Energy density

Energy density

Discussion
Ask a question about 'Energy density'
Start a new discussion about 'Energy density'
Answer questions from other users
Full Discussion Forum
 
Encyclopedia
Energy density is a term used for the amount of 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...

 stored in a given system or region of space per unit volume
Volume
Volume is the quantity of three-dimensional space enclosed by some closed boundary, for example, the space that a substance or shape occupies or contains....

. Often only the useful or extractable energy is quantified, which is to say that chemically inaccessible energy such as rest mass energy is ignored. Quantified energy is energy that has some sort of, as the name suggests, quantified magnitude with related units.

For fuels, the energy per unit volume is sometimes a useful parameter. Comparing, for example, the effectiveness of hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 fuel to gasoline
Gasoline
Gasoline , or petrol , is a toxic, translucent, petroleum-derived liquid that is primarily used as a fuel in internal combustion engines. It consists mostly of organic compounds obtained by the fractional distillation of petroleum, enhanced with a variety of additives. Some gasolines also contain...

, hydrogen has a higher specific energy
Specific energy
Specific energy is defined as the energy per unit mass. Common metric units are J/kg. It is an intensive property. Contrast this with energy, which is an extensive property. There are two main types of specific energy: potential energy and specific kinetic energy. Others are the gray and sievert,...

 (energy per unit mass) than gasoline does, but, even in liquid form, a much lower volumetric energy density.

Energy per unit volume has the same physical units as pressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...

, and in many circumstances is an exact synonym
Synonym
Synonyms are different words with almost identical or similar meanings. Words that are synonyms are said to be synonymous, and the state of being a synonym is called synonymy. The word comes from Ancient Greek syn and onoma . The words car and automobile are synonyms...

: for example, the energy density of the magnetic field may be expressed as (and behaves as) a physical pressure, and the energy required to compress a compressed gas a little more may be determined by multiplying the difference between the gas pressure and the pressure outside by the change in volume. In short, pressure is a measure of volumetric enthalpy
Enthalpy
Enthalpy is a measure of the total energy of a thermodynamic system. It includes the internal energy, which is the energy required to create a system, and the amount of energy required to make room for it by displacing its environment and establishing its volume and pressure.Enthalpy is a...

 of a system. A pressure gradient has a potential to perform work on the surroundings by converting enthalpy until equilibrium is reached.

Energy density in energy storage and in fuel


In energy storage
Energy storage
Energy storage is accomplished by devices or physical media that store some form of energy to perform some useful operation at a later time. A device that stores energy is sometimes called an accumulator....

 applications the energy density relates the mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...

 of an energy store to the volume of the storage facility, e.g. 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...

 tank. The higher the energy density of the fuel, the more energy may be stored or transported for the same amount of volume. The energy density of a fuel per unit mass is called the specific energy
Specific energy
Specific energy is defined as the energy per unit mass. Common metric units are J/kg. It is an intensive property. Contrast this with energy, which is an extensive property. There are two main types of specific energy: potential energy and specific kinetic energy. Others are the gray and sievert,...

 of that fuel. In general an engine
Engine
An engine or motor is a machine designed to convert energy into useful mechanical motion. Heat engines, including internal combustion engines and external combustion engines burn a fuel to create heat which is then used to create motion...

 using that fuel will generate less kinetic energy
Kinetic energy
The kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...

 due to inefficiencies
Inefficiency
The term inefficiency has several meanings depending on the context in which its used:*Algorithmic inefficiency - refers to less than optimum computer programs that might exhibit one of more of the symptoms of:** slow execution...

 and thermodynamic
Thermodynamics
Thermodynamics is a physical science that studies the effects on material bodies, and on radiation in regions of space, of transfer of heat and of work done on or by the bodies or radiation...

 considerations—hence the specific fuel consumption
Specific fuel consumption
Thrust specific fuel consumption or sometimes simply specific fuel consumption, SFC, is an engineering term that is used to describe the fuel efficiency of an engine design with respect to thrust output...

 of an engine will always be greater than its rate of production of the kinetic energy of motion.

The greatest energy source by far consists of mass itself. This energy, E = mc2, where m = ρV, ρ is the mass per unit volume, V is the volume of the mass itself and c is the speed of light. This energy, however, can be released only by the processes of nuclear fission
Nuclear fission
In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts , often producing free neutrons and photons , and releasing a tremendous amount of energy...

, nuclear fusion
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...

, or the annihilation of some or all of the matter in the volume V by matter-antimatter
Antimatter
In particle physics, antimatter is the extension of the concept of the antiparticle to matter, where antimatter is composed of antiparticles in the same way that normal matter is composed of particles...

 collisions. Nuclear reactions cannot be realized by chemical reactions such as combustion. Although greater matter densities can be achieved, the density of a neutron star
Neutron star
A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Such stars are composed almost entirely of neutrons, which are subatomic particles without electrical charge and with a slightly larger...

 would approximate the most dense system capable of matter-antimatter annihilation possible. A black hole
Black hole
A black hole is a region of spacetime from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that...

, although denser than a neutron star, doesn't have an equivalent anti-particle form.

If we thus consider the volume of the sphere around a proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....

 defined by the extent of its electric field
Electric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...

, we can get an approximate energy density for the proton, as seen in the table below.

The highest density sources of energy outside of antimatter are fusion
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...

 and fission
Nuclear fission
In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts , often producing free neutrons and photons , and releasing a tremendous amount of energy...

. Fusion includes energy from the sun which will be available for billions of years (in the form of sunlight
Sunlight
Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above the horizon.When the direct solar radiation is not blocked...

