Tobie Green Energy

Frequently Asked Questions

1. Why Wind?
2. Is Wind Power The Right Choice For My Application?
3. How Much Energy Will A 100kw Turbine Produce?
4. How Much Energy Do I Need To Produce For My Site?
5. How Can I Determine My Wind Source?
6. What If I Have A Low Wind Site?
7. How Can I Determine My Payback or ROI?
8. What Is A Power Curve?
9. Why The Tobie Green Turbine?
10. How Do I Purchase A Tobie Green Turbine For My Site?
11. What are wind turbines made of?
12. How big is a wind turbine?
13. How much electricity can one wind turbine generate?
14. How many homes can one megawatt of wind energy supply?
15. What is a wind power plant?
16. What is "capacity factor"?
17. If a wind turbine's capacity factor is 33%, doesn't that mean it is only running one-third of the time?
18. What is "availability" or "availability factor"?

1. Why Wind?

By producing your own power locally, you will be engaging in alternative energy, helping to support “green” technology, and saving the retail value of your energy costs at the same time.  For many, the cost savings alone make producing local wind power an imperative.

2. Is Wind Power The Right Choice For My Application?

After determining that you have at least a minimum of wind at your site, you will want to consider your main motivations for engaging in wind power. If you care only about being “green,” a specific payback time period is of no concern.  You should then consider erecting a turbine at even the lowest possible average wind speed.  If you care only about ROI, you will need to consider the retail costs of your current energy source as well as any incentives available to you: grants, tax incentives, and net metering laws.

Most people fall somewhere in the middle along that continuum of “green” versus “payback,” and require at least a basic idea of payback timing in order to make the decision to move forward.

3. How Much Energy Will A 100kW Turbine Produce?

A 100kW wind turbine will produce different amounts of electricity based on the average wind speed at your site. The Tobie Green turbine utilizes advanced turbine technology to ensure excellent energy capture for its size.  For example, if your site has an average wind resource measuring 4 meters per second (8.90 mph) and follows a standard distribution (i.e. a “bell curve” of wind speeds), you can expect the Tobie Green turbine to produce approximately 70,000 kilowatts-hours of energy in a year.  If your average wind speed is 6 meters per second (13.4 mph), the Tobie Green turbine will produce approximately 214,000 kilowatt-hours per year.

4. How Much Energy Do I Need To Produce For My Site?

Most areas in the United States and many in international markets have net metering laws, which allow individual sites to average out their annual production and get “credit” for what they produce to offset what they use.  But there are few places that allow for individuals, organizations, or communities to actually make money by selling excess power back to the utility.  Because of this, and because wind is an intermittent source of power, most people want to match their load (i.e. produce only what they will use in a given year and not more) fairly closely – or even produce a lot less than will be needed – to be sure that no wind power is wasted.

In the case of a Tobie Green turbine, if your facility uses significantly more power than what you expect to produce, you may consider erecting two or more turbines.

5. How Can I Determine My Wind Source?

There are a number of excellent websites that can help you determine what your wind resource is.

NREL (National Renewable Energy Laboratory) has done extensive studies across the United States.  You can find their maps at www.nrel.gov/gis/wind.

AWS Truewind has also done extensive work mapping wind resources in the US and internationally.  Their maps can be found at www.awstruewind.com. 

In most cases, the wind maps and modeling technologies that are currently available are extremely accurate.

You can also install an anemometer to determine your wind resource.  Some customers choose to install one for 3 months and then project the annual wind resource from that.  Others choose to leave an anemometer up for a full year.  Please note that even an anemometer installed for a full year will only measure the actual wind resource for that particular time period, and thus its accuracy for projecting future winds will still be burdened with some amount of standard deviation.

6. What If I Have A Low Wind Site?

The Tobie Green turbine will begin making power with a wind speed of 3-4 meters per second (8.9 mph), although the blades will spin at even lower wind speeds.  You will want an annual average wind speed of at least 4 meters per second at hub height for wind power to be a viable option, and even more if you are looking for a competitive Return on Investment (ROI).

Generally, wind is more abundant at higher levels.  For this reason, we have developed a low wind tower option for the Tobie Green turbine that raises the rotor hub height to 37 meters (approximately 121 ft) above the ground.  (Typical tower height is 30 meters – approximately 98 Feet - high.)

In many cases, the extra height is enough to make wind power an attractive option.

