The area affected by energy generation depends on the degree of concentration of the source. The energy in the diffuse sources such as wind and solar is widely spread and so collectors occupy a large area. Some sources, such as wind, require the generators to be sited on high ground, and so the area they affect is much larger than that occupied by the collectors themselves, and so is the corresponding visual and aural pollution.
Most people dislike the intrusive presence of many wind turbines, especially in areas of great natural beauty. The generators also emit a persistent humming noise which many people living nearby find intolerable, and results in the loss of value of their property. These disadvantages do not occur in the case of off-shore wind farms, but instead there is some danger to shipping and appreciably higher cost. Similar remarks apply to solar power, if ever the collectors were deployed on a large scale.
It is sometimes argued against wind power that the turbine blades kill large numbers of birds, estimated to be about 30,000 per year in Denmark and 70,000 per year in the USA. While this is of course regrettable, it may be put into perspective by comparing these numbers with the numbers of birds killed on motorways (a million a year in Denmark and 57 million per year in the USA), by colliding with glass windows (98 million per year in the USA), by domestic cats (55 million per year in Britain) (Lomborg 2004) and by massive habitat loss such as that at Saemangeum in Korea (Brown 2004).
In the case of hydropower, the collector is a mountain valley that remains unaltered, but the lake where the rainfall is collected inundates a large area, often of agricultural land that may also include ancient villages and valuable wilderness areas. In times of low rainfall ugly bands of mud may be exposed around the lake. The concentrated energy sources that generate energy inside themselves occupy far less land and, although they are large structures, they can be unobtrusively sited. Some comparative figures for the land occupied by various energy sources are shown in Table 6.1.
Table 6.1. Areas of Land Occupied by Various Power Sources in Square Metres Per Megawatt
1,700,000 265,000 100,000
2400 1500 870 630
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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.