Energy, Sustainability and Environmental Impact in Engineering
Energy, Sustainability and Environmental Impact in Engineering
The exam tests energy units, efficiency, renewable and non-renewable sources, life-cycle thinking and the environmental consequences of material and process choices.
Core rules
- Power is the rate of energy use (W or kW); energy is power × time (kWh). A 2 kW appliance for 30 minutes uses 1 kWh.
- Efficiency = useful energy output / energy input × 100%. Losses appear as heat, sound or friction.
- Embodied energy is the energy used to extract, process, manufacture and transport a material. It can dominate a product's total impact.
- Life-cycle assessment covers raw material, manufacture, use, maintenance and end-of-life. Recycling saves energy but may be downcycling if quality falls.
- Renewable sources include solar, wind, hydro and biomass; they are not automatically impact-free because of land use, materials and manufacture.
Worked example
A 2 kW kettle runs for 3 minutes. Energy = 2 kW × (3/60) h = 0.1 kWh. At €0.20 per kWh, cost = 0.1 × 0.20 = €0.02. A 10 W LED lamp run for 5 hours uses 0.05 kWh, half the energy. Reasoning: convert minutes to hours before multiplying; kW × h gives kWh, not kW.
Traps
Confusing kW and kWh; ignoring standby or transmission losses; treating recycling as impact-free; comparing materials by mass alone without embodied energy; forgetting end-of-life.