Introduction

Renewable energy is important as a substitute for finite and polluting fossil fuels and inflexible and ionising nuclear energy. It could conceivably power all of humanity’s energy needs, since the sun sends sufficient energy to earth to power human energy use many thousands of times – a huge resource. There could be many advantages to relying on renewable energy, in terms of stability of supply, environmental effects and cost, to name just a few. In fact, the world already does rely on renewable energy to an extent, as about 13-15 per cent or more of primary energy is derived from renewable sources – and always has been. This is mostly biomass (the use of plant and animal matter for energy) at about 10 per cent and hydro electricity at about 3 per cent primary energy but producing about 16 per cent of the world’s electricity. These sources can be considered as the traditional renewable energy sources, used for thousands (maybe 50,000 or more) of years in the case of biomass and for about 120 years in the case of hydro electricity. However, there are a variety of newer renewable energy sources, such as solar, wind, wave, tidal and geothermal which are now emerging as viable energy providers. Some of these, such as wind and solar, are now expanding rapidly, at up to about 20-30 per cent per year or more, while others are still relatively immature technologies but showing promise. As new renewable energy sources and technologies emerge, it is increasingly feasible to look ahead to a time when renewables will be able to provide energy for all of humanity’s needs. That would require a 6-fold increase in renewable supply to provide for today’s energy needs. However, much of humanity is still effectively starved of access to adequate energy, and given population growth it is more likely that at least a 20-fold increase in renewable energy supply will be required. Is this still feasible? The answer is yes, as the resource is thousands of times greater than human energy use, as stated above. However, although the solar resource may be thousands of times that of human energy use, other sources are not so abundant. Moreover, renewable energy sources are not incidental; they power the natural environment. The fundamental processes of the earth, such as the maintenance of hospitable conditions for

life, the warmth of the atmosphere and oceans, the hydrological cycle and photosynthesis, are all dependent on these natural energy flows. If a 20-fold increase in renewable energy supply is wanted, it will be important to understand how to achieve this without adversely affecting these vital natural systems. In fact, one of the main advantages of renewable sources over fossil fuel should be that it incurs less perturbation of natural systems. So it will be necessary to design and choose our resource exploitation carefully in order to avoid adverse effects and depletion.