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Small Wind Energy
Systems for the Homeowner
In the 1920s and '30s, farm families
throughout the Midwest used wind to generate enough electricity to power their
lights and electric motors. The use of wind power declined with the
government-subsidized construction of utility lines and fossil fuel power
plants. However, the energy crisis in the 1970s and a growing concern for the
environment generated an interest in alternative, environmentally friendly
energy resources. Today, homeowners in rural and remote locations across the
nation are once again examining the possibility of using wind power to provide
electricity for their domestic needs.
This publication will help you decide
whether a wind system is practical for you. It will explain the benefits, help
you assess your wind resource and possible sites, discuss legal and
environmental obstacles, and analyze economic considerations such as pricing.
Benefits of Wind Power
A wind energy system can provide you
with a cushion against electric power price increases. Wind energy systems
help reduce U.S. dependence on fossil fuels, and they are nonpolluting. If you
live in a remote location, a small wind energy system can help you avoid the
high costs of having the utility power lines extended to your site.
Although wind energy systems involve a
significant initial investment, they can be competitive with conventional
energy sources when you account for a lifetime of reduced or altogether
avoided utility costs. The length of the payback period—the time before the
savings resulting from your system equal the cost of the system itself—depends
on the system you choose, the wind resource on your site, electricity costs in
your area, and how you use your wind system.
Is Wind Power Practical
for You?
Small wind energy systems can be used in
connection with an electricity transmission and distribution system (called grid-connected
systems), or in stand-alone applications that are not connected to the utility
grid. A grid-connected wind turbine can reduce your consumption of
utility-supplied electricity for lighting, appliances, and electric heat. If
the turbine cannot deliver the amount of energy you need, the utility makes up
the difference. When the wind system produces more electricity than the
household requires, the excess can be sold to the utility. With the
interconnections available today, switching takes place automatically.
Stand-alone wind energy systems can be appropriate for homes, farms, or even
entire communities (a co-housing project, for example) that are far from the
nearest utility lines. Either type of system can be practical if the following
conditions exist.
Conditions for Stand-Alone
Systems
- You live in an area with average
annual wind speeds of at least 9 miles per hour (4.0 meters per
second).
- A grid connection is not available or
can only be made through an expensive extension. The cost of running a
power line to a remote site to connect with the utility grid can be
prohibitive, ranging from $15,000 to more than $50,000 per mile, depending
on terrain.
- You have an interest in gaining
energy independence from the utility.
- You would like to reduce the
environmental impact of electricity production.
- You acknowledge the intermittent
nature of wind power and have a strategy for using intermittent resources
to meet your power needs.
Conditions for Grid-Connected
Systems
- You live in an area with average
annual wind speeds of at least 10 miles per hour (4.5 meters per
second).
- Utility-supplied electricity is
expensive in your area (about 10 to 15 cents per kilowatt hour).
- The utility's requirements for
connecting your system to its grid are not prohibitively expensive.
- Local building codes or covenants
allow you to legally erect a wind turbine on your property.
- You are comfortable with long-term
investments.
Is Your Site Right?
The U.S. Department of Energy (DOE) has
compiled wind resource maps that are available from the American Wind Energy
Association and the National Technical Information Service (see Source
List). The DOE maps are good sources for regional information and can
show whether wind speeds in your area are generally strong enough to justify
investing in a wind system.
Wind-turbine manufacturers can use
computer models to predict their machines' performance at a specific location.
They can also help you size a system based on your electricity needs and the
specifics of local wind patterns. However, you will need site-specific data to
determine the wind resource of your exact location. If you do not have on-site
data and want to obtain a clearer, more predictable picture of your wind
resource, you may wish to measure wind speeds at your site for a year. You can
do this with a recording anemometer, which generally costs $500 to $1500. The
most accurate readings are taken at "hub height" (i.e., the
elevation at the top of the tower where you will install the wind turbine—see
the section on "Wind System Basics" that
follows). This requires placing the anemometer high enough to avoid turbulence
created by trees, buildings, and other obstructions. The standard wind sensor
height used to obtain data for the DOE maps is 33 feet (10 meters).
