Wind Electricity Basics

Small wind-electric systems can provide electricity on remote,

off-grid sites, or right in town connected to the utility grid.
Although wind systems require more maintenance and need
more attention than solar-electric or microhydro-electric systems, if you
invest up front in good equipment, design, and installation, wind-electric
systems can make economic and environmental sense. They also bring a
great deal of satisfaction—there´s nothing quite like watching your wind
generator convert a summer breeze or a winter storm into electrical
energy.

How It Works

Boiled down to its simplest principles, a wind generator´s rotating blades

convert the wind´s kinetic energy into rotational momentum in a shaft.
The rotating shaft turns an alternator, which makes electricity. This
electricity is transmitted through wiring down the tower to its end use.

The blades use engineered airfoils, matched to the alternator, that capture
the wind´s energy. Most modern wind generators use three blades, the
best compromise between the highest efficiency possible (one blade) and
the balance that comes with multiple blades. Together, the blades and the
hub they are attached to are termed the rotor, which is the collector of the
system, intercepting winds that pass by. Most turbines on the market
today are upwind machines—their blades are on the windward side of the
tower. A few downwind machines are available, but neither configuration
has a clear performance advantage over the other.

In most small-scale designs, the rotor is connected directly to the shaft of

a permanent magnet alternator, which creates wild, three-phase AC. Wild,
three-phase electricity means that the voltage and frequency vary
continuously with the wind speed. They are not fixed like the 60 Hz, 120
VAC electricity coming out of common household outlets. The wild output
is rectified to DC to either charge batteries or feed a grid-synchronous
inverter. In most designs (up to 15 KW in peak capacity), the rotor is
usually connected directly to the alternator, which eliminates the
additional maintenance of gears. In systems 20 KW and larger, as well as
some smaller wind systems (like the Endurance, Tulipo, or Aircon), a
gearbox is used to increase alternator speed from a slower
turning rotor.

The blades must turn to face the wind, so a yaw bearing is

needed, allowing the wind turbine to track the winds as they
shift direction. The tail directs the rotor into the wind. Some
sort of governing system limits the rotor rpm as well as
generator output to protect the turbine from high winds. A
shutdown mechanism is also useful to stop the machine when
necessary, such as during an extreme storm, when you do not
need the energy, or when you want to service the system.

How Wind Turbines are Rated

Wind turbine rating is a tricky affair. While solar-electric module or

microhydro-electric turbine production can be predicted fairly realistically
based on rated output, this number is very misleading with wind turbines.
Why? Because rated output is pegged to a particular wind speed, and
different manufacturers use different wind speeds to determine rated
output. Also, the power available in the wind varies with the cube of its
speed, so small increases in wind speed result in large increases in power
available to the rotor. A 10 percent increase in wind speed yields a 33
percent increase in power available in the wind. Conversely, this means
that a turbine rated at 1,000 watts at 28 mph might produce only 125 watts
or less at half that wind speed, 14 mph.

So what´s a wind turbine buyer to do? Ignore the peak output and the
power curve. Look for the monthly or annual energy numbers for the
turbine, estimated for the average wind speed you expect or measure at
your site. These will be given in KWH per month (or year) in the
manufacturer´s specifications for each turbine. Energy is what you´re
after, not peak power! If, for example, you are looking for a turbine that
can produce 300 KWH per month, and you know that you have a 10 mph
average wind speed at the proposed turbine height, you can shop for a
turbine that is predicted to generate that much energy in that average
wind speed.

If you can´t get energy production estimates from the manufacturer or a

turbine owner, look for a different manufacturer. This is basic information
that any manufacturer should supply. However, knowing a turbine´s swept
area may also help you calculate the annual energy output for the wind
turbine. All other things being equal, ″there´s no replacement for
displacement.″ Hugh Piggott gives a rough formula for calculating output
based on average wind speed and swept area in his HP102 article. Jim
Green at the National Renewable Energy Lab (NREL) developed a similar
formula: annual energy output (AEO) in KWH = 0.01328 x rotor diameter
(ft.) squared x average wind speed (mph) cubed.

