P to Z

PITA Factor (Pain In The Ass Factor): Cost you allocate to your psychological stress generated from dealing with faulty or cheap equipment, adverse weather, and/ or "challenging" people.

PTC: "PVUSA Test Conditions." For rating solar modules. PTC watt rating is based on 1000 Watt/m2 solar irradiance, 20 degree Celsius ambient temperature, and 1 meter/second wind speed. Since Cell temperatures of modules are much higher than ambient temperature, the PTC watt rating is significantly lower than the "Standard Test Conditions" (STC), a watt-rating used by manufacturers.

PV Cell: The doped semiconductor material that converts sunlight into electricity.

PV Module: Also known as Solar Panel, Solar Module, and PV Panel. Made of a number of separate PV cells soldered together, sealed, and framed into a single unit. Usually wired for 12 or 24 VDC nominal output.

PV Array: A group of photovoltaic (PV) modules connected together physically and/or electrically as part of a PV system.

PV System: An electric power generating system that gets some or all of its energy from a PV Array, usually stores energy in Batteries, and often has an Inverter as well as Balance of System equipment.

PVUSA:Photovoltaics for Utility Scale Applications is a national public-private partnership that began in 1986. PVUSA is supported by PG&E, the U.S. Department of Energy, the California Energy Commission, among others. As of December 1993, PVUSA’s 12 systems generated more than 2.5 million kWh. Our founder Ray Walters worked on one of these projects for Entech, Inc. at PG & E's Davis, CA site.

Panel: (See PV Module)

Parallel Connection: The interconnecting of PV modules or batteries in which like terminals are connected together (i.e. positive to positive, and negative to negative) Increases the current while keeping voltage the same.

Peak Power: Current produced by a module or array operating at the maximum power point of the module. (See Maximum Power Point Tracking)

Peak Sun Hours: The equivalent number of hours per day when solar irradiance averages 1,000 w/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 1,000 w/m².

Peak Wattage: The amount of power a photovoltaic module will produce at standard test conditions (normally 1,000 w/m² and 25º cell temperature).

Phantom Load (ghost load): Loads that take energy when they seem to be off (even after actually being "switched" off). Any device that uses a remote control, or has a clock, takes some power all day. The cure is to unplug those appliances or switch them off with a switched outlet or power strip. Phantom loads, while seemingly small can add up over a 24 hour period. Considering the sun may only shine for 4 to 6 hours a day, you would need 50 watts of PV to power a 10 watt phantom load.

Photovoltaic (PV): Specially treated (doped) silicon that creates electricity from light.

Polycrystalline (Multicrystalline) Silicon: A material used to make PV cells which consists of many crystals. Not as high a performance as single crystal cells.

Power: How fast energy is produced or used, measured in watts. A higher power device will use much more energy in a given time than a low power device. Even a low power device can still use alot of energy if left on for a long time. Amps x (See Energy)

Power Factor (PF): This is a measure of the relationship of the voltage wave to the current's wave, in AC power. A power factor of 1 indicates current and voltage are in phase and power is equal to the simple product of volts x amps (no reactive power). When Power Factor is "bad," less than 1, current and voltage peak at different times (are out of phase), and less power is actually available to the load than the product of volts x amps. The product of the volts x amps in a reactive circuit is called "apparent power" and is measured in "volt-amps" or VA. The "true power" that is useable by the load is measured in watts. The ratio of apparent power to true power is called the power factor.

Puekert's Number: Formula that expresses the relationship between battery capacity and rate of discharge. As rate of discharge lowers (lengthens), useable battery capacity increases. Less of a factor in residential power systems (with lower discharge rates--typically functioning on a 20 to 100 hour rate) than in electric vehicles (with higher discharge rates--typically functioning on a 1 to 6 hour rate).

Rated Battery Capacity: The term used by battery manufacturers to indicate the maximum amount of energy that can be withdrawn from a battery under specified discharge rate and temperature. (See Battery Capacity)

Rated Module Current: The current output of a PV module in Amps, measured at standard test conditions of 1,000 w/m² and 25ºC cell temperature.

Reactive Power: The sine of the phase angle between the current and voltage waveforms in an ac system. (See Power Factor)

Renewable Energy (RE): Energy from sustainable sources (that are inexhaustible and/or self-renewing), such as wind, hydro, solar, and biomass. As opposed to finite energy sources, such as petroleum.

