Energy is the ability to do work or produce change.

A source of energy is any material or process that provides energy for use, e.g., coal, sunlight.

A renewable source is replenished naturally on a human timescale, like solar or wind energy.

A non-renewable source exists in finite amounts and takes millions of years to form, e.g., coal.

Solar energy and wind energy.

Coal and petroleum (crude oil).

Commercial energy is energy sold in the market, such as electricity and petrol.

Energy not traded commercially, e.g., firewood or dung used locally.

Coal forms from plant remains compressed under high pressure over millions of years.

Coal is mainly used in thermal power plants to generate electricity.

Petroleum is a liquid mixture of hydrocarbons obtained from underground oil reservoirs.

Petrol and diesel (also kerosene and paraffin).

Natural gas is mainly composed of methane (CH₄).

They release greenhouse gases (CO₂), contributing to global warming.

Because they take millions of years to form and cannot be replenished quickly.

Petroleum (crude oil) is used in petrochemical industries.

Natural gas burns cleaner, producing less CO₂ and pollutants than coal.

Residue left after coal combustion; disposal causes environmental issues.

PV effect is the conversion of light into electricity using semiconductor materials in solar cells.

Heating water in solar water heaters.

It is clean and emits no greenhouse gases during operation.

Intermittency — it does not produce power at night or during heavy clouds.

A connected group of solar panels working together to increase power output.

Via batteries (electrical storage) or thermal storage systems (heat storage).

On homes, schools and institutions to generate electricity locally and reduce bills.

Wind turns the blades, spinning a rotor connected to a generator that produces electricity.

Coastal regions or open plateaus with steady wind speeds.

A plant that uses the potential energy of stored water to turn turbines and generate electricity.

Irrigation, drinking water supply and flood control.

Displacement of local communities and changes in river ecosystems.

A method to store energy by pumping water to an upper reservoir during low demand and releasing it to generate power when needed.

A rotor (or turbine blades) coupled to a generator.

Variable wind speeds cause fluctuating power output, needing backup or storage solutions.

Organic material (wood, crop residues, dung) used as fuel or converted to biogas.

A gas (mainly methane) produced by anaerobic digestion of organic matter, used for cooking and heating.

Uses agricultural waste and can be locally available and renewable if managed sustainably.

Energy obtained from the rise and fall of sea tides, typically using turbines in tidal barrages.

Energy from Earth’s internal heat, used for electricity or direct heating where resources exist.

Because it needs suitable tidal ranges and coastal geography to be practical.

A nuclear reaction where a heavy atomic nucleus splits into smaller nuclei, releasing energy.

Uranium (commonly uranium‑235).

Produces large amounts of electricity with low CO₂ emissions during operation.

Radioactive waste disposal and potential safety risks in accidents.

Chemical energy (coal) → thermal energy → mechanical energy (turbine) → electrical energy.

Using less energy to perform the same task, e.g., LED bulbs use less power for same light output.

Reducing energy use by changing behaviour, like switching off unused appliances.

Insulation reduces heat loss/gain, lowering the energy needed for heating or cooling.

Storing energy for later use — e.g., batteries storing electrical energy from solar panels.

They release pollutants like SO₂ and NOₓ, causing smog and respiratory problems.

Use LED bulbs and switch off lights/appliances when not in use; use public transport or carpooling.