) but so far (2011), sustained fusion power
Fusion power
Fusion power is the power generated by nuclear fusion processes. In fusion reactions two light atomic nuclei fuse together to form a heavier nucleus . In doing so they release a comparatively large amount of energy arising from the binding energy due to the strong nuclear force which is manifested...

 production continues to be elusive. Fission of U-235 in nuclear power
Nuclear power
Nuclear power is the use of sustained nuclear fission to generate heat and electricity. Nuclear power plants provide about 6% of the world's energy and 13–14% of the world's electricity, with the U.S., France, and Japan together accounting for about 50% of nuclear generated electricity...

 plants will be available for some decades even though the vast supply of the element on earth is being depleted (peak uranium
Peak uranium
Peak uranium is the point in time that the maximum global uranium production rate is reached. After that peak, the rate of production enters a terminal decline. While uranium is used in nuclear weapons, its primary use is for energy generation via nuclear fission of uranium-235 isotope in a nuclear...

) - it might, however be possible at some future time to extract uranium from seawater. Coal
Coal
Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...

, gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...

, and petroleum
Petroleum
Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling...

 are the current primary energy sources in the U.S. but have a much lower energy density. Burning local biomass
Biomass
Biomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel....

 fuels supplies household energy needs (cooking fires, oil lamp
Oil lamp
An oil lamp is an object used to produce light continuously for a period of time using an oil-based fuel source. The use of oil lamps began thousands of years ago and is continued to this day....

s, etc.) worldwide.

Energy density (how much energy you can carry) does not tell you about energy conversion efficiency
Energy conversion efficiency
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.-Overview:...

 (net output per input) or embodied energy
Embodied energy
Embodied energy is defined as the sum of energy inputs that was used in the work to make any product, from the point of extraction and refining materials, bringing it to market, and disposal / re-purposing of it...

 (what the energy output costs to provide, as harvesting
Energy industry
The energy industry is the totality of all of the industries involved in the production and sale of energy, including fuel extraction, manufacturing, refining and distribution...

, refining
Refinery
A refinery is a production facility composed of a group of chemical engineering unit processes and unit operations refining certain materials or converting raw material into products of value.-Types of refineries:Different types of refineries are as follows:...

, distributing, and dealing with pollution
Pollution
Pollution is the introduction of contaminants into a natural environment that causes instability, disorder, harm or discomfort to the ecosystem i.e. physical systems or living organisms. Pollution can take the form of chemical substances or energy, such as noise, heat or light...

 all use energy). Like any process occurring on a large scale, intensive energy use impacts the world. For example, climate change
Climate change
Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...

, nuclear waste storage, and deforestation
Deforestation
Deforestation is the removal of a forest or stand of trees where the land is thereafter converted to a nonforest use. Examples of deforestation include conversion of forestland to farms, ranches, or urban use....

 may be some of the consequences of supplying our growing energy demands from fossil fuels, nuclear fission, or biomass.

No single energy storage method boasts the best in specific power
Specific power
In physics and engineering, surface power density or sometimes simply specific power is power per unit area.-Applications:* The intensity of electromagnetic radiation can be expressed in W/m2...

, specific energy
Specific energy
Specific energy is defined as the energy per unit mass. Common metric units are J/kg. It is an intensive property. Contrast this with energy, which is an extensive property. There are two main types of specific energy: potential energy and specific kinetic energy. Others are the gray and sievert,...

, and energy density. Peukert's Law
Peukert's law
Peukert's law, presented by the German scientist W. Peukert in 1897, expresses the capacity of a lead–acid battery in terms of the rate at which it is discharged. As the rate increases, the battery's available capacity decreases....

 describes how the amount of useful energy that can be obtained (for a lead-acid cell) depends on how quickly we pull it out. To maximize both specific energy and energy density, one can compute the specific energy density of a substance by multiplying the two values together, where the higher the number, the better the substance is at storing energy efficiently.

Gravimetric and volumetric energy density of some fuels and storage technologies (modified from the Gasoline
Gasoline
Gasoline , or petrol , is a toxic, translucent, petroleum-derived liquid that is primarily used as a fuel in internal combustion engines. It consists mostly of organic compounds obtained by the fractional distillation of petroleum, enhanced with a variety of additives. Some gasolines also contain...

 article):
Note: Some values may not be precise because of isomers or other irregularities. See Heating value for a comprehensive table of specific energies of important fuels.
Note: Also it is important to realise that generally the density values for chemical fuels are without the including the weight of the oxygen required for combusiton. This is typically 2 oxygen atoms per carbon atom, and one per hydrogen atom. The <> of Carbon and Oxygen are similar, while hydrogen is much lighter than oxygen. Figures are presented this way for those fuels where in pracice air would only be drawn in locally to the burner. This explains the apparently lower energy density of materials that already include their own oxidiser (such as gunpower and TNT), where the mass of the oxidant is effectivly both adding a dead weight, and absorbs some of the energy of combustion to dissociate and liberate oxygen to continue the reaction. This also explains some apparent anomalies like the energy density of a sandwich appearing to be higher than that of a stick of dynamite.

Common energy densities


The following is a list of the energy densities of commonly used energy storage materials.
MJ
Joule
The joule ; symbol J) is a derived unit of energy or work in the International System of Units. It is equal to the energy expended in applying a force of one newton through a distance of one metre , or in passing an electric current of one ampere through a resistance of one ohm for one second...

 ≈ 0.28 kWh ≈ 0.37 HPh
Horsepower-hour
A Horsepower-hour is an outdated unit of energy, not used in the SI system of units. The unit represents an amount of work a horse is supposed capable of delivering during an hour...

.

{| class="wikitable"
|+List of Energy Densities
|- align="center"
! Storage material !! Energy type !! Energy per kilogram !! Energy per litre !! Direct uses
|- align="center"
| align="left" | Antimatter  ||Matter/Antimatter
Antimatter
In particle physics, antimatter is the extension of the concept of the antiparticle to matter, where antimatter is composed of antiparticles in the same way that normal matter is composed of particles...

 || 180 petajoules || || Theoretical
|- align="center"
| align="left" | Uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...

