Within the context of energy, sustainability means

 

 

The harnessing of energy sources:

That are not substantially depleted by continued use;

The use of which does not entail the emission of pollutants or other hazards to the environment on a substantial scale; and

The use of which does not involve the perpetuation of substantial health hazards or social injustices.

This is, of course, a very broad ideal. Although a few energy sources can come close to fulfilling these conditions, most fall considerably short of the optimum. This means that, in practice, sustainability is a relative rather than an absolute concept. It is not so much that some energy sources are sustainable and others not; it is more that some energy sources, in certain contexts, are more sustainable than others. Determining the relative sustainability of one energy system vis-à-vis another is usually a complex process, involving detailed consideration of the specific processes and technologies proposed, the context in which they are being used and the differing values and interests of the various parties involved.

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For example…

Suppose the government of a country is proposing to construct a large hydro-electric power plant. The villagers whose homes would be flooded by the associated reservoir would probably take a different view of the plant's sustainability to that taken by the city-based planners in the electricity utility proposing its construction, whose homes would be unaffected and whose careers would probably stand to benefit from such a major capital project

Kanose II Power Station, Japan

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http://www.flickr.com/photos/contri/4631598136/in/photostream

Similarly...

 
The closure of coal mines and coal-fired power stations is perhaps the inevitable result from the need to reduce carbon emissions and the associated growth of more sustainable sources of energy. However, pit closures, such as those witnessed in the UK during the 1980s, can devastated entire communities, which are unsustainable without the pits.


Decommissioned Battersea Power Station (London) and the closed Newstead Colliery (Notts)

Above images sourced from:

(Left) Flickr under a Creative Commons Attribution-ShareAlike 2.0 Generic License (CC BY-SA 2.0) http://www.flickr.com/photos/aguichard/4629638365/

(Right) Geograph under a Creative Commons Attribution-ShareAlike 2.0 Generic License (CC BY-SA 2.0)http://www.geograph.org.uk/photo/666592