Energy Glossary


Alternator Rotating electrical device that harnesses the principle of electromagnetic induction (or the Faraday law) to convert in a highly efficient way the mechanical energy deriving from an engine into electrical energy in the form of alternate current.

Biodiesel Fuel deriving from organic matter, obtained by refining plant oils and animal fats.

Bioenergy Energy derived from the conversion of biomass where biomass may be used directly as fuel, or processed into liquids and gases.

Biofuels Liquid or gaseous fuels produced from biomass feedstocks, used primarily for transportation.

Bioethanol Ethanol deriving from the fermentation of biomass, such as grains, sugar beet, etc.

Bioethanol is mainly used as an additive in petrol and as a heating fuel.

Biogas A mixture of various gases (mainly methane), produced from the anaerobic bacterial fermentation of waste organic material deriving from plants or animals: agro-industrial, food and animal husbandry waste. Entire crops of maize, sorghum, wheat, etc., are used, cultivated for the very purpose.

Biomethane Biogas produced from biomass and waste which has been upgraded to natural gas quality for the purpose of grid injection and Power-to-gas volumes.

Biomass Organic, i.e. decomposable, material of biological origin (from plants and animals), as well as the biodegradable fraction of industrial and municipal waste, constituting a renewable energy source.

Boe (BOE) Barrel of Oil Equivalent Unit of measurement of energy that corresponds to the energy released from the combustion of a barrel of crude oil. Boe is used by trade operators to equate reserves and the production of oil and natural gas in a single measurement.

Btu (BTU) British Thermal Unit Unit of measurement of energy, used in the United States and the United Kingdom. One Btu is defined as the amount of heat required to raise the temperature of 1 pound (i.e. approximately 453.6 grams) of water from 39°F to 40°F (3.8°C to 4.4°C). Btus are used to define the calorific power of fuels as well as the cooling power of air conditioning systems.


Calorific power The maximum amount of energy that can be obtained from the complete conversion of a unit of mass (or volume) of a given material. Measured in j/kg in the International System, in kcal/kg, btu/lb., etc.

Carbon dioxide (CO2) A colourless, odourless, non-poisonous gas that is a normal part of Earth's atmosphere. CO2 is a product of fossil-fuel combustion as well as other processes. It is considered a greenhouse gas as it traps heat radiated by the Earth into the atmosphere and thereby contributes to the potential for global warming.

Coal-bed Methane (CBM) Natural gas associated and produced from coal deposits or coal seams. Its composition is generally methane, but can also include other constituents (ethane, carbon dioxide, nitrogen and hydrogen).

Co-generation The production of electrical energy and another form of useful energy (such as heat or steam) through the sequential use of energy.

Compressed natural gas (CNG) It is obtained by compressing natural gas to less than 1% of the volume it occupies at normal atmospheric pressure. CNG is conserved in tanks at a pressure of 200-248 bar and is used as a fuel for natural gas-powered vehicles.

Compressor station Facility used to compress natural gas in order to create additional pressure to increase the amount of gas a pipeline can hold. Compressor stations are installed on long-distance gas pipelines which compress the gas to a specified pressure, thereby allowing it to continue traveling along the pipeline to its final destination.

Conventional gas Natural gas that can be produced from reservoirs using standard drilling, pumping and compression techniques.

Crude oil The oil in its purest form, as it is extracted from various reserves, hence with varying attributes of quality.

Diesel fuel A fuel composed of distillates obtained in petroleum refining operation or blends of such distillates with residual oil used in motor vehicles. The boiling point and specific gravity are higher for diesel fuels than for gasoline.

Dry natural gas Natural gas composed practically of pure methane. It is found naturally this way or it is what remains after all of the liquefiable hydrocarbons (hexane, octane, etc.) and non-hydrocarbon (helium, nitrogen, etc.) impurities are removed from the natural gas stream. Dry natural gas is the key measure of the natural gas output, as it is a saleable product.

Dynamo Rotating electrical device that transforms mechanical work into electric energy in the form of direct current. Unlike alternators, the dynamo is used specifically for small amounts of power.


Electric energy (electricity) Energy produced from the interaction between positive and negative charges found in matter. The flow of charges that is created in a closed circuit forms the electrical current used to generate thermal, magnetic, mechanical, chemical and light effects, whose applications have great economic importance.

Electricity generation The process of producing electric energy or the amount of electric energy produced by transforming other forms of energy, commonly expressed in kilowatt-hours (kWh) or multiples for larger amounts, i.e. megawatt-hours (MWh), gigawatt-hours (GWh), terawatt-hours (TWh), petawatt-hours (PWh).

