SMALL WIND ELECTRIC SYSTEM GENERAL IDEA
If you went through the
planning steps to evaluate whether a small wind electric system will work at
your location, you will already have a general idea about:
1.The amount of wind at your site
2.The
zoning requirements and covenants in your area
3.The
economics, payback, and incentives of installing a wind system at your site.
Now,
it is time to look at the issues associated with installing the wind system:
1.Siting
-- or finding the best location -- for your system
2.Estimating
the system’s annual energy output and choosing the correct size turbine and
tower
3.Deciding
whether to connect the system to the electric grid or not.
Installation
and Maintenance
The manufacturer of your wind system, or the dealer
where you bought it, should be able to help
you install your small wind electric system. You can install the system
yourself -- but before attempting the project, ask 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?
# Do I know the difference between alternating current
(AC) and direct current (DC) wiring?
# Do I know enough about electricity to safely wire my
turbine?
# Do I know how to safely handle and install
batteries?
If you answered no to any of the above questions, you
should probably choose to have your system installed by a system integrator or
installer. Contact the manufacturer for help, or contact your state energy
office and local utility for a list of local system installers. You can also
check the yellow pages for wind energy system service providers.
A credible installer may provide additional services
such as permitting. Find out if the installer is a licensed electrician, and
ask for references and check them. You may also want to check with the Better
Business Bureau.
With proper installation and maintenance, a small wind
electric system should last up to 20 years or longer. Annual maintenance can
include:
# Checking and tightening bolts and electrical
connections as necessary
# Checking machines for corrosion and the guy wires
for proper tension
# Checking for and replace any worn leading edge tape
on the turbine blades, if appropriate
# Replacing the turbine blades and/or bearings after
10 years if needed.
# If you do not have the expertise to maintain the
system, your installer may provide a service
and maintenance program.
Siting
a Small Electric Wind System
Your system manufacturer or dealer can also help you
with finding the best location for your wind system. Some general
considerations include:
Wind Resource Considerations -- If you live in complex
terrain, take care in selecting the installation site. If you site your wind
turbine on the top of 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. You can have varied wind
resources within the same property. In addition to measuring or finding out
about the annual wind speeds, you need to know about the prevailing directions
of the wind at your site. In addition to geological formations, you need to
consider existing obstacles, such as trees, houses, and sheds. You also need to
plan for future obstructions, such as new buildings or trees that have not
reached their full height. Your turbine needs to be sited upwind of any
buildings and trees, and it needs to be 30 feet above anything within 300 feet.
System Considerations -- Be sure to leave enough room
to raise and lower the tower for maintenance. If your tower is guyed, you must allow
room for the guy wires. Whether the system is stand-alone or grid-connected,
you also will need to take the length of the wire run between the turbine and
the load (house, batteries, water pumps, etc.) into consideration. A
substantial amount of electricity can be lost as a result of the wire
resistance—the longer the wire run, the more electricity is lost. Using more or
larger wire will also increase your installation cost. Your wire run losses are
greater when you have direct current (DC) instead of alternating current (AC).
If you have a long wire run, it is advisable to invert DC to AC.
Sizing
Small Wind Turbines
Small wind turbines used in residential applications
typically range in size from 400 watts to 20 kilowatts, depending on the amount
of electricity you want to generate.
A typical home uses approximately 10,932
kilowatt-hours of electricity per year (about 911 kilowatt-hours per month).
Depending on the average wind speed in the area, a wind turbine rated in the
range of 5–15 kilowatts would be required to make a significant contribution to
this demand. A 1.5-kilowatt wind turbine will meet the needs of a home
requiring 300 kilowatt-hours per month in a location with a 14 mile-per-hour
(6.26 meters-per-second) annual average wind speed.
To help you determine what size turbine you'll need,
first establish an energy budget. Because energy efficiency is usually less
expensive than energy production, reducing your home's electricity use will
probably be more cost effective and will reduce the size of the wind turbine
you need.
The height of a wind turbine's tower also affects how
much electricity the turbine will generate. A manufacturer should help you
determine the tower height you will need.
Estimating
Annual Energy Output
An estimate of the annual energy output from a wind
turbine (in kilowatt-hours per year) is the best way to determine whether it
and the tower will produce enough electricity to meet your needs.
A wind turbine manufacturer can help you estimate the
energy production you can expect. The manufacturer will use a calculation based
on these factors:
# Particular wind turbine power curve
# Average annual wind speed at your site
# Height of the tower that you plan to use
# Frequency distribution of the wind -- an estimate of
the number of hours that the wind will blow
at each speed during an average year.
The manufacturer should also adjust this calculation
for the elevation of your site.
To get a preliminary estimate of the performance of a
particular wind turbine, you can use the following formula:
AEO= 0.01328 D2 V3
Where:
AEO = Annual energy output (kilowatt-hours/year)
D = Rotor diameter, feet
V = Annual average wind speed, miles-per hour (mph),
at your site
Note: the difference between power and energy is that
power (kilowatts) is the rate at which electricity is consumed, while energy
(kilowatt-hours) is the quantity consumed.
Grid-Connected Small Wind Electric Systems
Small wind energy systems can be connected to the
electricity distribution system. These are called grid-connected systems. 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 your household requires,
the excess is sent or sold to the utility.
With this type of grid connection, your wind turbine
will operate only when the utility grid is available. During power outages, the
wind turbine is required to shut down due to safety concerns.
Grid-connected systems can be practical if the
following conditions exist:
# You live in an area with average annual wind speed
of at least 10 miles per hour (4.5 meters per second).
# Utility-supplied electricity is expensive in your
area (about 10–15 cents per kilowatt-hour).
# The utility's requirements for connecting your
system to its grid are not prohibitively expensive.
There are good incentives for the sale of excess
electricity or for the purchase of wind turbines. Federal regulations
(specifically, the Public Utility Regulatory Policies Act of 1978, or PURPA)
require utilities to connect with and purchase power from small wind energy
systems. However, you should contact your utility before connecting to its
distribution lines to address any power quality and safety concerns.
Your utility can provide you with a list of
requirements for connecting your system to the grid. For more information, see
grid-connected home energy systems.
Wind
Power in Stand-Alone Systems
Wind power can be used in off-grid systems, also
called stand-alone systems, not connected to an electric distribution system or
grid. In these applications, small wind electric systems can be used in
combination with other components -- including a small solar electric system --
to create hybrid power systems. Hybrid power systems can provide reliable
off-grid power for homes, farms, or even entire communities (a co-housing
project, for example) that are far from the nearest utility lines.
An off-grid, hybrid electric system may be practical
for you if the items below describe your situation:
# You live in an area with average annual wind speed
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.
# You would like to gain energy independence from the
utility.
# You would like to generate clean power.
