Portal:Energy

Introduction

The Sun is the source of energy for most of life on Earth. As a star, the Sun is heated to high temperatures by the conversion of nuclear binding energy due to the fusion of hydrogen in its core. This energy is ultimately transferred (released) into space mainly in the form of radiant (light) energy.

In physics, energy is the quantitative property that must be transferred to an object in order to perform work on, or to heat, the object. Energy is a conserved quantity; the law of conservation of energy states that energy can be converted in form, but not created or destroyed. The SI unit of energy is the joule, which is the energy transferred to an object by the work of moving it a distance of 1 metre against a force of 1 newton.

Common forms of energy include the kinetic energy of a moving object, the potential energy stored by an object's position in a force field (gravitational, electric or magnetic), the elastic energy stored by stretching solid objects, the chemical energy released when a fuel burns, the radiant energy carried by light, and the thermal energy due to an object's temperature.

Selected general articles

• 

  ' covers subjects of energy and electricity production. consumption and import/export and other energy related issues in Asia. '
• 

  

  
  In physics, the kinetic energy of an object is the energy that 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. The same amount of work is done by the body when decelerating from its current speed to a state of rest.
  
  In classical mechanics, the kinetic energy of a non-rotating object of mass m traveling at a speed v is ${\begin{smallmatrix}{\frac {1}{2}}mv^{2}\end{smallmatrix}}$. In relativistic mechanics, this is a good approximation only when v is much less than the speed of light. Read more...
• 

  In relativistic classical field theories of gravitation, particularly general relativity, an energy condition is one of various alternative conditions which can be applied to the matter content of the theory, when it is either not possible or desirable to specify this content explicitly. The hope is then that any reasonable matter theory will satisfy this condition or at least will preserve the condition if it is satisfied by the starting conditions.
  
  In general relativity, energy conditions are often used (and required) in proofs of various important theorems about black holes, such as the no hair theorem or the laws of black hole thermodynamics. Read more...
• 

  

  The Sun is the source of energy for most of life on Earth. As a star, the Sun is heated to high temperatures by the conversion of nuclear binding energy due to the fusion of hydrogen in its core. This energy is ultimately transferred (released) into space mainly in the form of radiant (light) energy.

  
  In physics, energy is the quantitative property that must be transferred to an object in order to perform work on, or to heat, the object. Energy is a conserved quantity; the law of conservation of energy states that energy can be converted in form, but not created or destroyed. The SI unit of energy is the joule, which is the energy transferred to an object by the work of moving it a distance of 1 metre against a force of 1 newton.
  
  Common forms of energy include the kinetic energy of a moving object, the potential energy stored by an object's position in a force field (gravitational, electric or magnetic), the elastic energy stored by stretching solid objects, the chemical energy released when a fuel burns, the radiant energy carried by light, and the thermal energy due to an object's temperature. Read more...
• 

  Energy development is the field of activities focused on obtaining sources of energy from natural resources. These activities include production of conventional, alternative and renewable sources of energy, and for the recovery and reuse of energy that would otherwise be wasted. Energy conservation and efficiency measures reduce the demand for energy development, and can have benefits to society with improvements to environmental issues.
  
  Societies use energy for transportation, manufacturing, illumination, heating and air conditioning, and communication, for industrial, commercial, and domestic purposes. Energy resources may be classified as primary resources, where the resource can be used in substantially its original form, or as secondary resources, where the energy source must be converted into a more conveniently usable form. Non-renewable resources are significantly depleted by human use, whereas renewable resources are produced by ongoing processes that can sustain indefinite human exploitation. Read more...
• 

  

  The Sun and Earth form an ongoing example of a heating process. Some of the Sun's thermal radiation strikes and heats the Earth. Compared to the Sun, Earth has a much lower temperature and so sends far less thermal radiation back to the Sun. The heat of this process can be quantified by the net amount, and direction (Sun to Earth), of energy it transferred in a given period of time.

  
  
  In thermodynamics, heat is energy in transfer to or from a thermodynamic system, by mechanisms other than thermodynamic work or transfer of matter. The mechanisms include conduction, through direct contact of immobile bodies, or through a wall or barrier that is impermeable to matter; or radiation between separated bodies; or isochoric mechanical work done by the surroundings on the system of interest; or Joule heating by an electric current driven through the system of interest by an external system; or a combination of these. When there is a suitable path between two systems with different temperatures, heat transfer occurs necessarily, immediately, and spontaneously from the hotter to the colder system. Thermal conduction occurs by the stochastic (random) motion of microscopic particles (such as atoms or molecules). In contrast, thermodynamic work is defined by mechanisms that act macroscopically and directly on the system's whole-body state variables; for example, change of the system's volume through a piston's motion with externally measurable force; or change of the system's internal electric polarization through an externally measurable change in electric field. The definition of heat transfer does not require that the process be in any sense smooth. For example, a bolt of lightning may transfer heat to a body.
  
