1.2 Where do we get our energy from?
Of course, not all energy sources are of fossil or nuclear origin. The renewable energy sources, principally solar energy and its derivatives in the form of bioenergy, hydroelectricity, wind and wave power, are increasingly considered likely to play an important role in the sustainable energy systems of the future. The 'renewables' are based on energy flows that are replenished by natural processes, and so do not become depleted with use as do fossil or nuclear fuels – although there may be other constraints on their use. The environmental impacts of renewable energy sources vary, but they are generally much lower than those of conventional fuels. However, the current costs of renewable energy sources are in many cases higher than those of conventional sources, and this has until recently retarded their deployment.
All these considerations suggest that in creating a sustainable energy future for humanity during the coming decades, it will be necessary:
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to implement greatly improved technologies for harnessing the fossil and nuclear fuels, to ensure that their use, if continued, creates much lower environmental and social impact;
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to develop and deploy the renewable energy sources on a much wider scale; and
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to make major improvements in the efficiency of energy conversion, distribution and use.
These three general approaches will be explored further, and in greater detail in the remaining sections of this course.