| 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. |
| Occupancy Sensor | A control device that senses the presence of a person in a given space, commonly used to control lighting systems in buildings. |
| Ocean Energy | can be used as either thermal energy or the mechanical energy of tides and waves. |
| 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. |
| 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 gasolineàs resistance to exploding too early in the engine cycle, which causes knocking. The higher the rating, the lower the chance of premature ignition. |
| Off-Peak | The period of low energy demand, as opposed to maximum or peak demand. |
| Off-Peak Power | The amount of power generation during a period of low consumer demand. |
| Offroad | Any nonstationary 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, offroad motorcycles, and offhighway vehicles. |
| Ohm | A measure of the electrical resistance of a material equal to the resistance of a circuit in which the potential difference of 1 volt produces a current of 1 ampere. |
| Ohm (Ω) | The unit that quantifies a material’s resistance to electron flow. |
| Ohm’s Law | Basic formula defining the relationship between voltage, amperage, and resistance. Commonly stated as E = I x R, or Voltage = Amperage x Resistance. |
| Ohm’s Law | A simple mathematical formula that allows either voltage, current or resistance to be calculated when the other two values are known. The formula is V = I x R, where V is the voltage, I is the current, and R is the resistance. |
| Oil (Fuel) | A product of crude oil that is used for space heating, diesel engines, and electricity generation. |
| Oil Shale | A type of rock containing organic matter that produces large amounts of oil when heated to high temperatures. |
| Oligopoly | A few sellers who exert market control overprices. |
| One-Axis Tracking | A PV System structure that is capable of rotating on a single axis in order to track the movement of the sun. |
| On-Peak | Energy supplied during periods of relatively high system demands as specified by the utility. |
| 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. |
| Open Circuit | When an electrical circuit is interrupted by breaking the path at one or more points, stopping the electrons from flowing. A light switch opens an electrical circuit when it turns off the light. |
| Open Circuit Voltage | The maximum voltage produced by an illuminated solar PV cell, module, or array when no load is connected. OCV increases as the temperature of the PV material decreases. |
| Open Circuit Voltage (Voc) | The maximum possible voltage across a PV array, module, or cell. The voltage across the terminals of a photovoltaic cell, module, or array with no load applied when the cell is exposed to standard insolation conditions, measured with a voltmeter. |
| Open Loop System | A fresh water or "direct" solar hot water system, generally for use in freeze-free climates. |
| Open-Circuit Volatage | The maximum possible voltage across a PV call or module when no current is flowing. |
| Open-Circuit Voltage (Voc) | The maximum possible voltage across a photovoltaic cell; the voltage across the cell in sunlight when no current is flowing. |
| Operating Point | Defined by the current and voltage that a module or array produces when connected to a load. It is dependent on the load or the batteries connected to the output terminals. |
| 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 | Placement according to the directions N, S, E, or W. |
| Original Equipment Manufacturer (Oem) | refers to the manufacturers of complete vehicles or heavyduty engines, as contrasted with remanufacturers, converters, retrofitters, up-fitters, and repowering 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. |
| Outgas | See gassing. |
| Outgassing | The emission of gasses by a material. See also GASSING. |
| 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. |
| Overcharge | Applying a current to a fully charged battery. This can damage the battery. |
| Overcurrent | Current that exceeds the rated current of the equipment or the ampacity of a conductor, resulting from overload, short circuit, or ground fault. |
| Overcurrent Device | A safety fuse or breaker designed to open a circuit when an overcurrent occurs. |
| Overhang | Any horizontal projection that serves as a shading element for a window. |
| Over-Speed | When the wind forces the blades to go faster than what your generator can handle. My blades slow down in higher winds. |
| Oxides Of Nitrogen | See NOx. |
| 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). |
