Energy conversion efficiency
Encyclopedia
Energy conversion efficiency is the ratio
Ratio
In mathematics, a ratio is a relationship between two numbers of the same kind , usually expressed as "a to b" or a:b, sometimes expressed arithmetically as a dimensionless quotient of the two which explicitly indicates how many times the first number contains the second In mathematics, a ratio is...

 between the useful output of an energy conversion machine and the input, in energy
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...

 terms. The useful output may be electric power
Electric power
Electric power is the rate at which electric energy is transferred by an electric circuit. The SI unit of power is the watt.-Circuits:Electric power, like mechanical power, is represented by the letter P in electrical equations...

, mechanical work
Mechanical work
In physics, work is a scalar quantity that can be described as the product of a force times the distance through which it acts, and it is called the work of the force. Only the component of a force in the direction of the movement of its point of application does work...

, or heat
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...

.

Overview

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
Waste heat
Waste heat sometimes called Secondary heat or Low-grade heat refers to heat produced by machines, electrical equipment and industrial processes for which no useful application is found. Energy is often produced by a heat engine, running on a source of high-temperature heat...

 if, for example, work is the desired output from a thermodynamic cycle
Thermodynamic cycle
A thermodynamic cycle consists of a series of thermodynamic processes transferring heat and work, while varying pressure, temperature, and other state variables, eventually returning a system to its initial state...

.
Even though the definition includes the notion of usefulness, efficiency is considered a technical
Technology
Technology is the making, usage, and knowledge of tools, machines, techniques, crafts, systems or methods of organization in order to solve a problem or perform a specific function. It can also refer to the collection of such tools, machinery, and procedures. The word technology comes ;...

 or physical
Physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...

 term. Goal or mission oriented terms include effectiveness
Effectiveness
Effectiveness is the capability of producing a desired result. When something is deemed effective, it means it has an intended or expected outcome, or produces a deep, vivid impression.-Etymology:...

 and efficacy
Efficacy
Efficacy is the capacity to produce an effect. It has different specific meanings in different fields. In medicine, it is the ability of an intervention or drug to reproduce a desired effect in expert hands and under ideal circumstances.- Healthcare :...

.

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
Perpetual motion
Perpetual motion describes hypothetical machines that operate or produce useful work indefinitely and, more generally, hypothetical machines that produce more work or energy than they consume, whether they might operate indefinitely or not....

 machine. However, other effectiveness measures
Thermal efficiency
In thermodynamics, the thermal efficiency is a dimensionless performance measure of a device that uses thermal energy, such as an internal combustion engine, a boiler, a furnace, or a refrigerator for example.-Overview:...

 that can exceed 1.0 are used for heat pumps and other devices that move heat rather than convert it.

When talking about the efficiency of heat engines and power stations the convention should be stated, i.e., HHV (aka Gross Heating Value etc.) or LCV (aka Net Heating value), and whether gross output (at the generator terminals) or net output (at the power station fence) are being considered. The two are separate but both must be stated. Failure to do so causes endless confusion.

Related, more specific terms include
  • Electrical efficiency, useful power output per electrical power consumed;
  • Mechanical efficiency
    Mechanical efficiency
    Mechanical efficiency measures the effectiveness of a machine in transforming the energy and power that is input to the device into an output force and movement...

    , where one form of mechanical energy (e.g. potential energy of water) is converted to mechanical energy (work
    Mechanical work
    In physics, work is a scalar quantity that can be described as the product of a force times the distance through which it acts, and it is called the work of the force. Only the component of a force in the direction of the movement of its point of application does work...

    );
  • Thermal efficiency
    Thermal efficiency
    In thermodynamics, the thermal efficiency is a dimensionless performance measure of a device that uses thermal energy, such as an internal combustion engine, a boiler, a furnace, or a refrigerator for example.-Overview:...

     or Fuel efficiency
    Fuel efficiency
    Fuel efficiency is a form of thermal efficiency, meaning the efficiency of a process that converts chemical potential energy contained in a carrier fuel into kinetic energy or work. Overall fuel efficiency may vary per device, which in turn may vary per application, and this spectrum of variance is...

    , useful heat
    Heat
    In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...

     and/or work
    Work (thermodynamics)
    In thermodynamics, work performed by a system is the energy transferred to another system that is measured by the external generalized mechanical constraints on the system. As such, thermodynamic work is a generalization of the concept of mechanical work in mechanics. Thermodynamic work encompasses...

     output
    Work output
    In physics, work output is the work done by a simple machine, compound machine, or any type of engine model. In common terms, it is the energy output, which for simple machines is always less than the energy input, even though the forces may be drastically different.In thermodynamics, work output...

     per input energy such as the fuel
    Fuel
    Fuel is any material that stores energy that can later be extracted to perform mechanical work in a controlled manner. Most fuels used by humans undergo combustion, a redox reaction in which a combustible substance releases energy after it ignites and reacts with the oxygen in the air...

     consumed;
  • 'Total efficiency', e.g., for cogeneration
    Cogeneration
    Cogeneration is the use of a heat engine or a power station to simultaneously generate both electricity and useful heat....

