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Why sustainable energy matters
Why sustainable energy matters

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5.1.1 Linking supply and demand

But apart from these relatively few enlightened examples, the efficiency with which humanity currently uses its energy sources is generally extremely low. At present, only about one-third of the energy content of the fuel the world uses emerges as 'useful' energy, at the end of the long supply chains we have established to connect our coal and uranium mines, our oil and gas wells, with our energy-related needs for warmth, light, motion, communication, etc.

Figure 41: An example of one of the energy 'chains' linking primary energy with delivered energy and useful energy, via various energy transformations

The remaining two-thirds usually disappears into the environment in the form of 'waste' heat. One of the reasons for our continuing inefficiency in energy use is that energy has been steadily reducing in price, in real terms, over the past 100 years.

Figure 42: Average household rates for US electricity, 1900–2000, expressed in real terms, i.e. taking into account the effects of inflation (source: Smil, 2000)

Energy's decreasing cost means that our society has only a relatively weak financial incentive to use it more wisely.

The chains that link energy supplies with users' demands are lengthy and complex, as Figure 41 illustrates. Each link in the chain involves converting energy from one form or another, for example in the burning of coal to generate electricity; or distributing energy via some kind of transmission link or network, such as a national electricity grid or gas pipeline infrastructure.