9 10
flagging you may want to obtain output of the system and also wind
A Siting Handbook for Small Wind speed data if available.
Energy Conversion Systems (see For
More Information). How Do I Choose the Best
Direct monitoring by a wind resource
Site for My Wind Turbine?
measurement system at a site pro- You can have varied wind resources
vides the clearest picture of the avail- within the same property. In addition
able resource. A good overall guide to measuring or finding out about the
on this subject is the Wind Resource annual wind speeds, you need to
Assessment Handbook (see For More know about the prevailing directions
Information). Wind measurement sys- of the wind at your site. If you live in
tems are available for costs as low as complex terrain, take care in selecting
$600 to $1200. This expense may or the installation site. If you site your
may not be hard to justify depending wind turbine on the top of or on the
on the exact nature of the proposed windy side of a hill, for example, you
small wind turbine system. The meas- will have more access to prevailing
urement equipment must be set high winds than in a gully or on the lee-
enough to avoid turbulence created ward (sheltered) side of a hill on the
by trees, buildings, and other obstruc- same property. In addition to geologic
tions. The most useful readings are formations, you need to consider
those taken at hub-height, the eleva- existing obstacles such as trees,
tion at the top of the tower where the houses, and sheds, and you need to
wind turbine is going to be installed. plan for future obstructions such as
If there is a small wind turbine system new buildings or trees that have not
in your area, you may be able to reached their full height. Your turbine
obtain information on the annual needs to be sited upwind of buildings
Small Wind Electric Systems 15
Obstruction of the Wind by a Building
or Tree of Height (H)
Region
of highly
02979307m
2H
turbulent
H flow
2H 20 H
and trees, and it needs to be 30 feet need, the utility makes up the differ- The farther you
above anything within 300 feet. You ence. When the wind system produces place your wind
turbine from
also need enough room to raise and more electricity than the household obstacles such
lower the tower for maintenance, and requires, the excess is sent or sold to as buildings or
if your tower is guyed, you must the utility. trees, the less
turbulence you
allow room for the guy wires. Grid-connected systems can be practi- will encounter.
Whether the system is stand-alone cal if the following conditions exist:
or grid-connected, you will also need • You live in an area with average
to take the length of the wire run annual wind speed of at least
between the turbine and the load 10 mph (4.5 m/s).
(house, batteries, water pumps, etc.)
into consideration. A substantial • Utility-supplied electricity is
amount of electricity can be lost as a expensive in your area (about 10 to
result of the wire resistance—the 15 cents per kilowatt-hour).
longer the wire run, the more electric- • The utility's requirements for
ity is lost. Using more or larger wire connecting your system to its grid
will also increase your installation are not prohibitively expensive.
cost. Your wire run losses are greater
• There are good incentives for the
when you have direct current (DC)
sale of excess electricity or for the
instead of alternating current (AC).
purchase of wind turbines.
So, if you have a long wire run, it is
advisable to invert DC to AC. Federal regulations (specifically, the
Public Utility Regulatory Policies Act
Can I Connect My System of 1978, or PURPA) require utilities
to the Utility Grid? to connect with and purchase power
Small wind energy systems can be from small wind energy systems.
connected to the electricity distribu- However, you should contact your
tion system and are called grid- utility before connecting to their dis-
connected systems. A grid-connected tribution lines to address any power
wind turbine can reduce your con- quality and safety concerns. Your
sumption of utility-supplied electrici- utility can provide you with a list of
ty for lighting, appliances, and requirements for connecting your sys-
electric heat. If the turbine cannot tem to the grid. The American Wind
deliver the amount of energy you Energy Association is another good
source for information on utility
16 Small Wind Electric Systems
A grid-connected
Grid-connected Systems
wind turbine can
reduce your
consumption of Meter
utility-supplied
electricity.
