Wind Electricity Basics

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Wind E lect r i c i t y Bas ics

Small wind-electric systems can provide electricity on remote, off-grid sites, or right in town connected to theutility grid. Although wind systems require more maintenance and need more attention than solar-electric ormicrohydro-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

theresnothing quite like watching your wind generator convert a summer breeze or a winter storm into electrical

energy.

Ho w I t Work s

Boiled down to its simplest principles, a wind generators rotatingblades convert the winds 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, thatcapture the winds 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 collectorof the system, intercepting winds that pass by. Mostturbines on the market today are upwind machinestheir blades are on

the windward side of the tower. A few downwind machines are available, but neither configuration has a clearperformance 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 varycontinuously with the wind speed. They are not fixed like the 60 Hz, 120 VAC electricity coming out of common

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Wind Electricity Basics

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household outlets. The wild output is rectified to DC to either charge batteries or feed a grid-synchronousinverter. 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 somesmaller 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 windsas 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 stopthe 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 ormicrohydro-electric turbine production can be predicted fairly

realistically based on rated output, this number is very misleading withwind turbines. Why? Because rated output is pegged to a particularwind speed, and different manufacturers use different wind speeds to

determine rated output. Also, the power available in the wind varies withthe 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 windspeed yields a 33 percent increase in power available in the wind.

Conversely, this means that a turbine rated at 1,000 watts at 28 mphmight produce only 125 watts or less at half that wind speed, 14 mph.

So whats a wind turbine buyer to do? Ignore the peak output and the

power curve. Look for the monthly or annual energy numbers for theturbine, estimated for the average wind speed you expect or measureat your site. These will be given in KWH per month (or year) in the

manufacturers specifications for each turbine. Energy is what youreafter, 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 aturbine that is predicted to generate that much energy in that average wind speed.

If you cant 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 turbinesswept area may also help you calculate the annual energy output for the wind turbine. All other things beingequal, theres 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 rotordiameter (ft.) squared x average wind speed (mph) cubed.

A turbines revolutions per minute (rpm) at its rated wind speed can give you some idea of the relativeaerodynamic sound of the machine, and also speaks to longevity. Slower-turning wind turbines tend to bequieter 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

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sound from the blades.

How To Choose A Wind Turbine

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

battle that youll soon tire of. But expect to pay more for a bettermachineits 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 agood warrantyfive years is preferable but not always available in the

small wind industry. A warranty is one indication of the manufacturersconfidence 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 youre 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 muchcustomer run-time in North America. These turbines include the ARE, Eoltec, Kestrel, and Skystream. Werecommend 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 inquireabout 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 evenincludes an inverter integrated with the turbine itself. Make sure youre buying a machine that is appropriate foryour intended use.

When you look at prices, keep in mind that just buying a wind turbine will not get you any wind-generated

electricity. Youll also need most or all of the components mentioned elsewhere. Also budget for equipmentrental, 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 toas much as 40 percent of the entire wind systems 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 didtheir homeworkpurchasing, designing, and installing rugged and well-thought-out systems on adequatelysized towers. In addition, they are either committed to maintaining the systems, or to hiring someone to do this



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regular work.

While many first-time wind turbine buyers may be looking for a bargain, second-time wind turbine buyers areseeking 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 dont want todepend 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 Buyers Guide

Estimating Wind Energy

Wind Generator Tower Basics

Wind-Electric Systems Simplified

Wind-Elect r ic System Types

Off-Grid Wind-Elect r ic System s

Off-grid wind-electric systems are battery based. People generally choose these systems because their homeor 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 renewableenergy 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 tolearn 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.

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Watts in the Wind

Gr id-T ied Wind-E lec t r ic Sys tem w i th Bat t e ry Backup

Connecting a wind-electric system to the utility grid with battery backup gives you the best of both worlds. Youhave 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 manygrid 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 batterybackup. See our Wind-Electric System Components section for an introduction to the function(s) of each

component.

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The First Small Wind System in Lassen County

Battery less Grid-Tied Wind-Electr ic 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 onlydrawback 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 yeara 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 inverters electronics can match the winds load moreexactly, 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.

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At Last....Simple Wind Grid-Tie

Betting the FarmWind Electricity Pays Off

Farming the Wind

Direct-Dr ive Battery less Wind-Electr ic 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, astock-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 its normallycolder when its 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.

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Wind-Elect r ic 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 varynot 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

http://homepower.com/basics/wind/#WindGeneratorhttp://homepower.com/basics/wind/#TowerComponenthttp://homepower.com/basics/wind/#BrakeComponenthttp://homepower.com/basics/wind/#ChargeControllerhttp://homepower.com/basics/wind/#DumpLoadhttp://homepower.com/basics/wind/#BatteryBankhttp://homepower.com/basics/wind/#SystemMeterhttp://homepower.com/basics/wind/#MainDCDisconnecthttp://homepower.com/basics/wind/#InverterComponenthttp://homepower.com/basics/wind/#ACBreakerPanelhttp://homepower.com/basics/wind/#BackupGeneratorhttp://homepower.com/basics/wind/#BackupGeneratorhttp://homepower.com/basics/wind/#BackupGeneratorhttp://homepower.com/basics/wind/#BackupGeneratorhttp://homepower.com/basics/wind/#ACBreakerPanelhttp://homepower.com/basics/wind/#InverterComponenthttp://homepower.com/basics/wind/#MainDCDisconnecthttp://homepower.com/basics/wind/#SystemMeterhttp://homepower.com/basics/wind/#BatteryBankhttp://homepower.com/basics/wind/#DumpLoadhttp://homepower.com/basics/wind/#ChargeControllerhttp://homepower.com/basics/wind/#BrakeComponenthttp://homepower.com/basics/wind/#TowerComponenthttp://homepower.com/basics/wind/#WindGeneratorhttp://homepower.com/basics/wind/#ChargeControllerhttp://homepower.com/basics/wind/#WindGeneratorhttp://homepower.com/basics/wind/#TowerComponent


