Non-renewable energy sources
Energy comes from many sources, and to describe these sources we use two terms: renewable and non-renewable.
Huntly power station
Huntly power station in the North Island of New Zealand is a coal and gas fired steam plant. Coal or gas is burnt to generate steam at 540ºC and 166 bars (2,300 psi) pressure, which drives a generator.
Non-renewable energy resources cannot be replaced – once they are used up, they will not be restored (or not for millions of years). Non-renewable energy resources include fossil fuels and nuclear power.
Fossil fuels
Fossil fuels (coal, oil and natural gas) were formed from animals and plants that lived hundreds of millions of years ago (before the time of the dinosaurs). They were formed during the Carboniferous period. The plants that lived millions of years ago converted the Sun's light energy into chemical energy through the process of photosynthesis. This 'solar' energy was (and still is) transferred down the food chain in animals, and when living organisms die, the chemical energy within them was trapped.
Non-renewable resources
Adam Vonk explains that oil is a non-renewable resource, which means that it will not be renewed within our lifetimes, and that the predictions are that the world will one day run out of oil.
People are interested to find out when this will occur. Adam highlights that, to answer this, we need to understand the concept of peak oil. Peak oil is a term used to describe a point that is reached when we have found most of the oil reserves and we are producing the maximum amount of oil.
When the amount we produce starts to drop while oil consumption remains the same, then there will be a shortage of supply – and there are fears that the demand can not be met. This would have an effect on the world economics, the price of oil will rise and so will the costs of any industry or service that relies on oil (which is almost everything). To counter this problem, we need to find new oil sources and explore alternative fuels.
For a fossil fuel to form, there are three important steps necessary: accumulation of organic matter (animal or plant remains), preservation of organic matter to prevent it from oxidising (exclusion of air, for example, by being in the sea or a swamp) and conversion of organic matter into a fossil fuel such as oil or natural gas. This would typically occur due to the organic matter being covered by layers of sediments, which increases pressure and heat (50–150°C). Fossil fuels are described as non-renewable because it takes millions of years for this process to occur.
Burning fossil fuels produces carbon dioxide – one of the greenhouse gases. Burning coal – one of the fossil fuels – produces not just carbon dioxide but also releases sulfur into the air, which increases air pollution.
Coal
Coal is a solid form fossil fuel that can be classed into three types: lignite, bituminous and anthracite. Lignite coal is found close to the Earth surface, making it easy to mine, but it has high sulfur content. Bituminous coal is the most common coal we burn, and it is less polluting than lignite. Anthracite is the highest quality of coal – it is dark and shiny and found deeper in the Earth.
Coal fire
Coal is a non renewable fossil fuel and commonly used for domestic heating in fireplaces and also in power plants to generate electricity.
In addition to pollutants from burning coal, coal mining creates problems for the environment, as the coal must be dug from the ground. Large volumes of unwanted dirt and rock are removed, which can lead to water pollution, unstable ground and, in many cases, it is not appealing to look at. Working in coal mines can also be very dangerous.
New Zealand has a number of coal reserves including the West Coast of the South Island and the Coromandel area.
Oil
Oil is a liquid fossil fuel that can be dark brown, yellow or even green. It is easier to mine once it is found because, being a liquid, it will flow through pipes, which makes it easier for transport. However, it can be difficult to locate – oil forms in reservoirs and, to find these reservoirs, scientists must study rocks and landforms to find potential drilling sites.
Oil formation
This animated video demonstrates the formation of hydrocarbons over millions of years in the depths of the Earth.
Oil and gas forms in sedimentary ocean basins. Dead plankton (organic plant and animal material) gets deposited together with mud, sand and other sediments. In this early stage the plankton/sediment layer is called sapropel. Through an increase in temperature the sapropel is converted into kerogen. Folding or faulting forms oil traps where oil and gas can accumulate in the pore space of a source rock below the trap otherwise it will escape to the earth's surface as seepage. The liquid or gas that forms is known as 'hydrocarbons
Once a hole is drilled and if oil is found, it is then piped to the surface. In this form, it is called ‘crude oil’. Crude oil is transported to a refinery that heats up the oil to different temperatures and sorts out the different types of fuel (such as petrol, jet-fuel and diesel) through a process called fractional distillation. Oil is used not just for transport but also in many different products such as plastics, tyres and synthetic material such as polyester.
Natural gas
As the name suggests, this is a fossil fuel in the form of a gas (for example, methane and LPG). It is often found under the oceans and near oil deposits. Surveying for natural gas reservoirs is similar to oil exploration. Once a natural gas field is found, the drilling process is similar to oil.
Gas burner
Natural gas is often used for cooking or heating. Natural gas is a fossil fuel which is a non-renewable resource.
Gas can be piped from the source and stored for later use. Natural gas is used for cooking and heating as well as making a number of products such as plastics, fertilisers and medicines.
