| P/N | A semiconductor photovoltaic device structure in which the junction is formed between a p-type layer and an n-type layer. |
| Packing Factor | The ratio of array area to actual land area or building envelope area for a system; or, the ratio of total solar cell area to the total module area, for a module. |
| PADD | The United States is divided by the U.S. Department of Energy into five PADD regions for planning purposes. The states within PADD V are Alaska, Arizona, California, Hawaii, Nevada, Oregon and Washington, which are linked closely by their oil supply network. Since very little petroleum product is export outside the district, PADD V is essentially a self-contained oil supply system with Alaska and California the main producers and California refining the majority of the crude oil consumed in the PADD. (Petroleum Administration For Defense Districts) |
| Panel | See photovoltaic (PV) panel. |
| Pangaea | the huge supercontinent which scientists think may have existed 250 million years ago. All of the continents may have at one time been joined together to make this huge land mass. |
| Parallel Connected | A method of connection in which positive terminals are connected together and negative terminals are connected together. Current output adds and voltage remains the same. |
| Parallel Connection | A way of joining solar cells or photovoltaic modules by connecting positive leads together and negative leads together; such a configuration increases the current, but not the voltage. |
| Parallel Path Flow | As defined by NERC, this refers to the flow of electric power on an electric system’s transmission facilities resulting from scheduled electric power transfers between two other electric systems. (Electric power flows on all interconnected parallel paths in amounts inversely proportional to each path’s resistance.) |
| Partial Load | An electrical demand that uses only part of the electrical power available. |
| Particulate Matter (Pm) | Unburned fuel particles that form smoke or soot and stick to lung tissue when inhaled. A chief component of exhaust emissions from heavy-duty diesel engines. |
| Particulates (Particulate Matter) |
dust, soot, smoke and other suspended matter; can be respiratory irritants. Particulate matter smaller than 10 microns (pm10) has been found to be particularly harmful to health. |
| Pascal | The pascal [Pa] is the SI unit of pressure. One pascal is the pressure generated by a force of 1 newton acting on an area of 1 square metre. It is a rather small unit as defined and is more often used as a kilopascal [kPa]. It is named after the French mathematician, physicist and philosopher Blaise Pascal (1623-62). |
| Passivation | A chemical reaction that eliminates the detrimental effect of electrically reactive atoms on a solar cell’s surface. |
| Passive Solar | Any use of the sun’s energy in a manner that is found in nature without the use of mechanical aid like pumps or fans. For example, heating a thermal mass (a concrete wall or slab, for instance) during the day with direct sunlight, and using the stored heat in that mass to warm a greenhouse or home at night. |
| Passive Solar Energy | Use of the sun to help meet a building¹s energy needs by means of architectural design (such as arrangement of windows) and materials (such as floors that store heat, or other thermal mass). |
| Passive Solar Energy Designs |
use the building itself as both the solar collector and storage medium, usually by increasing the window area on the south side of the building and the amount of thermal mass inside the building to absorb the solar heat that enters through the windows. |
| Passive Solar Home | A house that utilizes part of the building as a solar collector, as opposed to active solar, such as PV. |
| Passive Solar System | A solar heating or cooling system that uses no external mechanical power to move the collected solar heat. |
| Pasteurize | to use high temperatures to destroy disease-causing bacteria. |
| Payback | The period of time it takes for an energy generating device or system to pay for itself in fuel savings. |
| Pcbs (Polychloronated Biphenyls) |
A group of organic compounds used in the manufacture of plastics and formerly used as a coolant in electric transformers. In the environment, PCBs are highly toxic to aquatic life. They persist in the environment for long periods of time and are biologically accumulative. |
| Peak Demand | See PEAK LOAD. |
| Peak Demand/Load | The maximum energy demand or load in a specified time period. |
| Peak Load | The maximum load or electrical power draw occurring in a given period of time. |
| Peak Load Or Peak Demand | The electric load that corresponds to a maximum level of electric demand in a specified time period. |
| Peak Load Power Plant | A power generating station that is normally used to produce extra electricity during peak load times. |
| Peak Power Current | Amperes produced by a photovoltaic module or array operating at the voltage of the I-V curve that will produce maximum power from the module. |
| Peak Power Point | Operating point of the I-V (current-voltage) curve for a solar cell or photovoltaic module where the product of the current value times the voltage value is a maximum. |
| Peak Power Tracking | see maximum power tracking. |
| Peak Sun Hours | The equivalent number of hours per day when solar irradiance averages 1000 W/m2. |