You can have varied wind resources
within the same property. If you live in complex terrain, take care in
selecting the installation site. If you site your wind turbine on the top or
on the windy side of a hill, for example, you will have more access to
prevailing winds than in a gully or on the leeward (sheltered) side of a hill
on the same property. Consider existing obstacles and plan for future
obstructions, including trees and buildings, which could block the wind. Also
realize that the power available in the wind increases proportionally to its
speed (velocity) cubed (v3). This means that the amount of power
you get from your generator goes up exponentially as the wind speed increases.
For example, if your site has an annual average wind speed of about 12.6 miles
per hour (5.6 meters per second), it has twice the energy available as a site
with a 10 mile per hour (4.5 meter per second) average.
Additional Considerations
In addition to the factors listed
previously, you should also:
- research potential legal and
environmental obstacles,
- obtain cost and performance
information from manufacturers,
- perform a complete economic analysis
that accounts for a multitude of factors (see the case study),
- understand the basics of a small wind
system, and
- review possibilities for combining
your system with other energy sources, backups, and energy efficiency
improvements.
You should establish an energy budget to
help define the size of turbine that will be needed. Since energy efficiency
is usually less expensive than energy production, making your house more
energy efficient first will likely result in being able to spend less money
since you may need a smaller wind turbine to meet your needs.
Potential Legal and
Environmental Obstacles
Before you invest any time and money, research potential legal and
environmental obstacles to installing a wind system. Some jurisdictions, for
example, restrict the height of the structures permitted in residentially
zoned areas, although variances are often obtainable (see "Wind
System Basics," which follows). Your neighbors might object to a wind
machine that blocks their view, or they might be concerned about noise.
Consider obstacles that might block the wind in the future (large planned
developments or saplings, for example). If you plan to connect the wind
generator to your local utility company's grid, find out its requirements for
interconnections and buying electricity from small independent power
producers.
Pricing a System
When you are confident that you can install a wind machine legally and without
alienating your neighbors, you can begin pricing systems and components.
Approach buying a wind system as you
would any major purchase. Obtain and review the product literature from
several manufacturers. Lists of manufacturers are available from the American
Wind Energy Association (AWEA, see Source List);
however, not all small turbine manufacturers are members of AWEA. Manufacturer
information can also be found at times in the periodicals listed in the Reading
List. Once you have narrowed the field, research a few companies to be
sure they are recognized wind energy businesses and that parts and service
will be available when you need them. Also, find out how long the warranty
lasts and what it includes.
Ask for references of customers with
installations similar to the one you are considering. Ask system owners about
performance, reliability, and maintenance and repair requirements, and whether
the system is meeting their expectations.
The Economics of Wind Power
for Home Use
A residential wind energy system can be a good long-term investment. However,
because circumstances such as electricity rates and interest rates vary, you
need to decide whether purchasing a wind system is a smart financial move for
you. The case study that follows illustrates the many factors and calculations
you will need to consider. Be sure you or your financial adviser conduct a
thorough analysis before you buy a wind energy system.
Grid-connected-system owners may be
eligible to receive a small tax credit for the electricity they sell back to
the utility. For 1996, it was 1.6 cents per kilowatt hour. The National Energy
Policy Act of 1992 and the 1978 Public Utilities Regulatory Policy Act (PURPA)
are two programs that apply to small independent power producers. PURPA also
requires that the utility sell you power when you need it. Be sure you check
with your local utility or state energy office before you assume any buy-back
rate. Some Midwestern rates are very low (less than $.02/kWh), but some states
have state-supported buy-back rates that encourage renewable energy
generation. In addition, some states have "net billing," where
utilities purchase excess electricity for the same rate at which they sell it.
(The Energy Efficiency and Renewable Energy Clearinghouse—see Source
List—has more information on net billing.)
Also, some states offer tax credits and
some utilities offer rebates or other incentives that can offset the cost of
purchasing and installing wind systems. Check with your state's department of
revenue, your local utility, public utility commission, or your local energy
office for information.
Wind
System Basics
All wind systems consist of a wind turbine, a tower, wiring, and the
"balance of system" components: controllers, inverters, and/or
batteries.
