WIND FAQ

A wind turbine, which is installed on top of a tall tower, collects kinetic energy from the wind and converts it to electricity that is compatible with a home's electrical system.

In a normal residential application, a home is served simultaneously by the wind turbine and a local utility. If the wind speeds are below cut-in speed (7-10 mph) there will be no output from the turbine and all of the needed power is purchased from the utility. As wind speeds increase, turbine output increases and the amount of power purchased from the utility is proportionately decreased. When the turbine produces more power than the house needs, the extra electricity is sold to the utility. All of this is done automatically. There are no batteries in a modern residential wind system, unless you are using an off grid system. Then batteries are a necessity. Small wind systems for remote applications operate somewhat differently.

Do you have a good wind site?

Wind powered battery charging systems can be cost effective if the average wind speed is nine miles per hour (mph) or more at the location of the wind generator. If you are using wind in combination with photovoltaic power, it may be cost effective if you have good wind only during part of the year. The power available from the wind is proportional to the cube of the wind speed. When the wind speed doubles, the power delivered is eight times as great. Most wind generators are designed to deliver maximum power at a wind speed of 30 mph. At 15 mph, they will deliver about 1/8 their rated power. A wind generator should be mounted at least 20 feet higher than any obstruction within 300 feet to avoid turbulence.

Wind Speed/Wind Effect

Wind Speed (MPH)	Wind Effect
0-1	Smoke rises vertically.
2-3	Direction of wind shown by smoke drift, but not by wind vanes.
4-7	Wind felt on face; leaves rustle; ordinary wind vane moved by wind.
8-12	Leaves and twigs in constant motion; wind extends a light flag.
13-18	Raises dust, loose paper; small branches are moved.
19-24	Small trees in leaf begin to sway; crested wavelets form on inland waters.
25-31	Large branches in motion; whistling heard in power lines; umbrella use is difficult.

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Will a small wind turbine save me money?

The wind turbine typically lowers your electricity bill by 50 to 90 percent. It is not uncommon for wind turbine owners with total-electric homes to have monthly utility bills of only $8 to $15 for nine months of the year. In northern parts of the country where less air conditioning is used the bills can be very low year-round. The amount of money a small wind turbine saves you in the long run will depend upon its cost, the amount of electricity you use, the average wind speed at your site, and other factors.

What size turbine would I need for my home?

Homes use approximately 9,400 kilowatt-hours (kWh) of electricity per year (about 780 kWh per month). Depending upon the average wind speed in the area, a wind turbine rated in the range of 5 to 15 kilowatts would be required to make a significant contribution to meet this demand.

Who should consider buying a wind turbine?

A residential wind turbine can be a relatively large device and is not suitable for urban or small-lot suburban homes. Except for very small wind turbines (i.e., with rotors one meter or less in diameter) on very small towers, a property size of one acre or more is desirable.

The economics of a wind system are very sensitive to the average wind speed in the area, and to a lesser extent, the cost of purchasing electricity. As a general rule of thumb, if economics are a concern, a turbine owner should have at least a 10 mph average wind speed and be paying at least 10 cents/kWh for electricity.

Residential wind turbines have been installed in at least 47 of the 50 states, but the majority of the units have been installed in the Northeast and the Midwest.

Will it help the environment if I install a wind turbine at my home?

Yes. Wind turbines produce no pollution and by using wind power you will be offsetting pollution that would have been generated by your utility company. Over its life, a small residential wind turbine can offset approximately 1.2 tons of air pollutants and 200 tons of greenhouse gases (carbon dioxide and other gases which cause climate change).

Don't I have to take wind measurements for a year or more?

For most residential systems the cost of taking wind measurements is not justified. Wind resource data published by the US Department of Energy is sufficient for an experienced evaluator to predict wind turbine performance. In very hilly or mountainous areas, however, it may be best to collect wind data before purchasing a system to ensure that your site is not in a sheltered area.

Do wind turbines make noise or interfere with TV reception?

Small wind turbines do make some noise, but not enough to be found objectionable by most people. A typical residential wind system makes less noise than the average washing machine. Wind turbines do not interfere with TV reception.

Will my utility allow me to hook up a wind generator?

Federal regulations (specifically, the Public Utility Regulatory Policies Act of 1978, or PURPA) require utilities to connect with and purchase power from small (less than 80 MW) wind energy systems. A wind turbine manufacturer should be able to help arrange the required utility company approvals.

Will I have to change any of the wiring in my house?

No. A wind turbine is easily retrofitted to virtually any home without the need to change any wiring or appliances. In most cases, the utility will install a second utility meter to measure how much surplus electricity it is purchasing from the turbine owner.

What about towers?

