Saturday, January 29, 2011

Wind Turbine Cut-in Speed

Wind turbine cut-in speed means, the lowest wind speed at which the wind turbine will start to generate noticeable electrical output power. If you were to search for a wind turbine, don't consider cut-in wind speed as a primary goal. It is not desirable nor is it preferable to buy a wind turbine with low cut-in .

The reason why you should ignore cut-in speed is that the generator of the wind turbine won't start to charge your battery or battery banks till the output voltage from the alternator is higher than the battery voltage or battery bank.

However, if you were to find a suitable wind turbine and the turbine has a low cut-in wind speed you may consider it since this can produce at least some kind of electrical output power most of the times when wind speed is low and your battery or battery bank is fully discharged.

On the other hand, if you’re designing your own wind turbine, you may not need to worry about cut-in wind speed since you might be able to utilize funneling technique to your wind turbine to increase the wind speed.

Friday, January 28, 2011

Wind Turbine Power Curve

Take a look at the wind turbine power curve below; you will notice that there are two axes, the X-axis and the Y-axis. The X-axis represents the hub wind speed in meters per second (m/s) and the Y-axis represents the expected power output in kilo Watts (kW) of the wind turbine.
Wind Turbine Power Curve
If you have taken wind speed data at the location you intend to install your wind turbine, then you can predict the average power output from your wind turbine generator from the power curve. Just make sure that the wind speed data recorded is taken at the same height as the hub height, otherwise your wind speed data would be incorrect.

For example, if you are planning to install a 10kW wind turbine at your location and the average wind speed recorded over a week period during summer time was 5 m/s at ground level, then your site location may be ideal for installation of a wind turbine. You might not believe this if you were to look at the wind turbine power curve above since at 5 m/s the wind turbine would produce about ~2kW.

Actually, you may not have noted that you have taken your wind speed data at ground level. Usually the hub height is at least 10 meters above ground level and wind speed tend to approximately double every ~12 meters provided obstacles such as buildings and trees are not in close vicinity to your wind turbine.

However, 5 m/s at ground level during summer time (winter time wind speed is higher) is a good indication for a suitable location for wind turbine installation and you should take measurements at higher heights to be certain. It is highly recommended that you take several readings around the same location as wind paths can be a few meters away from where you are.

For homeowners who intend to install small permanent magnet generators (alternators) it is extremely important to get the power curve from the manufacturer since this power curve is different from one manufacturer to another. Furthermore, a wind turbine power curve is usually corrected if your site location is more than 300m above sea level or ambient temperature is far above 20 degrees C.

Thursday, January 27, 2011

Wind Turbines

Wind turbines are devices that transform wind energy into mechanical energy to generate electricity. Wind turbines can have one blade or multi-blades depending on their area of application.

There are two types of wind turbines; the vertical axis wind turbine (VAWT) and the horizontal axis wind turbine (HAWT). Today, most of the wind turbines use a horizontal axis with two or three blades due to their high tip speed and efficiency which contribute to good reliability.

There are two types of applications for wind turbines. Either stand-alone, or synchronized and connected  to the utility power grid. Also, wind turbines can be integrated with a photovoltaic (solar cell) system, batteries, and diesel generators and in such case they are known as hybrid systems.

Water pumping wind turbines are examples of a stand-alone application that doesn’t produce electricity and use multi-blades similar to the ones used in the old west. These days a large number of electricity generating wind turbines are being erected in close vicinity to each other in designated areas known as wind farms to harvest the wind energy and feed the utility power grid. However, in windy areas far away from the utility power grid, homeowners and farmers are utilizing wind turbines to generate electricity.

There are several factors that can be used to predict electrical power output that can be generated from a  wind turbine. These factors can be extracted from manufacturer’s data sheets and power curve. The most important of these factors include:
Based on these factors that can be extracted from the manufacturer’s data sheet  contribute to the wind turbine capacity factor.