 238
|| Nuclear
Nuclear power
Nuclear power is the use of sustained nuclear fission to generate heat and electricity. Nuclear power plants provide about 6% of the world's energy and 13–14% of the world's electricity, with the U.S., France, and Japan together accounting for about 50% of nuclear generated electricity...

 || 20 terajoules || || Electric power plants (nuclear reactors)
|- align="center"
| align="left" | Hydrogen
Compressed hydrogen
Compressed hydrogen is the gaseous state of the element hydrogen kept under pressure. Compressed hydrogen in hydrogen tanks at 350 bar and 700 bar is used for mobile hydrogen storage in hydrogen vehicles...

 (compressed at 700 bar)
|| Chemical || 123 megajoules || 5.6 megajoules || Experimental automotive engines
|- align="center"
| align="left" | Gasoline
Gasoline
Gasoline , or petrol , is a toxic, translucent, petroleum-derived liquid that is primarily used as a fuel in internal combustion engines. It consists mostly of organic compounds obtained by the fractional distillation of petroleum, enhanced with a variety of additives. Some gasolines also contain...

 (petrol)
|| Chemical || 47.2 megajoules || 34 megajoules || Automotive engines
|- align="center"
| align="left" | Diesel || Chemical || 45.4 megajoules || 38.6 megajoules || Automotive engines
|- align="center"
| align="left" | Propane
Propane
Propane is a three-carbon alkane with the molecular formula , normally a gas, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is commonly used as a fuel for engines, oxy-gas torches, barbecues, portable stoves, and residential central...

 (including LPG)
|| Chemical || 46.4 megajoules || || Cooking, home heating, automotive engines
|- align="center"
| align="left" | Jet fuel
Jet fuel
Jet fuel is a type of aviation fuel designed for use in aircraft powered by gas-turbine engines. It is clear to straw-colored in appearance. The most commonly used fuels for commercial aviation are Jet A and Jet A-1 which are produced to a standardized international specification...

, Kerosene
Kerosene
Kerosene, sometimes spelled kerosine in scientific and industrial usage, also known as paraffin or paraffin oil in the United Kingdom, Hong Kong, Ireland and South Africa, is a combustible hydrocarbon liquid. The name is derived from Greek keros...

|| Chemical || 43 megajoules || 33 megajoules || Jet engines
|- align="center"
| align="left" | Fat
Fat
Fats consist of a wide group of compounds that are generally soluble in organic solvents and generally insoluble in water. Chemically, fats are triglycerides, triesters of glycerol and any of several fatty acids. Fats may be either solid or liquid at room temperature, depending on their structure...

 (animal/vegetable)
|| Chemical || 37 megajoules || || Human/animal nutrition
|- align="center"
| align="left" | Coal
Coal
Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...

|| Chemical || 24 megajoules || || Electric power plants, home heating
|- align="center"
| align="left" | Carbohydrate
Carbohydrate
A carbohydrate is an organic compound with the empirical formula ; that is, consists only of carbon, hydrogen, and oxygen, with a hydrogen:oxygen atom ratio of 2:1 . However, there are exceptions to this. One common example would be deoxyribose, a component of DNA, which has the empirical...

s (including sugars)
|| Chemical || 17 megajoules || || Human/animal nutrition
|- align="center"
| align="left" | Protein
Protein in nutrition
Proteins are polymer chains made of amino acids linked together by peptide bonds. Proteins and carbohydrates contain 4 kcal per gram as opposed to lipids which contain 9 kcal per gram....

|| Chemical || 16.8 megajoules || || Human/animal nutrition
|- align="center"
| align="left" | Wood
Wood fuel
Wood fuel is wood used as fuel. The burning of wood is currently the largest use of energy derived from a solid fuel biomass. Wood fuel can be used for cooking and heating, and occasionally for fueling steam engines and steam turbines that generate electricity. Wood fuel may be available as...

|| Chemical || 16.2 megajoules || || Heating, outdoor cooking
|- align="center"
| align="left" | Lithium air battery
Lithium air battery
The lithium–air battery is a class of lithium battery that employs a cathode which relies on oxygen reduction forming a discharge product...

|| Electrochemical
Electrochemical cell
An electrochemical cell is a device capable of either deriving electrical energy from chemical reactions, or facilitating chemical reactions through the introduction of electrical energy. A common example of an electrochemical cell is a standard 1.5-volt "battery"...

 || 9 megajoules || || Portable electronic devices, electric vehicles
|- align="center"
| align="left" | Carbon nanotube springs
Carbon nanotube springs
Carbon nanotube springs are springs made of carbon nanotubes . They are an alternate form of high density, lightweight, reversible energy storage based on the elastic deformations of CNTs. Many previous studies on the mechanical properties of CNTs have revealed that they possess high stiffness,...

 
||Spring (device)
Spring (device)
A spring is an elastic object used to store mechanical energy. Springs are usually made out of spring steel. Small springs can be wound from pre-hardened stock, while larger ones are made from annealed steel and hardened after fabrication...

 || 7.2 megajoules || || Theoretical
|- align="center"
| align="left" | TNT || Chemical || 4.6 megajoules || || Explosives
|- align="center"
| align="left" | Gunpowder
Gunpowder
Gunpowder, also known since in the late 19th century as black powder, was the first chemical explosive and the only one known until the mid 1800s. It is a mixture of sulfur, charcoal, and potassium nitrate - with the sulfur and charcoal acting as fuels, while the saltpeter works as an oxidizer...

|| Chemical || 3 megajoules || || Explosives
|- align="center"
| align="left" | Lithium battery
Lithium battery
Lithium batteries are disposable batteries that have lithium metal or lithium compounds as an anode. Depending on the design and chemical compounds used, lithium cells can produce voltages from 1.5 V to about 3.7 V, over twice the voltage of an ordinary zinc–carbon battery or alkaline battery...

