# 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.