7. How Can I Determine My Payback Or ROI?

At Distributed Energy Systems, we have a basic modeling program that will help you determine a basic ROI.  It takes into account the Tobie Green turbines power curve and assumes a wind profile with a typical distribution around the average wind speed.  You will need to provide three things:

• Your current cost of energy.  Our model allows us to input an average cost (per kilowatt).  You can get this information from your utility or figure it out from a year’s worth of utility bills.
• Your wind resource.  The amount of power you can make and your potential payback is a function of how much wind you have at your site.  We can input your wind data in “meters per second” or in “miles per hour.”   See “How can I determine my wind resource” above for     more information.
• The value of incentives available to you.  In the US, there is a federal tax incentive, and many states have attractive cash grants and other incentives as well.  To find out more about what’s available to you in the United States, you can visit www.dsireusa.org

We will input your three numbers, plus a general cost for turbine and installation, to provide you with a basic payback scenario.

Many consulting companies have extensive knowledge of the local environment and can help you through the factors above, as well as many other assumptions such as the impact of low interest loans or tax credits and installation variables.  We will be glad to recommend a local consulting company who can discuss your specific application in more detail.

8. What Is A Power Curve?

Every wind turbine has a power curve, which describes the power output at different wind speeds.

The Tobie Green turbine utilizes a permanent magnet generator and gearless design to capture more energy than older turbine designs, which makes its power curve very attractive for a 100kW size.

9. Why The Tobie Green Turbine?

The Tobie Green turbine represents the latest turbine technology available today, most notably a gearless design and direct-drive architecture for best-in-class energy capture and low maintenance.

10. How Do I Purchase A Tobie Wind Turbine For My Site?

Erecting a wind turbine at your site requires that you have purchased a turbine, resolved any permitting issues, and that you have someone who can install and commission it for you.

Distributed Energy Systems produces and commissions world-class turbines but we rely on our close relationships with partner organizations in local markets who can provide the turn-key services that most of our customers require.  These partners can purchase the turbine from us, help navigate local permitting processes, provide installation services, and coordinate commissioning – all from a single, local source.

In the case of a region where we do not have a close relationship with a local consulting and installation organization, we will be glad to work with you from our Houston office to help find local consulting organizations and installers.

11. What are wind turbines made of?

The towers are mostly tubular and made of steel. The blades are made of fiberglass-reinforced polyester or wood-epoxy.

12. How big is a wind turbine?

Utility-scale wind turbines for land-based wind farms come in various sizes, with rotor diameters ranging from about 50 meters to about 90 meters, and with towers of roughly the same size. A 90-meter machine, definitely at the large end of the scale at this writing (2005), with a 90-meter tower would have a total height from the tower base to the tip of the rotor of approximately 135 meters (442 feet).

Offshore turbine designs now under development will have larger rotors—at the moment, the largest has a 110-meter rotor diameter—because it is easier to transport large rotor blades by ship than by land.

Small wind turbines intended for residential or small business use are much smaller. Most have rotor diameters of 8 meters or less and would be mounted on towers of 40 meters in height or less.

13. How much electricity can one wind turbine generate?

The ability to generate electricity is measured in watts. Watts are very small units, so the terms kilowatt (kW, 1,000 watts), megawatt (MW, 1 million watts), and gigawatt (pronounced "jig-a-watt," GW, 1 billion watts) are most commonly used to describe the capacity of generating units like wind turbines or other power plants.

Electricity production and consumption are most commonly measured in kilowatt-hours (kWh). A kilowatt-hour means one kilowatt (1,000 watts) of electricity produced or consumed for one hour. One 50-watt light bulb left on for 20 hours consumes one kilowatt-hour of electricity (50 watts x 20 hours = 1,000 watt-hours = 1 kilowatt-hour).

The output of a wind turbine depends on the turbine's size and the wind's speed through the rotor. Wind turbines being manufactured now have power ratings ranging from 100 watts to 5 megawatts (MW).

Example: A 10-kW wind turbine can generate about 10,000 kWh annually at a site with wind speeds averaging 12 miles per hour, or about enough to power a typical household. A 5-MW turbine can produce more than 15 million kWh in a year--enough to power more than 1, 400 households. The average household consumes about 10,000 kWh of electricity each year.

