What is energy?

Energy is everywhere, and in everything, on the planet. Without energy, nothing could move or grow. It’s the essence of life.

Scientists define it as “the ability or the capacity to do work or transfer heat”.

What are the forms of energy?

There are many different types of energy, broadly categorised into kinetic energy and potential energy.

  • Kinetic energy is energy in motion (such as flowing water, the wind, electricity being used to power a TV).
  • Potential energy is ‘stored’ energy waiting to be used – like petrol while it’s still in the pump, food, the electricity in a battery or the pressure in an unopened fizzy drinks can.

Other types of energy include mechanical energy, heat energy, chemical energy, electrical energy and gravitational energy, all of which have the ability to do something within their form. Rubbing two sticks together creates heat energy that sparks a fire, for example, while chemical energy creates chemical reactions that change food as it’s cooked.

Energy in our homes

When we talk about energy on a day-to-day basis, though – and not in relation to how tired we feel – we’re usually referring to the energy used to power our homes by two fuels: gas and electricity.

They can both help us to keep warm, prepare food and enjoy a long soak in the bath, while electricity also helps us to see in the dark, as well as enjoy activities such as watching TV, playing video games and listening to music.

What are the sources of energy?

Gas is a fuel that we use as an energy source in its natural form, burning it to provide heat energy. For this purpose we could also create heat from other energy sources, such as coal, oil, wood or biomass.

However, electricity has to be generated in some way. The electricity you use in your home is probably generated at a power station, fuelled by an energy source that could be nuclear power (uranium), coal, oil or gas. You may also be generating some electricity yourself, through photovoltaic solar panels. If you live in an extremely rural area, you may have to use a generator. Electricity could also be transported to your home from a wind farm, via the national grid. These are all sources of electricity.

So the sources of our domestic energy can be gas, coal, wood, oil, biomass, uranium or renewables (such as solar panels, wind farms or wave power).

The origins of coal, oil and gas

Over millions of years, as the Earth’s plants and animals died and decayed, their remains rotted down into thick layers of organic material and sank into the mud and soil. Gradually this mud and soil transformed into rock, still covering the organic material and trapping it underneath.

Pressure and heat changed some of this organic material into coal, some into oil, and some into natural gas. Continents moved, and seas formed, so now there are ‘reservoirs’ of oil and gas under the sea as well as on land.


Natural gas is mainly made up of methane, a gas composed of one carbon atom and four hydrogen atoms (CH4). 

Gas is generally used to power central heating systems and for cooking. If your home is on the mains network, gas reaches you through a network of wells and pipes, via a meter which measures the amount you use. If your home is not connected to the mains supply, you can still use gas in the form of liquid petroleum gas (LPG) – some boilers designed for mains gas can even be converted to use LPG.

Mains gas is the most popular heating fuel in the UK, for many reasons – here are just a few:

  • It’s normally the cheapest option.
  • It’s the cleanest ‘fossil fuel’ – its CO2 emissions are half those of oil-fired central heating and a third of those from coal.
  • It’s very efficient and delivers heat fast.
  • It’s piped direct to your home, so you don’t need to find space for storing wood, coal or a gas tank.


Electricity is created when the electrons orbiting around an atom begin flowing together in the same direction. While electricity occurs naturally in nature (such as during lightning storms), scientists have learnt to create electricity through generators, where fuel (such as oil or solar energy) is used to power a turbine which spins magnets surrounded by copper wire. This encourages electrons to flow, generating the electricity we use in our homes. You can find out more about electricity here.

Sources of electricity


Crude oil is mainly found in underground reservoirs. Geologists study rock samples and take measurements to find and evaluate possible new oil fields. If they find a promising site, oil companies will bid for the right to drill there and develop the site.

Oil is mainly used to generate electricity at power stations, but some homes in the UK, particularly if they’re not on the mains gas network, use oil to heat their homes. The two main varieties of domestic heating oil are gas oil and kerosene – which tends to be better value as it’s more efficient.


Coal has been mined in the UK since before Roman times. At first people simply gathered coal on the seashore, but as these supplies became used up, they would follow the coal seams inland by digging from the shore. Gradually, as the seams continued underground, people began to dig deeper for coal, leading to early mining operations.

In the UK, 31% of our electricity is still generated at coal-burning power stations, but at least one third of these power stations will probably close by 2016 as they don’t meet EU air quality legislation. This means the UK will be using less coal as a source of energy.

Coal can also be used in the home, although domestic coal fires are not as popular as they were 50 years ago. Many people still enjoy having a real fire in their sitting rooms, but coal now has to compete with wood and biomass as a fuel for open fires and fireplace stoves.

Nuclear energy

Instead of burning fuel like oil, gas or coal, nuclear plants use the heat created during nuclear fission to generate electricity.

The centre of a nuclear reactor is known as its ‘core’. This holds the uranium fuel needed for fission. The uranium takes the form of tiny pellets, stacked in 12-foot metal fuel rods, in bundles known as ‘fuel assemblies’. Each tiny pellet produces the same amount of energy as 150 gallons of oil.

Within the power station, fission generates heat that’s used to boil water into steam. The steam turns huge turbine blades, which in turn drive generators to make electricity. The steam is then turned back into water and cooled in a cooling tower so it can be used again.

Find out more about nuclear energy.


Renewable energy sources are those that can never run out or are regularly replenished naturally – like the sun, wind, rain and sea (tides and waves) and geothermal heat. They are becoming more popular as people’s understanding of, and concern for, the environment is growing.

They can be used to replace traditional non-renewable energy sources in three different ways: in generating energy at power plants, in heating or providing hot water for our homes (particularly in off-grid rural areas) and in powering vehicles.

  • Power stations can use hydroelectricity, wind farms and solar electricity.
  • Homes can be heated by solar panels – either photovoltaic or thermal.
  • Cars can be powered by renewable bio-fuels.

The future

Scientists are continually working to find new ways of harnessing the Earth’s resources in a sustainable way, so renewables should become more and more important in the future. At OVO, we fully support these efforts. We offer a minimum of 33% energy from renewable sources in all our energy plans, and 100% in our Greener plan. We’ve also eliminated coal from our fuel mix, as it produces twice the carbon emissions of gas, as well as being responsible for a host of devastating environmental and health impacts.

By doing so, we’ve reduced our carbon footprint by 34%.

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