# Energy Resources and Transfer: Efficiency

## 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.