    , useful electric power
    Electric power
    Electric power is the rate at which electric energy is transferred by an electric circuit. The SI unit of power is the watt.-Circuits:Electric power, like mechanical power, is represented by the letter P in electrical equations...

     and heat output per fuel energy consumed. Same as the thermal efficiency
    Thermal efficiency
    In thermodynamics, the thermal efficiency is a dimensionless performance measure of a device that uses thermal energy, such as an internal combustion engine, a boiler, a furnace, or a refrigerator for example.-Overview:...

    .
  • Luminous efficiency, that portion of the emitted electromagnetic radiation is usable for human vision.

Fuel heating values and efficiency

In Europe the usable energy content of fuel is typically calculated using the lower heating value (LHV) of that fuel, which definition assumes that the water vapor
Water vapor
Water vapor or water vapour , also aqueous vapor, is the gas phase of water. It is one state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from the sublimation of ice. Under typical atmospheric conditions, water vapor is continuously...

 produced during fuel combustion
Combustion
Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...

 (oxidation), remains gaseous, and is not condensed
Condensation
Condensation is the change of the physical state of matter from gaseous phase into liquid phase, and is the reverse of vaporization. When the transition happens from the gaseous phase into the solid phase directly, the change is called deposition....

 to liquid water so the latent heat of vaporization of that water is not usable. Using the LHV, a condensing boiler
Condensing boiler
A condensing boiler utilizes the latent heat of water produced from the burning of fuel, in addition to the standard sensible heat, to increase its efficiency.-Principles of work:...

 can achieve a "heating efficiency" in excess of 100% ( this does not violate the first law of thermodynamics
First law of thermodynamics
The first law of thermodynamics is an expression of the principle of conservation of work.The law states that energy can be transformed, i.e. changed from one form to another, but cannot be created nor destroyed...

 as long as the LHV convention is understood, but does cause confusion). This is because the apparatus recovers part of the heat of vaporization, which is not included in the definition of the lower heating value of fuel. In the U.S. and elsewhere, the higher heating value (HHV) is used, which includes the latent heat for condensing the water vapor, and thus the thermodynamic maximum of 100% efficiency cannot be exceeded with HHV's use.

Example of energy conversion efficiency

Conversion process Energy efficiency
Electricity generation
Gas turbine
Gas turbine
A gas turbine, also called a combustion turbine, is a type of internal combustion engine. It has an upstream rotating compressor coupled to a downstream turbine, and a combustion chamber in-between....

up to 40%
Gas turbine
Gas turbine
A gas turbine, also called a combustion turbine, is a type of internal combustion engine. It has an upstream rotating compressor coupled to a downstream turbine, and a combustion chamber in-between....

 plus steam turbine
Steam turbine
A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it into rotary motion. Its modern manifestation was invented by Sir Charles Parsons in 1884....

 (combined cycle
Combined cycle
In electric power generation a combined cycle is an assembly of heat engines that work in tandem off the same source of heat, converting it into mechanical energy, which in turn usually drives electrical generators...

)
up to 60%
Water turbine
Water turbine
A water turbine is a rotary engine that takes energy from moving water.Water turbines were developed in the 19th century and were widely used for industrial power prior to electrical grids. Now they are mostly used for electric power generation. They harness a clean and renewable energy...

up to 90% (practically achieved)
Wind turbine
Wind turbine
A wind turbine is a device that converts kinetic energy from the wind into mechanical energy. If the mechanical energy is used to produce electricity, the device may be called a wind generator or wind charger. If the mechanical energy is used to drive machinery, such as for grinding grain or...

up to 59% (theoretical limit)
Solar cell
Solar cell
A solar cell is a solid state electrical device that converts the energy of light directly into electricity by the photovoltaic effect....

6%-40% (technology dependent, 15% most often, 85%-90% theoretical limit)
Fuel cell
Fuel cell
A fuel cell is a device that converts the chemical energy from a fuel into electricity through a chemical reaction with oxygen or another oxidizing agent. Hydrogen is the most common fuel, but hydrocarbons such as natural gas and alcohols like methanol are sometimes used...

up to 85%
World Electricity generation
Electricity generation
Electricity generation is the process of generating electric energy from other forms of energy.The fundamental principles of electricity generation were discovered during the 1820s and early 1830s by the British scientist Michael Faraday...

 2008
Gross output 39%, Net output 33%.
Engine/Motor
Combustion engine
Combustion engine
Combustion engine may refer to:* Internal combustion engine* External combustion engine...

10-50%
Electric motor
Electric motor
An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...

s
30-60% (small ones < 10W); 50-90 (between 10-200W); 70-99.99% (above 200W)
Natural process
Photosynthesis
Photosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...

up to 6%
Muscle
Muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...