Wind Turbines
Home wind turbines consist of a rotor, a generator mounted on
a frame, and (usually) a tail. Through the spinning blades, the rotor
captures the kinetic energy of the wind and converts it into rotary motion
to drive the generator. Rotors can have two or three blades, with three
being more common. The best indication of how much energy a turbine will
produce is the diameter of the rotor, which determines its "swept
area," or the quantity of wind intercepted by the turbine. The frame is
the strong central axis bar onto which the rotor, generator, and tail are
attached. The tail keeps the turbine facing into the wind.
A 1.5-kilowatt (kW) wind turbine will
meet the needs of a home requiring 300 kilowatt-hours (kWh) per month, for a
location with a 14-mile-per-hour (6.26-meters-per-second) annual average
wind speed. The manufacturer will provide you with the expected annual
energy output of the turbine as a function of annual average wind speed. The
manufacturer will also provide information on the maximum wind speed in
which the turbine is designed to operate safely. Most turbines have
automatic speed-governing systems to keep the rotor from spinning out of
control in very high winds. This information, along with your local wind
speed distribution and your energy budget, is sufficient to allow you to
specify turbine size.
Towers
To paraphrase a noted author on wind energy, "the good winds are up
high." Because wind speeds increase with height in flat terrain, the
turbine is mounted on a tower. Generally speaking, the higher the tower, the
more power the wind system can produce. The tower also raises the turbine
above the air turbulence that can exist close to the ground. A general rule
of thumb is to install a wind turbine on a tower with the bottom of the
rotor blades at least 30 feet (9 meters) above any obstacle that is within
300 feet (90 meters) of the tower.
Experiments have shown that relatively
small investments in increased tower height can yield very high rates of
return in power production. For instance, to raise a 10-kW generator from a
60-foot tower height to a 100-foot tower involves a 10% increase in overall
system cost, but it can produce 25% more power.
There are two basic types of towers: self-supporting
(free standing) and guyed. Most home wind power systems use a guyed
tower. Guyed-lattice towers are the least expensive option. They consist of
a simple, inexpensive framework of metal strips supported by guy cables and
earth anchors.
However, because the guy radius must
be one-half to three-quarters of the tower height, guyed-lattice towers
require enough space to accommodate them. Guyed towers can be hinged at the
base so that they can be lowered to the ground for maintenance, repairs, or
during hazardous weather such as hurricanes. Aluminum towers are prone to
cracking and should be avoided.
Balance of System
Stand-alone systems require batteries to store excess power generated for
use when the wind is calm. They also need a charge controller to keep the
batteries from overcharging. Deep-cycle batteries, such as those used to
power golf carts, can discharge and recharge 80% of their capacity hundreds
of times, which makes them a good option for remote renewable energy
systems. Automotive batteries are shallow-cycle batteries and should not be
used in renewable energy systems because of their short life in deep cycling
operations.
In very small systems, direct current
(DC) appliances operate directly off the batteries. If you want to use
standard appliances that require conventional household alternating current
(AC), however, you must install an inverter to convert DC electricity 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 home buyers.
For safety, batteries should be
isolated from living areas and electronics because they contain corrosive
and explosive substances. Lead-acid batteries also require protection from
temperature extremes.
In grid-connected systems, the only
additional equipment is a power conditioning unit (inverter) that makes the
turbine output electrically compatible with the utility grid. No batteries
are needed. Work with the manufacturer and your local utility on this.
Hybrid Wind Systems
According to many renewable energy experts, a stand-alone "hybrid"
system that combines wind and photovoltaic (PV) technologies offers several
advantages over either single system. (For more information on solar electric—or
photovoltaic—systems, contact the Energy Efficiency and Renewable Energy
Clearinghouse—see Source List.)
In much of the United States, wind
speeds are low in the summer when the sun shines brightest and longest. The
wind is strong in the winter when there is less sunlight available. Because
the peak operating times for wind and PV occur at different times of the day
and year, hybrid systems are more likely to produce power when you need it.
For the times when neither the wind
generator nor the PV modules are producing electricity (for example, at night
when the wind is not blowing), most stand-alone systems provide power through
batteries and/or an engine-generator powered by fossil fuels.
If the batteries run low, the
engine-generator can be run at full power until the batteries are charged.
