Published by Patrick Mutisya · 14 days ago
Understand, qualitatively, the concept of efficiency of energy transfer.
Efficiency measures how well a device or process converts input energy into useful output energy. It is expressed as a percentage.
The general formula is
\$\eta = \frac{\text{Useful output energy}}{\text{Total input energy}} \times 100\%\$
where \$\eta\$ denotes efficiency.
| Energy Resource | Typical Efficiency of Conversion to Useful Energy | Comments |
|---|---|---|
| Coal (thermal power station) | 30–35 % | Large losses as waste heat; improved with combined‑cycle plants. |
| Natural gas (combined‑cycle) | 50–60 % | Higher than coal because of higher temperature and gas turbines. |
| Oil (internal combustion engine) | 20–25 % | Most energy lost as heat in exhaust and cooling system. |
| Solar photovoltaic (PV) panels | 15–22 % | Depends on cell material and sunlight intensity. |
| Wind turbines | 30–45 % | Varies with wind speed and turbine design. |
| Hydroelectric (large dam) | 80–90 % | One of the most efficient large‑scale conversions. |
Example 1 – Light bulb: An incandescent bulb converts about 5 % of electrical energy into visible light; the rest becomes heat.
Example 2 – Bicycle: Human muscles are roughly 20–25 % efficient at turning food energy into mechanical work; the rest is lost as heat.
Example 3 – Electric kettle: Converts nearly 100 % of electrical energy into heat, but only about 70 % of that heat actually raises the water temperature because of heat loss to the surroundings.