Electricity installed capacity Maximum electrical power that can be supplied for the production of active power within the network of electric power plants, assuming the full efficiency of the plants in optimal working conditions.

Energy intensity A ratio of energy consumption to another metric, typically national gross domestic product in the case of a country's energy intensity (total primary energy supply per unit of GDP). Improvements in energy intensity include energy efficiency and conservation as well as structural factors not related to technology or behaviour.

Energy efficiency A ratio of service provided to energy input. Services provided can include buildings-sector end uses such as lighting, refrigeration, and heating: industrial processes; or vehicle transportation. Unlike conservation, which involves some reduction of service, energy efficiency provides energy reductions without sacrifice of service. May also refer to the use of technology to reduce the energy needed for a given purpose or service.

FLNG (Floating Liquefied Natural Gas) This technology includes all systems to allows the offshore liquefaction of natural gas. FLNG facilities can be placed directly over offshore gas fields, thereby precluding the need for long distance pipelines and extensive onshore infrastructure.

FSRU (Floating Storage and Regasification Unit) A special type of vessel used for liquefied natural gas (LNG) transfer which is capable of transporting, storing, and regasifying LNG onboard. Floating regasification also requires either an offshore terminal, which typically includes a buoy and connecting undersea pipelines to transport regasified LNG to shore, or an onshore dockside receiving terminal.

Fracking or hydraulic fracturing Technique harnessing the pressure of a fluid to fracture an underground rocky stratum. Increases the permeability of rocks containing natural gas or oil, improving its ability to be salvaged.

Gasoline (Petrol) A product obtained from distilling crude oil at various temperatures. Highly flammable, clear, colourless and very aromatic liquid. Until 2000, in Europe lead compounds were added to gasoline for their nonexplosive effect. Alongside diesel fuel, gasoline is the most used vehicle fuel in the world.

Geothermal energy Hot water or steam extracted from geothermal reservoirs in the earth's crust. Water or steam extracted from geothermal reservoirs can be used for geothermal heat pumps, water heating, or electricity generation.

GDP (Gross Domestic Product) Total value of end goods and services produced by a country in a year through production factors (economic activities, jobs and trades, capital investments, etc.) used within the country itself. In this atlas it is expressed in millions of US dollars at current prices, namely at the prices in force in the year in question.


Heat content The amount of heat energy available to be released by the transformation or use of a specified physical unit of an energy form (e.g., a cubic metre of natural gas, a tonne of coal, a barrel of oil, a kilowatt-hour of electricity). The amount of heat energy is commonly expressed in British thermal units (Btu).

Henry Hub A pipeline hub on the Louisiana Gulf coast. It is the delivery point for the natural gas futures contract on the New York Mercantile Exchange (NYMEX).

HDI (Human Development Index) Published every year by the Human Development Report on behalf of the United Nations Development Programme, it is the weighted mean of certain development factors including life expectancy, level of education (school life expectancy and mean years of schooling) and available wealth (Gross National Income per capita). Expressed as a value in thousandths and the position of a country in the world rankings.

Hydrocarbons Organic compounds formed only by carbon and hydrogen atoms. Universally used as fuels, they derive from fossils and can be found in gas, liquid or waxy solid form.

Hydroelectric power The use of flowing water to produce electrical energy.

International aviation bunkers Aviation fuel quantities delivered to aircrafts for international aviation. Fuels used by airlines for their road vehicles are excluded. The domestic/international split is determined on the basis of departure and landing locations, and not by the nationality of the airline. For many countries this incorrectly excludes fuel used by domestically owned carriers for their international departures.

International marine bunkers Fuel quantities delivered to ships of all flags that are engaged in international navigation. The international navigation may take place at sea, on inland lakes and waterways, and in coastal waters. Consumption by ships engaged in domestic navigation is excluded. The domestic/international split is determined on the basis of port of departure and port of arrival, and not by the flag or nationality of the ship. Consumption by fishing vessels and by military forces is also excluded.

Joule (J) Unit of measurement (International System) of energy, work and heat. One joule equates to the work done by exercising the force of one newton (1kg∙m2/sec2) for the distance of one metre. One joule is also the work done to dispense the power of one watt for one second.


Kelvin (K) Unit of measurement of temperature (International System). The kelvin is defined as 1/273.16 of the absolute temperature of the triple point of water (approximately 0.01 °C). Zero on the kelvin scale equates to absolute zero (approximately -273°C), theoretically unreachable.

Kilocalorie (kcal) Unit of measurement of energy, defined as the energy needed to raise the temperature of 1 kg of distilled water from 14.5 to 15.5°C, pressurized by 1 atmosphere.