| Peak Watt | A unit used to rate the performance of solar cells, modules, or arrays; the maximum nominal output of a photovoltaic device, in watts (Wp) under standardized test conditions, usually 1,000 watts per square meter of sunlight with other conditions, such as temperature specified. |
| Peak Wind Speed | The maximum instantaneous wind speed that occurs within a specific period of time. |
| Peaker | A nickname for a power generating station that is normally used to produce extra electricity during peak load times. |
| Peaking Unit | A power generator used by a utility to produce extra electricity during peak load times. |
| Peat | A heterogeneous mixture of partly decomposed organic matter that has accumulated in a water saturated environment over a very long period of time. Peat geologically is considered a very young form of coal and has a heating value of 6,600 Btu/pound in situ. |
| Pelton Wheel | A common impulse turbine runner—the wheel that receives the water, changing the pressure and flow of the water to circular motion to drive an alternator, generator, or machine. Pelton wheels (named after inventor Lester Pelton) are made with a series of cups or “buckets” cast onto a hub. |
| Penstock | The pipe in a hydro system that carries the water from the intake to the turbine. |
| Perm | The measurement of water vapor through different materials measured in perm-inch (mass of water vapor moving through a unit area in unit time). |
| Permeable | able to transmit water or other liquids; for example, rock with tiny passageways between holes, fractured rock, and gravel are permeable. |
| Petrochemicals | Chemicals made from oil. |
| Petrodollars | Money paid to other countries for oil imported to the United States. |
| Petroleum | Oil as found it its natural state under the ground. |
| Phantom Load | A device that consumes energy even when its switch is off, such as the digital clock on a VCR. |
| Phosphorous (P) | A chemical element used as a dopant in making n-type semiconductor layers. |
| Photocell | A device that produces an electric reaction to visible radiant energy (light). |
| Photocurrent | |
| 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. |
| Photoelectrochemical Cell | A special kind of PV cell in which the electricity is used immediately to produce a chemical (Eg Hydrogen). |
| Photon | |
| Photosynthesis | A process by which green plants change carbon dioxide into oxygen and organic materials. The energy for this process comes from sunlight. |
| Photovoltaic | Capable of producing a voltage when exposed to light or other radiation. |
| Photovoltaic (PV) | Refers of converting light into electricity. |
| Photovoltaic (PV) Array | A number of PV modules connected together in a single structure. |
| Photovoltaic (PV) Cell | The smallest discrete element in a PV module that performs the conversion of light into electrical energy to produce a DC current and voltage. |
| Photovoltaic (PV) Conversion Efficiency |
The ratio of the electrical power generated by a PV device to the power of the light incident on it. This is typically in the range 5% to 15% for commercially available modules. |
| Photovoltaic (Pv) Device | A solid-state electrical device that converts light directly into direct current electricity of voltage-current characteristics that are a function of the characteristics of the light source and the materials in and design of the device. Solar photovoltaic devices are made of various semiconductor materials including silicon, cadmium sulfide, cadmium telluride, and gallium arsenide, and in single crystalline, multicrystalline, or amorphous forms. |
| Photovoltaic (Pv) Effect | The phenomenon that occurs when photons, the "particles" in a beam of light, knock electrons loose from the atoms they strike. When this property of light is combined with the properties of semiconductors, electrons flow in one direction across a junction, setting up a voltage. With the addition of circuitry, current will flow and electric power will be available. |
| Photovoltaic (PV) Generator | The total of all PV strings of a PV power supply system, which are electrically interconnected. |
| Photovoltaic (PV) Module | A single assembly of solar cells and ancillary parts, such as interconnections, terminals, (and protective devices such as diodes) intended to generate DC power under un-concentrated sunlight. The structural (load carrying) member of a module can either be the top layer (superstrate) or the back layer (substrate). [UL 1703] |
| Photovoltaic (PV) Panel | a term often used interchangeably with PV module (especially in single module systems). |
| Photovoltaic (PV) System | A complete set of components for converting sunlight into electricity by the photovoltaic process, including the array and balance of system components. |
| Photovoltaic Array | A collection of solar modules connected in series, parallel, or series-parallel combination to provide greater voltage, current, or power than can be furnished by a single solar module. Solar-electric arrays can be designed to furnish any desired voltage, current, or power. |
| Photovoltaic Cell | A device composed of specially prepared semiconductor material or material combinations exhibiting the ability to convert incident solar energy directly into electrical energy. |
| Photovoltaic Effect | The effect that causes a voltage to be developed across the junction of two different materials when they are exposed to light. |