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AKA: wind genny, wind turbine

The wind generator is what actually generates electricity in the system. Mostmodern wind generators are upwind designs (blades are on the side of the

tower that faces into the wind), and couple permanent magnet alternatorsdirectly 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 tiltingthe 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 alternatingcurrent (AC).

Its 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.


Wind Turbine Buyers 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 givethe most energy. Wind turbines should be sited at least 30 feet (9 m) higherthan 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 ofthe 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.


Wind Generator Tower Basics

What the Heck? Gin Pole

BrakeAKA: emergency shutdown mechanism

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Most wind turbines have some means of stopping the turbine for repairs, in an emergency, for routinemaintenance, 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 ordrum brake, activated by a small winch at the base of the tower. Still others have mechanical furling, whichswings the rotor out of the wind. Mechanical braking is usually more effective and reliable than dynamic braking.


Anatomy of a Wind Turbine

Charge Contro l ler AKA: controller, regulator

A wind-electric charge controllers primary function is to protect your battery bank fromovercharging. 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 theinverter is selling whatever energy the turbine is generating. But there will be somecontrol function in the case of grid failure, and there may be electronics before the

inverter to regulate the input voltage.


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


Wi d El t i it B i
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AKA: diversion load, shunt load

Solar-electric modules can be turned offopen circuitedwith no damage. Most windgenerators 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 chargecontroller 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. Incontrast, 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 waterheaters, and are activated by the charge controller whenever the batteries or the grid

cannot accept the energy being produced.

Bat te ry Bank AKA: storage battery

Your wind generator will produce electricity whenever the wind blows above thecut-in speed. If your system is off grid, youll need a battery banka group of

batteries wired together

to store energy so you can have electricity when itsnot windy. For off-grid systems, battery banks are typically sized to keep

household electricity running for one to three calm days. Grid-intertied systemsalso can include battery banks to provide emergency backup during blackoutsperfect for keeping critical electric loads operating until the grid is up again.

Use only deep-cycle batteries in wind-electric systems. Lead-acid batteries arethe most common battery type. Flooded lead-acid batteries are usually the leastexpensive, but require adding distilled water occasionally to replenish water lost

during the normal charging process. Sealed absorbent glass mat (AGM) batteries are maintenance free anddesigned 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.


Top 10 Battery Blunders and How to Avoid Them

Flooded Lead Acid Battery Maintenance

Battery Box Basics

Sys tem Mete r


Wind Elect icit Basics
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AKA: battery monitor, amp-hour meter, watt-hour meter

System meters can measure and display several different aspects of your wind-electric systems performance and statustracking how full your battery bank is, how

much electricity your wind generator is producing or has produced, and how muchelectricity is in use. Operating your system without metering is like running your car

without any gaugesalthough possible to do, its always better to know how muchfuel is in the tank.


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. Thisdisconnect 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, andprotects the inverter-to-battery wiring against electrical fires.


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 andappliances. Grid-tied inverters synchronize the electricity they produce withthe grids "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 orgrid-tie systems often include a battery charger, which is capable of charging a battery bank from either the grid


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or a backup generator during cloudy weather.


Whats Going OnThe 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 homes electrical wiring meets withthe provider of the electricity, whether thats the grid or a solar-electric system. This wall-

mounted panel or box is usually installed in a utility room, basement, garage, or on theexterior 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 tobe disconnected for servicing, and also protect the buildings wiring against electricalfires.

Just like the electrical circuits in your home or office, an inverters electrical output needsto be routed through an AC circuit breaker. This breaker is usually mounted inside thebuildings 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 circuits electrical wiring.

Additionally, for their use, utilities usually require an AC disconnect between the inverter and the grid that is fortheir use. These are usually located near the utility KWH meter.

Ki lowa t t -Hour Me te r AKA: KWH meter, utility meter

Most homes with a grid-tied wind-electric system will have AC electricity both coming fromand going to the electric utility grid. A bidirectional KWH meter can simultaneously keep

track of how much electricity youre using and how much your system is producing. Theutility company often provides intertie-capable meters at no cost.


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Backup GeneratorBackup Generator AKA: gas-guzzler, "the Noise"

Off-grid wind-electric systems can be sized to provide electricity during calmperiods when the wind doesnt 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 hugesurplus 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 benecessary.

Engine-generators can be fueled with biodiesel, petroleum diesel, gasoline, or propane, depending on thedesign. 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 themonly 50 to 200 hours a year or less.

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Wind Electricity Basics

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