As our followers know, the Orenda blog is a great source for the latest wind energy information. However, we also have a mini section of our site dedicated to wind energy FAQs and Facts, where you can also find a couple of in-depth and informative Whitepapers and even a Fact Sheet.
We encourage information sharing, and we would be honoured to have our information linked to on other pro-wind websites. If you want to host our whitepaper on your site, feel free to contact us.
Below, you will find a snippet from our Wind Turbine Investments: Determining Real-World Financial Returns whitepaper, where we explain the difference between power and energy:
Power versus energy
The amount of power that a wind turbine generates, measured in kilowatts (kW), is often used in advertising, but is actually a poor measure of wind turbine performance. Rated power is the value most often quoted, which refers to the maximum power output that can be achieved by the turbine at optimal wind speeds. Since wind conditions are never constant and power generation varies greatly with small wind changes, it is not useful to measure wind turbine performance in terms of kW.
Below is an example of a typical power curve for a small wind turbine. It shows the rated power of the turbine and the wind speed (in meters/second) at which it is achieved. It also shows the cut-in speed, where the turbine begins generating power, and the cut-out speed, where the turbine is automatically shut down to avoid sustaining damage from the high force of the wind.
It is easy to see that while there will be times when the wind turbine generates the rated amount of power, there will also be times when it will produce less than the rated power or none at all. This is why power measured in kW cannot be used to evaluate wind turbine performance.
Fluctuating wind conditions make it necessary to talk about annual energy production (AEP), measured in kilowatt hours (kWh), instead of power measured in kW. A kilowatt hour is the unit of power or energy, which is equal to 1000 watts operating for one hour. An estimate of AEP must take into consideration wind conditions over time to project the usable amount of energy produced in a year.
There are several different ways to calculate AEP: using the average wind speed at the location, monitoring actual wind conditions to determine wind bins (the amount of time in a year that the turbine will be exposed to each wind speed), or using a Rayleigh distribution, which combines the other two methods. The Rayleigh distribution model allows wind bins to be estimated using the average wind speed for the location, and it uses the turbine’s power curve to make a realistic estimation of AEP.
The following graph shows a projection of AEP, using a Rayleigh distribution, for the wind turbine detailed in the previous power curve graph. This information provides investors with a realistic estimation of annual energy production in kWh, which they can use to project revenue for the wind turbine.