Nacelle — The cover for the gear box, drive train, generator, and other components of a wind turbine.
Name Plate — A metal tag attached to a machine or appliance that contains information such as brand name, serial number, voltage, power ratings under specified conditions, and other manufacturer supplied data.
National Electrical Code (NEC) — The NEC is a set of regulations that have contributed to making the electrical systems in the United States one of the safest in the world. The intent of the NEC is to ensure safe electrical systems are designed and installed. The National Fire Protection Association has sponsored the NEC since 1911. The NEC changes as technology evolves and component sophistication increases. The NEC is updated every three years. Following the NEC is required in most locations.
National Rural Electric Cooperative Association (NRECA) — This is a national organization dedicated to representing the interests of cooperative electric power providers and the consumers they serve. Members come from the 46 states that have an electric distribution cooperative.
Natural Cooling — Space cooling achieved by shading, natural (unassisted, as opposed to forced) ventilation, conduction control, radiation, and evaporation; also called passive cooling.
Natural Draft — Draft that is caused by temperature differences in the air.
Natural Gas — A hydrocarbon gas obtained from underground sources, often in association with petroleum and coal deposits. It generally contains a high percentage of methane, varying amounts of ethane, and inert gases; used as a heating fuel.
Natural Gas Steam Reforming Production — A two step process where in the first step natural gas is exposed to a high-temperature steam to produce hydrogen, carbon monoxide, and carbon dioxide. The second step is to convert the carbon monoxide with steam to produce additional hydrogen and carbon dioxide.
Natural Ventilation — Ventilation that is created by the differences in the distribution of air pressures around a building. Air moves from areas of high pressure to areas of low pressure with gravity and wind pressure affecting the airflow. The placement and control of doors and windows alters natural ventilation patterns.
Net Energy Production (or Balance) — The amount of useful energy produced by a system less the amount of energy required to produce the fuel.
Net Generation — Equal to gross generation less electricity consumption of a power plant.
Net (Lower) Heating Value (NHV) — The potential energy available in a fuel as received, taking into account the energy loss in evaporating and superheating the water in the fuel. Equal to the higher heating value minus 1050W where W is the weight of the water formed from the hydrogen in the fuel, and 1050 is the latent heat of vaporization of water, in Btu, at 77 degrees Fahrenheit.
Net Metering — The practice of using a single meter to measure consumption and generation of electricity by a small generation facility (such as a house with a wind or solar photovoltaic system). The net energy produced or consumed is purchased from or sold to the power provider, respectively.
Net Present Value — The value of a personal portfolio, product, or investment after depreciation and interest on debt capital are subtracted from operating income. It can also be thought of as the equivalent worth of all cash flows relative to a base point called the present.
Nitrogen Dioxide — This compound of nitrogen and oxygen is formed by the oxidation of nitric oxide (NO) which is produced by the combustion of solid fuels.
Nitrogen Oxides (NOx) — The products of all combustion processes formed by the combination of nitrogen and oxygen.
Nominal Capacity — The approximate energy producing capacity of a power plant, under specified conditions, usually during periods of highest load.
Nominal Price — The price paid for goods or services at the time of a transaction; a price that has not been adjusted to account for inflation.
Nocturnal Cooling — The effect of cooling by the radiation of heat from a building to the night sky.
Nonrenewable Fuels — Fuels that cannot be easily made or "renewed," such as oil, natural gas, and coal.
Non-Utility Generator/Power Producer — A class of power generator that is not a regulated power provider and that has generating plants for the purpose of supplying electric power required in the conduct of their industrial and commercial operations.
Normal Recovery Capacity — A characteristic applied to domestic water heaters that is the amount of gallons raised 100 degrees Fahrenheit per hour (or minute) under a specified thermal efficiency.
N-Type Semiconductor — A semiconductor produced by doping an intrinsic semiconductor with an electron-donor impurity (e.g., phosphorous in silicon).
Nuclear Energy — Energy that comes from splitting atoms of radioactive materials, such as uranium, and which produces radioactive wastes.
Occupancy Sensor — An optical, ultrasonic, or infrared sensor that turns room lights on when they detect a person's presence and off after the space is vacated.
Occupied Space — The space within a building or structure that is normally occupied by people, and that may be conditioned (heated, cooled and/or ventilated).
Ocean Energy Systems — Energy conversion technologies that harness the energy in tides, waves, and thermal gradients in the oceans.
Ocean Thermal Energy Conversion (OTEC) — The process or technologies for producing energy by harnessing the temperature differences (thermal gradients) between ocean surface waters and that of ocean depths. Warm surface water is pumped through an evaporator containing a working fluid in a closed Rankine-cycle system. The vaporized fluid drives a turbine/generator. Cold water from deep below the surface is used to condense the working fluid. Open-Cycle OTEC technologies use ocean water itself as the working fluid. Closed-Cycle OTEC systems circulate a working fluid in a closed loop. A working 10 kilowatt, closed-cycle prototype was developed by the Pacific International Center for High Technology Research in Hawaii with U.s. Department of Energy funding, but was not commercialized.
Off-Peak — The period of low energy demand, as opposed to maximum, or peak, demand.
Ohms — 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's Law — In a given electrical circuit, the amount of current in amperes (i) is equal to the pressure in volts (V) divided by the resistance, in ohms (R).
Oil (fuel) — A product of crude oil that is used for space heating, diesel engines, and electrical generation.
One-Axis Tracking — A system capable of rotating about one axis.
One Sun — The maximum value of natural solar insolation.
On-Peak Energy — Energy supplied during periods of relatively high system demands as specified by the supplier.
On-Site Generation — Generation of energy at the location where all or most of it will be used.
Open Access — The ability to send or wheel electric power to a customer over a transmission and distribution system that is not owned by the power generator (seller).
Open-Circuit Voltage — The maximum possible voltage across a photovoltaic cell; the voltage across the cell in sunlight when no current is flowing.
Open-Loop Geothermal Heat Pump System — Open-loop (also known as "direct") systems circulate water drawn from a ground or surface water source. Once the heat has been transferred into or out of the water, the water is returned to a well or surface discharge (instead of being recirculated through the system). This option is practical where there is an adequate supply of relatively clean water, and all local codes and regulations regarding groundwater discharge are met.
Operating Cycle — The processes that a work input/output system undergoes and in which the initial and final states are identical.
Orientation — The alignment of a building along a given axis to face a specific geographical direction. The alignment of a solar collector, in number of degrees east or west of true south.
Outage — A discontinuance of electric power supply.
Outgassing — The process by which materials expel or release gasses.
Outside Air — Air that is taken from the outdoors.
Outside Coil — The heat-transfer (exchanger) component of a heat pump, located outdoors, from which heat is collected in the heating mode, or expelled in the cooling mode.
Overhang — A building element that shades windows, walls, and doors from direct solar radiation and protects these elements from precipitation.
Overload — To exceed the design capacity of a device.
Ovonic — A device that converts heat or sunlight directly to electricity, invented by Standford Ovshinsky, that has a unique glass composition that changes from an electrically non-conducting state to a semiconducting state.
Oxygenates — Gasoline fuel additives such as ethanol, ETBE, or MTBE that add extra oxygen to gasoline to reduce carbon monoxide pollution produced by vehicles.
Air Conditioning Units