  Convective circulation allows one body to heat another, through an intermediate circulating fluid that carries energy from a boundary of one to a boundary of the other; the actual heat transfer is by conduction and radiation between the fluid and the respective bodies. Though spontaneous, convective circulation does not necessarily and immediately occur merely because of temperature difference; for it to occur in a given arrangement of systems, there is a threshold temperature difference that needs to be exceeded. Read more...
• 

  

  Liquid helium retains kinetic energy and does not freeze regardless of temperature due to zero-point energy. When cooled below its Lambda point, it exhibits properties of superfluidity

  
  Zero-point energy (ZPE) is the difference between the lowest possible energy that a quantum mechanical system may have, and the classical minimum energy of the system. Unlike in classical mechanics, quantum systems constantly fluctuate in their lowest energy state due to the Heisenberg uncertainty principle. As well as atoms and molecules, the empty space of the vacuum has these properties. According to quantum field theory, the universe can be thought of not as isolated particles but continuous fluctuating fields: matter fields, whose quanta are fermions (i.e. leptons and quarks), and force fields, whose quanta are bosons (e.g. photons and gluons). All these fields have zero-point energy. These fluctuating zero-point fields lead to a kind of reintroduction of an aether in physics, since some systems can detect the existence of this energy. However this aether cannot be thought of as a physical medium if it is to be Lorentz invariant such that there is no contradiction with Einstein's theory of special relativity.
  
  Physics currently lacks a full theoretical model for understanding zero-point energy; in particular the discrepancy between theorized and observed vacuum energy is a source of major contention. Physicists Richard Feynman and John Wheeler calculated the zero-point radiation of the vacuum to be an order of magnitude greater than nuclear energy, with a single light bulb containing enough energy to boil all the world's oceans. Yet according to Einstein's theory of general relativity any such energy would gravitate and the experimental evidence from both the expansion of the universe, dark energy and the Casimir effect show any such energy to be exceptionally weak. A popular proposal that attempts to address this issue is to say that the fermion field has a negative zero-point energy while the boson field has positive zero-point energy and thus these energies somehow cancel each other out. This idea would be true if supersymmetry were an exact symmetry of nature. However, the LHC at CERN has so far found no evidence to support supersymmetry. Moreover, it is known that if supersymmetry is valid at all, it is at most a broken symmetry, only true at very high energies, and no one has been able to show a theory where zero-point cancellations occur in the low energy universe we observe today. This discrepancy is known as the cosmological constant problem and it is one of the greatest unsolved mysteries in physics. Many physicists believe that "the vacuum holds the key to a full understanding of nature". Read more...
• 

  

  Typical shape of an interatomic pair potential.

  
  Interatomic potentials are mathematical functions for calculating the potential energy of a system of atoms with given positions in space. Interatomic potentials are widely used as the physical basis of molecular mechanics and molecular dynamics simulations in chemistry, molecular physics and materials physics, sometimes in connection with such effects as cohesion, thermal expansion and elastic properties of materials. Read more...
• 

  

  Anacortes Refinery (Marathon), on the north end of March Point southeast of Anacortes, Washington, United States

  
  Oil refinery or petroleum refinery is an industrial process plant where crude oil is transformed and refined into more useful products such as petroleum naphtha, gasoline, diesel fuel, asphalt base, heating oil, kerosene, liquefied petroleum gas, jet fuel and fuel oils. Petrochemicals feed stock like ethylene and propylene can also be produced directly by cracking crude oil without the need of using refined products of crude oil such as naphtha.
  
  Oil refineries are typically large, sprawling industrial complexes with extensive piping running throughout, carrying streams of fluids between large chemical processing units, such as distillation columns. In many ways, oil refineries use much of the technology of, and can be thought of, as types of chemical plants. Read more...
• 

  

  An example of a mechanical system: A satellite is orbiting the Earth influenced only by the conservative gravitational force; its mechanical energy is therefore conserved. The satellite’s acceleration is represented by the green vector and its velocity is represented by the red vector. If the satellite’s orbit is an ellipse the potential energy of the satellite, and its kinetic energy, both vary with time but their sum remains constant.

  
  In physical sciences, mechanical energy is the sum of potential energy and kinetic energy. It is the energy associated with the motion and position of an object. The principle of conservation of mechanical energy states that in an isolated system that is only subject to conservative forces, the mechanical energy is constant. If an object is moved in the opposite direction of a conservative net force, the potential energy will increase and if the speed (not the velocity) of the object is changed, the kinetic energy of the object is changed as well. In all real systems, however, nonconservative forces, like frictional forces, will be present, but often they are of negligible values and the mechanical energy's being constant can therefore be a useful approximation. In elastic collisions, the mechanical energy is conserved but in inelastic collisions, some mechanical energy is converted into heat. The equivalence between lost mechanical energy (dissipation) and an increase in temperature was discovered by James Prescott Joule.
  
