Sources of energy including fossil fuels, nuclear power and renewable energy, the generation and storage of energy, and how energy is used to power products and processes.

What this dot point is asking

This is AQA section 3.1.2. AQA wants you to know the main sources of energy, classify them as finite (non-renewable) or renewable, and explain how energy is generated, stored and used to power products and manufacturing. You should compare the advantages and disadvantages of each source. In Paper 1 this is examined through short recall questions and through extended Evaluate or Discuss questions that ask you to weigh sources against each other for a given context.

Finite (non-renewable) energy sources

• Fossil fuels are burned to heat water into steam, which drives a turbine connected to a generator. They give a reliable, controllable and high energy output and the power stations are relatively cheap to build, which is why they still supply much of the grid. The drawbacks are that they release carbon dioxide (the main greenhouse gas) along with sulphur dioxide and particulates, they are finite, and their price is volatile.
• Nuclear power uses the heat from nuclear fission of uranium to raise steam in the same way. One advantage is a very high energy output with no carbon dioxide released during generation, and a small mass of fuel lasts a long time. The drawbacks are radioactive waste that stays dangerous for thousands of years, very high build and decommissioning costs, and public concern after accidents.

Renewable energy sources

• Wind: turbines convert the kinetic energy of moving air into electricity through a generator. Clean and free to run, but intermittent (no output when calm or in very high winds), visually intrusive, and best sited offshore or on exposed land.
• Solar: photovoltaic (PV) cells convert sunlight directly into electricity; solar thermal panels heat water. Clean and silent, but they only generate in daylight, output drops on cloudy days, and they need a large area.
• Tidal and hydroelectric: use the potential and kinetic energy of moving water to drive turbines. Tidal output is highly predictable and hydroelectric is reliable, but both need specific geography (an estuary or a dammed valley) and a very high set-up cost, and dams can flood habitats.
• Biomass: burns organic matter such as wood pellets or crop waste. It is renewable because crops regrow, and it is roughly carbon-neutral over its life, but burning it still releases carbon dioxide and particulates at the point of use.
• Geothermal: uses heat from underground rock to raise steam; reliable but limited to volcanic or hot-rock regions.

Energy storage

Generation and storage are different stages: a turbine or cell generates energy, a battery or other store holds it for later. Products that are not plugged into the mains need to store energy.

• Alkaline (non-rechargeable) batteries: cheap, widely available and hold charge well in storage, but are single-use and create waste, so they suit low-drain products such as remote controls and smoke alarms.
• Rechargeable batteries such as lithium-ion and nickel-metal hydride (NiMH) are reused hundreds of times, cutting waste and running cost. Lithium-ion has a high energy density (energy stored per unit mass), which keeps phones, laptops and power tools light, while NiMH is cheaper and safer but heavier.
• Capacitors store small amounts of charge and release it very quickly, useful for camera flashes and smoothing supplies. Kinetic storage (a flywheel) and fuel cells (which generate electricity from hydrogen and oxygen, emitting only water) are emerging alternatives.

Powering products and processes

Manufacturing draws mostly on mains electricity, supplemented by generators for portable or backup supply, while products use mains, batteries or, increasingly, solar charging. Designers choose a source by balancing cost, reliability, portability, energy density and environmental impact. A factory line that must not stop favours reliability; a handheld product favours a light, high-density rechargeable cell.