AC
Inverter
Load
Wind
turbine
02979301m
interconnection requirements. The the NEG credit can be carried for up
following information about utility to a year.
grid connection requirements was Most of North America gets more
taken from AWEA's Web site. For wind in the winter than in the sum-
more detailed information, visit mer. For people using wind energy to
http://www.awea.org/ or contact displace a large load in the summer
AWEA (see For More Information). like air-conditioning or irrigation
Net Metering water pumping, having an annual
The concept of net metering programs NEG credit allows them to produce
is to allow the electric meters of cus- NEG in the winter and be credited in
tomers with generating facilities to the summer.
turn backwards when their generators Safety Requirements
are producing more energy than the Whether or not your wind turbine is
customers’ demand. Net metering connected to the utility grid, the
allows customers to use their genera- installation and operation of the wind
tion to offset their consumption over turbine is probably subject to the elec-
the entire billing period, not just trical codes that your local govern-
instantaneously. This offset would ment (city or county) or in some
enable customers with generating instances your state government has
facilities to receive retail prices for in place. The government’s principal
more of the electricity they generate. concern is with the safety of the
Net metering varies by state and by facility, so these code requirements
utility company, depending on emphasize proper wiring and installa-
whether net metering was legislated tion, and the use of components
or directed by the Public Utility that have been certified for fire and
Commission. Net metering programs electrical safety by approved testing
all specify a way to handle the net laboratories, such as Underwriters
excess generation (NEG) in terms of Laboratories. Most local electrical
payment for electricity and/or length codes requirements are based on the
of time allowed for NEG credit. If the National Electrical Code (NEC),
net metering requirements define which is published by the National
NEG on a monthly basis, the con- Fire Protection Association. As of
sumer can only get credit for their 1999, the latest version of the NEC did
excess that month. But if the net not have any sections specific to the
metering rules allow for annual NEG, installation of wind energy facilities,
Small Wind Electric Systems 17
consequently wind energy installa- agreement with each company.
tions are governed by the generic Usually these agreements are written
provisions of the NEC. by the utility or the electricity
If your wind turbine is connected to provider. In the case of private
the local utility grid so that any of the (investor-owned) utilities, the terms
power produced by your wind tur- and conditions in these agreements
bine is delivered to the grid, then your must be reviewed and approved by
utility also has legitimate concerns state regulatory authorities.
about safety and power quality that Insurance
need to be addressed. The utility’s Some utilities require small wind
principal concern is that your wind turbine owners to maintain liability
turbine automatically stops delivering insurance in amounts of $1 million or
any electricity to its power lines dur- more. Utilities consider these require-
ing a power outage. Otherwise line ments are necessary to protect them
workers and the public, thinking that from liability for facilities they do not
the line is "dead," might not take nor- own and have no control over. Others
mal precautions and might be hurt or consider the insurance requirements
even killed by the power from your excessive and unduly burdensome,
turbine. Another concern among utili- making wind energy uneconomic. In
ties is that the power from your facili- This grid-
the 21 years since utilities have been connected,
ty synchronize properly with the required to allow small wind systems 10 kW Bergey
utility grid, and that it match the util- to interconnect with the grid there wind turbine
ity’s own power in terms of voltage, has never been a liability claim, let
offsets electrical
frequency, and power quality. power
alone a monetary award, relating to consumption for
A few years ago, some state govern- electrical safety. a small business
in Norman,
ments started developing new
Oklahoma.
standardized interconnection require-
ments for small renewable energy
generating facilities (including wind
turbines). In most cases the new
requirements have been based on con-
sensus-based standards and testing
procedures developed by independ-
ent 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
Bergey Windpower/PIX07166
have retail competition for electricity
service (e.g., your utility operates
the local wires, but you have a
choice of electricity provider)
you may have to sign a separate
18 Small Wind Electric Systems
In six states (California, Maryland, generating facilities, utilities often
Nevada, Oklahoma, Oregon, and want customers to indemnify them
Washington), laws or regulatory for any potential liability arising from
authorities prohibit utilities from the operation of the customer’s generat-
imposing any insurance requirements ing facility. Although the basic princi-
on small wind systems that qualify for ple is sound—utilities should not be
"net metering." In at least three other held responsible for property damage
states (Idaho, New York, Virginia) reg- or personal injury attributable to
ulatory authorities have allowed utili- someone else—indemnity provisions
ties to impose insurance requirements, should not favor the utility but should
but have reduced the required cover- be fair to both parties. Look for lan-
age amounts to levels consistent with guage that says, "each party shall
conventional residential or commer- indemnify the other . . ." rather than
cial insurance policies (e.g., $100,000 "the customer shall indemnify the
to $300,000). If your insurance utility . . ."
amounts seem excessive, you can ask
Customer Charges
for a reconsideration from regulatory
authorities (in the case of private Customer charges can take a variety
investor-owned utilities) or to the of forms, including interconnection
utility’s governing board (in the case charges, metering charges, and
of publicly-owned utilities). standby charges, among others. You
should not hesitate to question any
Indemnification charges that seem inappropriate to
An indemnity is an agreement you. Federal law (Public Utility
between two parties where one agrees Regulatory Policies Act of 1978, or
to secure the other against loss or PURPA, Section 210) prohibits utilities
damage arising from some act or from assessing discriminatory charges
some assumed responsibility. In to customers who have their own
the context of customer-owned generation facilities.
Connecting to the Utility Grid—
A Success Story
This 10-kW Bergey wind turbine, installed on a
farm located in Southwestern Kansas in 1983,
produces 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 damage caused by
a lightning strike. Insurance covered all but $500
of the $9000 cost of damages. The basic system
Warren Gretz, NREL/PIX09634
parts include:
Bergey XL.10 wind turbine
100-foot free-standing lattice tower
Inverter
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.
PV modules
Generator
AC or Load
Regulation and DC
conversion
02979301m
Wind
turbine
Battery bank
Can I Go "Off-Grid"? For the times when neither the wind
nor the PV modules are producing,
Hybrid Systems
most hybrid systems provide power
Hybrid wind energy systems can through batteries and/or an engine-
provide reliable off-grid power for generator powered by conventional
homes, farms or even entire com- fuels such as diesel. If the batteries
munities (a co-housing project, for run low, the engine-generator can
example) that are far from the nearest provide power and recharge the bat-
utility lines. According to many teries. Adding an engine-generator
renewable energy experts, a "hybrid" makes the system more complex, but
system that combines wind and modern electronic controllers can
photovoltaic (PV) technologies offers operate these systems automatically.
several advantages over either single An engine-generator can also reduce
system. In much of the United States, the size of the other components
wind speeds are low in the summer needed for the system. Keep in mind
when the sun shines brightest and that the storage capacity must be
longest. The wind is strong in the large enough to supply electrical
winter when there is less sunlight needs during non-charging periods.
available. Because the peak operating Battery banks are typically sized to
times for wind and PV occur at differ- supply the electric load for one to
ent times of the day and year, hybrid 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 practical for you if:
PV systems, contact the Energy • You live in an area with average
Efficiency and Renewable Energy annual wind speed of at least
Clearinghouse—see For More 9 mph (4.0 m/s).
Information.)
• A grid connection is not available
or can only be made through an
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 in Ward, Colorado (at an elevation of 9000 feet), has
been off-grid since it was built in 1972. When the house was built, the near-
est utility 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,
particularly when the washing machine
is in use. Propane serves the other major
Jim Green, NREL/PIX02796
loads in the home: range, refrigerator, hot
water, and space heat. Solar collectors on
the roof provide pre-heating for the hot
water.
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 of for the quan- wind turbine, containing the gearbox,
tity of electricity obtained by integrat- generator, blade hub, and other parts.
ing current flow in amperes over the
O&M Costs—Operation and mainte-
time in hours for its flow; used as a
nance costs.
measure 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 wind turbine's power output across
that 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 is blowing. power of a wind turbine is produced.
Furling—A passive protection for the Rotor—The rotating part of a wind
turbine where typically the rotor folds turbine, including either the blades
either 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 begin to spin. See also cut-in wind
for electrical current (1000 watts). speed.
22 Small Wind Electric Systems
Swept area—The area swept by the wind technology. Available through
turbine rotor, A = πR2, where R is the AWEA. (202) 383-2500. http://www.
radius of the rotor. awea.org and Chelsea Green
Tip speed ratio—The speed at the tip Publishing Company, White River
of the rotor blade as it moves through Junction, Vermont. 1999. ISBN
the air divided by the wind velocity. 1-890132-07-01. http://www.