| Photovoltaic Module | A PV module consists of series and/or parallel wired cells typically made from layered silicon crystals that convert light energy to DC electricity. The number of modules in a given system varies depending on the combined load being powered. |
| Photovoltaic System | All the parts connected together that are required to produce solar electricity. |
| Photovoltaic(S) (PV) | Pertaining to the direct conversion of light into electricity. |
| Photovoltaics (PV) | convert sunlight directly into electricity using PV cells made of semiconductor material. |
| Photovoltaic-Thermal (PV/T) System |
A photovoltaic system that, in addition to converting sunlight into electricity, collects the residual heat energy and delivers both heat and electricity in usable form. Also called a total energy system. |
| Physical Vapor Deposition | A method of depositing thin semiconductor photovoltaic films. With this method, physical processes, such as thermal evaporation or bombardment of ions, are used to deposit elemental semiconductor material on a substrate. |
| P-I-N | A semiconductor photovoltaic (PV) device structure that layers an intrinsic semiconductor between a p-type semiconductor and an n-type semiconductor; this structure is most often used with amorphous silicon PV devices. |
| PIPE LOSS (Frictional Head Loss) |
The amount of energy or pressure lost due to friction between a flowing liquid and the inside surface of a pipe. |
| Pipeline | A line of pipe with pumping machinery and apparatus (including valves, compressor units, metering stations, regulator stations, etc.) for conveying a liquid or gas. |
| Plate Tectonics | the study of the movement of large crustal plates (lithospheric plates) of the Earth’s shell. The earth’s shell is broken into several pieces (12 large ones and several smaller ones). These plates move toward and away from one another at about the rate our fingernails grow. The process that creates the dynamic movement of the plates includes the convection of magma in the mantle and lithosphere. Plate tectonics helps to explain continental drift, seafloor spreading, volcanic eruptions and other geothermal phenomena, earthquakes, mountain formation and the distribution of some plant and animal species. |
| Plates | A metal plate, usually lead or lead compound, immersed in the electrolyte in a battery. |
| PM | Permanent Magnet, a magnet that retains its magnetism after the removal of the magnetizing force. |
| PMA | Permanent Magnet Alternator. |
| P-N Junction | The semiconductor junction in a photovoltaic cell that shunts electrons into a circuit. Electrons are bumped across this junction by photons (light particles). |
| Pocket Plate | A plate for a battery in which active materials are held in a perforated metal pocket. |
| Point-Contact Cell | A high efficiency silicon photovoltaic concentrator cell that employs light trapping techniques and point-diffused contacts on the rear surface for current collection. |
| Polar Night Jets | An intermittent form of jet stream that occurs above the earth’s poles during the dark winter months. |
| Pole Mount | A PV mount that is installed on the top or side of a pole usually set in concrete. Can be fixed or seasonally tilted. |
| Polycrystalline | See Multicrystalline. |
| Polycrystalline Cell | a wafer of silicon with a multi-grained structure. All grains have the same atomic crystal lattice, however, each grain has a unique orientation in space thereby producing a unique reflection of light. |
| Polycrystalline Silicon | A material used to make photovoltaic cells, which consist of many crystals unlike single-crystal silicon. |
| Poly-Vinyl Chloride (PVC) | A plastic used as an insulator on electrical cables. A toxic material, which is being replaced with alternatives made from more benign chemicals |
| Porous | full of small holes (pores); able to be filled (permeated) by water, air, or other materials. |
| Post And Beam Construction | A traditional building technique in which post and beam framing units are the basic load-bearing members. Post and beams may be of wood, structural steel, or concrete. In this system, there are fewer framing members, leaving more open space for in-fill. Often used in straw bale construction. |
| Power | |
| Power (Watts) | Basic unit of electricity equal to the product of current and voltage (in DC circuits). |
| Power Authorities | Quasi-governmental agencies that perform all or some of the functions of a public utility. |
| Power Conditioning | The process of modifying the characteristics of electrical power (for e.g., inverting direct current to alternating current). |
| Power Conditioning Equipment | Electrical equipment, or power electronics, used to convert power from a photovoltaic array into a form suitable for subsequent use. A collective term for inverter, converter, battery charge regulator, and blocking diode. |
| Power Conversion Efficiency | The ratio of output power to input power e.g. Of an inverter. |
| Power Density | The ratio of the power available from a battery to its volume (Watts per liter) or weight (Watts per kilogram). |
| Power Factor | The cosine of the phase angle between the voltage and the current waveforms in an AC circuit. A measure of inverter performance. |
| Power Factor (Pf) | The ratio of actual power being used in a circuit, expressed in watts or kilowatts, to the power that is apparently being drawn from a power source, expressed in volt-amperes or kilovolt-amperes. |
