## Info

1

95,420 95.4 kWh

FIGURE 5-21: Monthly energy from wind turbines A and B for previous wind-distribution curve.

All that is required to make such a chart is to write down for each 20-hour section of the curve the average wind speed aid the watts of power at that speed for each wind turbine (from Figures 5-20 and 5-19; you can use time intervals other than hours if you wish). Then, multiply each power value times the ¿C hour duration. This yields watt-hours. Add up all the watt-hour produced by each machine. Convert to kWh by dividing by 1000. this example, wind turbine B yields roughly 230 kWh to wind turbine A*s 95 kWh.*

As indicated, a lower-rated speed implies a higher energy yield. If, for example, in the case just illustrated, all characteristics were the same, and wind turbine C is added to the comparison with a rated wind speed equal to the average wind velocity, which in this case is about 13 mph (value at 360 hours), the yield would be considerably greater. Wind turbine A is about 6 feet in diameter, wind turbine B is about 12 feet in diameter while wind turbine C is about 20 feet in diameter.

You can expect the initial cost per kilowatt of rated povs-to increase with decreasing rated wind speed; at the same time yield (kWh) will increase, unless your wind distribution shows a considerable number of hours with wind speeds greater than 20 mo* For this reason, you need to know more than price and power rating. As you can see, rated wind speed is a valuable tool in wind turbine comparison.

•You can plot a wind duration curve from the average wind records of a nearby weather station and apply this technique for calculating wind energy if you desire. As an example the "Percentage Frequency of Wind" table for Amchitka Island, Figure 3-22 can be used. Along the top line are wind speed categories, and along the bottom line, the percentage time the wind was blowing in each of these categories. Also, the percentage of tine there was no wind, 0.9%, is listed in the second line from the bottom. January, the month for this record has 30 days, or 744 hours. Starting with the fastest speed category 56, the number of accumulated hours is simply:

etc.

The numbers in the rignt coiui>in are then plotted to make a cur -e similar to t»iat in Figure 5-20.

## 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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