Resistive Load:any electrical device that uses electricity like a simple resistor and has no inductive behavior. As opposed to an Inductive Load.

Resistance (R): The property of a conductor which opposes the flow of an electric current, resulting in the generation of heat in the conducting material and the lowering of voltage in the conductor. The measure of the resistance of a given circuit is the voltage drop across that circuit divided by the current passing through it. The unit of resistance is the ohm.

Reverse Current Protection: Any method of preventing the reverse flow of electricity through PV modules at night, when power is not being generated. (See Blocking Diode; Relay)

Sealed Battery: Battery type that can't be opened to add water. Include "Maintenance free", Absorbed Glass Mat, & Gel Cell batteries.

Self-Discharge: Slow discharge of a battery in storage due to internal losses.

Sell back: The sale of electric energy generated in a local RE grid-tied system to the grid. (See Distributed Generation)

Semiconductor: A material that has a limited capacity for conducting electricity. The silicon used to make PV cells is a semiconductor.

Series Connection: The interconnecting of PV modules or batteries in which opposite terminals are connected together (i.e. positive to negative). Increases the voltage while keeping the amount of current the same.

Shallow Cycle Battery: type of battery that should not be discharged more than 25 percent. (I.e. Auto starter battery)

Shock: Muscular spasm caused by charge flow.

Short Circuit Current (ISC): The current produced by an illuminated PV cell, module, or array when its output terminals are shorted.

Single Axis Tracking: (See Tracking Array)

Silicon: A semiconductor material used to make photovoltaic cells.

Single-Crystal Silicon: Material with a single crystalline formation. Many PV cells are made from single crystal silicon. (See Monocrystalline Cell)

Society of Automotive Engineers (SAE): Provides standards for wiring of most low voltage DC systems in the U.S. (i.e. autos & RVs). Automotive type fusing, battery cables, & batteries are usually SAE approved, but may not be UL listed.

Solar Cell: (See Photovoltaic Cell)

Solar Insolation: (See Insolation)

Solar Irradiance: (See Irradiance)

Solar Noon: The midpoint of time between sunrise and sunset. The point when the sun reaches its highest point in its daily traversal of the sky.

Solar panel: (See PV Module)

Solar Resource: The amount of solar insolation a site receives, usually measured in kWh/m²/day which is equivalent to the number of peak sun hours. (See Insolation; Peak Sun Hours)

Solstice: Time of year when the sun is at its highest (summer solstice) or lowest (winter solstice) point in the sky. The summer solstice occurs around June 21 and is the longest day and shortest night. The winter solstice is around Dec. 21 and is the shortest day and longest night.

South, True: Cardinal direction opposite true north. Points directly towards the south pole of the earth and the sun at solar noon. Direction you should face your solar modules for optimum performance. (See North, True; North, Magnetic; Declination)

Specific Gravity: The ratio of the weight of the solution to the weight of an equal volume of water at a specified temperature. Battery acid can be measured with a hydrometer for an indication of battery state of charge.

Stand-alone PV System: A photovoltaic system that operates independent of the utility grid

Standard Test Conditions (STC): All solar modules are rated under these conditions: 1 kW/m2 of light, and cell temperature of 25ºC (77ºF). STC conditions are only reached in the real world in ideal solar locations like Taos on cool clear days. Some very high altitude sites at noon in mid winter can exceed STC conditions by up to 25%. (See also PTC)

State of Charge (SOC): (See Battery State of Charge)

Strand Count: number of seperate strands of copper making a single wire or cable, A strand count of one is solid core wire, while finely stranded welding cable can have a strand count of 418.

Stratification: Occurs when the acid concentration varies from top to bottom inside the battery electrolyte. Periodic equalization produces gassing that will mix the electrolyte. (See Equalization)

String: A number of solar modules or batteries connected in series to produce higher operating voltages at the same current. (See Series Connection)

Subarray: An array, usually 2 or more modules connected together electrically, which, along with other subarrays, makes up a larger array.

Sulfating: The formation of lead-sulfate crystals on the plates of a lead-acid battery, which reduces its capacity. If the crystals get large enough, shorting of the cell may occur. Light sulfate is dissolved when the battery is recharged

Surge Capacity: The ability of an inverter or generator to deliver high AC current momentarily when starting motors, etc.