  Many devices are used to convert mechanical energy to or from other forms of energy, e.g. an electric motor converts electrical energy to mechanical energy, an electric generator converts mechanical energy into electrical energy and a steam engine converts heat energy to mechanical energy. Read more...
• 

  

  A Stirling engine capable of producing electricity from biomass combustion heat

  
  Bioenergy is renewable energy made available from materials derived from biological sources. Biomass is any organic material which has stored sunlight in the form of chemical energy. As a fuel it may include wood, wood waste, straw, and other crop residues, manure, sugarcane, and many other by-products from a variety of agricultural processes. By 2010, there was 35 GW (47,000,000 hp) of globally installed bioenergy capacity for electricity generation, of which 7 GW (9,400,000 hp) was in the United States.
  
  In its most narrow sense it is a synonym to biofuel, which is fuel derived from biological sources. In its broader sense it includes biomass, the biological material used as a biofuel, as well as the social, economic, scientific and technical fields associated with using biological sources for energy. This is a common misconception, as bioenergy is the energy extracted from the biomass, as the biomass is the fuel and the bioenergy is the energy contained in the fuel Read more...
• 

  

  Annotated color version of the original 1824 Carnot heat engine showing the hot body (boiler), working body (system, steam), and cold body (water), the letters labeled according to the stopping points in Carnot cycle.

  
  Thermodynamics is the branch of physics that has to do with heat and temperature and their relation to energy and work. The behavior of these quantities is governed by the four laws of thermodynamics, irrespective of the composition or specific properties of the material or system in question. The laws of thermodynamics are explained in terms of microscopic constituents by statistical mechanics. Thermodynamics applies to a wide variety of topics in science and engineering, especially physical chemistry, chemical engineering and mechanical engineering.
  
  Historically, thermodynamics developed out of a desire to increase the efficiency of early steam engines, particularly through the work of French physicist Nicolas Léonard Sadi Carnot (1824) who believed that engine efficiency was the key that could help France win the Napoleonic Wars. Scots-Irish physicist Lord Kelvin was the first to formulate a concise definition of thermodynamics in 1854 which stated, "Thermo-dynamics is the subject of the relation of heat to forces acting between contiguous parts of bodies, and the relation of heat to electrical agency." Read more...
• 

  Energy conservation is the effort made to reduce the consumption of energy by using less of an energy service. This can be achieved either by using energy more efficiently (using less energy for a constant service) or by reducing the amount of service used (for example, by driving less). Energy conservation is a part of the concept of eco-sufficiency. Energy conservation reduces the need for energy services and can result in increased environmental quality, national security, personal financial security and higher savings.
  It is at the top of the sustainable energy hierarchy.
  It also lowers energy costs by preventing future resource depletion.
  
  Energy can be conserved by reducing wastage and losses, improving efficiency through technological upgrades and improved operation and maintenance. On a global level energy use can also be reduced by the stabilisation of population growth. Read more...
• 

  High-altitude wind power (HAWP) is the harnessing of the power of winds high in the sky by use of tether and cable technology. An atlas of the high-altitude wind power resource has been prepared for all points on Earth. A similar atlas of global assessment was developed at Joby Energy. The results were presented at the first annual Airborne Wind Energy Conference held at Stanford University by Airborne Wind Energy Consortium.
  
  Various mechanisms are proposed for capturing the kinetic energy of winds such as kites, kytoons, aerostats, gliders, gliders with turbines for regenerative soaring, sailplanes with turbines, or other airfoils, including multiple-point building- or terrain-enabled holdings. Once the mechanical energy is derived from the wind's kinetic energy, then many options are available for using that mechanical energy: direct traction, conversion to electricity aloft or at ground station, conversion to laser or microwave for power beaming to other aircraft or ground receivers. Energy generated by a high-altitude system may be used aloft or sent to the ground surface by conducting cables, mechanical force through a tether, rotation of endless line loop, movement of changed chemicals, flow of high-pressure gases, flow of low-pressure gases, or laser or microwave power beams. Read more...
• 

  Binding energy (also called separation energy) is the minimum energy required to disassemble a system of particles into separate parts. This energy is equal to the mass defect - the amount of energy, or mass, that is released when a bound system (which typically has a lower potential energy than the sum of its constituent parts) is created, and is what keeps the system together. If the energy supplied is more than the binding energy, then the disassembled constituents possess non-zero kinetic energy. Read more...
• 

  Energy consumption is the amount of energy or power used. Read more...
• 

  Quantum thermodynamics is the study of the relations between two independent physical theories: thermodynamics and quantum mechanics. The two independent theories address the physical phenomena of light and matter.
  In 1905 Einstein argued that the requirement of consistency between thermodynamics and electromagnetism leads to the conclusion that light is quantized obtaining the relation $E=h\nu$. This paper is the dawn of quantum theory. In a few decades
  quantum theory became established with an independent set of rules. Currently quantum thermodynamics addresses the emergence of thermodynamic laws from quantum mechanics.
  It differs from quantum statistical mechanics in the emphasis on dynamical processes out of equilibrium.
  In addition there is a quest for the theory to be relevant for a single individual quantum system. Read more...
• 

  Quantum chromodynamics binding energy (QCD binding energy), gluon binding energy or chromodynamic binding energy is the energy binding quarks together into hadrons. It is the energy of the field of the strong force, which is mediated by gluons. QCD binding energy contributes most of the hadron's mass. Read more...
• 

  A thermodynamic free entropy is an entropic thermodynamic potential analogous to the free energy. Also known as a Massieu, Planck, or Massieu–Planck potentials (or functions), or (rarely) free information. In statistical mechanics, free entropies frequently appear as the logarithm of a partition function. The Onsager reciprocal relations in particular, are developed in terms of entropic potentials. In mathematics, free entropy means something quite different: it is a generalization of entropy defined in the subject of free probability.
  
