|SI unit||J/m 3|
|In SI base units||m−1⋅kg⋅s−2|
|U = E/V|
In physics, energy density is the amount of energy stored in a given system or region of space per unit volume. It may also be used for energy per unit mass, though a more accurate term for this is specific energy (or gravimetric energy density).
Often only the useful or extractable energy is measured, which is to say that inaccessible energy (such as rest mass energy) is ignored.In cosmological and other general relativistic contexts, however, the energy densities considered are those that correspond to the elements of the stress–energy tensor and therefore do include mass energy as well as energy densities associated with the pressures described in the next paragraph.
Energy per unit volume has the same physical units as pressure, and in many circumstances is a synonym: for example, the energy density of a 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 external pressure by the change in volume. A pressure gradient has the potential to perform work on the surroundings by converting internal energy to work until equilibrium is reached.
There are different types of energy stored in materials, and it takes a particular type of reaction to release each type of energy. In order of the typical magnitude of the energy released, these types of reactions are: nuclear, chemical, electrochemical, and electrical.
Nuclear reactions take place in stars and nuclear power plants, both of which derive energy from the binding energy of nuclei. Chemical reactions are used by animals to derive energy from food, and by automobiles to derive energy from gasoline. Liquid hydrocarbons (fuels such as gasoline, diesel and kerosene) are today the most dense way known to economically store and transport chemical energy at a large scale (1 kg of diesel fuel burns with the oxygen contained in ≈15 kg of air). Electrochemical reactions are used by most mobile devices such as laptop computers and mobile phones to release the energy from batteries.
There are several different types of energy content. One is the theoretical total amount of thermodynamic work that can be derived from a system, with a given temperature and pressure for the surroundings. This is called exergy. Another is the theoretical amount of work that can be derived from reactants that are initially at room temperature and atmospheric pressure. This is given by the change in standard Gibbs free energy. But as a source of heat or for use in a heat engine, the relevant quantity is the change in standard enthalpy or the heat of combustion.
There are two kinds of heat of combustion:
A convenient table of HHV and LHV of some fuels can be found in the references.
In energy storage applications the energy density relates the energy in an energy store to the volume of the storage facility, e.g. the fuel 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 of that fuel. In general an engine using that fuel will generate less kinetic energy due to inefficiencies and thermodynamic considerations—hence the specific fuel consumption of an engine will always be greater than its rate of production of the kinetic energy of motion.
Energy density differs from energy conversion efficiency (net output per input) or embodied energy (the energy output costs to provide, as harvesting, refining, distributing, and dealing with pollution all use energy). Large scale, intensive energy use impacts and is impacted by climate, waste storage, and environmental consequences.
No single energy storage method boasts the best in specific power, specific energy, and energy density. Peukert's law describes how the amount of useful energy that can be obtained (for a lead-acid cell) depends on how quickly it is pulled 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.
Alternative options are discussed for energy storage to increase energy density and decrease charging time.
The figure on the right shows the gravimetric and volumetric energy density of some fuels and storage technologies (modified from the Gasoline article).
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.
Generally the density values for chemical fuels do not include the weight of oxygen required for combustion. This is typically two oxygen atoms per carbon atom, and one per two hydrogen atoms. The atomic weight of carbon and oxygen are similar, while hydrogen is much lighter than oxygen. Figures are presented this way for those fuels where in practice air would only be drawn in locally to the burner. This explains the apparently lower energy density of materials that already include their own oxidizer (such as gunpowder and TNT), where the mass of the oxidizer in effect adds 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, such as the energy density of a sandwich appearing to be higher than that of a stick of dynamite.
This article or section appears to contradict itself.(April 2019)
The following unit conversions may be helpful when considering the data in the tables: 3.6 MJ = 1 kW⋅h ≈ 1.34 hp⋅h. Since 1 J = 10−6 MJ and 1 m3 = 103 L, divide joule/m 3 by 109 to get MJ/L = GJ/m3. Divide MJ/L by 3.6 to get kW⋅h/L.