A turbine´s revolutions per minute (rpm) at its rated wind speed can give
you some idea of the relative aerodynamic sound of the machine, and also
speaks to longevity. Slower-turning wind turbines tend to be
quieter and last longer. High rpm machines wear out
components, such as bearings, much faster. In addition, the
faster blades move through the air, the greater the possibility
that they will waste some of that energy as sound from the
blades.

How To Choose A Wind Turbine

Trying to keep an inexpensive wind generator running can be an uphill

battle that you´ll soon tire of. But expect to pay more for a better
machine—it´s a tough job to design and manufacture a long-lasting,
small-scale wind generator.
The bottom line: Buy a turbine that has a very good track record and a
good warranty—five years is preferable but not always available in the
small wind industry. A warranty is one indication of the manufacturer´s
confidence in their product, and their intention to stand behind it.

Real-world reports from users carry even more weight than a warranty, so
search for people who own the model of turbine you´re considering
buying, and get the straight scoop from them about performance,
durability, reliability, and maintenance issues.

Note that a number of the wind turbines listed here are relatively new
introductions with not very much customer run-time in North America.
These turbines include the ARE, Eoltec, Kestrel, and Skystream. We
recommend that you contact either your local wind turbine installer, or the
manufacturers or importers and find out how many of these machines are
actually operating in North America. Then contact the owners, and inquire
about their experience and satisfaction with both the machine and the
manufacturer or importer.

Some manufacturers make only battery-charging machines, and may offer

a variety of turbine voltages. Others produce machines intended to
connect to grid-synchronous inverters without batteries. One machine
even includes an inverter integrated with the turbine itself. Make sure
you´re buying a machine that is appropriate for your intended use.

When you look at prices, keep in mind that just buying a wind turbine will
not get you any wind-generated electricity. You´ll also need most or all of
the components mentioned elsewhere. Also budget for equipment rental,
like a backhoe and crane, concrete and rebar, electrical components,
shipping, and sales tax. Unless you do all of the work yourself, also factor
in installation labor expenses. These costs can add up significantly, so
make sure that you research and understand all of the associated
expenses before committing to a purchase. Many people are quite
surprised to learn that the wind turbine cost can range from only 10
percent to as much as 40 percent of the entire wind system´s expenses.
Small-scale wind energy is not for the half-hearted, uninvolved, or
uncommitted, and probably not for folks who never change the oil in their
vehicles (or are willing to spend the bucks to hire someone to do the
tower work). The North American landscape is littered with failed
installations: Designs not fully thought-out or tested, machines bought
because they were cheap, and installations that required more time and
money for repairs than they ever yielded in electricity generated. Many of
the failures were the result of wishful thinking and too little research. That
said, there are tens of thousands of happy wind-electric system owners.
These owners did their homework—purchasing, designing, and installing
rugged and well-thought-out systems on adequately sized towers. In
addition, they are either committed to maintaining the systems, or to
hiring someone to do this regular work.

While many first-time wind turbine buyers may be looking for a bargain,
second-time wind turbine buyers are seeking the most rugged machine
they can afford. You can avoid a painful "learning experience″ by focusing
on durability, production, warranty, and track record, and not on price
alone, or on peak output. You don´t want to depend on the low bidder for
something as important to you as your long-term energy investment.

See also the following Home Power feature articles:

How To Buy a Wind-Electric System

Wind Turbine Buyer´s Guide
Estimating Wind Energy
Wind Generator Tower Basics
Wind-Electric Systems Simplified

Wind-Electric System Types

Off-Grid Wind-Electric Systems

Off-grid wind-electric systems are battery based. People generally choose

these systems because their home or other energy use is not connected
to the grid, and connection would be expensive. Others prefer the
independence of off-grid systems, or live where utilities and governments
make it difficult to tie a renewable energy system to the grid.