  A free entropy is generated by a Legendre transformation of the entropy. The different potentials correspond to different constraints to which the system may be subjected. Read more...
• 

  

  The Three Gorges Dam in China; the hydroelectric dam is the world's largest power station by installed capacity.

  
  Hydropower or water power (from Greek: ὕδωρ, "water") is power derived from the energy of falling water or fast running water, which may be harnessed for useful purposes. Since ancient times, hydropower from many kinds of watermills has been used as a renewable energy source for irrigation and the operation of various mechanical devices, such as gristmills, sawmills, textile mills, trip hammers, dock cranes, domestic lifts, and ore mills. A trompe, which produces compressed air from falling water, is sometimes used to power other machinery at a distance.
  
  In the late 19th century, hydropower became a source for generating electricity. Cragside in Northumberland was the first house powered by hydroelectricity in 1878 and the first commercial hydroelectric power plant was built at Niagara Falls in 1879. In 1881, street lamps in the city of Niagara Falls were powered by hydropower. Read more...
• 

  Cogeneration or combined heat and power (CHP) is the use of a heat engine or power station to generate electricity and useful heat at the same time. Trigeneration or combined cooling, heat and power (CCHP) refers to the simultaneous generation of electricity and useful heating and cooling from the combustion of a fuel or a solar heat collector. The terms cogeneration and trigeneration can be also applied to the power systems generating simultaneously electricity, heat, and industrial chemicals – e.g., syngas or pure hydrogen (article: combined cycles, chapter: natural gas integrated power & syngas (hydrogen) generation cycle).
  
  Cogeneration is a more efficient use of fuel because otherwise wasted heat from electricity generation is put to some productive use. Combined heat and power (CHP) plants recover otherwise wasted thermal energy for heating. This is also called combined heat and power district heating. Small CHP plants are an example of decentralized energy. By-product heat at moderate temperatures (100–180 °C, 212–356 °F) can also be used in absorption refrigerators for cooling. Read more...
• 

  Sound is transmitted through gases, plasma, and liquids as longitudinal waves, also called compression waves. It requires a medium to propagate. Through solids, however, it can be transmitted as both longitudinal waves and transverse waves. Longitudinal sound waves are waves of alternating pressure deviations from the equilibrium pressure, causing local regions of compression and rarefaction, while transverse waves (in solids) are waves of alternating shear stress at right angle to the direction of propagation.
  
  Sound waves may be "viewed" using parabolic mirrors and objects that produce sound. Read more...
• 

  Two physical systems are in thermal equilibrium if there is no net flow of thermal energy between them when they are connected by a path permeable to heat. Thermal equilibrium obeys the zeroth law of thermodynamics. A system is said to be in thermal equilibrium with itself if the temperature within the system is spatially uniform and temporally constant.
  
  Systems in thermodynamic equilibrium are always in thermal equilibrium, but the converse is not always true. If the connection between the systems allows transfer of energy as heat but does not allow transfer of matter or transfer of energy as work, the two systems may reach thermal equilibrium without reaching thermodynamic equilibrium. Read more...
• 

  

  Physical components of a generic energy system supplying fuels and electricity (but not district heat) to end-users

  
  
  An energy system is a system primarily designed to supply energy-services to end-users. Taking a structural viewpoint, the IPCC Fifth Assessment Report defines an energy system as "all components related to the production, conversion, delivery, and use of energy". The field of energy economics includes energy markets and treats an energy system as the technical and economic systems that satisfy consumer demand for energy in the forms of heat, fuels, and electricity.
  
  The first two definitions allow for demand-side measures, including daylighting, retrofitted building insulation, and passive solar building design, as well as socio-economic factors, such as aspects of energy demand management and even telecommuting, while the third does not. Neither does the third account for the informal economy in traditional biomass that is significant in many developing countries. Read more...
• 

  Natural uranium (NU, U_nat) refers to uranium with the same isotopic ratio as found in nature. It contains 0.711% uranium-235, 99.284% uranium-238, and a trace of uranium-234 by weight (0.0055%). Approximately 2.2% of its radioactivity comes from uranium-235, 48.6% from uranium-238, and 49.2% from uranium-234.
  