|Antimatter||89,875,517,874 ≈ 90 PJ/kg||Depends on the density of the antimatter's form||24,965,421,631,578 ≈ 25 TW⋅h/kg||Depends on the density of the antimatter's form||Annihilation, counting both the consumed antimatter mass and ordinary matter mass|
|Hydrogen (fusion)||639,780,320 but at least 2% of this is lost to neutrinos.||Depends on conditions||177,716,755,600||Depends on conditions||Reaction 4H→4He|
| Deuterium (fusion)||571,182,758||Depends on conditions||158,661,876,600||Depends on conditions||Proposed fusion scheme for D+D→4He, by combining D+D→T+H, T+D→4He+n, n+H→D and D+D→3He+n, 3He+D→4He+H, n+H→D|
|Deuterium+tritium (fusion)||337,387,388||Depends on conditions||93,718,718,800||Depends on conditions||D + T → 4He + n|
|Lithium-6 deuteride (fusion)||268,848,415||Depends on conditions||74,680,115,100||Depends on conditions||6LiD → 24He|
Used in weapons.
|Plutonium-239||83,610,000||1,300,000,000–1,700,000,000 (Depends on crystallographic phase)||23,222,915,000||370,000,000,000–460,000,000,000 (Depends on crystallographic phase)||Heat produced in Fission reactor|
|Plutonium-239||31,000,000||490,000,000–620,000,000 (Depends on crystallographic phase)||8,700,000,000||140,000,000,000–170,000,000,000 (Depends on crystallographic phase)||Electricity produced in Fission reactor|
|Uranium||80,620,000||1,539,842,000||22,394,000,000||Heat produced in breeder reactor|
|Thorium||79,420,000||929,214,000||22,061,000,000||Heat produced in breeder reactor (Experimental)|
|Plutonium-238||2,239,000||43,277,631||621,900,000||Radioisotope thermoelectric generator. The heat is only produced at a rate of 0.57 W/g.|
Unless otherwise stated, the values in the following table are lower heating values for perfect combustion, not counting oxidizer mass or volume. When used to produce electricity in a fuel cell or to do work, it is the Gibbs free energy of reaction (ΔG) that sets the theoretical upper limit. If the produced H
2O is vapor, this is generally greater than the lower heat of combustion, whereas if the produced H
2O is liquid, it is generally less than the higher heat of combustion. But in the most relevant case of hydrogen, ΔG is 113 MJ/kg if water vapor is produced, and 118 MJ/kg if liquid water is produced, both being less than the lower heat of combustion (120 MJ/kg).
|Hydrogen, liquid||141.86 (HHV)|
|Energy figures apply after reheating to 25 °C. |
See note above about use in fuel cells.
|Hydrogen, gas (69 MPa, 25 °C)||141.86 (HHV)|
|Date from same reference as for liquid hydrogen. |
See note above about use in fuel cells.
|Hydrogen, gas (1 atm or 101.3 kPa, 25 °C)||141.86 (HHV)|
|Methane (101.3 kPa, 15 °C)||55.6||0.0378||15,444.5||10.5|
|LNG (NG at −160 °C)||53.6||22.2||14,888.9||6,166.7|
|CNG (NG compressed to 25 MPa ≈ 3600 psi)||53.6||9||14,888.9||2,500.0|
|Residential heating oil||46.2||37.3||12,833.3||10,361.1|
|Jet fuel (e.g. kerosene)||43||35||Aircraft engine|
|Gasohol E10 (10% ethanol 90% gasoline by volume)||43.54||33.18||12,094.5||9,216.7|
|Biodiesel oil (vegetable oil)||42.20||33||11,722.2||9,166.7|
|DMF (2,5-dimethylfuran)||42||37.8||11,666.7||10,500.0||[ clarification needed ]|
|Crude oil (tonne of oil equivalent)||41.868||37||11,630||10,278|
|Body fat||38||35||10,555.6||9,722.2||Metabolism in human body (22% efficiency )|
|Gasohol E85 (85% ethanol 15% gasoline by volume)||33.1||25.65[ citation needed ]||9,194.5||7,125.0|
|Coal, anthracite||26–33||34–43||7,222.2–9,166.7||9,444.5–11,944.5||Figures represent perfect combustion not counting oxidizer, but efficiency of conversion to electricity is ≈36%|
|Silicon||1.790||4.5||500||1,285||Energy stored through solid to liquid phase change of silicon|
|PET plastic (impure)||23.5||6,527.8|
|Hydrazine (combusted to N2+H2O)||19.5||19.3||5,416.7||5,361.1|
|Liquid ammonia (combusted to N2+H2O)||18.6||11.5||5,166.7||3,194.5|
|PVC plastic (improper combustion toxic)||18.0||25.2||5,000.0||7,000.0||[ clarification needed ]|
|Sugars, carbohydrates, and protein||17||26.2 (dextrose)||4,722.2||7,277.8||Metabolism in human body (22% efficiency )[ citation needed ]|
|Calcium||15.9||24.6||4,416.7||6,833.3||[ citation needed ]|
|Dry cow dung and camel dung||15.5||4,305.6|
|Coal, lignite||10–20||2,777.8–5,555.6||[ citation needed ]|
