33 Wind Power

Wind-driven electric generators can also be used to charge the batteries of stationary electric vehicles. Stationary wind generators, such as smaller versions of the one illustrated in Figure 10.6, are common methods of supplying power in areas without mains electricity.

A stationary wind generator could be used in the same way as a stationary photovoltaic array. Alternatively it would be possible to mount a small generator on the roof of an electric vehicle, for charging when the vehicle was stationary. There would be no point in using it when the vehicle was in motion, as the power gained from the wind generator would be considerably less than the power lost by dragging the wind generator through the wind, the efficiency being less than 100%. Ideally, for aerodynamic reasons the wind generator would fold away when the vehicle was travelling. The concept of an onboard wind generator is illustrated in Figure 3.1. In windy places a wind generator 1.2m in diameter could produce up to 500 W continuously whilst the wind speed averaged 10 ms-1. Whether such an idea is practical for general use is debatable.

The power from the wind has a similar energy per square metre as solar radiation. The actual power P in W is given by the formula:

where p is the air density (kgm 3), v is the wind speed (ms 1) and A is the area (m2) through which the wind passes. Hence with a 10 ms-1 wind the power is 625 Wm-2,

Wind generator raised into wind when vehicles is parked

Wind generator raised into wind when vehicles is parked

Telescopic pole

Wind generator

Figure 3.1 Concept of onboard wind generator for charging, which would only be practical in very limited circumstances

Telescopic pole

Wind generator

Figure 3.1 Concept of onboard wind generator for charging, which would only be practical in very limited circumstances assuming an air density of 1.25 kgm-3. The amount of electrical power realised is typically around 30% of this. (It is governed by the theoretical Betz efficiency and the relative efficiency of the wind/electric generator in question.)

Solar and wind energy can be used in conjunction. The potential of wind energy being used for transport when supplied to the grid is discussed in greater detail in Chapter 10.

Renewable Energy 101

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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