Adding a fossil-fuel-powered generator makes the system more complex, but
modern electronic controllers can operate these complex systems automatically.
Adding an engine-generator can also reduce the number of PV modules and
batteries in the system. Keep in mind that the storage capability must be
large enough to supply electrical needs during noncharging periods. Battery
banks are typically sized for one to three days of windless operation.
The Future of Wind Power
By investing in a small wind system, you
can reduce your exposure to future fuel shortages and price increases and
reduce pollution. Deciding whether to purchase a wind system, however, is
complicated; there are many factors to consider. But if you have the right set
of circumstances, a well-designed wind energy system can provide you with many
years of cost-effective, clean, and reliable electricity.
| Case Study: Wind Power
Economics of a Home System
Note: In this analysis, we have
assumed a certain set of conditions, such as wind regime, maintenance
costs, etc. Your analysis will differ for your set of circumstances. This
case study is for illustration purposes only.
A New England homeowner is
considering taking out a 20-year loan to purchase a $10,000 wind system
(turbine, tower, inverter, and battery storage) for generating her own
electricity, instead of paying her full electricity bills for the next 20
years.
Assume that the wind turbine she has
chosen is rated at 3 kilowatts with the turbine 80 feet (24 meters) above
the ground, and that she lives in a Class 4 wind regime (average wind
speed of 12.5 to 13.4 miles per hour [5.6 to 6 meters per second] measured
at 33 feet [10 meters] above the ground). Given these assumptions, the
turbine can produce an estimated 9000 kilowatt hours (kWh) per year, or
750 kWh per month. Also assume, for the sake of simplicity, that she will
use all of the electricity herself and will not sell any back to the
utility. Therefore, the value of the electricity to her is equal to the
retail price she pays the utility; in this case, 12 cents per kWh.
Continuing to Pay
Electricity Bills
If she continues to pay her electricity bills without the wind turbine,
the retail value of the electricity is $1,080 the first year. In later
years, the price of electricity increases. For this analysis, we assume
that the cost of electricity increases at the same rate as inflation—3%
a year. Thus, the 9000 kWh will cost $1,112 in the second year, $1,146 the
third year, and so forth, until the total inflation-adjusted cost of
electricity for 20 years is $29,020.
Purchasing a Wind System
She can obtain the least-expensive loan by taking out a second mortgage on
her home. She can borrow $10,000 at 8%, and make payments of $1,019 for 20
years. But she can deduct the portion of her payments that go toward
interest at her 30% combined federal and state tax rate. Thus, after
taxes, her annual payment is $779 for the first year, and increases to
$996 as the interest deduction decreases in later years.
However, there are other costs to
owning a wind turbine. Her property taxes will be higher because the wind
turbine increases the value of her property. She will pay additional
insurance since her standard homeowner's policy does not cover liability
from the wind tower. And she will hire a local mechanic to climb the tower
and grease the bearings every year. Altogether, she figures these
operations and maintenance (O&M) costs will be about 1 cent/kWh or
$100 per year in today's dollars. Let us assume for this analysis that
taxes, insurance, and labor rates increase at the same rate as inflation.
Thus, annual O&M costs increase to $175 in the 20th year. So, over 20
years, her total inflation-adjusted cost for buying a wind system is
$19,678.
Net Present Value of Both
Options
However, our example is still not complete. Economists tell us that future
dollars are worth less than present dollars. It is better to have money
now, rather than in the future, so we can use it to invest and earn more
money. Even though inflation increases her annual electricity payments
after 20 years to $1,894, those are future dollars, so they are
worth less than today's dollars. Economists refer to this devaluation as
the net present value factor, the rate at which future dollars are
discounted compared to present dollars. This discount rate is equal to the
rate of return that she could make on an investment of equivalent risk and
liquidity to a wind turbine. In this evaluation, assume her opportunity
for return on investment with today's dollars (i.e., the discount rate for
her future dollars) is 10% a year.