|| Electrochemical || 1.30 megajoules || || Portable electronic devices, flashlights
|- align="center"
| align="left" | Lithium-ion battery || Electrochemical || 720 kilojoules || || Laptop computers, mobile devices, some modern automotive engines
|- align="center"
| align="left" | Alkaline battery
Alkaline battery
Alkaline batteries are a type of primary batteries dependent upon the reaction between zinc and manganese dioxide . A rechargeable alkaline battery allows reuse of specially designed cells....

|| Electrochemical || 590 kilojoules || || Portable electronic devices, flashlights
|- align="center"
| align="left" | Supercapacitor
Supercapacitor
An electric double-layer capacitor , also known as supercapacitor, supercondenser, electrochemical double layer capacitor, or ultracapacitor, is an electrochemical capacitor with relatively high energy density. Their energy density is typically hundreds of times greater than conventional...

 (graphene/SWCNT electrode)
|| Electrical || 560 kilojoules || || Electric vehicles, DC power smoothing
|- align="center"
| align="left" | Sodium aqueous battery || Electrochemical || 367 kilojoules || || Load levelling, power smoothing, grid storage
|- align="center"
| align="left" | Nickel-metal hydride battery || Electrochemical || 288 kilojoules || || Portable electronic devices, flashlights
|- align="center"
| align="left" | Supercapacitor || Electrical
Electricity
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...

 || 100 kilojoules || || DC Supply smoothing
|- align="center"
| align="left" | Lead-acid battery
Lead-acid battery
Lead–acid batteries, invented in 1859 by French physicist Gaston Planté, are the oldest type of rechargeable battery. Despite having a very low energy-to-weight ratio and a low energy-to-volume ratio, their ability to supply high surge currents means that the cells maintain a relatively large...

|| Electrochemical || 100 kilojoules || || Automotive engine igniton
|- align="center"
| align="left" | Electrostatic capacitor
Capacitor
A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...

|| Electrical || 360 joules || || Electronic circuits
|- align="center"
{| class="wikitable"
|+List of Energy Capacities of Common Storage Units
|- align="center"
! Storage device !! Energy type !! Energy content !! Typical mass !! W × H × D (mm)!! Uses
|- align="center"
| align="left" | Automotive battery
Lead-acid battery
Lead–acid batteries, invented in 1859 by French physicist Gaston Planté, are the oldest type of rechargeable battery. Despite having a very low energy-to-weight ratio and a low energy-to-volume ratio, their ability to supply high surge currents means that the cells maintain a relatively large...

 (lead-acid)
|| Electrochemical || 2.6 megajoules || 15 kilograms || 230 × 180 × 185 || Automotive starter motor and accessories
|- align="center"
| align="left" | Club sandwich (Subway
Subway (restaurant)
Subway is an American restaurant franchise that primarily sells submarine sandwiches and salads. It is owned and operated by Doctor's Associates, Inc. . Subway is one of the fastest growing franchises in the world with 35,519 restaurants in 98 countries and territories as of October 25th, 2011...

 6 inch
Inch
An inch is the name of a unit of length in a number of different systems, including Imperial units, and United States customary units. There are 36 inches in a yard and 12 inches in a foot...

)
|| Chemical || 1.3 megajoules || 240 grams || 150 × ? × ? || Human nutrition
|- align="center"
| align="left" | Alkaline "battery" (AA size
AA battery
An AA battery is a standard size of battery. Batteries of this size are the most commonly used type of in portable electronic devices. An AA battery is composed of a single electrochemical cell...

)
|| Electrochemical || 15.4 kilojoules || 23 grams || 14.5 × 50.5 × 14.5 || Portable electronic equipment, flashlights
|- align="center"
| align="left" | lithium-ion battery (Nokia BL-5C) || Electrochemical || 12.9 kilojoules || 18.5 grams || 54.2 × 33.8 × 5.8 || Mobile phones
|}

Energy densities ignoring external components


This table lists energy densities of systems that require external components, such as oxidisers or a heat sink or source. These figures do not take into account the mass and volume of the required components as they are assumed to be freely available and present in the atmosphere. Such systems cannot be compared with self-contained systems.

{|class="wikitable sortable" style="text-align: right;"
|+Energy Densities Table - Energy Media Only
!Storage type
!Specific energy (MJ/kg)
!Energy density (MJ/L)
!Peak recovery efficiency %
!Practical recovery efficiency %
|-
|align=left | Planck energy density
Planck units
In physics, Planck units are physical units of measurement defined exclusively in terms of five universal physical constants listed below, in such a manner that these five physical constants take on the numerical value of 1 when expressed in terms of these units. Planck units elegantly simplify...

 || || || ||
|-
|align=left | Hydrogen, liquid
Liquid hydrogen
Liquid hydrogen is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H2 form.To exist as a liquid, H2 must be pressurized above and cooled below hydrogen's Critical point. However, for hydrogen to be in a full liquid state without boiling off, it needs to be...

 || 141.86 || 8.491 || ||
|-
|align=left | Hydrogen, at 690 bar and 15ºC || 141.86|| 4.5 || ||
|-
|align=left|Hydrogen, gas || 141.86|| 0.01005 || ||
|-
|align=left|Beryllium
Beryllium
Beryllium is the chemical element with the symbol Be and atomic number 4. It is a divalent element which occurs naturally only in combination with other elements in minerals. Notable gemstones which contain beryllium include beryl and chrysoberyl...

 ||67.6||125.1|| ||
|-
|align=left|Lithium borohydride
Lithium borohydride
Lithium borohydride is a tetrahydroborate and known in organic synthesis as a reducing agent for esters. Although less common than the related sodium borohydride, the lithium salt offers some advantages of being highly soluble in ethers and being a stronger reducing agent but still safer to...

 ||65.2||43.4|| ||
|-
|align=left|Boron
Boron
Boron is the chemical element with atomic number 5 and the chemical symbol B. Boron is a metalloid. Because boron is not produced by stellar nucleosynthesis, it is a low-abundance element in both the solar system and the Earth's crust. However, boron is concentrated on Earth by the...

  ||58.9||137.8|| ||
|-
|align=left|Methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...

