Energy Sources
Cambridge IGCSE Physics Revision Guide
💡 Different energy resources have different origins, efficiencies, and environmental impacts — choosing the right one depends on location, reliability, and sustainability
Quick Summary
Energy comes from many different sources, and each has advantages and disadvantages. Some energy sources (like coal, oil, uranium) come from limited reserves and will eventually run out. Others (like wind, water, solar) are renewable — they're constantly replenished and won't run out. Your job is to understand how each works, why it's good or bad, and which is best in different situations.
- Renewable resources: Wind, solar, water, geothermal, biofuels — can be used indefinitely.
- Non-renewable resources: Coal, oil, natural gas, uranium — limited supply that will eventually run out.
- Energy efficiency: Percentage of energy input that becomes useful output. Solar cells ≈ 20–40%, wind turbines ≈ 50%, tidal ≈ 80%.
- Environmental impact: Some produce greenhouse gases or pollution; others produce no emissions but have geographical limits.
Energy from the Sun
The Big Picture: Where Does Energy Come From?
The Sun is the ultimate energy source for most of Earth's energy. Every hour, the Sun transfers more energy to Earth than the entire world uses in a year. That's enormous. But we don't use it directly — we capture it in different ways:
- The Sun's heat evaporates water → water falls as rain → fills reservoirs → we use that water to generate electricity.
- The Sun heats the atmosphere → creates wind → wind turbines spin and generate electricity.
- The Sun's energy grew plants millions of years ago → plants became fossil fuels → we burn them today.
- We can capture sunlight directly using solar cells or solar panels.
Solar Cells (Photovoltaic Cells)
What they do: Solar cells are made of semiconducting materials (usually silicon). When sunlight hits them, the energy of the photons (light particles) knocks electrons free. These electrons flow as an electric current. It's converting light directly into electricity — no moving parts, no combustion.
How efficient are they? Around 20–40%. That means if 100 J of sunlight hits a solar cell, only 20–40 J becomes electricity. The rest is lost as heat. This is a real limitation: you need a lot of surface area to collect enough energy.
How are they used? A single cell produces a tiny amount of electricity. Cells are connected in strings to form panels. Panels are connected together in arrays to power homes, businesses, or entire solar farms.
Advantages of Solar Cells
- ✅ Renewable: The Sun will shine for billions of years.
- ✅ No pollution during operation: Once installed, solar cells produce electricity with zero emissions.
- ✅ Reliable in sunny regions: In places with consistent sunlight, they're dependable.
- ✅ Readily available: You can buy them relatively easily now.
- ✅ Scalable: You can put a few panels on a house or thousands in a solar farm.
- Quick to build:
- ✅ Cheap to run: No fuel costs, minimal maintenance.
- Can go remote: