Energy Resources and Transfer: Efficiency

Efficiency is a comparison of the useful energy or power output against the total energy or power input.
It is expressed as a percentage using the following equation: Efficiency (%) = (Useful output energy or power / Total input energy or power) x 100%
In practical situations, not all input energy is converted into useful output. There are always energy losses in the form of waste energy which is usually heat.
Energy can be lost in a number of ways: in an electrical circuit, energy can be lost as heat due to resistance; in a mechanical system, energy can be lost as heat due to friction; in a thermal system, energy can be lost as heat due to poor insulation.
The more efficient an appliance or system is, the higher the proportion of the input energy is converted into useful output energy.
To improve the efficiency of energy transfer in a device or system, reduce the wastage of energy. This could be by using better insulation, lubrication, or choosing materials with less resistance, for example.
In a Sankey diagram, energy input is represented by a vertical line, with energy output and losses represented by lines to the sides. The thickness of the lines is proportional to the amount of energy involved.
A perfect, 100% efficient system is theoretically impossible. This is due to the Second Law of Thermodynamics stating that it is impossible to have a system with no energy losses.
Energy efficiency is important because it can save resources, reduce pollution and it’s usually more cost-effective. Improving efficiency often involves using modern technology or improving designs.
Major ways to improve energy efficiency in everyday life include improving insulation in buildings, using energy-saving light bulbs, and selecting appliances with high energy efficiency ratings.