 (1.013 bar, 15°C) ||55.6||0.0378 || ||
|-
|align=left|Natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...

 |||53.6||0.0364|| ||
|-
|align=left|LNG
Liquefied natural gas
Liquefied natural gas or LNG is natural gas that has been converted temporarily to liquid form for ease of storage or transport....

 (NG at −160°C)|||53.6||22.2|| ||
|-
|align=left|CNG
Compressed natural gas
Compressed natural gas is a fossil fuel substitute for gasoline , diesel, or propane/LPG. Although its combustion does produce greenhouse gases, it is a more environmentally clean alternative to those fuels, and it is much safer than other fuels in the event of a spill...

 (NG compressed to 250 bar/~3,600 psi) || 53.6 || 9 ||
|-
|align=left | LPG propane
Propane
Propane is a three-carbon alkane with the molecular formula , normally a gas, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is commonly used as a fuel for engines, oxy-gas torches, barbecues, portable stoves, and residential central...

 || 49.6 || 25.3 || ||
|-
|align=left| LPG butane
Butane
Butane is a gas with the formula C4H10 that is an alkane with four carbon atoms. The term may refer to any of two structural isomers, or to a mixture of them: in the IUPAC nomenclature, however, butane refers only to the unbranched n-butane isomer; the other one being called "methylpropane" or...

 || 49.1 || 27.7 || ||
|-
|align=left|Gasoline (petrol)
Gasoline
Gasoline , or petrol , is a toxic, translucent, petroleum-derived liquid that is primarily used as a fuel in internal combustion engines. It consists mostly of organic compounds obtained by the fractional distillation of petroleum, enhanced with a variety of additives. Some gasolines also contain...

 || 46.4 || 34.2 || ||
|-
|align=left|Diesel fuel/residential heating oil
Heating oil
Heating oil, or oil heat, is a low viscosity, flammable liquid petroleum product used as a fuel for furnaces or boilers in buildings. Home heating oil is often abbreviated as HHO...

 ||46.2||37.3|| ||
|-
|align=left|Nitromethane
Nitromethane
Nitromethane is an organic compound with the chemical formula . It is the simplest organic nitro compound. It is a slightly viscous, highly polar liquid commonly used as a solvent in a variety of industrial applications such as in extractions, as a reaction medium, and as a cleaning solvent...

 ||11.3|| || ||
|-
|align=left|Polyethylene
Polyethylene
Polyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons...

 plastic||46.3||42.6|| ||
|-
|align=left|Polypropylene
Polypropylene
Polypropylene , also known as polypropene, is a thermoplastic polymer used in a wide variety of applications including packaging, textiles , stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and polymer banknotes...

 plastic||46.4||41.7|| ||
|-
|align=left|100LL Avgas ||44.0||31.59|| ||
|-
|align=left|Gasohol E10 (10% ethanol 90% gasoline by volume)||43.54||33.18|| ||
|-
|align=left|Lithium
Lithium
Lithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number 3. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly...

 ||43.1||23.0|| ||
|-
|align=left|Jet A
Jet fuel
Jet fuel is a type of aviation fuel designed for use in aircraft powered by gas-turbine engines. It is clear to straw-colored in appearance. The most commonly used fuels for commercial aviation are Jet A and Jet A-1 which are produced to a standardized international specification...

 aviation fuel
Aviation fuel
Aviation fuel is a specialized type of petroleum-based fuel used to power aircraft. It is generally of a higher quality than fuels used in less critical applications, such as heating or road transport, and often contains additives to reduce the risk of icing or explosion due to high temperatures,...

/kerosene
Kerosene
Kerosene, sometimes spelled kerosine in scientific and industrial usage, also known as paraffin or paraffin oil in the United Kingdom, Hong Kong, Ireland and South Africa, is a combustible hydrocarbon liquid. The name is derived from Greek keros...

||42.8||33|| ||
|-
|align=left|Biodiesel
Biodiesel
Biodiesel refers to a vegetable oil- or animal fat-based diesel fuel consisting of long-chain alkyl esters. Biodiesel is typically made by chemically reacting lipids with an alcohol....

 oil (vegetable oil)||42.20||33|| ||
|-
|align=left|DMF
2,5-Dimethylfuran
2,5-Dimethylfuran is a heterocyclic compound with the formula 2C4H2O. Although often abbreviated DMF, it should not be confused with dimethylformamide. A derivative of furan, this simple compound is a potential biofuel, being derivable from cellulose.-Production:Fructose can be converted into...

 (2,5-dimethylfuran) ||42 ||37.8|| ||
|-
|align=left|Crude oil (according to the definition of ton of oil equivalent
Ton of oil equivalent
The tonne of oil equivalent is a unit of energy: the amount of energy released by burning one tonne of crude oil, approximately 42 GJ .The toe is sometimes used for large...

)||46.3||37|| ||
|-
|align=left|Polystyrene
Polystyrene
Polystyrene ) also known as Thermocole, abbreviated following ISO Standard PS, is an aromatic polymer made from the monomer styrene, a liquid hydrocarbon that is manufactured from petroleum by the chemical industry...

 plastic||41.4||43.5|| ||
|-
|align=left|Body fat metabolism
Fatty acid metabolism
Fatty acids are an important source of energy and adenosine triphosphate for many cellular organisms. Excess fatty acids, glucose, and other nutrients can be stored efficiently as fat. Triglycerides yield more than twice as much energy for the same mass as do carbohydrates or proteins. All cell...

||38||35|||22||
|-
|align=left|Butanol
Butanol fuel
Butanol may be used as a fuel in an internal combustion engine. Because its longer hydrocarbon chain causes it to be fairly non-polar, it is more similar to gasoline than it is to ethanol...

||36.6||29.2|| ||
|-
|align=left|Gasohol E85
E85
E85 is an abbreviation for an ethanol fuel blend of up to 85% denatured ethanol fuel and gasoline or other hydrocarbon by volume. E85 is commonly used by flex-fuel vehicles in the US, Canada, and Europe. Some of the benefits of E85 over conventional gasoline powered vehicles include the potential...