|Sodium||13.3||12.8||3,694.5||3,555.6||burned to wet sodium hydroxide|
|Sulfur||9.23||19.11||2,563.9||5,308.3||burned to sulfur dioxide|
|Sodium||9.1||8.8||2,527.8||2,444.5||burned to dry sodium oxide|
|Battery, lithium-air rechargeable||9.0||2,500.0||Controlled electric discharge|
|Iron||5.2||40.68||1,444.5||11,300.0||burned to iron(III) oxide|
|Teflon plastic||5.1||11.2||1,416.7||3,111.1||combustion toxic, but flame retardant|
|Iron||4.9||38.2||1,361.1||10,611.1||burned to iron(II) oxide|
|Battery, zinc-air||1.59||6.02||441.7||1,672.2||Controlled electric discharge|
|Liquid nitrogen||0.77||0.62||213.9||172.2||Maximum reversible work at 77.4 K with 300 K reservoir|
|Sodium sulfur battery||0.54–0.86||150–240|
|Compressed air at 30 MPa||0.5||0.2||138.9||55.6||Potential energy|
|Latent heat of fusion of ice[ citation needed ] (thermal)||0.33355||0.33355||93.1||93.1|
|Lithium metal battery||1.8||4.32||Controlled electric discharge|
|Lithium-ion battery||0.36–0.875||0.9–2.63||100.00–243.06||250.00–730.56||Controlled electric discharge|
|Alkaline battery||0.48||1.3||Controlled electric discharge|
|Nickel-metal hydride battery||0.41||0.504–1.46||Controlled electric discharge|
|Lead-acid battery||0.17||0.56||Controlled electric discharge|
|Supercapacitor (EDLC)||0.01–0.030||0.006–0.06||up to 8.57||Controlled electric discharge|
|Water at 100 m dam height||0.000981||0.000978||0.272||0.272||Figures represent potential energy, but efficiency of conversion to electricity is 85–90%|
|Electrolytic capacitor||0.00001–0.0002||0.00001–0.001||Controlled electric discharge|
The mechanical energy storage capacity, or resilience, of a Hookean material when it is deformed to the point of failure can be computed by calculating tensile strength times the maximum elongation dividing by two. The maximum elongation of a Hookean material can be computed by dividing stiffness of that material by its ultimate tensile strength. The following table lists these values computed using the Young's modulus as measure of stiffness:
|Material||Energy density by mass |
| Resilience: Energy density by volume |
| Density |
| Young's modulus |
|Tensile yield strength |
|Steel, ASTM A228 (yield, 1 mm diameter)||1,440–1,770||11,200–13,800||7.80||210||2,170–2,410|
|Copper Beryllium 25-1/2 HT (yield)||684||5,720||8.36||131||1,224|
|ABS plastics||241–534||258–571||1.07||1.4–3.1||40 (ultimate)|
|Aluminium 7077-T8 (yield)||399||1120||2.81||71.0||400|
|Steel, stainless, 301-H (yield)||301||2,410||8.0||193||965|
|Aluminium 6061-T6 (yield @ 24 °C)||205||553||2.70||68.9||276|
|Epoxy resins||113–1810||2–3||26–85 (ultimate)|
|Douglas fir Wood||158–200||96||.481–.609||13||50 (compression)|
|Steel, Mild AISI 1018||42.4||334||7.87||205||370 (440 Ultimate)|
|Aluminium (not alloyed)||32.5||87.7||2.70||69||110 (ultimate)|
|Pine (American Eastern White, flexural)||31.8–32.8||11.1–11.5||.350||8.30–8.56 (flexural)||41.4 (flexural)|
|Storage device||Energy content|
(diameter × height in mm)
|Typical volume (mL)||Energy density|
by volume (MJ/L)
by mass (MJ/kg)
|Alkaline AA battery||9,360||2.6||Electrochemical||24||14.2 × 50||7.92||1.18||0.39|
|Alkaline C battery||34,416||9.5||Electrochemical||65||26 × 46||24.42||1.41||0.53|
|NiMH AA battery||9,072||2.5||Electrochemical||26||14.2 × 50||7.92||1.15||0.35|
|NiMH C battery||19,440||5.4||Electrochemical||82||26 × 46||24.42||0.80||0.24|
|Lithium-ion 18650 battery||28,800–46,800||10.5–13||Electrochemical||44–49||18 × 65||16.54||1.74–2.83||0.59–1.06|
The greatest energy source by far is 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 (0.1%), nuclear fusion (1%), or the annihilation of some or all of the matter in the volume V by matter-antimatter collisions (100%).[ citation needed ] Nuclear reactions cannot be realized by chemical reactions such as combustion. Although greater matter densities can be achieved, the density of a neutron star would approximate the most dense system capable of matter-antimatter annihilation possible. A black hole, although denser than a neutron star, does not have an equivalent anti-particle form, but would offer the same 100% conversion rate of mass to energy in the form of Hawking radiation. In the case of relatively small black holes (smaller than astronomical objects) the power output would be tremendous.