An 80- to 120-foot tower is usually supplied along with the wind turbine. Towers this tall are necessary to raise the wind turbine above turbulence generated by obstacles on the ground and trees. Wind velocity and, therefore wind turbine performance, increases with altitude. Several different types of towers are available, depending upon which manufacturer you select. Each type has its advantages; the most economical type of tower is the guyed lattice tower, but a hinged tower can be easier for you to install yourself and provides easier access for maintenance.

How much does a wind system cost?

A small turbine can greatly vary in cost, depending upon size, application and service agreements with the manufacturer/installer/company.

How reliable are wind turbines? Will I have to perform much maintenance?

Most small turbines have very few moving parts and do not require any regular maintenance. They are designed for a long life (up to 20 years) and operate completely automatically.

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How do wind turbines perform as an investment?

The wind system will usually recoup its investment through utility savings within six to 15 years and after that the electricity it produces will be virtually free. Over the long term, a wind turbine is a good investment because a well-sited wind system increases property value, similar to any other home improvement. Many people buy wind systems in preparation for their retirement because they don't want to be subject to unpredictable increases in utility rates.

How would I have a wind turbine installed at my home?

Self-installation offers significant savings and a hands-on understanding of the turbine. Prospective owners can discuss the options available with suppliers to decide which method best suits their budget and technical skills.

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What are the factors in the cost of electricity from wind turbines?

The cost of electricity from utility-scale wind systems has dropped by more than 80% over the last 20 years.

In the early 1980's, when the first utility-scale wind turbines were installed, wind-generated electricity cost as much as 30 cents per kilowatt-hour. Now, state-of-the-art wind power plants are generating electricity at costs as low as 4 cents/kWh, a price that is competitive with many conventional energy technologies. Costs are continuing to decline as more and larger plants are built and advanced technology is introduced.

Aside from actual cost, wind energy offers other economic benefits which make it even more competitive in the long term: Greater fuel diversity and less dependence on fossil fuels, which are often subject to rapid price fluctuations and supply problems. This is a significant issue around the world today, with many countries rushing to install gas-fired electric generating capacity because of its low capital cost. As world gas demand increases, the prospect of supply interruptions and fluctuations will grow, making further reliance on it unwise and increasing the value of diversity. Greatly reduced environmental impacts per unit of energy produced, compared with conventional power plants. Environmental costs are becoming an increasingly important factor in utility resource planning decisions. More jobs per unit of energy produced than other forms of energy. Long-term income to ranchers and farmers who own the land on which wind farms are built.

Selection of a suitable site is key to the economics of wind energy. The power available from the wind is a function of the CUBE of the wind speed, which means that, all other things being equal, a turbine at a site with 5 meters/second (m/s) winds will produce nearly twice as much power as a turbine at a location where the wind averages 4 m/s. In the electric power business, where technology options often hinge on very small economic differences, good wind resource assessment and siting is critical.

In general, winds exceeding 5 m/s (11 mph) are required for cost-effective application of small grid-connected wind machines, while wind farms require wind speeds of 6 m/s (13 mph). For applications that are not grid-connected, of course, these requirements may vary, depending on the other power alternatives available and their costs.

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What are the Basic Principles of

Wind Resource Evaluation ?

Wind resource evaluation is a critical element in projecting turbine performance at a given site. The energy available in a wind stream is proportional to the cube of its speed, which means that doubling the wind speed increases the available energy by a factor of eight. Furthermore, the wind resource itself is seldom a steady, consistent flow. It varies with the time of day, season, height above ground, and type of terrain. Proper siting in windy locations, away from large obstructions, enhances a wind turbine's performance.

In general, annual average wind speeds of 5 meters per second (11 miles per hour) are required for grid-connected applications. Annual average wind speeds of 3 to 4 m/s (7-9 mph) may be adequate for non-connected electrical and mechanical applications such as battery charging and water pumping. Wind resources exceeding this speed are available in many parts of the world.

Wind Power Density is a useful way to evaluate the wind resource available at a potential site. The wind power density, measured in watts per square meter, indicates how much energy is available at the site for conversion by a wind turbine. Classes of wind power density for two standard wind measurement heights are listed in the table below. Wind speed generally increases with height above ground.