  Natural uranium can be used to fuel both low- and high-power nuclear reactors. Historically, graphite-moderated reactors and heavy water-moderated reactors have been fueled with natural uranium in the pure metal (U) or uranium dioxide (UO₂) ceramic forms. However, experimental fuelings with uranium trioxide (UO₃) and triuranium octaoxide, (U₃O₈) have shown promise. Read more...
• 

  In physics, quintessence is a hypothetical form of dark energy, more precisely a scalar field, postulated as an explanation of the observation of an accelerating rate of expansion of the universe. The first example of this scenario was proposed by Ratra and Peebles (1988). The concept was expanded to more general types of time-varying dark energy and the term "quintessence" was first introduced in a paper by Robert R. Caldwell, Rahul Dave and Paul Steinhardt.
  It has been proposed by some physicists to be a fifth fundamental force. Quintessence differs from the cosmological constant explanation of dark energy in that it is dynamic; that is, it changes over time, unlike the cosmological constant which, by definition, does not change.
  It is suggested that quintessence can be either attractive or repulsive depending on the ratio of its kinetic and potential energy. Those working with this postulate believe that quintessence became repulsive about ten billion years ago, about 3.5 billion years after the Big Bang. Read more...
• 

  Thermodynamic equilibrium is an axiomatic concept of thermodynamics. It is an internal state of a single thermodynamic system, or a relation between several thermodynamic systems connected by more or less permeable or impermeable walls. In thermodynamic equilibrium there are no net macroscopic flows of matter or of energy, either within a system or between systems. In a system in its own state of internal thermodynamic equilibrium, no macroscopic change occurs. Systems in mutual thermodynamic equilibrium are simultaneously in mutual thermal, mechanical, chemical, and radiative equilibria. Systems can be in one kind of mutual equilibrium, though not in others. In thermodynamic equilibrium, all kinds of equilibrium hold at once and indefinitely, until disturbed by a thermodynamic operation. In a macroscopic equilibrium, almost or perfectly exactly balanced microscopic exchanges occur; this is the physical explanation of the notion of macroscopic equilibrium.
  
  A thermodynamic system in its own state of internal thermodynamic equilibrium has a spatially uniform temperature. Its intensive properties, other than temperature, may be driven to spatial inhomogeneity by an unchanging long range force field imposed on it by its surroundings. Read more...
• 

  

  Wind, solar, and hydroelectricity are three emerging renewable sources of energy.

  
  Renewable energy is energy that is collected from renewable resources, which are naturally replenished on a human timescale, such as sunlight, wind, rain, tides, waves, and geothermal heat. Renewable energy often provides energy in four important areas: electricity generation, air and water heating/cooling, transportation, and rural (off-grid) energy services.
  
  Based on REN21's 2017 report, renewables contributed 19.3% to humans' global energy consumption and 24.5% to their generation of electricity in 2015 and 2016, respectively. This energy consumption is divided as 8.9% coming from traditional biomass, 4.2% as heat energy (modern biomass, geothermal and solar heat), 3.9% hydro electricity and 2.2% is electricity from wind, solar, geothermal, and biomass. Worldwide investments in renewable technologies amounted to more than US$286 billion in 2015, with countries such as China and the United States heavily investing in wind, hydro, solar and biofuels. Globally, there are an estimated 7.7 million jobs associated with the renewable energy industries, with solar photovoltaics being the largest renewable employer. As of 2015 worldwide, more than half of all new electricity capacity installed was renewable. Read more...
• 

  

  Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements; chiefly hydrogen, sulfur, oxygen, and nitrogen.
  Coal is formed if dead plant matter decays into peat and over millions of years the heat and pressure of deep burial converts the peat into coal.
  
  As a fossil fuel burned for heat, coal supplies about a quarter of the world's primary energy and two-fifths of its electricity. Some iron and steel making and other industrial processes burn coal. Read more...
• 

  A thermal reservoir, a short-form of thermal energy reservoir, or thermal bath is a thermodynamic system with a heat capacity that is large enough that when it is in thermal contact with another system of interest or its environment, its temperature remains effectively constant. It is an effectively infinite pool of thermal energy at a given, constant temperature. The temperature of the reservoir does not change when heat is added or extracted because of the infinite heat capacity. As it can act as a source and sink of heat, it is often also referred to as a heat reservoir or heat bath.
  
  Lakes, oceans and rivers often serve as thermal reservoirs in geophysical processes, such as the weather. In atmospheric science, large air masses in the atmosphere often function as thermal reservoirs. Read more...
• 

  In theoretical physics, negative mass is matter whose mass is of opposite sign to the mass of normal matter, e.g. −1 kg. Such matter would violate one or more energy conditions and show some strange properties, stemming from the ambiguity as to whether attraction should refer to force or the oppositely oriented acceleration for negative mass. It is used in certain speculative hypotheses, such as on the construction of traversable wormholes and the Alcubierre drive. Initially, the closest known real representative of such exotic matter is a region of negative pressure density produced by the Casimir effect.
  