14% - 27%
Appliance
Household refrigerator
Refrigerator
A refrigerator is a common household appliance that consists of a thermally insulated compartment and a heat pump that transfers heat from the inside of the fridge to its external environment so that the inside of the fridge is cooled to a temperature below the ambient temperature of the room...

s
low end systems ~ 20%; high end systems ~ 40-50%
Incandescent light bulb
Incandescent light bulb
The incandescent light bulb, incandescent lamp or incandescent light globe makes light by heating a metal filament wire to a high temperature until it glows. The hot filament is protected from air by a glass bulb that is filled with inert gas or evacuated. In a halogen lamp, a chemical process...

0.7-5.1%, 5-10%
Light-emitting diode
Light-emitting diode
A light-emitting diode is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting...

4.2-14.9%, up to 35%
Fluorescent lamp
Fluorescent lamp
A fluorescent lamp or fluorescent tube is a gas-discharge lamp that uses electricity to excite mercury vapor. The excited mercury atoms produce short-wave ultraviolet light that then causes a phosphor to fluoresce, producing visible light. A fluorescent lamp converts electrical power into useful...

s
8.0-15.6%, 28%
Low-pressure sodium lamps 15.0-29.0%, 40.5%
Metal halide lamp
Metal halide lamp
Metal-halide lamps, a member of the high-intensity discharge family of lamps, produce high light output for their size, making them a compact, powerful, and efficient light source. By adding rare earth metal salts to the mercury vapor lamp, improved luminous efficacy and light color is obtained...

s
9.5-17.0%, 24%
Switched-mode power supply
Switched-mode power supply
A switched-mode power supply is an electronic power supply that incorporates a switching regulator in order to be highly efficient in the conversion of electrical power...

currently up to 95% practically
Electric shower 90-95% ( Overall it would be more efficient to use a heat pump
Heat pump
A heat pump is a machine or device that effectively "moves" thermal energy from one location called the "source," which is at a lower temperature, to another location called the "sink" or "heat sink", which is at a higher temperature. An air conditioner is a particular type of heat pump, but the...

, requiring less electric energy)
Electric heaters
Electric heating
Electric heating is any process in which electrical energy is converted to heat. Common applications include space heating, cooking, water heating and industrial processes. An electric heater is an electrical appliance that converts electrical energy into heat...

100% (all energy is always converted into heat)
others
Firearm
Firearm
A firearm is a weapon that launches one, or many, projectile at high velocity through confined burning of a propellant. This subsonic burning process is technically known as deflagration, as opposed to supersonic combustion known as a detonation. In older firearms, the propellant was typically...

~30% (.300 Hawk ammunition)
Electrolysis of water
Electrolysis of water
Electrolysis of water is the decomposition of water into oxygen and hydrogen gas due to an electric current being passed through the water.-Principle:...

50%-70% (80%-94% theoretical maximum)

See also

  • Energy efficiency (disambiguation)
  • EROEI
  • Exergy efficiency
    Exergy efficiency
    Exergy efficiency computes the efficiency of a process taking the second law of thermodynamics into account.-Motivation:...

  • Figure of merit
    Figure of merit
    A figure of merit is a quantity used to characterize the performance of a device, system or method, relative to its alternatives. In engineering, figures of merit are often defined for particular materials or devices in order to determine their relative utility for an application...

  • Fuel efficiency
    Fuel efficiency
    Fuel efficiency is a form of thermal efficiency, meaning the efficiency of a process that converts chemical potential energy contained in a carrier fuel into kinetic energy or work. Overall fuel efficiency may vary per device, which in turn may vary per application, and this spectrum of variance is...

  • International Electrotechnical Commission
    International Electrotechnical Commission
    The International Electrotechnical Commission is a non-profit, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies – collectively known as "electrotechnology"...

  • Sensitivity (electronics)
    Sensitivity (electronics)
    The sensitivity of an electronic device, such as a communications system receiver, or detection device, such as a PIN diode, is the minimum magnitude of input signal required to produce a specified output signal having a specified signal-to-noise ratio, or other specified criteria.Sensitivity is...

  • Thermal efficiency
    Thermal efficiency
    In thermodynamics, the thermal efficiency is a dimensionless performance measure of a device that uses thermal energy, such as an internal combustion engine, a boiler, a furnace, or a refrigerator for example.-Overview:...

  • Relative cost of electricity generated by different sources
  • Electrical efficiency
  • Mechanical efficiency
    Mechanical efficiency
    Mechanical efficiency measures the effectiveness of a machine in transforming the energy and power that is input to the device into an output force and movement...

  • Figure of merit
    Figure of merit
    A figure of merit is a quantity used to characterize the performance of a device, system or method, relative to its alternatives. In engineering, figures of merit are often defined for particular materials or devices in order to determine their relative utility for an application...

  • Heat of combustion
    Heat of combustion
    The heat of combustion is the energy released as heat when a compound undergoes complete combustion with oxygen under standard conditions. The chemical reaction is typically a hydrocarbon reacting with oxygen to form carbon dioxide, water and heat...

  • Lower heating value
  • Higher heating value
  • Perpetual motion
    Perpetual motion
    Perpetual motion describes hypothetical machines that operate or produce useful work indefinitely and, more generally, hypothetical machines that produce more work or energy than they consume, whether they might operate indefinitely or not....

  • Power generating equipment efficiency and carbon footprint

External links

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