Off-grid systems are limited in capacity by the size of the generating

sources (wind turbine, solar-electric array, fuel-fired generator, etc.), the
resources available, and the battery bank size. Off-grid homeowners have
to learn to live within the limitations of their system capacity.

The following illustration includes the primary components of any off-grid

wind-electric system with battery backup. See our Wind-Electric System
Components section for an introduction to the function(s) of each
component.

See also the following Home Power feature articles:

Watts in the Wind

Grid-Tied Wind-Electric System with Battery Backup

Connecting a wind-electric system to the utility grid with battery backup
gives you the best of both worlds. You have the unlimited capacity of the
grid at your disposal, and you can send your surplus wind energy to the
grid. When the grid is down, you can still use your system, within the
limitations of the battery bank and turbine. Wind-electric systems can be a
much better match for utility backup than solar-electric systems, since
many grid outages are caused by high winds. The drawback is that this is
the most expensive type of wind-electric system you can install.

The following illustration includes the primary components of any grid-

tied wind-electric system with battery backup. See our Wind-Electric
System Components section for an introduction to the function(s) of each
component.

See also the following Home Power feature articles:

The First Small Wind System in Lassen County

Batteryless Grid-Tied Wind-Electric System

Connecting to the grid without batteries is the most cost-effective and
environmentally friendly way to go. You eliminate batteries, which are
costly, require maintenance, and carry a significant efficiency penalty. The
only drawback of batteryless systems is that when the grid is down, your
system shuts down. But in most grid-serviced areas, utility outages are
only a few hours a year—a small inconvenience to endure for the
efficiency, environmental friendliness, and thriftiness of these systems.

Batteryless grid-tie systems may see increased performance (sometimes

dramatically) from the wind turbine compared to battery-based systems.
This is because the inverter´s electronics can match the wind´s load more
exactly, running the turbine at optimum speed, and extracting the
maximum energy.

The following illustration includes the primary components of any

batteryless grid-tied wind-electric system. See our Wind-Electric System
Components section for an introduction to the function(s) of each
component.

See also the following Home Power feature articles:

At Last....Simple Wind Grid-Tie
Betting the Farm—Wind Electricity Pays Off
Farming the Wind

Direct-Drive Batteryless Wind-Electric System

These are the least common wind-electric systems, typically used for
water pumping. A turbine is matched to a pump, often through an
electronic controller. When the wind blows, water is pumped to an
elevated tank, a stock-watering tank, or directly to the land to irrigate.
These systems can be simple and cost effective in the right situation.
Direct-drive systems are also used for heating, which can be a good
match, since it´s normally colder when it´s windy. But heating is a big load,
so large turbines are needed.

The following illustration includes the primary components of any

batteryless grid-tied wind-electric system. See our Wind-Electric System
Components section for an introduction to the function(s) of each
component.

Wind-Electric System Components

 Understanding the basic components of an RE system and how
they function is not an overwhelming task. Here are some brief
descriptions of the common equipment used in grid-intertied and off-grid
wind-electric systems. Systems vary—not all equipment is necessary for
every system type.

Wind Generator
Tower
Brake
Charge Controller
Dump Load
Battery Bank
System Meter
Main DC Disconnect
Inverter
AC Breaker Panel
Kilowatt-Hour Meter
Backup Generator

Wind Generator
AKA: wind genny, wind turbine

The wind generator is what actually generates electricity in the system.

Most modern wind generators are upwind designs (blades are on the side
of the tower that faces into the wind), and couple permanent magnet
alternators directly to the rotor (blades). Three-bladed wind generators are
most common, providing a good compromise between efficiency and
rotor balance.

Small wind turbines protect themselves from high winds (governing) by

tilting the rotor up or to the side, or by changing the pitch of the blades.
Electricity is transmitted down the tower on wires, most often as three-
phase wild alternating current (AC).
 It´s called "wild" because the voltage and frequency vary with the
rotational speed of the wind turbine. The output is then rectified
to direct current (DC) to charge batteries or to be inverted for grid
connection.