  General relativity describes gravity and the laws of motion for both positive and negative energy particles, hence negative mass, but does not include the other fundamental forces. On the other hand, the Standard Model describes elementary particles and the other fundamental forces, but it does not include gravity. A unified theory that explicitly includes gravity along with the other fundamental forces may be needed for a better understanding of the concept of negative mass. Read more...
• 

  

  Pelamis machine at the Aguçadoura Wave Farm

  
  A wave farm – or wave power farm or wave energy park – is a collection of machines in the same location and used for the generation of wave power electricity. Wave farms can be either offshore or nearshore, with the former the most promising for the production of large quantities of electricity for the grid. The first wave farm was constructed in Portugal, the Aguçadoura Wave Farm, consisting of three Pelamis machines. The world's largest is planned for Scotland. Read more...
• 

  

  Nuclear Fuel Process

  
  Nuclear fuel is material used in nuclear power stations to produce heat to power turbines. Heat is created when nuclear fuel undergoes nuclear fission.
  
  Most nuclear fuels contain heavy fissile actinide elements that are capable of undergoing and sustaining nuclear fission. The three most relevant fissile isotopes are Uranium-233, Uranium-235 and Plutonium-239. When the unstable nuclei of these atoms are hit by a slow-moving neutron, they split, creating two daughter nuclei and two or three more neutrons. These neutrons then go on to split more nuclei. This creates a self-sustaining chain reaction that is controlled in a nuclear reactor, or uncontrolled in a nuclear weapon. Read more...
• 

  In thermodynamics, the exergy of a system is the maximum useful work possible during a process that brings the system into equilibrium with a heat reservoir. When the surroundings are the reservoir, exergy is the potential of a system to cause a change as it achieves equilibrium with its environment. Exergy is the energy that is available to be used. After the system and surroundings reach equilibrium, the exergy is zero. Determining exergy was also the first goal of thermodynamics. The term "exergy" was coined in 1956 by Zoran Rant (1904–1972) by using the Greek ex and ergon meaning "from work", but the concept was developed by J. Willard Gibbs in 1873.
  Energy is neither created nor destroyed during a process. Energy changes from one form to another (see First Law of Thermodynamics). In contrast, exergy is always destroyed when a process is irreversible, for example loss of heat to the environment (see Second Law of Thermodynamics). This destruction is proportional to the entropy increase of the system together with its surroundings (see Entropy production). The destroyed exergy has been called anergy. For an isothermal process, exergy and energy are interchangeable terms, and there is no anergy. Read more...
• 

  

  Sihwa Lake Tidal Power Station, located in Gyeonggi Province, South Korea, is the world's largest tidal power installation, with a total power output capacity of 254 MW.

  
  Tidal power or tidal energy is a form of hydropower that converts the energy obtained from tides into useful forms of power, mainly electricity.
  
  Although not yet widely used, tidal energy has potential for future electricity generation. Tides are more predictable than the wind and the sun. Among sources of renewable energy, tidal energy has traditionally suffered from relatively high cost and limited availability of sites with sufficiently high tidal ranges or flow velocities, thus constricting its total availability. However, many recent technological developments and improvements, both in design (e.g. dynamic tidal power, tidal lagoons) and turbine technology (e.g. new axial turbines, cross flow turbines), indicate that the total availability of tidal power may be much higher than previously assumed, and that economic and environmental costs may be brought down to competitive levels. Read more...
• 

  

  
  A capacitor is a passive two-terminal electronic component that stores electrical energy in an electric field. The effect of a capacitor is known as capacitance. While some capacitance exists between any two electrical conductors in proximity in a circuit, a capacitor is a component designed to add capacitance to a circuit. The capacitor was originally known as a condenser or condensator. The original name is still widely used in many languages, but not commonly in English.
  
  The physical form and construction of practical capacitors vary widely and many capacitor types are in common use. Most capacitors contain at least two electrical conductors often in the form of metallic plates or surfaces separated by a dielectric medium. A conductor may be a foil, thin film, sintered bead of metal, or an electrolyte. The nonconducting dielectric acts to increase the capacitor's charge capacity. Materials commonly used as dielectrics include glass, ceramic, plastic film, paper, mica, and oxide layers. Capacitors are widely used as parts of electrical circuits in many common electrical devices. Unlike a resistor, an ideal capacitor does not dissipate energy. Read more...
• 

  

  Biomass briquettes are an example fuel for production of dendrothermal energy

  
  Biomass is waste material from plants or animals that is not used for food or feed; it can be waste from farming (like wheat stalks) or horticulture (yard waste), food processing (like corn cobs), animal farming (manure rich in nitrogen and phosphorus), or human waste from sewage plants. It is used in various industrial processes, like energy production or as raw materials for manufacturing chemicals.
  
  Burning biomass releases carbon emissions, but has been classed as a renewable energy source in the EU and UN legal frameworks, because plant stocks can be replaced with new growth. It has become popular among coal power stations, which switch from coal to biomass in order to convert to renewable energy generation without wasting existing generating plant and infrastructure. Biomass most often refers to an energy source; biomass can either be used directly via combustion to produce heat, or indirectly after converting it to various forms of biofuel. Conversion of biomass to biofuel can be achieved by different methods which are broadly classified into: thermal, chemical, and biochemical. Some chemical constituents of plant biomass include lignins, cellulose, and hemicellulose. Read more...
• 

  Read more... Read more...
• 

  Latent heat is thermal energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process — usually a first-order phase transition.
  
