Non-Renewable Sources of Energy
Simple Explanation
Non-renewable sources — coal, oil, natural gas, and nuclear fuel — release large amounts of energy but exist in finite supply, forming over millions of years and being used up far faster than they can be replaced.
Why Do We Need It?
These sources still supply most of the world's energy today, so understanding how much energy they release — and the fact that supply is genuinely limited — is essential to understanding the energy crisis.
Formula
Energy Released from Fuel (Calorific Value)
E = mq
The total energy released by completely burning a fuel equals its mass times its calorific value — the amount of energy stored per kilogram of that particular fuel.
- E
- — total energy released, in joules (J) or megajoules (MJ)
- m
- — mass of fuel burned, in kilograms (kg)
- q
- — the fuel's calorific value (specific energy content), in joules per kilogram (J/kg) or megajoules per kilogram (MJ/kg)
When to use it: Whenever the total energy released by burning a known mass of a non-renewable fuel needs to be found.
Worked Example
Find the energy released by burning coal
Find the energy released by completely burning 2 kg of coal, which has a calorific value of 30 MJ/kg.
Why Does This Work?
A fuel's calorific value is, by definition, the energy released per kilogram when it is burned — so multiplying by however many kilograms are actually burned scales that per-kilogram energy up to the total energy released.
Real-Life Example
A power plant's daily coal consumption
A coal-fired power plant burns a known mass of coal each day to generate electricity for a city.
Engineers use this exact formula to calculate the total thermal energy released daily, which then determines how much electrical power the plant can generate.
Practice
Find the energy released by burning 5 kg of petrol, which has a calorific value of 45 MJ/kg.
MediumCommon mistake
Assuming all fuels release the same energy per kilogram — different fuels have very different calorific values (coal, oil, and natural gas all differ), so q must always be looked up for the specific fuel in question.
Quick Review
- E = mq — total energy from mass times calorific value.
- Coal, oil, natural gas, and nuclear fuel are the main non-renewable sources.
- Finite supply: forms over millions of years, used far faster than it replenishes.