Kilowatt-hour (kWh) Unit of measurement of energy, defined as the energy needed to supply power of 1000 Watt (W) for one hour (h). Used as a sales unit of electric energy, often in multiples of MWh (megawatt-hours) = 103 kWh, GWh (gigawatt-hours) = 106 kWh and TWh (terawatt-hours) = 109 kWh.

Kinetic energy Energy possessed by a body due to the movement that it has or that it acquires: also defined as the work needed to take a body from stationary to a known speed. Kinetic energy is therefore associated with the mass and speed of the same body.

Liquefaction system Industrial infrastructure built to liquefy natural gas (LNG) and to be able to store it easily on LNG carrier ships. Liquefaction is carried out via one of more lines functioning in parallel, each of which purifies and dehydrates the gas, removing any heavy fractions, cooling it in excess of -160°C and sending it to be stocked on the ships.

LNG (Liquefied Natural Gas) Obtained from natural gas, purified and dehydrated, which is cooled at -160°C and condensed. A clear, odourless liquid. The method enables easier storage and transportation.

LPG (Liquefied Petroleum Gas) A group of hydrocarbon gases, primarily propane and butane or a combination of the two, derived from crude oil refining or natural gas processing. LPG are normally liquefied under pressure for transportation or storage.


Methane (CH4) A colourless, flammable, odourless hydrocarbon gas which is the major component of natural gas. It is also an important source of hydrogen in various industrial processes.

Middle distillates Fraction of refined products (e.g. diesel and heating oil) of intermediate weight between heavy distillates (fuel oils) and light distillates (e.g. gasoline and LPG).

Modern energy access Household access to a minimum level of electricity; household access to safer and more sustainable cooking and heating fuels and stoves; access that enables productive economic activity; and access for public services.

Modern use of biomass The use of solid biomass in improved cookstoves and modern technologies using processed biomass such as pellets.

Natural gas A gaseous mixture of hydrocarbon compounds, the primary one being methane.

Natural gas hydrates (NGH) Compounds where methane molecules are trapped in a solid lattice of water molecules under specific conditions of temperature and pressure. They occur in permafrost, on submarine continental slopes and in deep ocean floor sediment.

Non-energy use Fuels that are used as raw materials in the different sectors and are not consumed as a fuel or transformed into another fuel. Non-energy use also includes petrochemical feedstocks.

Nuclear fission Physical/chemical reaction whereby the nucleus of a heavy element or its isotope (e.g. uranium 235 or plutonium 239) decays into smaller nuclei, with higher emission of energy and radioactivity. Fission can be produced artificially through the bombardment of neutrons.

Nuclear reactor Extremely complex infrastructure capable of keeping a nuclear fission reaction under control. There are many types of reactors, but the operating method is always the same: the fissile fuel (bars of metallic uranium and/or plutonium inserted into a central block known as the “core”) is bombarded with neutron beams regulated by designated silver alloy bars or another material. The reaction generates heat, which is used to make vapour and to set in motion a turbine.

Nuclear (electric) power Electricity generated by the use of the thermal energy released from the fission of nuclear fuel in a reactor.

Oil sands Formed by clay, sand, water and bitumen. The latter is extracted outdoors or in wells using particular techniques (vapour or solvents). Oil is obtained from the bitumen.


Petrochemical industry Industrial sector that produces semi-finished products, mainly oil and natural gas. Compared with refinement, it tends to produce materials and not energy.

Photovoltaic cell Electrical device (in actual terms, a small current generator) able to convert light energy into electricity. The cell is the unitary element of photovoltaic modules (or solar panels).

Pipeline (natural gas) A continuous pipe conduit, complete with such equipment as valves, compressor stations, communications systems, and metres for transporting natural and/or supplemental gas from one point to another, usually from a point in or beyond the producing field or processing plant to another pipeline or to points of utilization.

Pipeline, distribution A pipeline that conveys gas from a transmission pipeline to its ultimate consumer.

Pipeline, gathering A pipeline that conveys gas from a production well/field to a gas processing plant or transmission pipeline for eventual delivery to end-use consumers.

Pipeline, transmission A pipeline that conveys gas from a region where it is produced to a region where it is to be distributed.

Potential energy Energy possessed by an object due to its position or orientation. It can also be defined as the potentiality of an object to transform its energy into kinetic energy.

Power The rate of producing, transferring, or using energy, most commonly associated with electricity. It is measured in watts and often expressed in kilowatts (kW) or multiples thereof.