 (85% ethanol 10% gasoline by volume)||33.1||25.65|| ||
|-
|align=left|Graphite
Graphite
The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Ancient Greek γράφω , "to draw/write", for its use in pencils, where it is commonly called lead . Unlike diamond , graphite is an electrical conductor, a semimetal...

 ||32.7||72.9|| ||
|-
|align=left|Coal
Coal
Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...

, anthracite||32.5||72.4|| |||36
|-
|align=left|Silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...

  ||32.2||75.1|| ||
|-
|align=left|Aluminum ||31.0||83.8|| ||
|-
|align=left|Sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...

 (burned to Sulfur Dioxide
Sulfur dioxide
Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...

) ||9.23||19.11 ||
|-
|align=left|Ethanol
Ethanol
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...

||30||24|| ||
|-
|align=left|Polyester
Polyester
Polyester is a category of polymers which contain the ester functional group in their main chain. Although there are many polyesters, the term "polyester" as a specific material most commonly refers to polyethylene terephthalate...

 plastic||26.0 ||35.6|| ||
|-
|align=left|Magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...

 ||24.7||43.0|| ||
|-
|align=left|Coal
Coal
Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...

, bituminous ||24||20|| ||
|-
|align=left|PET
Polyethylene terephthalate
Polyethylene terephthalate , commonly abbreviated PET, PETE, or the obsolete PETP or PET-P, is a thermoplastic polymer resin of the polyester family and is used in synthetic fibers; beverage, food and other liquid containers; thermoforming applications; and engineering resins often in combination...

 plastic||23.5 (impure) || || ||
|-
|align=left|Methanol
Methanol
Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...

||19.7||15.6|| ||
|-
|align=left|Hydrazine
Hydrazine
Hydrazine is an inorganic compound with the formula N2H4. It is a colourless flammable liquid with an ammonia-like odor. Hydrazine is highly toxic and dangerously unstable unless handled in solution. Approximately 260,000 tons are manufactured annually...

 (toxic) combusted to N2+H2O||19.5||19.3|| ||
|-
|align=left|Liquid ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

 (combusted to N2+H2O)||18.6||11.5|| ||
|-
|align=left|PVC
PVC
Polyvinyl chloride is a plastic.PVC may also refer to:*Param Vir Chakra, India's highest military honor*Peripheral venous catheter, a small, flexible tube placed into a peripheral vein in order to administer medication or fluids...

 plastic (improper combustion toxic)||18.0||25.2|| ||
|-
|align=left|Peat
Peat
Peat is an accumulation of partially decayed vegetation matter or histosol. Peat forms in wetland bogs, moors, muskegs, pocosins, mires, and peat swamp forests. Peat is harvested as an important source of fuel in certain parts of the world...

 briquette
Briquette
A briquette is a block of flammable matter used as fuel to start and maintain a fire. Common types of briquettes are charcoal briquettes and biomass briquettes.-Constituents of charcoal briquettes:...

  ||17.7|| || ||
|-
|align=left|Sugars, carbohydrates, and protein metabolism
Fatty acid metabolism
Fatty acids are an important source of energy and adenosine triphosphate for many cellular organisms. Excess fatty acids, glucose, and other nutrients can be stored efficiently as fat. Triglycerides yield more than twice as much energy for the same mass as do carbohydrates or proteins. All cell...

||17||26.2(dextrose)|||2222 ||
|-
|align=left|Coal
Coal
Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...

, lignite
Lignite
Lignite, often referred to as brown coal, or Rosebud coal by Northern Pacific Railroad,is a soft brown fuel with characteristics that put it somewhere between coal and peat...

||14.0|| || ||
|-
|align=left|Calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

 ||15.9||24.6|| ||
|-
|align=left|Glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...

||15.55||23.9|| ||
|-
|align=left|Dry cowdung and cameldung||15.5 || || ||
|-
|align=left|Wood
Wood
Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...

 ||18.0 || || ||
|-
|align=left|Sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...

 (burned to wet sodium hydroxide)||13.3||12.8|| ||
|-
|align=left | Battery, lithium-air rechargeable
Lithium air battery
The lithium–air battery is a class of lithium battery that employs a cathode which relies on oxygen reduction forming a discharge product...

||9.0 || || ||
|-
|align=left|Household waste|||8.0|| || ||
|-
|align=left|Sod peat
Peat
Peat is an accumulation of partially decayed vegetation matter or histosol. Peat forms in wetland bogs, moors, muskegs, pocosins, mires, and peat swamp forests. Peat is harvested as an important source of fuel in certain parts of the world...

 ||12.8|| || ||
|-
|align=left|Sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...

 (burned to dry sodium oxide
Sodium oxide
Sodium oxide is a chemical compound with the formula Na2O. It is used in ceramics and glasses, though not in a raw form. Treatment with water affords sodium hydroxide....

)||9.1||8.8|| ||
|-
|align=left|Zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...

 ||5.3||38.0|| ||
|-
|align=left|Teflon plastic (combustion toxic, but flame retardant)||5.1||11.2|| ||
|-
|align=left|Iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

 (burned to iron(III) oxide
Iron(III) oxide
Iron oxide or ferric oxide is the inorganic compound with the formula Fe2O3. It is one of the three main oxides of iron, the other two being iron oxide , which is rare, and iron oxide , which also occurs naturally as the mineral magnetite. As the mineral known as hematite, Fe2O3 is the main...

