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Energy.gov - Energy industry terms Category: Earth and Environment > Energy industry terms Date & country: 26/02/2017, USA Words: 1299

Photovoltaic (Conversion) Efficiency
The ratio of the electric power produced by a photovoltaic device to the power of the sunlight incident on the device.

Photovoltaic (PV; Solar) Array
A group of solar photovoltaic modules connected together.

Photovoltaic (Solar) Cell
Treated semiconductor material that converts solar irradiance to electricity.

Photovoltaic (Solar) System
A complete PV power system composed of the module (or array), and balance-of-system (BOS) components including the array supports, electrical conductors/wiring, fuses, safety disconnects, and grounds, charge controllers, inverters, battery storage, etc.

Photon
A particle of light that acts as an individual unit of energy.

Photoelectrochemical Cell
A type of photovoltaic device in which the electricity induced in the cell is used immediately within the cell to produce a chemical, such as hydrogen, which can then be withdrawn for use.

Photoelectrolysis Hydrogen Production
The production of hydrogen using a photoelectrochemical cell.

Photogalvanic Processes
The production of electrical current from light.

Photoelectric Cell
A device for measuring light intensity that works by converting light falling on, or reach it, to electricity, and then measuring the current; used in photometers.

Photobiological Hydrogen Production
A hydrogen production process that process uses algae. Under certain conditions, the pigments in certain types of algae absorb solar energy. An enzyme in the cell acts as a catalyst to split water molecules. Some of the bacteria produces hydrogen after they grow on a substrate.

Photocurrent
An electric current induced by radiant energy.

Phase
Alternating current is carried by conductors and a ground to residential, commercial, or industrial consumers. The waveform of the phase power appears as a single continuous sine wave at the system frequency whose amplitude is the rated voltage of the power.

Phase Change
The process of changing from one physical state (solid, liquid, or gas) to another, with a necessary or coincidental input or release of energy.

Phase-Change Material
A material that can be used to store thermal energy as latent heat. Various types of materials have been and are being investigated such as inorganic salts, eutectic compounds, and paraffins, for a variety of applications, including solar energy storage (solar energy heats and melts the material during the day and at night it releases the stored heat and reverts to a solid state).

Perimeter Heating
A term applied to warm-air heating systems that deliver heated air to rooms by means of registers or baseboards located along exterior walls.

Permeance
A unit of measurement for the ability of a material to retard the diffusion of water vapor at 73.4 F (23 C). A perm, short for permeance, is the number of grains of water vapor that pass through a square foot of material per hour at a differential vapor pressure equal to one inch of mercury.

Peak Demand/Load
The maximum energy demand or load in a specified time period.

Perfluorocarbon Tracer Gas Technique
(PFT) An air infiltration measurement technique developed by the Brookhaven National Laboratory to measure changes over time (one week to five months) when determining a building's air infiltration rate. This test cannot locate exact points of infiltration, but it does reveal long-term infiltration problems.

Performance Ratings
Solar collector thermal performance ratings based on collector efficiencies, usually expressed in Btu per hour for solar collectors under standard test or operating conditions for solar radiation intensity, inlet working fluid temperatures, and ambient temperatures.

Penstock
A component of a hydropower plant; a pipe that delivers water to the turbine.

Pelton Turbine
A type of impulse hydropower turbine where water passes through nozzles and strikes cups arranged on the periphery of a runner, or wheel, which causes the runner to rotate, producing mechanical energy. The runner is fixed on a shaft, and the rotational motion of the turbine is transmitted by the shaft to a generator. Generally used for high head, low flow applications.

Pellets
Solid fuels made from primarily wood sawdust that is compacted under high pressure to form small (about the size of rabbit feed) pellets for use in a pellet stove.

Peaking Capacity
Power generation equipment or system capacity to meet peak power demands.

Peaking Hydropower
A hydropower plant that is operated at maximum allowable capacity for part of the day and is either shut down for the remainder of the time or operated at minimal capacity level.

Pellet Stove
A space heating device that burns pellets; are more efficient, clean burning, and easier to operate relative to conventional cord wood burning appliances.

Peak Wind Speed
The maximum instantaneous wind speed (or velocity) that occurs within a specific period of time or interval.

Peak Watt
A unit used to rate the performance of a solar photovoltaic (PV) cells, modules, or arrays; the maximum nominal output of a PV device, in Watts (Wp) under standardized test conditions, usually 1000 Watts per square meter of sunlight with other conditions, such as temperature specified.

Peak Sun Hours
The equivalent number of hours per day when solar irradiance averages 1 kW/m². For example, six peak sun hours means that the energy received during total daylight hours equals the energy that would have been received had the irradiance for six hours been 1 kW/m².

Peak Shifting
The process of moving existing loads to off-peak periods.

Passive Solar Home
A house built using passive solar design techniques.