Therefore, projecting her electric
utility payments into the future to, say, the end of the first year, the
dollars are worth 90% of what they were at the beginning of the year. At
the end of the second year, the dollars are worth 90% of what they were at
end of the previous year. (Notice the value of her future dollars
depreciates at a compounded rate.) Considering these adjustments, her
annual electricity payment in the 20th year is actually worth only $156 in
today's dollars. Thus, her total cost of buying electricity for 20 years,
adjusted for inflation and present value factors, is only $8,927 in
today's dollars.
Another way to think of it is that
her payment in the 20th year is really a deferred payment. She does
not have to pay $29,020 today. Since the utility company allows her to pay
her bills as she uses the electricity, she does not have to make
any large capital expenditures. So she has more of her money to invest for
20 years. This would not be true if she had to pay for 20 years of
electricity up front.
But net present value factors also
apply to purchasing a wind system, because she is making deferred payments
on her loan. Her payments of $1,154 in year 20 are really worth only $95
in today's dollars, for instance. Therefore, her total cost for buying a
wind system, adjusted for inflation and net present value, is only $6,426
in today's dollars.
The Final Analysis
So in real terms, she saves $2,501 over 20 years by purchasing a wind
system, as opposed to continuing to pay her electricity bills. An added
benefit is that she would avoid the release of 40 tons (40 metric tons) of
carbon dioxide, 800 pounds (363 kilograms) of nitrogen oxide, and 280
pounds (127 kilograms) of sulfur dioxide into the atmosphere—the amount
of pollution that a utility company in the Northeast would emit to supply
her electric load for 20 years, on average. |
Source List
The following organizations can provide
you with information to help decide whether a wind energy system is right for
you.
Alternative Energy Institute (AEI)
West Texas A&M University
P.O. Box 60248
Canyon, TX 79016
(806) 651-2296
Fax: (806) 651-2233
AEI conducts field trials at its Wind
Turbine Test Center and is a source of information on small wind turbines.
American Wind Energy Association (AWEA)
122 C Street, NW, 4th Floor
Washington, DC 20001
(202) 383-2500
Fax: (202) 383-2505
AWEA is a source for DOE wind maps, lists
of manufacturers and dealers, information on wind power tax credits, and other
wind energy information.
National Technical Information
Service (NTIS)
U.S. National Department of Commerce
5285 Port Royal Road
Springfield, VA 22161
(703) 487-4650
http://www.ntis.gov
NTIS has over 3 million publications that
are available to the public. They offer a free catalog that lists a selection of
these documents.
For free information about many
kinds of energy efficiency and renewable energy topics, contact:
The Energy Efficiency and
Renewable Energy Clearinghouse EREC)
P.O. Box 3048
Merrifield, VA 22116
(800) 363-3732
Fax: (703) 893-0400
E-mail: doe.erec@nciinc.com
EREC provides free general and technical
information to the public on the many topics and technologies pertaining to
energy efficiency and renewable energy.
You may also contact your state
and local energy offices for information on region-specific information on small
wind energy systems.
Reading List
Periodicals
Backwoods Home
1257 Siskiyou Boulevard, #213
Ashland, OR 97520
(916) 459-3300
This publication is devoted to independent
living, including independent energy systems.
Home Energy
2124 Kittredge Street, No. 95
Berkeley, CA 94704-9942
(510) 524-5405
This source provides information on
reducing energy consumption.
Home Power P.O. Box 520
Ashland, OR 97520-0520
(916) 475-3179
This periodical provides practical
information, case studies, and advice on designing, installing, and living with
small power systems.
Books
A Sitting Handbook for Small Wind
Energy Conversion Systems, Battelle Pacific Northwest Laboratory, National
Technical Information Service, U.S. Department of Commerce, 5285 Port Royal
Road, Springfield, VA 22161, 1980.
The Wind Power Book, J. Park,
Chesire Books, Palo Alto, CA, 1981. This book is currently out of print, so
check your local library for availability.
Wind Power for Home & Business,:
Renewable Energy for the 1990s and Beyond, P. Gipe, Chelsea Green Publishing
Company, P.O. Box 130, Route 113, Post Mills, VT 05058-0130, 1993.
Wind Energy Resource Atlas of the U.S.,
Battelle Pacific Northwest Laboratories. Available from the American Wind Energy
Association or the National Information Service (see Source
List).
U.S. Department of Energy
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