Understanding Wind Power: Watts vs. Watt-hours

There's a difference between the peak performance, and how much useful energy you'll make. 

It's dependent on several technical parameters:

Average wind speed: How much is the wind blowing? Wind is not constant, meaning when you're out experiencing it, it will fluctuate. How much it fluctuates is most often called the turbulence intensity. At one point it can be 3 m/s (7mph) - the next it can be 6 m/s (14mph). 

Swept area: Is the area of a wind turbine that is facing the wind. For a horizontal axis wind turbine like Wind Catcher it's calculated by the radius of the rotor, which often is the length of the blade: Area = π * (rotor-radius)^2.

Available energy: The amount of energy a turbine can make is proportional to its swept area and the wind speed. The formula is: Power = 0.5 * air density * swept area * wind speed^3. 
It's actually even more complicated, as you'll have to take into account friction losses, cable losses etc. We won't bore you with this here. 

Watts (noted as: W): Energy output from the turbine at a given point. 

Watt-hours (noted as: Wh): How many watts per hour the turbine has made. Example: A turbine making 100W on average over 24 hours, would have made 100W * 24h = 2400Wh. 

The most important thing here is to notice the difference between Watts and watt-hours. If you're running any kind of battery system, it's the Watt-hours that are the most important. This tells you how much energy you'll actually get from the turbine.