See also the following Home Power feature articles:

Wind Turbine Buyer´s Guide

How to Buy a Wind-Electric System
Anatomy of a Wind Turbine

Tower

A wind generator tower is very often more expensive than the turbine. The
tower puts the turbine up in the "fuel"—the smooth strong winds that give
the most energy. Wind turbines should be sited at least 30 feet (9 m)
higher than anything within 500 feet (152 m).

Three common types of towers are tilt-up, fixed-guyed, and freestanding.

Towers must be specifically engineered for the lateral thrust and weight of
the turbine, and should be adequately grounded to protect your
equipment against lightning damage. See Wind Generator Tower Basics in
HP105 for information about choosing a tower.

See also the following Home Power feature articles:

Wind Generator Tower Basics

What the Heck? Gin Pole

Brake
AKA: emergency shutdown mechanism

Most wind turbines have some means of stopping the turbine for repairs,
in an emergency, for routine maintenance, or when the energy is not
needed. Many turbines have "dynamic braking," which simply shorts out
 the three electrical phases and acts as a
disconnect. Others have mechanical braking, either via a disc or drum
brake, activated by a small winch at the base of the tower. Still others
have mechanical furling, which swings the rotor out of the wind.
Mechanical braking is usually more effective and reliable than dynamic
braking.

See also the following Home Power feature articles:

Anatomy of a Wind Turbine

Charge Controller
AKA: controller, regulator

A wind-electric charge controller´s primary function is to protect your

battery bank from overcharging. It does this by monitoring the battery
bank— when the bank is fully charged, the controller sends energy from
the battery bank to a dump (diversion) load.

Many wind-electric charge controllers are built into the same box as the
rectifiers (AC-to-DC converters). Overcurrent protection is needed
between the battery and controller/dump load.

In batteryless grid-tie systems, there is no controller in normal operation,

since the inverter is selling whatever energy the turbine is generating. But
there will be some control function in the case of grid failure, and there
may be electronics before the inverter to regulate the input voltage.

See also the following Home Power feature articles:

Under Control: Charge Controllers for Whole-House Systems

What is a Charge Controller?
Get Maximum Power From Your Solar Panels with MPPT
What The Heck? Charge Controller
 Dump Load
AKA: diversion load, shunt load

Solar-electric modules can be turned off—open circuited—with no

damage. Most wind generators should not run unloaded. They will run too
fast and too loud, and may self-destruct. They must be connected to a
battery bank or load. So normally, a charge controller that has the
capability of being a diversion controller is used. A diversion controller
takes surplus energy from the battery bank and sends it to a dump load.
In contrast, a series controller (commonly used in PV systems), actually
opens the circuit.

A dump load is an electrical resistance heater, and it must be sized to

handle the full generating capacity of the wind generator used. These
dump loads can be air or water heaters, and are activated by the charge
controller whenever the batteries or the grid cannot accept the energy
being produced.

Battery Bank
AKA: storage battery

Your wind generator will produce electricity whenever the wind blows
above the cut-in speed. If your system is off grid, you´ll need a battery
bank—a group of batteries wired together—to store energy so you can
have electricity when it´s not windy. For off-grid systems, battery banks
are typically sized to keep household electricity running for one to three
calm days. Grid-intertied systems also can include battery banks to
provide emergency backup during blackouts—perfect for keeping critical
electric loads operating until the grid is up again.
 Use only deep-cycle batteries in wind-electric systems. Lead-acid
batteries are the most common battery type. Flooded lead-acid batteries
are usually the least expensive, but require adding distilled water
occasionally to replenish water lost during the normal charging process.
Sealed absorbent glass mat (AGM) batteries are maintenance free and
designed for grid-tied systems where the batteries are typically kept at a
full state of charge. Sealed gel-cell batteries can be a good choice to
use in unheated spaces due to their freeze-resistant qualities.

