Efficiency

What Is Efficiency?

Efficiency measures how effectively a system converts input energy into useful output energy. It is expressed as a percentage and is always less than 100% in real systems because some energy is always converted to waste (usually heat).

$$\eta = \frac{E_{useful output}}{E_{input}} \times 100\%$$

KEY TAKEAWAY: No real system is 100% efficient. Understanding efficiency allows engineers to quantify energy waste, compare design options, and identify where improvements will have the greatest impact.

Why Efficiency Matters

• Economic: Lower efficiency means higher operating costs (more energy input to achieve the same output)
• Environmental: Lower efficiency means more fuel burned or more emissions produced
• Thermal management: Energy losses become heat — high losses may require cooling systems
• System sizing: Lower efficiency requires a larger, more expensive energy source and storage

Key Concepts in This Section

1. Concept and calculation of efficiency — the formula, units, and worked examples
2. Methods to improve efficiency — engineering strategies to reduce losses
3. Environmental and economic impacts — why efficiency matters beyond the calculation

VCAA FOCUS: Efficiency calculations appear in almost every VCAA Systems Engineering exam. Practise calculating efficiency from power or energy data, working backwards from efficiency to find input or output, and comparing efficiencies of different design options.