Example: A 250-kW turbine installed at the elementary school in Spirit Lake, Iowa, provides an average of 350,000 kWh of electricity per year, more than is necessary for the 53,000-square-foot school. Excess electricity fed into the local utility system earned the school $25,000 in its first five years of operation. The school uses electricity from the utility at times when the wind does not blow. This project has been so successful that the Spirit Lake school district has since installed a second turbine with a capacity of 750 kW. Wind speed is a crucial element in projecting turbine performance, and a site's wind speed is measured through wind resource assessment prior to a wind system's construction. Generally, an annual average wind speed greater than four meters per second (m/s) (9 mph) is required for small wind electric turbines (less wind is required for water-pumping operations). Utility-scale wind power plants require minimum average wind speeds of 6 m/s (13 mph).

The power available in the wind is proportional to the cube of its speed, which means that doubling the wind speed increases the available power by a factor of eight. Thus, a turbine operating at a site with an average wind speed of 12 mph could in theory generate about 33% more electricity than one at an 11-mph site, because the cube of 12 (1,768) is 33% larger than the cube of 11 (1,331). (In the real world, the turbine will not produce quite that much more electricity, but it will still generate much more than the 9% difference in wind speed.) The important thing to understand is that what seems like a small difference in wind speed can mean a large difference in available energy and in electricity produced, and therefore, a large difference in the cost of the electricity generated. Also, there is little energy to be harvested at very low wind speeds (6-mph winds contain less than one-eighth the energy of 12-mph winds).

14. How many homes can one megawatt of wind energy supply?

An average household uses about 10,655 kilowatt-hours (kWh) of electricity each year. One megawatt of wind energy can generate from 2.4 to more than 3 million kWh annually. Therefore, a megawatt of wind generates about as much electricity as 225 to 300 households use. It is important to note that since the wind does not blow all of the time, it cannot be the only power source for that many households without some form of storage system. The "number of homes served" is just a convenient way to translate a quantity of electricity into a familiar term that people can understand. (Typically, storage is not needed, because wind generators are only part of the power plants on a utility system, and other fuel sources are used when the wind is not blowing. According to the U.S. Department of Energy , "When wind is added to a utility system, no new backup is required to maintain system reliability."

15. What is a wind power plant?

The most economical application of wind electric turbines is in groups of large machines (660 kW and up), called "wind power plants" or "wind farms." For example, a 107-MW wind farm near the community of Lake Benton, Minn., consists of turbines sited far apart on farmland along windy Buffalo Ridge. The wind farm generates electricity while agricultural use continues undisturbed.

Wind plants can range in size from a few megawatts to hundreds of megawatts in capacity. Wind power plants are "modular," which means they consist of small individual modules (the turbines) and can easily be made larger or smaller as needed. Turbines can be added as electricity demand grows. Today, a 50-MW wind farm can be completed in 18 months to two years. Most of that time is needed for measuring the wind and obtaining construction permits—the wind farm itself can be built in less than six months.

16. What is "capacity factor"?

Capacity factor is one element in measuring the productivity of a wind turbine or any other power production facility. It compares the plant's actual production over a given period of time with the amount of power the plant would have produced if it had run at full capacity for the same amount of time.

A conventional utility power plant uses fuel, so it will normally run much of the time unless it is idled by equipment problems or for maintenance. A capacity factor of 40% to 80% is typical for conventional plants.

A wind plant is "fueled" by the wind, which blows steadily at times and not at all at other times. Although modern utility-scale wind turbines typically operate 65% to 90% of the time, they often run at less than full capacity. Therefore, a capacity factor of 25% to 40% is common, although they may achieve higher capacity factors during windy weeks or months.

It is important to note that while capacity factor is almost entirely a matter of reliability for a fueled power plant, it is not for a wind plant—for a wind plant, it is a matter of economical turbine design. With a very large rotor and a very small generator, a wind turbine would run at full capacity whenever the wind blew and would have a 60-80% capacity factor—but it would produce very little electricity. The most electricity per dollar of investment is gained by using a larger generator and accepting the fact that the capacity factor will be lower as a result. Wind turbines are fundamentally different from fueled power plants in this respect.

17. If a wind turbine's capacity factor is 33%, doesn't that mean it is only running one-third of the time?

No. A wind turbine at a typical location in the Midwestern U.S. should run about 65-90% of the time. However, much of the time it will be generating at less than full capacity (see previous answer), making its capacity factor lower.

18. What is "availability" or "availability factor"?

Availability factor (or just "availability") is a measurement of the reliability of a wind turbine or other power plant. It refers to the percentage of time that a plant is ready to generate (that is, not out of service for maintenance or repairs). Modern wind turbines have an availability of more than 98%--higher than most other types of power plant. After more than two decades of constant engineering refinement, today's wind machines are highly reliable.