## Rotor Area and Wind

The amount of energy produced by a wind turbine primarily depends on the rotor area, also referred to as cross-sectional area, swept area, or intercept area. The swept area for different types of wind turbines can be calculated from the dimensions of the rotor (see Figure 1.7).

HAWT area = n r2, where r = radius. VAWT, where H = height and D = diameter of rotor: Giromill area = H*D Savonius area = H*D Darrieus area = 0.65 H*D

The annual average power/area can be obtained from a wind map, and then the energy produced by the rotor can be calculated from

where Ar is the area of the rotor, m2; WM = power/area from a wind map, W/m2; and 8.76 gives the answer in kWh/year, the conversion W to kW.

Again, the capacity factor reflects the annual average efficiency of the wind turbine, around 0.20 to 0.35.

EXAMPLE 5.2

Use the wind turbine in Example 5.1, and from wind map: WM = 200 W/m2

Area = n r2 = 3.14*25 m2 = 78.5 m2 AKWH = 0.25 * 78.5 m2*200 W/m2* 8.76 kWh/year = 34,000 kWh/year

4 5 6 7 Average Wind Speed, m/s

FIGURE 5.16 Estimated annual energy production based on annual average wind speed.

4 5 6 7 Average Wind Speed, m/s

FIGURE 5.16 Estimated annual energy production based on annual average wind speed.

Notice the large difference in the answers for the two examples, which could be related to two factors: generator size is too large for rotor size, or the wind regime is low, that is, the wind map value is low. With this estimate of energy production, the wind map value should be selected or estimated for the hub height of the wind turbine, especially when estimating energy production for large wind turbines.

## Renewable Energy Eco Friendly

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.

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