  Latent heat can be understood as heat energy in hidden form which is supplied or extracted to change the state of a substance without changing its temperature. Examples are latent heat of fusion and latent heat of vaporization involved in phase changes, i.e. a substance condensing or vaporizing at a specified temperature and pressure. Read more...
• 

  

  Properties of Isolated, closed, and open systems in exchanging energy and matter.

  
  In physical science, an isolated system is either of the following:
  

  1. a physical system so far removed from other systems that it does not interact with them.
  2. a thermodynamic system enclosed by rigid immovable walls through which neither mass nor energy can pass.

  Read more...
• 

  

  Roof-mounted close-coupled thermosiphon solar water heater.

  
  Solar thermal energy (STE) is a form of energy and a technology for harnessing solar energy to generate thermal energy or electrical energy for use in industry, and in the residential and commercial sectors. Read more...
• 

  Heat capacity or thermal capacity is a measurable physical quantity equal to the ratio of the heat added to (or removed from) an object to the resulting temperature change. The unit of heat capacity is joule per kelvin $\mathrm {\tfrac {J}{K}}$, or kilogram metre squared per kelvin second squared $\mathrm {\tfrac {kg\cdot m^{2}}{K\cdot s^{2}}}$ in the International System of Units (SI). The dimensional form is L²MT⁻²Θ⁻¹. Specific heat is the amount of heat needed to raise the temperature of one kilogram of mass by 1 kelvin.
  
  Heat capacity is an extensive property of matter, meaning that it is proportional to the size of the system. When expressing the same phenomenon as an intensive property, the heat capacity is divided by the amount of substance, mass, or volume, thus the quantity is independent of the size or extent of the sample. The molar heat capacity is the heat capacity per unit amount (SI unit: mole) of a pure substance, and the specific heat capacity, often called simply specific heat, is the heat capacity per unit mass of a material. Nonetheless some authors use the term specific heat to refer to the ratio of the specific heat capacity of a substance at any given temperature to the specific heat capacity of another substance at a reference temperature, much in the fashion of specific gravity. In some engineering contexts, the volumetric heat capacity is used. Read more...
• 

  

  
  Geothermal power is power generated by geothermal energy. Technologies in use include dry steam power stations, flash steam power stations and binary cycle power stations. Geothermal electricity generation is currently used in 24 countries, while geothermal heating is in use in 70 countries.
  
  As of 2015, worldwide geothermal power capacity amounts to 12.8 gigawatts (GW), of which 28 percent or 3,548 megawatts (MW) are installed in the United States. International markets grew at an average annual rate of 5 percent over the three years to 2015, and global geothermal power capacity is expected to reach 14.5–17.6 GW by 2020. Based on current geologic knowledge and technology the GEA publicly discloses, the Geothermal Energy Association (GEA) estimates that only 6.9 percent of total global potential has been tapped so far, while the IPCC reported geothermal power potential to be in the range of 35 GW to 2 TW. Countries generating more than 15 percent of their electricity from geothermal sources include El Salvador, Kenya, the Philippines, Iceland, New Zealand and Costa Rica. Read more...
• 

  

  Galaxy clusters are the largest known gravitationally bound structures in the universe.

  
  
  A gravitational binding energy is the minimum energy that must be added to a system for the system to cease being in a gravitationally bound state. A gravitationally bound system has a lower (i.e., more negative) gravitational potential energy than the sum of its parts—this is what keeps the system aggregated in accordance with the minimum total potential energy principle.
  
  For a spherical mass of uniform density, the gravitational binding energy U is given by the formula Read more...
• 

  Chemical energy is the potential of a chemical substance to undergo a transformation through a chemical reaction to transform other chemical substances. Examples include batteries, food, gasoline, and etc. Breaking or making of chemical bonds involves energy, which may be either absorbed or evolved from a chemical system.
  
  Energy that can be released or absorbed because of a reaction between a set of chemical substances is equal to the difference between the energy content of the products and the reactants, if the initial and final temperatures are the same. This change in energy can be estimated from the bond energies of the various chemical bonds in the reactants and products. It can also be calculated from $\Delta {U_{f}^{\circ }}_{\mathrm {reactants} }$, the internal energy of formation of the reactant molecules, and $\Delta {U_{f}^{\circ }}_{\mathrm {products} }$ the internal energy of formation of the product molecules. The internal energy change of a chemical process is equal to the heat exchanged if it is measured under conditions of constant volume and equal initial and final temperature, as in a closed container such as a bomb calorimeter. However, under conditions of constant pressure, as in reactions in vessels open to the atmosphere, the measured heat change is not always equal to the internal energy change, because pressure-volume work also releases or absorbs energy. (The heat change at constant pressure is called the enthalpy change; in this case the enthalpy of reaction, if initial and final temperatures are equal). Read more...
• 

  The four laws of thermodynamics define fundamental physical quantities (temperature, energy, and entropy) that characterize thermodynamic systems at thermal equilibrium. The laws describe how these quantities behave under various circumstances, and preclude the possibility of certain phenomena (such as perpetual motion).
  