Primary energy Energy in the form of oil, natural gas, coal, nuclear, hydro, geothermal, wind, solar and bioenergy sources (biofuels, municipal solid waste, traditional biomass).

Proven reserves Estimated quantities of sources (e.g. oil and gas) that analysis of geologic and engineering data demonstrates with reasonable certainty are recoverable under existing economic and operating conditions.


Radiant energy The energy possessed by electromagnetic waves such as visible light, radio waves, ultraviolet (UV) rays, infrared (IR) ways, etc. The main characteristic of this energy is that it propagates into the vacuum without any conductor material. The Sun is the main source of this energy.

Refinement A process aimed at purifying a chemical substance. In the case of oil, refinement, in addition to improving combustion, generates sizeable residue (bitumen, heavy oil, combustible oil, fuels), in turn used in many industrial and transportation sectors. The distinguishing structure in a refinery is the fractionating column, from which various products are extracted at varying heights.

Regasification plant Industrial plant on land, on offshore platforms or on special ships known as “Floating Storage & Regasification Units”. The plant is able to restore the LNG to its natural gaseous state. The gas is liquefied via cooling (in excess of -160°C), an expansion process, which allows transportation in vast quantities by ship (the LNG occupies approximately 600 times less volume than the same quantity of natural gas in its gaseous state). These ships, known as “LNG carrier ships” are equipped with huge storage barrels able to withstand very low operating temperatures.

Secondary energy Energy types, including electricity and market heat, which are derived from primary energy sources. For example, electricity is a secondary energy type generated using natural gas, wind or other primary energy sources. Sedimentary rock Rock characterized by layers that are accumulated during geological era, typically in a marine or lagoon environment.

Semiconductors Materials with intermediate conductivity between conductor and insulator materials. Used in all main electronic devices, such as light emitting diodes (LED) and photovoltaic solar panels (silicon).

Shale gas Natural gas trapped in rock formations with ultra-low permeability dominated by shale. Because of the types of reservoir, it is sometimes considered a sub-category of tight gas. Solar photovoltaic (PV) electricity Electricity produced from solar photovoltaics, i.e. by the direct conversion of solar radiation through photovoltaic processes in semiconductor devices (solar cells), including concentrating photovoltaic systems.

Solar photovoltaic (PV) electricity Electricity produced from solar photovoltaics, i.e. by the direct conversion of solar radiation through photovoltaic processes in semiconductor devices (solar cells), including concentrating photovoltaic systems.


TFC (Total Final Consumption) The sum of energy consumption by the different end-use sectors, including non-energy use and excluding backflows from the petrochemical industry. It excludes international marine and aviation bunkers, except at world level where it is included in the transport sector.

Thermoelectric plant A plant that uses the heat generated from combustion to product electric energy. Fossil fuel is usually used: natural gas, coal and combustible oil. The heat generated in a boiler creates vapour, which sets in motion a turbine, which via an alternator generates electrical current. At present, combined cycle plants are the most common, which use an air-gas mixture.

Tight gas Similar to shale gas, tight gas is natural gas trapped in extremely low-permeable and low-porous rock, sandstone or limestone formations. Such gas may contain condensates.

toe (TOE) Tonne of Oil Equivalent A unit of measurement of energy. Represents the amount of energy obtained from the combustion of a tonne of crude oil, the equivalent of 4.187 GJ, a conventionally set value.

TPES (Total Primary Energy Supply) Energy production plus imports, minus exports, minus international marine and/or aviation bunkers, then plus or minus stock changes. For the world total, international marine bunkers and international aviation bunkers are included.

Traditional biomass use The use of wood, charcoal, animal dung and agricultural residues with basic technologies, such as in stoves with very low efficiencies, a three-stone fire (often with no or poorly operating chimneys), or burned in open fires.

Transformer A static electrical device used to transform the voltage and intensity of the incoming current compared to the outgoing current, while keeping the electric power unchanged.

Turbine A rotating device capable of transforming the kinetic energy of a fluid into movement (typically liquid water or vapour) into mechanical energy.

UGS (Underground Gas Storage) The use of sub-surface facilities for storing natural gas for use at a later time. The facilities are usually hollowed-out salt caverns, geological reservoirs (depleted oil or gas fields) or water-bearing sands (called aquifers).

Unconventional gas Natural gas that requires special or advanced production techniques to be extracted. Main types include gas within tight pore spaces (shale gas and coal-bed methane) and gas that is trapped in ice on the sea floor (natural gas hydrates).

Wind power electricity Electricity produced from devices driven by wind.

Working gas capacity The amount of total natural gas storage capacity that can be used to store natural gas available for withdrawal.