## Mode and Mean Speeds

We now define the following terms applicable to the wind speed:

Mode speed is defined as the speed corresponding to the hump in the distribution function. This is the speed the wind blows most of the time.

Mean speed over the period is defined as the total area under the h-v curve integrated from v = 0 to divided by the total number of hours in the period (8,760 if the period is one year). The annual mean speed is therefore the weighted average speed and is as follows:

Vmean 8760

For c and k values in the range found at most sites, the integral expression can be approximated to the Gamma function:

For the Rayleigh distribution with k = 2, the Gamma function can be further approximated to the following:

This is a very simple relation between the scale parameter c and Vmean, which can be used with reasonable accuracy. For example, most sites are reported in terms of their mean wind speeds. The c parameter in the corresponding Rayleigh distribution is then c = Vmean/0.9. The k parameter is of course 2.0 for the Rayleigh parameters. Thus, we have the Rayleigh distribution of the site using the generally reported mean speed as follows:

## Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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