Generating electricity

Generators are the devices that transfer kinetic energy into electrical energy.

Sources of electricity were fossil fuels 67%, renewable energy 16% (mainly hydroelectric, wind, solar and biomass), and nuclear power 13%, and other sources were 3%. The majority of fossil fuel usage for the generation of electricity was coal and gas.

Generators can be turned directly, for example, by:

• wind turbines
• hydroelectric turbines
• wave and tidal turbines

When electricity is generated using wave, wind, tidal or hydroelectric power (HEP) there are two steps:

1. The turbine turns a generator.
2. Electricity is produced.

Generators can be turned indirectly using fossil or nuclear fuels. The heat from the fuel boils water to make steam, which expands and pushes against the blades of a turbine. The spinning turbine then turns the generator.

These are the steps by which electricity is generated from fossil fuels:

1. Heat is released from fuel and boils the water to make steam.
2. The steam turns the turbine.
3. The turbine turns a generator and electricity is produced.
4. The electricity goes to the transformers to produce the correct voltage.

"Wasted" energy

Energy cannot be created or destroyed. It can only be transferred from one form to another, or moved. Energy that is "wasted", like the heat energy from an electric lamp, does not disappear.

Instead, it is transferred to its surroundings and spreads out so much that it becomes difficult to do anything useful with it.

Ordinary electric lamps contain a thin metal filament that glows when electricity passes through it.

However, most of the electrical energy is transferred as heat rather than light energy.

This is the Sankey diagram for a typical filament lamp.

The energy produced by burning fuel is transferred as heat and stored in water as steam.

The energy in steam is transferred to movement in a turbine, then to electrical energy in the turbine.Energy is lost to the environment at each stage. Here is a Sankey diagram to show these losses. Note that only about a third of the energy stored in the fuel was transferred as electrical energy to customers.

Renewable energy sources

Our renewable energy resources will never run out. Their supply is not limited. There are no fuel costs either. And they typically generate far less pollution than fossil fuels.

Renewable energy resources include:

• wind energy
• water energy, such as wave machines, tidal barrages and hydroelectric power
• geothermal energy
• solar energy
• biomass energy, for example energy released from wood

There is a limited supply of non-renewable energy resources, which will eventually run out. They include:

• fossil fuels, such as coal, oil and natural gas
• nuclear fuels, such as uranium

Fossil fuels release carbon dioxide when they burn, which adds to the greenhouse effect and increases global warming. Of the three fossil fuels, coal produces the most carbon dioxide, for a given amount of energy released, while natural gas generates the least.

The fuel for nuclear power stations is relatively cheap. But the power stations themselves are expensive to build. It is also very expensive to dismantle old nuclear power stations or store radioactive waste, which is a dangerous health hazard.

The main nuclear fuels are uranium and plutonium, both of which are radioactive metals. Nuclear fuels are not burned to release energy. Instead, heat is released from changes in the nucleus.

Just as with power stations burning fossil fuels, the heat energy is used to boil water. The kinetic energy in the expanding steam spins turbines, which drive generators to produce electricity

Advantages

Unlike fossil fuels, nuclear fuels do not produce carbon dioxide.

Disadvantages

Like fossil fuels, nuclear fuels are non-renewable energy resources. And if there is an accident, large amounts of radioactive material could be released into the environment. In addition, nuclear waste remains radioactive and is hazardous to health for thousands of years. It must be stored safely.

Nuclear waste is given different categories.

Nuclear waste categories

CategoryExamplesDisposal Low level Contaminated equipment, materials and protective clothing They are put in drums and surrounded by concrete, and put into clay lined landfill sites. Intermediate level Components from nuclear reactors, radioactive sources used in medicine or research They are mixed with concrete, then put in a stainless steel drum in a purpose-built store. High level Used nuclear fuel and chemicals from reprocessing fuels They are stored underwater in large pools for 20 years, then placed in storage casks in purpose-built underground store where air can circulate to remove the heat produced. High level waste decays into intermediate level waste over many thousands of years.

The National Grid is the high-voltage electric power transmission network in Great Britain, connecting power stations and major substations and ensuring that electricity generated anywhere in England, Scotland and Wales can be used to satisfy demand elsewhere.