Energy Production » Types of Energy

Renewable and non-renewable energy

Every home, factory and car needs energy. It comes from a small number of sources, and the spec sorts them into two groups.

Key terms:

• Renewable energy: energy from sources that are naturally replaced as fast as we use them, so they will not run out.
• Non-renewable energy: energy from sources that took millions of years to form and cannot be replaced in a human lifetime, so they will run out.
• Primary energy: energy in its original form, such as coal, oil, gas, wood, wind or sunlight.
• Turbine: a machine with blades that spin when pushed by steam, water or wind. The spinning drives a generator that makes electricity.

Renewable energy: how each type works

Most renewable types follow the same pattern: a natural movement or heat source turns a turbine, and the turbine drives a generator.

Type	What it is	How it makes electricity or heat
Wind	Moving air	Wind pushes the blades of a turbine round. Turbines can be on land (onshore) or in the sea (offshore).
Solar	Energy from the Sun	Solar panels (photovoltaic cells) turn sunlight directly into electricity. Other panels use sunlight to heat water for homes.
HEP	Hydroelectric power: energy from moving water	A dam stores water in a reservoir. The water is released and flows down through turbines, which drive generators.
Tidal	The rise and fall of the sea twice a day	The moving tide flows through turbines in a barrage (a dam across an estuary) or turns underwater turbines.
Wave	The up and down movement of waves	Floating or fixed devices move with the waves. The movement drives a generator.
Geothermal	Heat from hot rocks deep underground	Water is pumped down to the hot rocks and comes back as steam. The steam spins turbines, or the hot water is used directly to heat buildings.
Biomass	Plant material and animal waste	It is burned to give heat, or to boil water to make steam for turbines. It can also be made into biofuels or biogas.

Geothermal energy works best in places where hot rock is close to the surface, such as volcanic areas and places near plate boundaries. HEP needs steep valleys and plenty of rain to fill a reservoir.

Non-renewable energy: how each type works

Fossil fuels (coal, oil and gas) formed from the remains of dead plants and animals, squashed and heated underground over millions of years. They store energy that the living things took from the Sun. Burning them releases it as heat.

Nuclear energy comes from uranium, a metal that is mined. Inside a nuclear power station, uranium atoms are split. This releases a lot of heat, which boils water to make steam and spin turbines. Uranium is limited, so nuclear is non-renewable.

Fuelwood: renewable or non-renewable?

Fuelwood is wood burned for cooking and heating. Many of the world's poorest households rely on it. It is the one source on the spec that can be in either group. It depends on how fast the trees are replaced.

Primary energy and electricity

Coal, oil, gas, wood, wind and sunlight are all primary energy. Electricity is a secondary form: we make it from a primary source, usually with a turbine and a generator. Electricity is only part of the energy we use. Much of the world's oil, for example, goes straight into vehicles as fuel and never becomes electricity.

The global energy mix

The mix of primary energy used across the world is often shown as a pie chart. In words, a pie chart for about 2023 looks like this (rounded figures):

• Oil: about 32%, the largest slice.
• Coal: about 26%.
• Gas: about 23%.
• HEP: about 6%.
• Nuclear: about 4%.
• Wind, solar and other modern renewables: about 8%.

The three fossil fuels together give more than 80% of the world's energy. All the renewables together give less than a fifth. That is the key message.

Exam-style question

Fig. 1.1 shows the energy mix of Country X. The data is made up.

Source	Share of energy (%)
Coal	40
Oil	20
Gas	15
Nuclear	5
HEP	10
Wind and solar	8
Fuelwood	2

(a) Identify the source that gives the largest share of energy. [1 mark]

(b) Calculate the percentage of energy that comes from fossil fuels. [2 marks]

(c) Define the term non-renewable energy. [2 marks]

(d) State what is meant by primary energy. [1 mark]

(e) Explain why fuelwood can be renewable or non-renewable, and describe how two other types of energy make electricity or heat. [6 marks]