Glossary of Energy Terms

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A B C D E F G H I J K L M N O P Q R S T U V W X-Z Acronyms

Note: No entries for Y or Z.

Letter O

OAPEC -- Acronym for Organization of Arab Petroleum Exporting Countries founded in 1968 for cooperation in economic and petroleum affairs. See OPEC.

OBLIGATION TO SERVE -- The obligation of a utility to provide electric service to any customer who seeks that service, and is willing to pay the rates set for that service. Traditionally, utilities have assumed the obligation to serve in return for an exclusive monopoly franchise.

OCEAN THERMAL GRADIENT (OTG) -- Temperature differences between deep and surface water. Deep water is likely to be 25 to 45 degrees Fahrenheit colder. The term also refers to experimental technology that could use the temperature differences as a means to produce energy.

OCCUPANCY SENSOR -- A control device that senses the presence of a person in a given space, commonly used to control lighting systems in buildings.

OCTANE -- A rating scale used to grade gasoline as to its antiknock properties. Also any of several isometric liquid paraffin hydrocarbons, C8H18. Normal octane is a colorless liquid found in petroleum boiling at 124.6 degrees Celsius.

OCTANE RATING -- A measure of a gasoline's resistance to exploding too early in the engine cycle, which causes knocking. The higher the rating, the lower the chance of premature ignition.

OFF-ROAD -- Any non-stationary device, powered by an internal combustion engine or motor, used primarily off the highways to propel, move, or draw persons or property, and used in any of the following applications: marine vessels, construction/farm equipment, locomotives, utility and lawn and garden equipment, off-road motorcycles, and off-highway vehicles.

OHM --A unit of measure of electrical resistance. One volt can produce a current of one ampere through a resistance of one ohm.

OIL SHALE -- A type of rock containing organic matter that produces large amounts of oil when heated to high temperatures.

Once-through cooling - Water that is withdrawn from a source, circulated through the heat exchangers, and then returned to a water body at a higher temperature.

OLIGOPOLY -- A few sellers who exert market control overprices.

OPEC -- Acronym for Organization of Petroleum Exporting Countries founded in 1960 for unify and coordinate petroleum polices of the members. Headquarters is in Vienna, Austria.

OPTIONS -- An option is a contractual agreement that gives the holder the right to buy (call option) or sell (put option) a fixed quantity of a security or commodity (for example, a commodity or commodity futures contract), at a fixed price, within a specified period of time. May either be standardized, exchange-traded, and government regulated, or over-the-counter customized and non-regulated.

ORIENTATION -- the position of a building relative to the points of a compass.

ORIGINAL EQUIPMENT MANUFACTURER (OEM) -- refers to the manufacturers of complete vehicles or heavy-duty engines, as contrasted with remanufacturers, converters, retrofitters, up-fitters, and re-powering or rebuilding contractors who are overhauling engines, adapting or converting vehicles or engines obtained from the OEMs, or exchanging or rebuilding engines in existing vehicles.

OUTAGE (Electric utility) -- An interruption of electric service that is temporary (minutes or hours) and affects a relatively small area (buildings or city blocks). See BLACKOUT.

OUTER CONTINENTAL SHELF (OCS) -- The submerged lands extending from the out limit of the historic territorial sea (typically three miles) to some undefined outer limit, usually a depth of 600 feet. In the United States, this is the portion of the shelf under federal jurisdiction. See CONTINENTAL SHELF.

OUTSIDE AIR -- Air taken from outdoors and not previously circulated through the HVAC system.

OVER GENERATION -- A condition that occurs when total PX participant demand is less that or equal to the sum of regulatory must-take generation, regulatory must-run generation, and reliability must-run generation.

OVERHANG -- Any horizontal projection that serves as a shading element for a window.

OXYGENATE -- a term used in the petroleum industry to denote octane components containing hydrogen, carbon and oxygen in their molecular structure. Includes ethers such as MTBE and ETBE and alcohols such as ethanol or methanol. The oxygenate is a prime ingredient in reformulated gasoline. The increased oxygen content given by oxygenates promotes more complete combustion, thereby reducing tailpipe emissions.


OZONE - A kind of oxygen that has three atoms per molecule instead of the usual two. Ozone is a poisonous gas, but the ozone layer in the upper atmosphere shields life on earth from deadly ultraviolet radiation from space. The molecule contains three oxygen atoms (O3).

A B C D E F G H I J K L M N O P Q R S T U V W X-Z Acronyms

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