)||5.2||40.68|| ||
|-
|align=left|Iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

 (burned to iron(II) oxide
Iron(II) oxide
Iron oxide, also known as ferrous oxide, is one of the iron oxides. It is a black-colored powder with the chemical formula . It consists of the chemical element iron in the oxidation state of 2 bonded to oxygen. Its mineral form is known as wüstite. Iron oxide should not be confused with rust,...

)||4.9||38.2|| ||
|-
| align=left | ANFO
ANFO
ANFO is a widely used bulk industrial explosive mixture. It consists of 94 percent porous prilled ammonium nitrate , that acts as the oxidizing agent and absorbent for the fuel — six percent Number 2 Fuel Oil...

 || 3.7 || ||
|-
|align=left | Battery, zinc-air
Zinc-air battery
Zinc–air batteries , and zinc–air fuel cells, are electro-chemical batteries powered by oxidizing zinc with oxygen from the air. These batteries have high energy densities and are relatively inexpensive to produce...

 || 1.59 || 6.02 || ||
|-
|align=left | Liquid nitrogen||0.77 || 0.62 || ||
|-
|align=left | Compressed air
Compressed air
Compressed air is air which is kept under a certain pressure, usually greater than that of the atmosphere. In Europe, 10 percent of all electricity used by industry is used to produce compressed air, amounting to 80 terawatt hours consumption per year....

 at 300 bar (potential energy) || 0.5 || 0.2 || || >50%
|-
|align=left|Latent heat of fusion
Enthalpy of fusion
The enthalpy of fusion is the change in enthalpy resulting from heating one mole of a substance to change its state from a solid to a liquid. The temperature at which this occurs is the melting point....

 of ice (thermal)||0.335||0.335|| ||
|-
|align=left|Water at 100 m dam height
Hydroelectricity
Hydroelectricity is the term referring to electricity generated by hydropower; the production of electrical power through the use of the gravitational force of falling or flowing water. It is the most widely used form of renewable energy...

 (potential energy)||0.001||0.001|| ||8585-90%
|- class="sortbottom"
!Storage type
!Energy density by mass (MJ/kg)
!Energy density by volume (MJ/L
Litér
- External links :*...

)
!Peak recovery efficiency %
!Practical recovery efficiency %
|}

Divide Joule
Joule
The joule ; symbol J) is a derived unit of energy or work in the International System of Units. It is equal to the energy expended in applying a force of one newton through a distance of one metre , or in passing an electric current of one ampere through a resistance of one ohm for one second...

 meter
Metre
The metre , symbol m, is the base unit of length in the International System of Units . Originally intended to be one ten-millionth of the distance from the Earth's equator to the North Pole , its definition has been periodically refined to reflect growing knowledge of metrology...

−3 with 109 to get MJ L
Litér
- External links :*...

−1.

Energy density of electric and magnetic fields


Electric
Electric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...

 and magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...

s store energy. In a vacuum, the (volumetric) energy density (in SI units) is given by


where E is the electric field
Electric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...

 and B is the magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...

. In the context of magnetohydrodynamics
Magnetohydrodynamics
Magnetohydrodynamics is an academic discipline which studies the dynamics of electrically conducting fluids. Examples of such fluids include plasmas, liquid metals, and salt water or electrolytes...

, the physics of conductive fluids, the magnetic energy density behaves like an additional pressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...

 that adds to the gas pressure of a plasma
Plasma (physics)
In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...

.

In normal (linear) substances, the energy density (in SI units) is


where D is the electric displacement field and H is the magnetizing field.

Energy density of empty space


In physics
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...

, "vacuum energy
Vacuum energy
Vacuum energy is an underlying background energy that exists in space even when the space is devoid of matter . The concept of vacuum energy has been deduced from the concept of virtual particles, which is itself derived from the energy-time uncertainty principle...

" or "zero-point energy
Zero-point energy
Zero-point energy is the lowest possible energy that a quantum mechanical physical system may have; it is the energy of its ground state. All quantum mechanical systems undergo fluctuations even in their ground state and have an associated zero-point energy, a consequence of their wave-like nature...

" is the volumetric energy density of empty space. More recent developments have expounded on the concept of energy in empty space.

Modern physics
Modern physics
The term modern physics refers to the post-Newtonian conception of physics. The term implies that classical descriptions of phenomena are lacking, and that an accurate, "modern", description of reality requires theories to incorporate elements of quantum mechanics or Einsteinian relativity, or both...

 is commonly classified into two fundamental theories: quantum field theory
Quantum field theory
Quantum field theory provides a theoretical framework for constructing quantum mechanical models of systems classically parametrized by an infinite number of dynamical degrees of freedom, that is, fields and many-body systems. It is the natural and quantitative language of particle physics and...

 and general relativity
General relativity
General relativity or the general theory of relativity is the geometric theory of gravitation published by Albert Einstein in 1916. It is the current description of gravitation in modern physics...

. Quantum field theory takes quantum mechanics
Quantum mechanics
Quantum mechanics, also known as quantum physics or quantum theory, is a branch of physics providing a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter. It departs from classical mechanics primarily at the atomic and subatomic...

 and special relativity
Special relativity
Special relativity is the physical theory of measurement in an inertial frame of reference proposed in 1905 by Albert Einstein in the paper "On the Electrodynamics of Moving Bodies".It generalizes Galileo's...

 into account, and it's a theory of all the forces and particles except gravity. General relativity is a theory of gravity, but it is incompatible with quantum mechanics. Currently these two theories have not yet been reconciled into one unified description, though research into "quantum gravity
Quantum gravity
Quantum gravity is the field of theoretical physics which attempts to develop scientific models that unify quantum mechanics with general relativity...

