Uses and Reliability of Energy Resources

From an energy resource to a useful service

An energy resource is something from which energy can be transferred for a useful purpose. The three uses you need to compare are transport, electricity generation and heating.

Electricity is not one of the primary energy resources in the specification. It is an energy carrier: energy from resources such as wind, nuclear fuel or natural gas can be transferred electrically to homes, businesses and vehicles. Electricity is especially useful because it can operate many different devices. For example, a kettle transfers energy electrically to the thermal energy store of its water, while an electric motor transfers energy to a kinetic energy store.

A resource can also be used more directly. A gas boiler burns natural gas for heating, and a car engine uses petrol for transport. Direct use can sometimes be cheaper or easier because it avoids first generating and distributing electricity.

Resources used for transport

Transport requires a supply that can travel with the vehicle or reach it continuously.

Fossil-fuel products are widely used because they store a large amount of energy in a relatively small mass. Petrol and diesel can power road vehicles, while kerosene is used by aircraft. A vehicle can carry these liquid fuels in a tank and refill quickly. This high concentration is particularly useful for aircraft, which must lift their energy supply as they fly.

Bio-fuels can also be made for transport, including fuels such as methanol. They come from recently living material rather than ancient fossil-fuel deposits. However, bio-fuels are generally less concentrated than fossil fuels, so a larger mass may be needed to provide the same amount of energy.

Electricity is used by trains and electric road vehicles. Electrified railway lines can supply a train as it moves, so the train does not have to carry all its energy supply. Battery vehicles do carry an energy store, but batteries must be recharged. Electricity is less convenient for most aircraft because carrying enough battery capacity would add considerable mass.

Resources used to generate electricity

Electricity can be generated using fossil fuels, nuclear fuel, bio-fuel, wind, hydro-electricity, geothermal energy, tides, sunlight and water waves. You are expected to compare their uses and reliability, but AQA does not require a description of the machinery or detailed process by which each one generates electricity.

Fossil fuels, nuclear fuel and bio-fuels can be stored and used when required. Wind, waves and sunlight instead depend on changing natural conditions. Hydroelectric schemes depend on water supplies, tidal schemes operate when tidal conditions are suitable, and geothermal resources are useful only where accessible underground heat can be exploited.

Electricity generation allows one resource to serve many final uses. Electricity from a wind turbine, for example, can ultimately operate a train, a heater or household appliances. This flexibility is one reason that much of an industrial society's energy demand is met through electricity.

Resources used for heating

Fossil fuels can be burned directly for heating. Natural gas and heating oil are examples used in buildings. Bio-fuels such as wood pellets can also provide heating, although more bio-fuel may be required because its energy is less concentrated.

Geothermal energy can provide hot water or space heating where suitable hot rocks are accessible. Solar energy can heat water directly, although its output depends on the available sunlight. Electricity can also operate heaters, heat pumps and kettles, regardless of which resource was originally used to generate it.

This gives an important comparison: one resource may be used directly, while another may first be used to generate electricity. The best route depends on factors such as convenience, cost, storage, location and whether a supply is available when required.

What makes an energy resource reliable?

A reliable resource can provide energy when it is required. Reliability is not the same as whether a resource is renewable. A non-renewable resource may give a controllable, dependable supply, while a renewable resource may be intermittent.

Fossil fuels and nuclear fuel can be stored, so power stations using them can operate for long periods and their output can be planned. Bio-fuels can also be stored, provided that a sufficient supply has been produced and delivered. Geothermal energy is generally reliable because the underground heat supply is continuous.

Hydroelectricity is usually reliable when a reservoir holds enough water, and stored water can be used when demand is high. A drought can reduce the water supply or cause a reservoir to run dry, so reliability still depends on rainfall over time.

Variable and predictable resources

Solar power is intermittent: there is no sunlight at night, and cloud reduces the available radiation. Solar-powered equipment may therefore need a rechargeable battery or another supply for periods without enough sunlight.

Wind power depends on wind speed. Little wind gives little output, while turbines may also be stopped in excessively strong winds. Wave power is likewise variable because calm conditions produce little or no useful wave motion. These resources cannot be relied upon to produce a chosen output at every moment.

Tidal power is different. Tides do not provide a continuous supply, but their timing is highly predictable. A tidal scheme can therefore be planned around known periods of tidal flow even though another supply may be required between them.

Reliability must also be separated from site availability. Tides may be predictable, yet there are relatively few suitable places for tidal schemes. Geothermal supplies may be steady, but accessible hot rocks are not available everywhere. Wave power is useful only where coastlines receive sufficient wave energy. These limitations affect where a resource can be used, not simply whether its output varies with time.

Comparing resources in context

There is no single resource that is best for every use. A fair comparison starts with the task.

For an aircraft, a concentrated fuel that can be carried on board is advantageous. For an electrified train, a continuous electrical connection avoids carrying a large fuel load. For domestic heating, gas, electricity, bio-fuel, geothermal heat or solar heating may be possible, depending on the building and local supply. For electricity generation, stored fuels and geothermal energy can provide dependable output, while wind and solar output changes with conditions and tidal output is intermittent but predictable.

A strong conclusion therefore links the resource's properties to the particular use: how energy reaches the user, whether it can be stored, what natural conditions it needs, and whether it will be available at the required time.

Three uses

• Transport: petrol, diesel and kerosene; bio-fuels; electricity for trains and electric vehicles.
• Electricity generation: fossil fuels, nuclear fuel, bio-fuel, wind, hydro-electricity, geothermal energy, tides, sunlight and waves.
• Heating: natural gas, oil and bio-fuels directly; geothermal and solar heating; electrically powered heating.

Electricity is an energy carrier, not a primary energy resource.

Reliability

• Stored and controllable: fossil fuels, nuclear fuel and bio-fuels.