  The four laws of thermodynamics are: Read more...
• 

  An integrated gasification combined cycle (IGCC) is a technology that uses a high pressure gasifier to turn coal and other carbon based fuels into pressurized gas—synthesis gas (syngas). It can then remove impurities from the syngas prior to the power generation cycle. Some of these pollutants, such as sulfur, can be turned into re-usable byproducts through the Claus process. This results in lower emissions of sulfur dioxide, particulates, mercury, and in some cases carbon dioxide. With additional process equipment, a water-gas shift reaction can increase gasification efficiency and reduce carbon monoxide emissions by converting it to carbon dioxide. The resulting carbon dioxide from the shift reaction can be separated, compressed, and stored through sequestration. Excess heat from the primary combustion and syngas fired generation is then passed to a steam cycle, similar to a combined cycle gas turbine. This process results in improved thermodynamic efficiency compared to conventional pulverized coal combustion. Read more...
• 

  Energy use, import and production in South America is described in the following articles:

  • Energy in Argentina
  • Energy in Brazil
  • Energy in Chile
  • Energy in Colombia
  • Energy in Peru
  • Energy in Uruguay
  • Energy in Venezuela

  Read more...
• 

  Electric potential energy, or electrostatic potential energy, is a potential energy (measured in joules) that results from conservative Coulomb forces and is associated with the configuration of a particular set of point charges within a defined system. An object may have electric potential energy by virtue of two key elements: its own electric charge and its relative position to other electrically charged objects.
  
  The term "electric potential energy" is used to describe the potential energy in systems with time-variant electric fields, while the term "electrostatic potential energy" is used to describe the potential energy in systems with time-invariant electric fields. Read more...

Did you know...

• ... that Grace Bochenek, an engineer and director of the U.S. National Energy Technology Laboratory, is the acting Secretary of Energy?
• ... that physicists Justin Khoury and Amanda Weltman proposed an explanation for the existence of dark energy when the latter was 24 years old?
• ... that optically stimulated luminescence thermochronometry determines when rocks cooled, by measuring light released from energy stored in minerals?
• ... that, using data collected from the Dark Energy Survey, a team of researchers led by David Gerdes discovered a new dwarf planet nicknamed DeeDee?
• ... that the blazar TXS 0506+056 is the first identified source of high-energy astrophysical neutrinos?
• ... that Captain Ruck-Keene's command of HMS Cochrane ended a few days after Admiral Jellicoe wrote that he had become "lazy, lacks energy & has run to seed"?

Need help?

Do you have a question about Energy that you can't find the answer to?

Consider asking it at the Wikipedia reference desk.

Get involved

For editor resources and to collaborate with other editors on improving Wikipedia's Energy-related articles, see WikiProject Energy.

Selected images

• 

  Thomas Young – the first to use the term "energy" in the modern sense.

• 

  Basic overview of energy and human life.

• 

  A turbo generator transforms the energy of pressurised steam into electrical energy

• 

  The Sun is the source of energy for most of life on Earth. As a star, the Sun is heated to high temperatures by the conversion of nuclear binding energy due to the fusion of hydrogen in its core. This energy is ultimately transferred (released) into space mainly in the form of radiant (light) energy.

• 

  In a typical lightning strike, 500 megajoules of electric potential energy is converted into the same amount of energy in other forms, mostly light energy, sound energy and thermal energy.

• 

  Joule's apparatus for measuring the mechanical equivalent of heat. A descending weight attached to a string causes a paddle immersed in water to rotate.

• 

  Thermal energy is energy of microscopic constituents of matter, which may include both kinetic and potential energy.

In the news

1 February 2019 – January 2019 North American cold wave

A large-scale natural gas shortage in the U.S. state of Michigan is averted following the compliance of an emergency request from Consumers Energy for state residents to lower thermostats, after a fire at a natural gas compressor station threatened to halt the delivery of gas to consumers. The public's observance of the request resulted in a 10 percent decrease in natural gas usage across the state. (WNEM-TV) (Associated Press)

30 January 2019 – January 2019 North American cold wave

After a fire at a Consumers Energy natural gas compressor station, Michigan residents are asked to turn down their heat to conserve natural gas. (MLive.com), (WEYI-TV)

Subcategories

Select [►] to view subcategories

▼ Energy

► Energy by continent

► Energy by country

► Energy by region

► Energy-related lists

► Alternative energy

► Attacks on energy sector

► Energy conversion

► Energy democracy

► Energy development

► Electric power

► Energetics

► Energy accidents and incidents

► Energy economics

► Energy education

► Energy (physics)

► Energy industry

► Energy recovery

► Energy weapons

► Forms of energy

► History of energy

► Energy infrastructure

► Energetic materials

► Energy measurement

► Energy models

► Energy organizations

► People associated with energy

► Energy policy

► Energy sources

► Energy storage

► Sustainable energy

► Energy technology

► Energy in transport

► Works about energy

► Energy stubs

Subtopics

Associated Wikimedia