Generating electricity
Electricity is usually generated from some form of turbine. Turbines can be driven indirectly by a variety of different energy sources, ranging from a hamster on his wheel to nuclear power. The electricity energy sources used traditionally in the UK have been coal and oil, nuclear to a lesser extent, with gas coming on stream in the last 2 decades. (See diagram below for historic breakdown of fuel sources for the UK). Both fossil fuels and nuclear fuels must be turned into heat (thermal energy) before they can be turned into electricity.

Diagram from the DTI Document:
Energy – its impact on the environment and society

Renewable and non-renewable fuel sources for generating electricity
The traditional energy sources, with the exception of nuclear energy, are all derived from fossils – hence the term fossil fuel. As there is a finite source of these fuels they have become known in recent years as non-renewable.

In contrast, renewable energy sources have no finite limit and include such sources as wind, sun and wave power. Their use has been limited traditionally for two main reasons: they are difficult, and therefore expensive, to harvest; their efficiency levels are low in comparison with fossil fuels, especially gas. Nevertheless, their use has increased substantially in recent years as both economic and political considerations move in their favour.

Clean versus dirty energy fuel sources for generating electricity
Using fossil fuels to generate electricity (and to produce any other kind of power) results in carbon dioxide (CO₂) being released into the atmosphere. Since industrialisation began in the 19th century, the levels of carbon dioxide in the atmosphere have increased from 290 to 380 parts per million (ppm). The potential effect of this on our climate (see Why the world needs geo-pressure for more information) has long been a source of interest, and subsequently concern, to the world’s scientists (see Timeline earth: the history of climate change science) this has lead to a search for clean energy sources.

Not surprisingly perhaps, most clean energy sources are also renewable energy sources.

What about nuclear energy?
Increasingly, experts and politicians are proposing nuclear energy as a potential saviour because it is both: less finite than traditional fossil fuels, and cleaner since it produces significantly less carbon than fossil fuels; nevertheless its use is tricky for several reasons. First and foremost, its waste products are dangerous contaminants and therefore expensive to process (life expectancy is measured in 1,000s of years); second it generates more carbon than most proponents admit, since electricity is needed to both create the fissile material, that is the nuclear energy source, and power the whole supply chain namely operating power stations, re-processing and decommissioning. (Indeed, Professors Smith and Van Leeuwen at the University of Groningen in The Netherlands estimate the carbon emissions from using nuclear energy to be one third of the carbon emissions of a gas fired generator.)