Why sustainable energy matters
Why sustainable energy matters

Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available.

Free course

Why sustainable energy matters

4 Renewable energy sources

Fossil and nuclear fuels are often termed non-renewable energy sources. This is because, although the quantities in which they are available may be extremely large, they are nevertheless finite and so will in principle 'run out' at some time in the future.

By contrast, hydropower and bioenergy (from biofuels grown sustainably) are two examples of renewable energy sources – that is, sources that are continuously replenished by natural processes. Renewable energy sources are essentially flows of energy, whereas the fossil and nuclear fuels are, in essence, stocks of energy.

World-wide, there has been a rapid rise in the development and deployment of renewable energy sources during the past few decades, not only because, unlike fossil or nuclear fuels, there is no danger of their 'running out', but also because their use normally entails no (or few) greenhouse gas emissions and therefore does not contribute to global climate change.

Renewable energy sources range from solar power in its various forms, through bioenergy and hydro to wind, wave, tidal and geothermal energy (Figure 27).

Figure 27: The various forms of renewable energy depend primarily on incoming solar radiation, which totals some 5.4 million Exajoules (EJ) per year. Of this, approximately 30 per cent is reflected back into space. The remaining 70 per cent is in principle available for use on Earth, as shown, and amounts to approximately 3.8 million EJ. This is some 10,000 times the current rate of consumption of fossil and nuclear fuels, which in 2000 amounted to some 360 EJ. Two other, non-solar, renewable energy sources are shown in the figure. These are the motion of the ocean tides, caused principally by the moon's gravitational pull (with a small contribution from the sun's gravity); and geothermal heat from the earth's interior, which manifests itself in convection in volcanoes and hot springs, and in conduction in rocks

The general nature and scope of the various 'renewables' can be briefly summarised as follows, beginning with the most important renewable source, solar energy.


Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to University-level study, we offer two introductory routes to our qualifications. You could either choose to start with an Access module, or a module which allows you to count your previous learning towards an Open University qualification. Read our guide on Where to take your learning next for more information.

Not ready for formal University study? Then browse over 1000 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus371