# Energy: Efficiency

## 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.