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Energy conversion efficiency

Contents

Idea

Wikipedia defines:

Energy conversion efficiency is the ratio between the useful output of an energy conversion machine and the input, in energy terms. The useful output may be electric power, mechanical work, or heat. Energy conversion efficiency is not defined uniquely, but instead depends on the usefulness of the output. All or part of the heat produced from burning a fuel may become rejected waste heat if, for example, work is the desired output from a thermodynamic cycle.

Even though the definition includes the notion of usefulness, efficiency is considered a technical or physical term. Goal or mission oriented terms include effectiveness and efficacy.

Generally, energy conversion efficiency is a dimensionless number between 0 and 1.0, or 0 to 100%. Efficiencies may not exceed 100%, e.g., for a perpetual motion machine. However, other effectiveness measures that can exceed 1.0 are used for heat pumps and other devices that move heat rather than convert it.

Details

This table shows in descending efficiency order some well known energy conversion examples:

ExampleEnergy efficiency (%)Energy Transformation
Large electric motors90-97electrical (e) -> mechanical (m)
Dry batteries85-95c -> e
Solar cellcurrent maximum 85radiant (r) -> electrical (e)
Fuel cellup to 85c -> e
Water turbine60-90m -> m
Gas turbine plus steam turbine (combined cycle)up to 60c ->e
Wind turbineup to 59 (theoretical limit)m->m
Combustion engine10-50chemical (c) -> mechanical (m)
Gas turbineup to 40c -> e
Firearm~30c -> m
Muscle14 - 27c -> m
Photosynthesisup to 6r -> c

Here are some additional examples

  • Electrolysis of water 50%-70% (80%-94% theoretical maximum)

  • Electric motors 30-60% (small ones < 10W); 50-90 (middle ones between 10-200W); 70-99.99% above 200W

  • Household refrigerators low end systems ~ 20%; high end systems ~ 40-50%

  • Incandescent light bulb 5-10%

  • Light-emitting diode up to 35%

  • Fluorescent lamps 28%

  • Low-pressure sodium lamps 40.5%

  • Metal halide lamps 24%

  • Switched-mode power supply currently up to 95% practically

  • Electric shower 90-95% (Overall it would be more efficient to use a heat pump, requiring less electric energy)

  • Electric heaters around 95% (all energy is always converted into heat anyway)

References

Efficiency on Wikipedia

category: energy