" and, more recently, stochastic electrodynamics
Stochastic electrodynamics
In theoretical physics, Stochastic Electrodynamics is a variant of Classical Electrodynamics which posits the existence of a classical Lorentz Invariant radiation field having statistical properties similar to that of the electromagnetic zero-point field of Quantum Electrodynamics...

, seeks to bridge this divide.

In general relativity
General relativity
General relativity or the general theory of relativity is the geometric theory of gravitation published by Albert Einstein in 1916. It is the current description of gravitation in modern physics...

, the cosmological constant
Cosmological constant
In physical cosmology, the cosmological constant was proposed by Albert Einstein as a modification of his original theory of general relativity to achieve a stationary universe...

 is proportional to the energy density of empty space, and can be measured by the curvature of space.

Quantum field theory considers the vacuum ground state not to be completely empty, but to consist of a seething mass of virtual particle
Virtual particle
In physics, a virtual particle is a particle that exists for a limited time and space. The energy and momentum of a virtual particle are uncertain according to the uncertainty principle...

s and fields
Field (physics)
In physics, a field is a physical quantity associated with each point of spacetime. A field can be classified as a scalar field, a vector field, a spinor field, or a tensor field according to whether the value of the field at each point is a scalar, a vector, a spinor or, more generally, a tensor,...

. These fields are quantified as probabilities—that is, the likelihood of manifestation based on conditions. Since these fields do not have a permanent existence, they are called vacuum fluctuations. In the Casimir effect
Casimir effect
In quantum field theory, the Casimir effect and the Casimir–Polder force are physical forces arising from a quantized field. The typical example is of two uncharged metallic plates in a vacuum, like capacitors placed a few micrometers apart, without any external electromagnetic field...

, two metal plates can cause a change in the vacuum energy density between them which generates a measurable force.

Some believe that vacuum energy might be the "dark energy
Dark energy
In physical cosmology, astronomy and celestial mechanics, dark energy is a hypothetical form of energy that permeates all of space and tends to accelerate the expansion of the universe. Dark energy is the most accepted theory to explain recent observations that the universe appears to be expanding...

" (also called Quintessence
Quintessence (physics)
In physics, quintessence is a hypothetical form of dark energy postulated as an explanation of observations of an accelerating universe. It has been proposed by some physicists to be a fifth fundamental force...

) associated with the cosmological constant in general relativity, thought to be similar to a negative force of gravity (or antigravity). Observations that the expanding universe appears to be accelerating seem to support the cosmic inflation
Cosmic inflation
In physical cosmology, cosmic inflation, cosmological inflation or just inflation is the theorized extremely rapid exponential expansion of the early universe by a factor of at least 1078 in volume, driven by a negative-pressure vacuum energy density. The inflationary epoch comprises the first part...

 theory—first proposed by Alan Guth
Alan Guth
Alan Harvey Guth is an American theoretical physicist and cosmologist. Guth has researched elementary particle theory...

 in 1981—in which the nascent universe passed through a phase of exponential expansion driven by a negative vacuum energy density (positive vacuum pressure).

See also


  • Power density
    Power density
    Power density is the amount of power per unit volume....

     and specifically
    • Power-to-weight ratio
      Power-to-weight ratio
      Power-to-weight ratio is a calculation commonly applied to engines and mobile power sources to enable the comparison of one unit or design to another. Power-to-weight ratio is a measurement of actual performance of any engine or power sources...

  • Orders of magnitude (specific energy density)
    Orders of magnitude (specific energy density)
    This is a table of specific energy densities by magnitude. Unless otherwise noted, these values assume standard ambient temperature and pressure....

  • 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...

  • Energy content of biofuel
    Energy content of biofuel
    - A table of energy content and CO2 output of common fuels :Energy is the ability to do work. Per kilogram of mass, different substances can do different amounts of work. Of course to do work we usually use a machine of some type. These machines vary in efficiency, or useful work done, and none...

  • 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...

  • Heating value
  • Rechargeable battery
    Rechargeable battery
    A rechargeable battery or storage battery is a group of one or more electrochemical cells. They are known as secondary cells because their electrochemical reactions are electrically reversible. Rechargeable batteries come in many different shapes and sizes, ranging anything from a button cell to...

  • Specific impulse
    Specific impulse
    Specific impulse is a way to describe the efficiency of rocket and jet engines. It represents the derivative of the impulse with respect to amount of propellant used, i.e., the thrust divided by the amount of propellant used per unit time. If the "amount" of propellant is given in terms of mass ,...

  • Vacuum energy
    Vacuum energy
    Vacuum energy is an underlying background energy that exists in space even when the space is devoid of matter . The concept of vacuum energy has been deduced from the concept of virtual particles, which is itself derived from the energy-time uncertainty principle...


Zero point energy

  1. Eric Weisstein's world of physics: energy density
  2. Baez physics: Is there a nonzero cosmological constant?
  3. Introductory review of cosmic inflation
  4. An exposition to inflationary cosmology

Density data

"Aircraft Fuels." Energy, Technology and the Environment Ed. Attilio Bisio. Vol. 1. New York: John Wiley and Sons, Inc., 1995. 257–259
  • Fuels of the Future for Cars and Trucks” - Dr. James J. Eberhardt - Energy Efficiency and Renewable Energy, U.S. Department of Energy - 2002 Diesel Engine Emissions Reduction (DEER) Workshop San Diego, California - August 25–29, 2002

Books

  • The Inflationary Universe: The Quest for a New Theory of Cosmic Origins by Alan H. Guth (1998) ISBN 0-201-32840-2
  • Cosmological Inflation and Large-Scale Structure by Andrew R. Liddle, David H. Lyth (2000) ISBN 0-521-57598-2
  • Richard Becker, "Electromagnetic Fields and Interactions", Dover Publications Inc., 1964