Energy sources and conversion
Societies need energy for lighting, transport, industry and cooking. Energy cannot be created; it is converted from one form to another, and some of it is always wasted as heat. The efficiency of a device is the useful energy output divided by the total energy input.
| Source | Type | Advantages | Problems |
|---|---|---|---|
| Coal, oil, natural gas | Non-renewable fossil fuel | Concentrated, cheap, reliable | Release carbon dioxide; will run out; air pollution |
| Nuclear | Non-renewable | Very large energy from little fuel; no carbon dioxide while running | Radioactive waste; accident risk; costly |
| Hydroelectric | Renewable | Clean, reliable and storable | Needs dams, floods land; depends on rainfall |
| Solar | Renewable | Clean, free fuel, good for rural homes | Only in daylight; large area; costly cells |
| Wind | Renewable | Clean | Needs steady wind; noise; visual impact |
| Geothermal | Renewable | Reliable, low emissions | Only in volcanic areas such as the Rift Valley |
| Biomass and biogas | Renewable | Uses waste | Smoke from burning; needs land |
Solar, wind and hydroelectric power
| Source | Power equation |
|---|---|
| Solar panel | P = I × A × η (I = solar intensity, about 1 000 W/m² at noon; A = area; η = efficiency about 15–20%) |
| Wind turbine | P = ½ρAv³ × efficiency |
| Hydroelectric | P = η ρ g Q h (Q = water flow rate in m³/s, h = height) |
Choose the water flow rate, the height of the fall and the efficiency of the plant. Find the electrical power. (ρ = 1 000 kg/m³, g = 9.8 m/s²)
Choose the area of the panel, the sunshine intensity and the efficiency. Find the electrical power and the energy in a day with 6 hours of sunshine.
The greenhouse effect and global warming
Without the natural greenhouse effect the Earth’s average temperature would be about −18 °C instead of +15 °C. The increase in greenhouse gases from burning fossil fuels and clearing forests strengthens the effect (global warming). Consequences include melting ice, rising sea level, more extreme weather and shifts in rainfall that affect crops and water supplies. Reduce the problem with renewable energy, energy efficiency, protecting forests and capturing carbon.
Pollution and its control
| Pollution | Cause | Reduction |
|---|---|---|
| Air pollution | Fuel burning, vehicles, factories | Catalytic converters, cleaner fuels, public transport |
| Noise pollution | Traffic, machinery, loud music | Barriers, silencers, planning; noise above 85 dB over a long time damages hearing |
| Thermal pollution | Hot water from power stations | Cooling towers |
| Radioactive waste | Nuclear power and medical use | Sealed storage deep underground |
| Light pollution | Streetlights, advertising | Shielded lamps; switching off |
Key terms
- Renewable energy
- Energy from sources that are replaced naturally.
- Efficiency
- The useful energy output divided by the total energy input.
- Greenhouse effect
- Warming of the Earth’s surface by gases that absorb and re-emit infrared radiation.
- Biomass
- Fuel from plant or animal material.
Summary
- Energy is conserved; efficiency = useful output ÷ total input.
- Renewable sources (hydro, solar, wind, geothermal, biomass) are sustainable; fossil fuels add carbon dioxide.
- Power equations: hydro P = ηρgQh; wind ½ρAv³; solar I A η.
- Reduce pollution with efficiency, cleaner fuels and better planning.