This is typically a design requirement chelseagreen.com
for the turbine. Wind Energy Resource Atlas of the
Turbulence—The changes in wind United States by D. Elliott et al.
speed and direction, frequently Available from the American Wind
caused by obstacles. Energy Association, 122 C. Street
N.W., Washington D.C. 20001.
Upwind—On the same side as the http://rredc.nrel.gov/wind/pubs/
direction from which the wind is atlas
blowing—windward.
Wind Power for Home and Business by
VAWT—Vertical axis wind turbine. Paul Gipe—A comprehensive guide
Wind farm—A group of wind tur- to modern small wind technology.
bines, often owned and maintained by Available through AWEA. (202) 383-
one company. Also known as a wind 2500. http://www.awea.org and
power plant. Chelsea Green Publishing Company,
White River Junction, Vermont. 1999.
Yaw—The movement of the tower top
ISBN - 0-930031-64-4. http://www.
turbine that allows the turbine to stay
chelseagreen.com
into the wind.
Wind Power Workshop by Hugh
For More Information Piggott—Provides an overview on
Books how to design a home-built wind tur-
bine. Available from The Center for
A Siting Handbook for Small Wind
Alternative Technology, Machynlleth,
Energy Conversion Systems. H. Wegley,
Powys, SY20 9AZ, UK Phone: 06154-
J. Ramsdell, M. Orgill and R. Drake,
702400, FAX: 01654 702782. E-mail:
Report No. PNL-2521 Rev.1, 1980;
help@catinfo.demon.co.uk,
available from National Technical
http://www.foe.co.uk/CAT
Information Service, 5285 Port Royal
Rd., Springfield, VA 22151. Wind Resource Assessment Handbook:
(800) 553-6847. http://www.ntis. Fundamentals for Conducting a
gov/ordering.htm Successful Monitoring Program—This
handbook presents industry-accepted
Energy Savers Tips on Saving Energy
guidelines for planning and conduct-
and Money at Home—A consumer's
ing a wind resource measurement
guide for saving energy and reducing
program. These guidelines, which are
utility bills. Available from U.S.
detailed and highly technical, empha-
Department of Energy's Energy
size the tasks of selecting, installing,
Efficiency and Renewable Energy
and operating wind measurement
Clearinghouse (EREC), P.O. Box 3048,
equipment, as well as collecting and
Merrifield, Virginia 22116. (800)
analyzing the associated data.
363-3732. http://www.eren.doe.gov/
Prepared by AWS Scientific, Inc.
consumerinfo/energy_savers.
Available electronically in NREL's
Wind Energy Basics by Paul Gipe—A publication database at http://www.
comprehensive guide to modern small nrel.gov/publications.
Small Wind Electric Systems 23
Government Agencies systems. Order from AWEA (202) 383-
Energy Efficiency and Renewable 2500, http://www.awea.org
Energy Clearinghouse, P.O. Box 3048, Web Sites
Merrifield, Virginia 22116 800-DOE-
AWEA Small Wind Systems Web
EREC (363-3732). http://www.eren.
site—Includes answers to frequently
doe.gov
asked questions and information on
National Climatic Data Center, U.S. manufacturers. http://www.
Federal Building, 151 Patton Avenue, awea.org/smallwind.html
Asheville, North Carolina, 28801-5001.
Database of State Incentives for
(828) 271-4800. Fax (828) 271-4876.
Renewable Energy—On the Web at
http://www.ncdc.noaa.gov
http://www.dcs.ncsu.edu/solar/
U.S. Department of Commerce, dsire/dsire.html
National Technical Information
Green Power Network Net Metering
Service, 5285 Port Royal Road,
Web Site—Net metering programs are
Springfield, Virginia 22161. (800)
now available in 30 states. Visit this
553-6847. http://www.ntis.gov/
DOE Web site for information:
ordering.htm
http://www.eren.doe.gov/
Non-Government Organizations greenpower/netmetering
American Wind Energy Association, Small Wind "Talk" on the Web—
122 C Street, N.W. 4th Floor, AWEA's Home Energy Systems elec-
Washington, D.C. 20001. (202) 383- tronic mailing list is designed as a
2500. http://www.awea.org forum for the discussion of small-scale
Solar Energy International—Short energy systems that include wind. To
courses on renewable energy and subscribe, send a subscription request
sustainable development, in awea-wind-home-subscribe@
Carbondale, Colorado. (970) 963-8855. egroups.com.
http://www.solarenergy.org Wind Energy for Homeowners—This
Periodicals Web site discusses things you should
consider before investing in a small
"Apples and Oranges" by Mick
wind energy system and provides
Sagrillo—A comprehensive compari-
basic information about the systems.
son of available small wind turbines.
http://www.eren.doe.gov/wind/
On Home Power Magazine Web site:
homeowner.html
http://www.homepower.com
Home Power Magazine—The defini-
tive bimonthly magazine for the
homemade power enthusiast.
(800)707-6586 or on the Web at:
http://www.homepower.com
Videos
An Introduction to Residential Wind
Systems with Mick Sagrillo—A 63-
minute video answering questions
most often asked by homeowners
as they consider purchasing and
installing their own wind power
24 Small Wind Electric Systems
Notes
Small Wind Electric Systems
Oregon Incentives forward for up to 8 years. The tax credit applica-
Net metering—Utilities offer net metering for all tion must be submitted to the Oregon Office of
customers for wind generating systems that are Energy before starting the project. A pass-through
25 kilowatts or less. The utility may value at its option allows another Oregon business or resi-
avoided cost the excess power generated by the dent to claim the tax credit if it pays the applicant
customer. When the total customer-generation the net present value.
capacity exceeds 0.5% of a utility’s historic Property tax exemption—Additional property
single-hour peak load, net metering eligibility value resulting from the installation of solar,
can be limited by the regulatory authority. geothermal, wind, water, fuel cell, or methane
Residential energy tax credit—A tax credit of gas energy systems for the purpose of heating,
60¢ per kilowatt-hour saved, up to $1,500, cooling, or generating electrical energy is exempt
is available for wind power systems. The credit from property tax under state law until Dec. 31,
may be taken in one year or carried forward for up 2012.
to 5 years. Additions to systems in future years Energy loan program—Secured, low-interest,
are also eligible for the tax credit. The credit fixed-rate loans ranging from 5 to 20 years
cannot exceed the tax liability of the project are available from the Oregon Office of Energy
owner. Tax credit applications should be submit- for renewable resources. Individuals, businesses,
ted to the Oregon Office of Energy. A pass- schools, cities, counties, special districts, state
through option allows another Oregon resident and federal agencies, public corporations,
or business to claim the tax credit if they pay cooperatives, tribes, and nonprofits may apply.
the applicant the net present value. Loans range from $20,000 to $20 million.
Business energy tax credit—Wind systems Energy Trust of Oregon, Inc.—The Energy Trust
installed by businesses are eligible for a tax of Oregon is a new nonprofit organization set up
credit of 35% of the eligible project costs based to invest the public purpose funds collected
on a maximum 15-year simple payback. Eligible from Portland General Electric and Pacific
costs are prorated if the payback is greater Power customers in conservation and renewable
than 15 years. The tax credit for projects under resources. Small wind projects that significantly
$20,000 can be taken in one year. For larger boost wind development may receive Energy
projects, the tax credit is taken over 5 years: Trust funding through its programs or unsolicited
10% in the first and second years and 5% each proposals process. For more information, visit
year thereafter. The tax credit can be carried www.energytrust.org.
Oregon Contacts
Oregon Office of Energy
625 Marion Street, N.E.
Salem, OR 97301
1-800-221-8035
www.energy.state.or.us
Curtis Framel
U.S. Department of Energy
Regional Office
800 Fifth Avenue, Suite 3950
Seattle, WA 98104-3122
Phone: 206 553-7841
www.eren.doe.gov/sro/
Wind Powering America
www.windpoweringamerica.gov
U.S. Department of Energy
Wind Energy Program
www.eren.doe.gov/wind/
Produced for the U.S. Department of Energy by the
National Renewable Energy Laboratory,
a DOE national laboratory
DOE/GO-102002-1576
May 2002
Printed with a renewable-source ink on paper containing at least 50% wastepaper, including 20% postconsumer waste
