Defining sustainable and renewable energy

1 Defining sustainable and renewable energy

Concerns about the ‘sustainability’ of humanity’s use of fossil and nuclear fuels have been a major catalyst of renewed interest in the renewable energy sources in recent decades. A sustainable energy source can be defined as one that:

• is not substantially depleted by continued use
• does not produce significant pollution or other environmental problems
• does not cause health hazards or social injustices.

In practice, few energy sources come close to these ideals, but renewable energy sources are generally more sustainable than fossil or nuclear fuels: they are essentially inexhaustible, and their use usually involves fewer health hazards and much lower emissions of greenhouse gases and other pollutants.

1.1 Renewed interest in renewables

Renewable energy sources are derived principally from the enormous power radiated by the Sun.

Solar power, both in the form of direct solar radiation and in indirect forms such as bioenergy, water or wind power, was the energy source upon which early human societies were based. When our ancestors first used fire fuelled by burning wood, they were harnessing the power of photosynthesis, the solar-driven process by which plants materials such as wood are created from water and atmospheric carbon dioxide. Societies went on to develop ways of harnessing the movements of water and wind, both caused by solar heating of the oceans and atmosphere respectively, to grind corn, irrigate crops and propel ships. As civilizations became more sophisticated, architects began to design buildings to take advantage of the Sun’s energy by enhancing their natural use of its heat and light, so reducing the need for artificial sources of warmth and illumination.

Technologies for harnessing the power of the Sun, firewood, water and wind continued to improve right up to the early years of the Industrial Revolution, but by then, the advantages of coal, the first of the fossil fuels to be exploited on a large scale, had become apparent. These highly concentrated energy sources soon displaced wood, wind and water in the homes, industries and transport systems of the industrial nations. Today the fossil fuel trio of coal, oil and natural gas provides around 80% of the world’s energy.

Concerns about the adverse environmental and social consequences of fossil fuel use have been voiced intermittently for several centuries, but it was not until the 1970s that humanity began to take more seriously the prospect of fossil fuels ‘running out’, and that their continued use could be affecting the planet’s natural ecosystems and global climate. The development of nuclear energy following the Second World War raised hopes of a cheap, plentiful and clean alternative to fossil fuels. But nuclear power’s contribution to electricity supply has in some countries stalled in recent years, due to concerns about safety, cost, waste disposal and weapons proliferation. In other nations nuclear power supplies continue to expand.

These concerns have been a major catalyst of renewed interest in the renewable energy sources in recent decades, but before going on to introduce the ‘renewables’ in more detail, let’s start by introducing some energy definitions and concepts.