Nonrenewable Energy and Fossil Fuels
Nonrenewable energy resources are sources that are used faster than they are formed and therefore will run out, including the fossil fuels (coal, oil and natural gas), which formed from ancient organisms over millions of years, and nuclear fuels such as uranium. In brief: fossil fuels supply roughly 80 percent of the world’s primary energy. Burning them releases the stored chemical energy and produces carbon dioxide, a greenhouse gas, as well as pollutants such as sulfur dioxide and particulates. Their advantages are high energy density and reliability.
Modern industry, transport and electricity systems developed on fossil fuels. This guide explains how fossil fuels formed, how they are used, what problems they cause, compares the three fuels and uranium in a table, works through a calculation of coal use and carbon dioxide and corrects common mistakes.
How were fossil fuels formed?
- Coal: from plants in swamps, mainly in the Carboniferous period (about 300 to 360 million years ago). The plant matter was buried, and heat and pressure turned it first into peat and then into coal.
- Oil (petroleum) and natural gas: from marine plankton and algae that sank to the sea floor, were buried under sediment and heated for millions of years. Oil and gas migrate up through porous rock and collect under impermeable layers (traps).
The energy in these fuels is solar energy that was captured by photosynthesis long ago. They are considered nonrenewable because formation takes millions of years, while consumption takes decades to centuries.
How are they used?
- Electricity generation: coal and gas are burned to boil water, and the steam turns turbines connected to generators. Gas can also drive turbines directly (combined-cycle plants are about 55 to 60 percent efficient).
- Transport: petrol, diesel and jet fuel from refining crude oil.
- Heating and industry: natural gas for homes, coal in steel making, and oil and gas as feedstock for plastics, fertilizers and chemicals.
What are the problems?
- Climate change: burning fossil fuels releases CO2. Fossil fuels are the largest source of human-caused greenhouse gas emissions. Natural gas emits less CO2 per unit of energy than coal, but methane leaks are a concern.
- Air pollution: sulfur dioxide and nitrogen oxides cause acid rain, and particulates harm health.
- Environmental damage: oil spills, mining damage and habitat loss.
- Supply and security: reserves are limited and unevenly distributed, which creates economic and political issues.
What about nuclear fuel?
Uranium is also nonrenewable, as uranium ore is finite, though the energy per kilogram is millions of times higher than that of fossil fuels, so supplies would last for a long time at present rates, and breeder reactors could extend them. Nuclear power stations produce almost no CO2 in operation, but they produce radioactive waste that must be stored safely for long periods, and there is a risk of accidents, as at Chernobyl (1986) and Fukushima (2011).
Nonrenewable resources compared
| Fuel | Energy per kg | CO2 in operation | Main concern |
|---|---|---|---|
| Coal | about 24 MJ | Highest | CO2, pollution, mining |
| Oil (petroleum) | about 42 to 46 MJ | High | CO2, spills |
| Natural gas | about 50 MJ | Lower than coal | CO2, methane leaks |
| Uranium-235 | about 8 × 107 MJ | None directly | Waste, accidents |
Worked example: coal consumption and carbon dioxide
A coal power station is 38 percent efficient, and the coal releases 24 MJ per kg when burned. Assume that 1 kg of coal produces about 2.5 kg of CO2 (coal is about 70 percent carbon by mass, and each kg of carbon gives 44/12 kg of CO2: 0.70 × 3.67 = 2.57 kg).
- Electrical energy of 1 kWh: 3.6 MJ.
- Heat input needed: 3.6 ÷ 0.38 = 9.5 MJ.
- Coal needed: 9.5 ÷ 24 = 0.40 kg of coal per kWh.
- CO2 emitted: 0.40 × 2.57 = 1.0 kg per kWh, roughly.
- For a 1,000 MW station running for a day (24,000 MWh = 2.4 × 107 kWh): 2.4 × 107 × 0.40 = 9.6 × 106 kg = about 9,600 tonnes of coal per day, and about 24,000 tonnes of CO2 (2.4 × 107 × 1.0 kg).
The result is an estimate, because the carbon content and efficiency of real plants differ.
How did fossil fuel use grow?
Coal was used in China and Europe for centuries, but its use expanded with the steam engine in the eighteenth century and the Industrial Revolution. The first commercial oil well in the US was drilled by Edwin Drake in 1859 in Pennsylvania. The internal combustion engine and electricity generation made oil and coal dominant in the twentieth century, and natural gas use increased after the 1950s with pipelines. Since the 1990s, climate agreements have aimed to reduce fossil fuel use.
Which mistakes are common?
Mistake 1: Saying that fossil fuels are made from dinosaurs
They come mostly from plants and plankton, not dinosaurs.
Mistake 2: Thinking that nonrenewable means about to run out
It means that the resource is finite on a human timescale. Reserves can last for decades to centuries, depending on the resource.
Mistake 3: Forgetting that burning is a conversion, not production, of energy
The fuel releases stored chemical energy, and a part is always wasted as heat.
Mistake 4: Saying that gas has no emissions
It produces less CO2 than coal per unit of energy, but not none.