| Power Grid (Also “Utility Grid”) | A common term referring to an electricity transmission and distribution system. |
| Power Plant | a central station where electricity is produced using turbines and generators. |
| Power Pool | An entity established to coordinate short-term operations to maintain system stability and achieve least-cost dispatch. The dispatch provides backup supplies, short-term excess sales, reactive power support, and spinning reserve. Historically, some of these services were provided on an unpriced basis as part of the members’ utility franchise obligations. Coordinating short-term operations includes the aggregation and firming of power from various generators, arranging exchanges between generators, and establishing (or enforcing) the rules of conduct for wholesale transactions. The pool may own, manage and/or operate the transmission lines ("wires") or be an independent entity that manages the transactions between entities. Often,the power pool is not meant to provide transmission access and pricing, or settlement mechanisms if differences between contracted volumes among buyers and sellers exist. |
| Power Quality | Stability of frequency and voltage and lack of electrical noise on the power grid. |
| Ppm (Parts Per Million) | The unit commonly used to represent the degree of pollutant concentration where the concentrations are small. |
| Preferred Hour-Ahead Schedule | A Scheduling Coordinator’s preferred schedule for the ISO hour-ahead scheduling process. |
| Pressure | The “push” behind liquid or gas in a tank, reservoir, or pipe. Water pressure is directly related to “head”—the height of the top of the water over the bottom. Every 2.31 feet of vertical head gives 1 psi (pound per square inch) of water pressure. |
| Pressurized Water Reactor (Pwr) |
A nuclear power unit cooled by water that is pressurized to keep it from boiling when it reaches high temperatures. |
| Prevailing Wind Direction | The direction from which the wind predominantly blows as a result of the seasons, high and low pressure zones, the tilt of the earth on its axis, and the rotation of the earth. |
| Primary Battery | A battery that cannot be re-charged. |
| Primary Cell | A primary cell is an electrochemical cell (battery) that cannot be recharged. The chemical process within the primary cell is only one way—discharge. When a primary cell is discharged it is discarded. Common flashlight batteries are primary cells; they are disposable batteries that should be avoided. |
| Primary Fuel | Fuel consumed in the original production of energy, before conversion takes place. |
| Programmable Controller | A device that controls the operation of electrical equipment (such as air conditioning units and lights) according to a preset time schedule. |
| Projected Area | The net south-facing glazing area projected on a vertical plane. |
| Propane | A gas that is both present in natural gas and refined from crude oil. It is used for heating, lighting and industrial applications. See also LPG. |
| Propeller | A blade that propels or acts as an airscrew turning by the oncoming wind. Also known as Prop. "slang term for the rotor" |
| Proton | A basic particle present in an atom’s nucleus, which has a positive charge. |
| Provider Of Last Resort | A legal obligation(traditionally given to utilities) to provide service to a customer where competitors have decided they do not want that customer’s business. |
| Psi | See PRESSURE. |
| P-Type Semiconductor | A semiconductor in which holes carry the current. It is produced by doping an intrinsic semiconductor with an an electron accepting impurity. (Eg adding born to silicon) |
| Puelche | A warm, dry wind that blows easterly off the Andes of South America. |
| Pulse Width Modulation (Pwm) | Varying the amount of DC energy sent to a load or other device by changing the length of time a pulse is left on compared to when it is off. The wider the pulse, the greater the energy transfer. |
| Pulse-Width-Modulated (Pwm) Wave Inverter |
A type of power inverter that produce a high quality (nearly sinusoidal) voltage, at minimum current harmonics. |
| Pumped Hydroelectric Storage | Commercial method used for large-scale storage of power. During off-peak times, excess power is used to pump water to a reservoir. During peak times, the reservoir releases water to operate hydroelectric generators. |
| PURPA | The Public Utility Regulatory Policies Act, passed in 1978. Requires utilities to purchase excess generation from small-scale generators. However, without net metering, this can amount to a fraction of retail prices. |
| PV | See PHOTOVOLTAIC |
| PV Array | Two or more photovoltaic modules wired in series or parallel. |
| PV Array-Direct | The use of electricity directly from a photovoltaic array, without batteries or other electrical storage. Many solar water pumps work this way, using a tank to store water. |
| PV Components | The individual parts of a PV System. Individual items like Batteries, Inverters, Regulators, Wiring |
| PV System | All the parts in combination required to generate solar electricity |
| Pyranometer | An instrument for measuring total hemispherical solar irradiance on a flat surface, or "global" irradiance; thermopile sensors have been generally identified as pyranometers, however, silicon sensors are also referred to as pyranometers. |
| Pyrheliometer | An instrument used for measuring direct beam solar irradiance. Uses an aperture of 5.7° to transcribe the solar disc. |