The highest density sources of energy aside from antimatter are fusion and fission. Fusion includes energy from the sun which will be available for billions of years (in the form of sunlight) but so far (2021), sustained fusion power production continues to be elusive.
Power from fission of uranium and thorium in nuclear power plants will be available for many decades or even centuries because of the plentiful supply of the elements on earth,though the full potential of this source can only be realized through breeder reactors, which are, apart from the BN-600 reactor, not yet used commercially. Coal, gas, and petroleum are the current primary energy sources in the U.S. but have a much lower energy density. Burning local biomass fuels supplies household energy needs (cooking fires, oil lamps, etc.) worldwide.
The density of thermal energy contained in the core of a light water reactor (PWR or BWR) of typically 1 GWe (1 000 MW electrical corresponding to ≈3 000 MW thermal) is in the range of 10 to 100 MW of thermal energy per cubic meter of cooling water depending on the location considered in the system (the core itself (≈30 m3), the reactor pressure vessel (≈50 m3), or the whole primary circuit (≈300 m3)). This represents a considerable density of energy which requires under all circumstances a continuous water flow at high velocity in order to be able to remove the heat from the core, even after an emergency shutdown of the reactor. The incapacity to cool the cores of three boiling water reactors (BWR) at Fukushima in 2011 after the tsunami and the resulting loss of the external electrical power and of the cold source was the cause of the meltdown of the three cores in only a few hours, even though the three reactors were correctly shut down just after the Tōhoku earthquake. This extremely high power density distinguishes nuclear power plants (NPP's) from any thermal power plants (burning coal, fuel or gas) or any chemical plants and explains the large redundancy required to permanently control the neutron reactivity and to remove the residual heat from the core of NPP's.
Electric and magnetic fields store energy. In a vacuum, the (volumetric) energy density is given by
where E is the electric field and B is the magnetic field. The solution will be (in SI units) in Joules per cubic metre. In the context of magnetohydrodynamics, the physics of conductive fluids, the magnetic energy density behaves like an additional pressure that adds to the gas pressure of a plasma.
In normal (linear and nondispersive) substances, the energy density (in SI units) is
where D is the electric displacement field and H is the magnetizing field.
In the case of absence of magnetic fields, by exploiting Fröhlich's relationships it is also possible to extend these equations to anisotropic and nonlinear dielectrics, as well as to calculate the correlated Helmholtz free energy and entropy densities.
When a pulsed laser impacts a surface, the radiant exposure, i.e. the energy deposited per unit of surface, may be called energy density or fluence.
properly trained athlete will have efficiencies of 22 to 26%
The Higher Heating Values are 22.7, 29.7 or 31.7 MJ/kg for methanol, ethanol and DME, respectively, while gasoline contains about 45 MJ per kg.
Let ε = 0.85, signifying an 85% efficiency rating, typical of an older powerplant.
Energy storage is the capture of energy produced at one time for use at a later time to reduce imbalances between energy demand and energy production. A device that stores energy is generally called an accumulator or battery. Energy comes in multiple forms including radiation, chemical, gravitational potential, electrical potential, electricity, elevated temperature, latent heat and kinetic. Energy storage involves converting energy from forms that are difficult to store to more conveniently or economically storable forms.
Liquid hydrogen (LH2 or LH2) is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H2 form.
A combined cycle power plant is an assembly of heat engines that work in tandem from the same source of heat, converting it into mechanical energy. On land, when used to make electricity the most common type is called a combined cycle gas turbine (CCGT) plant. The same principle is also used for marine propulsion, where it is called a combined gas and steam (COGAS) plant. Combining two or more thermodynamic cycles improves overall efficiency, which reduces fuel costs.
Alternative fuel, known as non-conventional and advanced fuels, are any materials or substances that can be used as fuels, other than conventional fuels like; fossil fuels, as well as nuclear materials such as uranium and thorium, as well as artificial radioisotope fuels that are made in nuclear reactors.
The hydrogen economy is an envisioned future in which hydrogen is used as a fuel for heat and hydrogen vehicles, for energy storage, and for long distance transport of energy. In order to phase out fossil fuels and limit global warming, hydrogen can be created from water using intermittent renewal sources such as wind and solar, and its combustion only releases water vapor to the atmosphere.
Hydrogen fuel is a zero carbon fuel burned with oxygen. It can be used in fuel cells or internal combustion engines. Regarding hydrogen vehicles, hydrogen has begun to be used in commercial fuel cell vehicles, such as passenger cars, and has been used in fuel cell buses for many years. It is also used as a fuel for spacecraft propulsion.
The heating value of a substance, usually a fuel or food, is the amount of heat released during the combustion of a specified amount of it.
A fossil fuel power station is a thermal power station which burns a fossil fuel, such as coal or natural gas, to produce electricity. Fossil fuel power stations have machinery to convert the heat energy of combustion into mechanical energy, which then operates an electrical generator. The prime mover may be a steam turbine, a gas turbine or, in small plants, a reciprocating gas engine. All plants use the energy extracted from expanding gas, either steam or combustion gases. Although different energy conversion methods exist, all thermal power station conversion methods have efficiency limited by the Carnot efficiency and therefore produce waste heat.
Grid energy storage is a collection of methods used for energy storage on a large scale within an electrical power grid. Electrical energy is stored during times when electricity is plentiful and inexpensive or when demand is low, and later returned to the grid when demand is high, and electricity prices tend to be higher.
Nuclear fuel is material used in nuclear power stations to produce heat to power turbines. Heat is created when nuclear fuel undergoes nuclear fission.
A thermal power station is a power station in which heat energy is converted to electricity. Typically, water is heated into steam, which is used to drive an electrical generator. After it passes through the turbine the steam is condensed in a steam condenser and recycled to where it was heated. This is known as a Rankine cycle. The greatest variation in the design of thermal power stations is due to the different heat sources: fossil fuel, nuclear energy, solar energy, biofuels, and waste incineration are all used. Certain thermal power stations are also designed to produce heat for industrial purposes, for district heating, or desalination of water, in addition to generating electrical power.
A sodium-cooled fast reactor is a fast neutron reactor cooled by liquid sodium.
The energy content of biofuel is a description of the chemical energy contained in a given biofuel, measured per unit mass of that fuel, as specific energy, or per unit of volume of the fuel, as energy density. A biofuel is a fuel, produced from living organisms. Biofuels include bioethanol, an alcohol made by fermentation—often used as a gasoline additive, and biodiesel, which is usually used as a diesel additive. Specific energy is energy per unit mass, which is used to describe the energy content of a fuel, expressed in SI units as joule per kilogram (J/kg) or equivalent units. Energy density is the amount of energy stored in a fuel per unit volume, expressed in SI units as joule per litre (J/L) or equivalent units.
A load following power plant, regarded as producing mid-merit or mid-priced electricity, is a power plant that adjusts its power output as demand for electricity fluctuates throughout the day. Load following plants are typically in-between base load and peaking power plants in efficiency, speed of start up and shut down, construction cost, cost of electricity and capacity factor.
The Glossary of fuel cell terms lists the definitions of many terms used within the fuel cell industry. The terms in this fuel cell glossary may be used by fuel cell industry associations, in education material and fuel cell codes and standards to name but a few.
Energy technology is an interdisciplinary engineering science having to do with the efficient, safe, environmentally friendly, and economical extraction, conversion, transportation, storage, and use of energy, targeted towards yielding high efficiency whilst skirting side effects on humans, nature, and the environment.
A fuel is any material that can be made to react with other substances so that it releases energy as heat energy or to be used for work. The concept was originally applied solely to those materials capable of releasing chemical energy but has since also been applied to other sources of heat energy such as nuclear energy.
A supercapacitor (SC), also called an ultracapacitor, is a high-capacity capacitor with a capacitance value much higher than other capacitors, but with lower voltage limits, that bridges the gap between electrolytic capacitors and rechargeable batteries. It typically stores 10 to 100 times more energy per unit volume or mass than electrolytic capacitors, can accept and deliver charge much faster than batteries, and tolerates many more charge and discharge cycles than rechargeable batteries.
Moorside clean energy hub is a proposal put forward on 30 June 2020 by two consortia, one led by EDF and the other by Rolls-Royce, to create an energy hub that would produce electricity and hydrogen through the use of nuclear power and renewable energy.