Classes of Wind Power Density at 10 m and 50 m(a)
.	10 m (33 ft)		50 m (164 ft)

Wind Power Class	Wind Power Density (W/m2)	Speed(b) m/s (mph)	Wind Power Density (W/m2)	Speed(b) m/s (mph)
1	<100	<4.4 (9.8)	<200	<5.6 (12.5)
2	100 - 150	4.4 (9.8)/5.1 (11.5)	200 - 300	5.6 (12.5)/6.4 (14.3)
3	150 - 200	5.1 (11.5)/5.6 (12.5)	300 - 400	6.4 (14.3)/7.0 (15.7)
4	200 - 250	5.6 (12.5)/6.0 (13.4)	400 - 500	7.0 (15.7)/7.5 (16.8)
5	250 - 300	6.0 (13.4)/6.4 (14.3)	500 - 600	7.5 (16.8)/8.0 (17.9)
6	300 - 400	6.4 (14.3)/7.0 (15.7)	600 - 800	8.0 (17.9)/8.8 (19.7)
7	>400	>7.0 (15.7)	>800	>8.8 (19.7)

(a) Vertical extrapolation of wind speed based on the 1/7 power law
(b) Mean wind speed is based on the Rayleigh speed distribution of equivalent wind power density. Wind speed is for standard sea-level conditions. To maintain the same power density, speed increases 3%/1000 m (5%/5000 ft) of elevation.

In general, sites with a Wind Power Class rating of 4 or higher are now preferred for large scale wind plants. Research conducted by industry and the US government is expanding the applications of grid- connected wind technology to areas with more moderate wind speeds.

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How Can I Calculate the Amount of Power Available at a Given Wind Speed?

Because air has mass and it moves to form wind, it has kinetic energy. You may remember from science class that:

kinetic energy (joules) = 0.5 x m x V2

where:

m = mass (kg) (1 kg = 2.2 pounds)

V = velocity (meters/second) (meter = 3.281 feet = 39.37 inches)

Usually, we're more interested in power (which changes moment to moment) than energy. Since energy = power x time and density is a more convenient way to express the mass of flowing air, the kinetic energy equation can be converted into a flow equation:

Power in the area swept by the wind turbine rotor:

P = 0.5 x rho x A x V3

where:

P = power in watts (746 watts = 1 hp) (1,000 watts = 1 kilowatt)

rho = air density (about 1.225 kg/m3 at sea level, less higher up)

A = rotor swept area, exposed to the wind (m2)

V = wind speed in meters/sec (20 mph = 9 m/s) (mph/2.24 = m/s)

This yields the power in a free flowing stream of wind. Of course, it is impossible to extract all the power from the wind because some flow must be maintained through the rotor (otherwise a brick wall would be a 100% efficient wind power extractor). So, we need to include some additional terms to get a practical equation for a wind turbine.

Wind Turbine Power:

P = 0.5 x rho x A x Cp x V3 x Ng x Nb

where:

P = power in watts (746 watts = 1 hp) (1,000 watts = 1 kilowatt)

rho = air density (about 1.225 kg/m3 at sea level, less higher up)

A = rotor swept area, exposed to the wind (m2)

Cp = Coefficient of performance (.59 {Betz limit} is the maximum theoretically possible, .35 for a good design)

V = wind speed in meters/sec (20 mph = 9 m/s)

Ng = generator efficiency (50% for car alternator, 80% or possibly more for a permanent magnet generator or grid-connected induction generator)

Nb = gearbox/bearings efficiency (depends, could be as high as 95% if good)

If there is any single equation that the beginning wind enthusiast should memorize, this is it.

I'm concerned, but face it, I'm not going to put up a windmill in my backyard. So realistically, what can I do to help bring about clean energy?

There are two very important ways you can help make the clean energy transition happen. First, express yourself! Tell your neighbors about clean energy, send a letter to the editor of your paper, or write your elected representative. Second, reduce your energy use. The cleanest energy of all is the energy you save. We are living at an exciting time in history. Clean energy is coming -- be part of the solution!

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Clean Energy Basics

Where does my electricity come from?

That depends on where you live. The sun, wind, and other clean, renewable energy sources make up a small yet fast-growing share of total power generation. Some of your electricity may also come from hydropower or nuclear power. It is likely, however, that most of it comes from fossil fuels -- coal, oil, and natural gas -- that have been burned to produce energy. Fossil fuels formed underground from the remains of plants and animals that lived millions of years ago.

How much fossil fuel do we have left?

There is no way to know for sure how much fossil fuel remains, and we can't afford to find out. Using even current known reserves would cause massive releases of heat-trapping gases, speeding up global warming.

How does energy use affect the environment?

Pollution from fossil fuels and nuclear power is contaminating our air, water, and food supply: Acid rain and mercury pollution from coal power plants damage forests, wildlife, and human health. Oil spills and energy-related toxic wastes destroy marine ecosystems and contaminate soil and water. Nuclear power produces radioactive wastes that will poison the environment for thousands of years.

What exactly causes global warming?

The burning of fossil fuels releases over six billion tons of heat-trapping gases like carbon dioxide into the atmosphere each year. These gases blanket the Earth, warming it. Forests are a primary way that the Earth controls the amount of atmospheric carbon dioxide, so deforestation is also an important factor in global warming.

Does this mean palm trees can grow in Finland?

Unlikely. We can expect to see more "freak" weather conditions like cyclones, floods and droughts; potentially enormous loss of life; millions of people displaced from their homes in the worst-affected areas; greater risk from diseases like malaria as mosquitoes widen their reach; and threats to entire species as their habitat is wiped out.

That's scary. What can we do?

Heat-trapping gases stay in the atmosphere for a hundred years or

more, so we are going to be dealing with this problem for a long time. There is no doubt that we will face some degree of global warming; the question is, how bad will it be? The severity of climate changes will be affected primarily by how much, and how soon, we reduce our fossil fuel use and embrace clean, renewable energy sources.

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What do you mean by "clean, renewable energy sources?"

Renewable sources of energy are virtually inexhaustible and are naturally and quickly replenished. They are called "clean" because they generate energy without producing pollution. Switching to clean, renewable energy will bring us cleaner air and water, while improving human health and increasing energy security.

Solar photovoltaic (PV) energy converts sunlight directly into electricity using photovoltaic cells. It is fuel-free, reliable, silent, and durable. Solar thermal energy uses technologies and building-design to warm our houses, heat our bath water, and power solar cookers by trapping heat from the sun. Wind power produces electricity by turning the blades on a wind turbine (similar to a windmill). Wind is the world's fastest growing energy source. Biomass is humanity's oldest source of renewable energy. Produced by plants through photosynthesis, it is stored in organic matter such as wood, agricultural wastes, and animal wastes. Biomass can be converted into liquid or gaseous fuels, or it can be burned to generate electricity. Geothermal power is a form of renewable energy that uses natural heat from the Earth's core to warm buildings and generate electricity. Hydropower, which harnesses the energy in flowing water, represents the largest share of renewable energy currently in use. Unfortunately, large-scale hydropower causes severe environmental impacts. Large dams displace local inhabitants, destroy habitat, and prevent fish from reaching their spawning grounds.

So natural gas and nuclear power aren't considered "clean and renewable"?

Natural gas is the cleanest of the fossil fuels. Still, it is a significant source of carbon dioxide, the main cause of global warming. Natural gas is nonrenewable, meaning that supplies are limited.

Nuclear energy is fueled by uranium, also a nonrenewable resource. Along with the risk of catastrophic accidents, nuclear power plants produce toxic radiation that will remain dangerous for many thousands of years.

What about birds getting caught in wind turbines? Or toxins used to make solar panels? Doesn't renewable energy cause environmental problems too?

No energy source is perfect, and yes, there are environmental issues to be addressed with renewable energy sources. Yet these challenges should not stop us from addressing global warming. If we fail to reverse course, we will jeopardize the natural systems on which all of life depends. Above all, we must slow global warming through a rapid transition away from fossil fuels.

Is a worldwide conversion to clean energy realistic?

In a world of rising energy prices and increasing instability in the international oil market, renewable energy has two huge advantages: It has no fuel costs, and it is freely available.

Clean, renewable energy is already being used successfully around the world. The missing ingredient preventing more widespread use is a significant commitment of human and financial resources.

In other words, clean energy costs a lot more?

One of the reasons that the transition to renewable energy sources has been slow is that fossil fuel prices have been kept down artificially through subsidies. Still, wind power is already cost-competitive with fossil fuels. Sales of solar cells are surging, and their cost has fallen sharply over the past twenty years. For people not connected to the electricity grid, solar energy's cost is comparable to conventional sources. As demand for renewable energy grows, economies of scale will reduce prices further. When you consider the savings from prevented damage to our health and the environment, clean energy is even cheaper.

Won't the global economy be dragged down in an energy transition?

Changing to clean energy and installing energy efficiency retrofits will create millions of new jobs. Renewable energy jobs will be more geographically balanced and will offer greater stability than jobs in the fossil fuel economy. Cleaner air and water will result in billions of dollars in health care savings. Preventing runaway escalation in heat-trapping carbon dioxide emissions is the best insurance policy we can buy against the potentially devastating worldwide impacts of global warming.

If we mobilize our financial and human resources to make this essential energy transition now, we can minimize economic disruption and ensure a livable planet for future generations.

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What are world leaders doing about this?

Representatives of most of the world's nations have met to address the dangers of global warming. They produced an international agreement known as the Kyoto Protocol, that has been ratified by many countries. Implementing the Kyoto Protocol around the world is important. Yet it is only a small step, given the magnitude of changes needed to stabilize our climate and prevent further environmental destruction.

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I'm concerned, but face it, I'm not going to put up a windmill in my backyard. So realistically, what can I do to help bring about clean energy?

Oil Pollution Fact - Just one gallon of oil improperly disposed of can contaminate the fresh water supply for 50 people for one year!

For every 1 ton of waste a person generates,

another 20 tons of waste are generated to produce the products you use!

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E-mail us at info@windvolt.com for free information

or call us at 641-683-7413

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