Energy: Efficiency

Energy Transfers and Efficiency

Energy can be transferred usefully, stored or dissipated (wasted), but it cannot be created or destroyed – this is known as the principle of conservation of energy.
Efficiency is a measure of how much input energy is transferred into useful output energy.
In real-world energy transfers, some energy always ends up being wasted, often as thermal energy due to friction.
The less energy is wasted in an energy transfer, the more efficient the process is.

Calculating Efficiency

The efficiency of an energy transfer can be calculated using the formula: efficiency = (useful power output / total power input)
This can also be calculated using the formula: efficiency = (useful energy output / total energy input)

Improving Energy Efficiency

Efficiency can be improved in various ways. One example is lubrication, which reduces friction — and hence energy wasted as heat — in machines.
Insulating buildings can improve energy efficiency by reducing the amount of thermal energy that escapes.
Using energy-saving light bulbs can increase efficiency by converting a greater proportion of electrical energy into light and less into wasted heat.

Energy and Power

Power is the rate of energy transfer, measured in watts (W). One watt equals one joule of energy transferred per second.
Therefore, the more powerful a device, the more energy it transfers per unit time.
Power can be calculated using the formula: P = E/t, where P is power, E is the energy transferred, and t is the time taken.

Sankey Diagrams

A Sankey diagram is a visual representation of energy transfers.
The width of the lines in a Sankey diagram represents the amount of energy being transferred.
Inefficient devices or processes will have a larger proportion of their energy transfers represented as wasted energy, usually shown as a downward arrow.
By improving efficiency, more of the initial energy input can be converted into useful output, increasing the upward portion of the diagram.