Passive/Natural Cooling
To allow or augment the natural movement of cooler air from exterior, shaded areas of a building through or around a building.

Payback Period
The amount of time required before the savings resulting from your system equal the system cost.

Peak Clipping/Shaving
The process of implementing measures to reduce peak power demands on a system.

Peak Power
Power generated that operates at a very low capacity factor; generally used to meet short-lived and variable high demand periods.

Passive Solar Heater
A solar water or space-heating system in which solar energy is collected, and/or moved by natural convection without using pumps or fans. Passive systems are typically integral collector/storage (ICS; or batch collectors) or thermosyphon systems. The major advantage of these systems is that they do not use controls, pumps, sensors, or other mechanical parts, so little or no maintenance is required over the lifetime of the system.

Passivation
A chemical reaction that eliminates the detrimental effect of electrically reactive atoms on a photovoltaic cell's surface.

Passive Solar (Building) Design
A building design that uses structural elements of a building to heat and cool a building, without the use of mechanical equipment, which requires careful consideration of the local climate and solar energy resource, building orientation, and landscape features, to name a few. The principal elements include proper building orientation, proper window sizing and placement and design of window overhangs to reduce summer heat gain and ensure winter heat gain, and proper sizing of thermal energy storage mass (for example a Trombe wall or masonry tiles). The heat is distributed primarily by natural convection and radiation, though fans can also be used to circulate room air or ensure proper ventilation.

Particulates
The fine liquid or solid particles contained in combustion gases. The quantity and size of particulates emitted by cars, power and industrial plants, wood stoves, etc are regulated by the U.S. Environmental Protection Agency.

Parallel
A configuration of an electrical circuit in which the voltage is the same across the terminals. The positive reference direction for each resistor current is down through the resistor with the same voltage across each resistor.

Parallel Connection
A way of joining photovoltaic cells or modules by connecting positive leads together and negative leads together; such a configuration increases the current, but not the voltage.

Parabolic Aluminized Reflector Lamp
A type of lamp having a lens of heavy durable glass that focuses the light. They have longer lifetimes with less lumen depreciation than standard incandescent lamps.

Parabolic Dish
A solar energy conversion device that has a bowl shaped dish covered with a highly reflective surface that tracks the sun and concentrates sunlight on a fixed absorber, thereby achieving high temperatures, for process heating or to operate a heat (Stirling) engine to produce power or electricity.

Parabolic Trough
A solar energy conversion device that uses a trough covered with a highly reflective surface to focus sunlight onto a linear absorber containing a working fluid that can be used for medium temperature space or process heat or to operate a steam turbine for power or electricity generation.

Pane
(Window) The area of glass that fits in the window frame.

Panel
(Solar) A term generally applied to individual solar collectors, and typically to solar photovoltaic collectors or modules.

Panel Radiator
A mainly flat surface for transmitting radiant energy.

Panemone
A drag-type wind machine that can react to wind from any direction.

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.

Packing Factor
The ratio of solar collector array area to actual land area.

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.

Open-Circuit Voltage
The maximum possible voltage across a photovoltaic cell; the voltage across the cell in sunlight when no current is flowing.

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.

One Sun
The maximum value of natural solar insolation.

One-Axis Tracking
A system capable of rotating about one axis.

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).

Oil
(fuel) A product of crude oil that is used for space heating, diesel engines, and electrical generation.

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).

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.

Ocean Energy Systems
Energy conversion technologies that harness the energy in tides, waves, and thermal gradients in the oceans.

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).

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.

Nuclear Energy
Energy that comes from splitting atoms of radioactive materials, such as uranium, and which produces radioactive wastes.

Nocturnal Cooling
The effect of cooling by the radiation of heat from a building to the night sky.

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.

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.

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
(NO_x) The products of all combustion processes formed by the combination of nitrogen and oxygen.

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 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.

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
(Lower) 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.

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 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.

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.

Municipal Waste to Energy Project
(or Plant) A facility that produces fuel or energy from municipal solid waste.

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.

Multijunction Device
A high-efficiency photovoltaic device containing two or more cell junctions, each of which is optimized for a particular part of the solar spectrum.

Multi-Zone System
A building heating, ventilation, and/or air conditioning system that distributes conditioned air to individual zones or rooms.

Municipal Solid Waste
(MSW) Waste material from households and businesses in a community that is not regulated as hazardous.

MTBE
Methyl Tertiary Butyl Ether (MTBE) is an ether compound used as a gasoline blending component to raise the oxygen content of gasoline. MTBE is made by combining isobutylene (from various refining and chemical processes) and methanol (usually made from natural gas).

Movable Insulation
A device that reduces heat loss at night and during cloudy periods and heat gain during the day in warm weather. A movable insulator could be an insulative shade, shutter panel, or curtain.