See also the following Home Power feature articles:

Top 10 Battery Blunders and How to Avoid Them

Flooded Lead Acid Battery Maintenance
Battery Box Basics

System Meter
AKA: battery monitor, amp-hour meter, watt-hour meter

System meters can measure and display several different aspects of your
wind-electric system´s performance and status—tracking how full your
battery bank is, how much electricity your wind generator is producing or
has produced, and how much electricity is in use. Operating your system
without metering is like running your car without any gauges—although
possible to do, it´s always better to know how much fuel is in the tank.

See also the following Home Power feature articles:

The Whole Picture: Computer-Based Solutions for PV System Monitoring

Mutichannel Metering: Beta-Testing a New System Monitor
Control Your Energy Use & Costs with Solar Monitoring
Main DC Disconnect
AKA: battery / inverter disconnect

In battery-based systems, a disconnect between the batteries and inverter

is required. This disconnect is typically a large, DC-rated breaker mounted
in a metal enclosure. This breaker allows the inverter to be quickly
disconnected from the batteries for service, and protects the
inverter-to-battery wiring against
electrical fires.

See also the following Home Power

feature articles:

What The Heck? Disconnect

Inverter
AKA: DC-to-AC converter

Inverters transform the electricity produced by your wind generator into

the AC electricity commonly used in most homes for powering lights and
appliances. Grid-tied inverters synchronize the electricity they produce
with the grid´s "utility grade" AC electricity, allowing the system to feed
wind electricity to the utility grid.

Grid-tie inverters are either designed to operate with or without batteries.

Battery-based inverters for off-grid or grid-tie systems often include a
battery charger, which is capable of charging a battery bank from either
the grid or a backup generator during cloudy weather.

See also the following Home Power feature articles:

What’s Going On—The Grid? A New Generation of Grid-Tied PV Inverters

Off-Grid Inverter Efficiency
AC Breaker Panel
AKA: mains panel, breaker box, fuse box

The AC breaker panel is the point at which all of a home’s electrical wiring
meets with the provider of the electricity, whether that’s the grid or a
solar-electric system. This wall-mounted panel or box is usually installed
in a utility room, basement, garage, or on the exterior of the building. It
contains a number of labeled circuit breakers that route electricity to the
various rooms throughout a house. These breakers allow electricity to be
disconnected for servicing, and also protect the building’s wiring against
electrical fires.

Just like the electrical circuits in your home or office, an inverter’s

electrical output needs to be routed through an AC circuit breaker. This
breaker is usually mounted inside the building’s mains panel, which
enables the inverter to be disconnected from either the grid or from
electrical loads if servicing is necessary, and also safeguards the circuit’s
electrical wiring.

Additionally, for their use, utilities usually require an AC disconnect

between the inverter and the grid that is for their use. These are usually
located near the utility KWH meter.

Kilowatt-Hour Meter
AKA: KWH meter, utility meter

Most homes with a grid-tied wind-electric system will have AC electricity

both coming from and going to the electric utility grid. A bidirectional
KWH meter can simultaneously keep track of how much electricity you´re
using and how much your system is producing. The utility company often
provides intertie-capable meters at no cost.
Backup Generator
Backup Generator AKA: gas-guzzler, "the Noise"

Off-grid wind-electric systems can be sized to provide electricity during

calm periods when the wind doesn´t blow. But sizing a system to cover a
worst-case scenario, like several calm weeks during the summer, can
result in a very large, expensive system that will rarely get used to its
capacity and will run a huge surplus in windy times. To spare your
pocketbook, go with at least two sources of energy. Wind-PV hybrid
systems are often an excellent fit with local renewable resources. But a
backup, fuel-powered generator still may be necessary.

Engine-generators can be fueled with biodiesel, petroleum diesel,

gasoline, or propane, depending on the design. Most generators produce
AC electricity that a battery charger (either stand-alone or incorporated
into an inverter) converts to DC energy, which is stored in batteries. Like
most internal combustion engines, generators tend to be loud and stinky,
but a well-designed renewable energy system will require running them
only 50 to 200 hours a year or less.