(207) 797-0979

Windmills

wind turbines outside town

Wind Turbines are a popular and cost effective choice for producing electricity provided the location has sufficient average wind speed. The majority of suburban lots are not good wind sites due to structural wind blockages. Many communities have restrictions to insure that tower heights do not exceed the lot size.  The cost of solar electric has dropped significantly so without a good site a PV system is going to cost less unless you are on a hill top or the coast.

Determining your wind speed

Government wind charts can be a starting point, but unless you are positive you have sufficient wind, you should have a wind study done at the location. An anemometer will be placed at the expected turbine height for a period of time and it will accurately track the wind. This information is critical since it tells the whole story; maximum, frequency of occurrence, and average wind speed over the seasons. This data is crucial to finding a wind turbine that fits your situation.

Types of wind turbines

Traditional wind turbines, often called windmills, have 3 long propeller type blades and are mounted 30+ feet in the air.  Commercial size turbines are often hundreds of feet tall.  Wind speeds increase with height so it is wise to put up a tower that is as high as feasable. 

Urban Green Wind Turbine UGE-4

Tangarie makes a double helix design looks like vertical twisted ribbons. It has no arms. You can see it in action on their website. Their vertical turbines do not strobe, are quiet, and are “bird safe” since they are seen as solid objects by wildlife.  Tangarie has models from 1 kw to 10 kw.  The vertical design of the Tagarie makes it look like a peice of art.  You can even choose to customize your turbine with graphics.  

 

Urban Green also makes vertical windmills.  They have a unique bladed design. The have models as small as 200 watts.  These would normally be used in conjuction with a PV system to provide energy during storms.  Their largest unit is 10 kw

Site selection

Especially with regular windmills, it is very important to install the unit in a clear open area. Putting a windmill between, or close to buildings or trees means the wind flow is blocked. “Clean wind” blows in one direction. When an object disrupts this pattern the turbulence impacts the wind turbine. Sometimes this can be used as an advantage. The small Tangarie GALE 1 can be roof mounted and the wind blowing over the roof actually increases the turbines operation. A standard rule is the turbine motor should be 30ft above anything that is within a 500ft radius; more is better.

Tower height greatly impacts performance since usually the higher up, the greater the wind speed. Unfortunately towers are expensive and building codes may restrict the height. Unlike PV, you cannot “add on” to a wind turbine. Picking the right turbine and the correct tower size to start is critically important.

One note about roof mounted turbines; they can cause vibration noise and their output is normally quite low. One feasible use is if your turbine is just a supplement to PV and you have a garage or barn to mount a small unit.

Wind turbines are excellent complement to a photovoltaic (PV) electric system. Winds increase in stormy weather, and still blow at night, times when a PV panels output drops.

Sizing your wind turbine

Turbines have a kilowatt rating but there is no solid standard that allows fair comparisons between manufactures. While a turbine may say it starts at a wind speed as low as 4 mph, substantial generation does not start until the wind speed is near15- 20 mph. A turbine rating gives a wind speed and kilowatt output. Standard residential system sizes range from 1kw (1000 watts) to 10kw (10,000 watts).  A 1 kw system is  small but is great when combined with a solar electric system.  Only at the stated wind speed do you get the rated output. If the wind speed is less than the rating, the output drops exponentially. It is wise to carefully review the units wind graph and compare it to your average wind speeds.

Power Curve graphs

Some manufactures are optimistic in describing their product performance.  Purchasing a wind turbine, and making sure you have a good site, is a buyer beware proposition at times.  Make sure your contract clearly spells out the expected annual output.  We are happy to help you “do your homework” if you give us a call.

Wind power curve

 

This is an old graph and does not reflect current product lines

 

All manufactures should provide you with a wind chart like this one.  These graphs show the wind speed and expected killowatt output.   This chart is from an older model but a great example of how wind speed impact the energy generated. 

The blue line represents this company's 10 kw unit.  The only time the turbine generated 10 kw is when the wind speet is about 23-25 mph.  Once the wind speed exceeds 25 mph the output starts to drop.  When it exceeds 33 mph the unit will shut down to prevent damage.   With the smaller unit shown in red thre is a pretty consistant output from about 25-35.  At 20 mph you are only get 50% of the maximum output and it shuts down at 35 mph.   With the larger unit at 20 mph you are getting just over 70% of the maxumum power.  In both cases at 15 mph the output is so low you could not justify the investment in the turbine.  The blue unit has a narrower peak operating range.

The importance of doing a long wind study is revealed with this sample chart.  Power increases exponentially with wind speed.  Every model will have a different curve.  Without a solid wind study you will not know what the wind patterns are at your site. 

NOTE: This chart is in MPH but other manufactures use differnt units.  Make sure you are comparing turnbines base on the same units.  This is NOT a current chart.

 

Helpful Information

The US government publishes wind charts base on location. Two good links are:

While they can be a good starting point, relying solely on their data could prove to be a very costly mistake. If the chart shows you are in a good wind area, and you consistently note, through all seasons, high average wind speeds then you may opt to skip having a wind study done. Mountain top ridges and islands often have unquestionable winds. You are taking the risk of selecting a model that may not be the best fit.   For most locations a 12 month wind study should be performed.

The output for wind turbines increases exponentially with wind speed. In simple terms this means if you get X kilowatts at 20mph, at 10mph you will not get half of X. The power available in the wind is related to the cube of wind speed/velocity (V3 ). Doubling the wind speed gives 8 times the energy. (20mph wind: 20 x 20 x 20=8,000  vs  10 x 10 x 10=1,000)

Some windmills do well at 20mph and then the output curve flattens out as the wind speed increases. Some perform best in the 25-30mph ranges but not at lower speeds. A wind study will help you analyze your site and determine the right turbine for the location.

 

Ready to get started?

Contact us today with your questions or to set up your free consultation.

Contact Us

 

PV Cost and Net Metering

Podcast explains Net Metering &  how much cheaper PV electric is vs. the utlity

Solaris

600 Riverside St.

Portland ME 04103

(207) 797-0979

Copyright 2017 Solaris Thermal. All rights reserved.

Website designed and maintained by