Sustainable: Said of a product or activity that can be replenished or continued indefinitely. Petroleum products are not sustainable since petroleum is being used up and cannot be replaced. Wind and sunshine are examples of sustainable power sources. They will continue regardless of what we do. Timber CAN be sustainable, if replanting, and thinning techniques are used instead of clear cutting.

System Operating Voltage: The nominal DC voltage at which the batteries, inverter, charge controller, etc. are designed to operate.

TC: Wire type that is outdoor rated, sunlight resistant, and flexible. Consists of 2 or more insulated stranded wires within an outer jacket. Excellent for interconnect wiring of solar arrays

THHN: Common wire type that needs to be protected either by placement in conduit or junction box.

Temperature Compensation: An allowance made in charge voltages of charge controllers and battery chargers for battery temperature. Feature recommended when battery temperatures are expected to exceed ±5ºC from ambient.

Temperature Factors: It is common for three elements in PV system sizing to have distinct temperature corrections. A factor used to decrease battery capacity at cold temperatures. A factor used to decrease PV module voltage at high temperatures. A factor used to decrease the current carrying capacity of wire at high temperatures.

Terrorist: Any person, group, or government that uses violence or threats of violence to get its way.

Thin Film PV Module: A PV module constructed with sequential layers of thin film semiconductor materials. (See Amorphous Silicon)

Three Stage Charging: Battery charging sequence that consists of bulk charge, absorption charge, and then is held indefinitely at float charge. This type of charging allows batteries to be more fully charged without being overcharged.

Tilt Angle: The angle of inclination of a solar collector measured from the horizontal.

Torque: a rotational force measured in Foot - Lbs, Inch - Lbs, & Newton - Meters (metric). 1 foot-lb. is 1 lb exerted against a 1 ft lever (like a wrench) around a pivot point (the screw). 1 in-lb. of torque is 1 lb. of force applied to 1" of leverage. Finally, 12 inch-lbs = 1 ft-lb. see Torque Table in Wire & connectors.

Tracking Array: A PV array that follows the path of the sun. This can mean single-axis, east to west (azimuth) daily tracking, or dual-axis tracking where the array follows the sun's azimuth and seasonal elevation.

Transformer: A device that transforms AC electricity from one voltage to another (up or down). (See EMF; Inductance)

Trickle Charge: A small charge current intended to maintain a battery in a fully charged condition.

UF: Multi-conductor wire type that is outdoor rated, water proof, sunlight resistant, and suitable for direct burial.

USE: Single conductor wire type that is outdoor rated, water proof, sunlight resistant, and suitable for direct burial.

UL Listed: Means that a specific electrical device or complete assembly has been tested and approved by UL.

UL Recognized: Means that a device is a component that has been tested and approved by UL for a specific purpose and that it can be used with other UL recognized components to make a UL listed assembly. The specific assembly of UL recognized components would still need to be tested to gain a full UL listing. Often it is cost prohibitive to test every possible arrangement of components for full listing. Generally, for home systems to pass local inspection a full system listing is unnecessary, and an unlisted assembly of UL recognized components assembled to be NEC code compliant will almost always be satisfactory.

Underwriters' Laboratories (UL): Nonprofit organization that tests electrical equipment and labels equipment with its seal of approval to indicate it's safe design.

Uninterruptible Power Supply (UPS): A device that provides temporary, emergency power when normal power (from electrical grid) fails. Often used with computers to prevent the loss of data. Usually consists of a mod-sine inverter, batteries, and automatic transfer switch.

Ultra Violet (UV)radiation: Higher frequency light radiation on the upper end of the visible light spectrum.

Volt (V): The unit of electromotive force that will force a current of one ampere through a resistance of one ohm.

Voltage (E): Can be thought of as electrical "pressure," the force that moves electricity. It is not an indication of electrical capacity, because the same pressure can exist in a tiny capillary and a huge viaduct which have very different capacities. Also known as electromotive force and electrical potential. (See Amperage)

Volt-Amps (VA): (See Power Factor)

Warranty: Written guarantee from the manufacturer of a product that they will repair or replace defective parts for a specified time after the purchase

Watt (W): The unit of electrical power. The power developed when a current of one ampere flows through a potential difference of one volt. One watt = one volt x one amp. One watt = 1/746 of a horsepower.

Wattage (P): This is the rate of energy flow, the amount of power in a circuit.

Watt Hour (Wh): A unit of energy equal to one watt of power connected for one hour.

Waveform: The characteristic shape of an AC current or voltage output.