Renewable Energy Glossary

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P-N Junction

The region of a silicon PV cell where the positive and negative layers come together and an electric field is created with a 0.5 volt DC potential difference between the two layers.

Parallel Connections

Those made between wires with the same polarity (positive or negative), and cause current to be additive while voltage remains the same.

Passive

Needs no electromechanical device to operate.

Passive Solar

A building design that uses structural elements of a building for heating and cooling, without the use of mechanical equipment; requires careful consideration of the local climate and solar energy resource, building orientation and proper window sizing, overhangs, and thermal mass for storage.

Passive Solar Design

A system that uses a building's structural elements to heat and cool the building, in order to reduce the use of fuel and mechanical equipment.

Passive Solar Energy System

A system designed to collect, store, and distribute solar energy without the aid of mechanical or electrical devices.

Passive Trackers

Trackers that use a non-motorized mechanism to track the sun's path from east to west throughout the day.

Passive Ventilation

Passive or natural ventilation optimizes natural convective air flow to distribute warm, cool, or fresh air throughout the house. Properly sized and placed doors, operable windows, and skylights can maximize cross-ventilation and air movement

PBI

A performance-based incentive (PBI) is a financial incentive which pays for electricity generated, usually designed as payment per kilowatt-hour for a set number of years.

Peak Demand

Refers to the period of time when a maximum amount of power supply is needed from the utility. Typically, peak-demand periods reflect higher electricity rates than non-peak demand periods.

Peak Sun Hours

A measure of insolation. One peak sun hour is the equivalent amount of time during which irradiance averages 1,000 W/m2 (or 1 kW/m2). Because it is based on amount of time (for example, a day, month, or year), it is the daily, monthly, or annual insolation received by a surface given a specific location, tilt angle, and orientation.

Pelton Runner

A popular impulse turbine runner--a wheel that receives the jet(s) of water, arresting its motion to convert kinetic energy into mechanical power that drives an alternator, generator, or machine. Pelton wheels are made with a series of cups or “buckets” cast on the edge of a rotating disk.

Penstock

The pipe in a hydro system that carries the water from the intake to the turbine.

Performance-Based Incentive

A financial incentive which pays money for electricity generated, usually designed as payment per kilowatt-hour for a set number of years.

Permanent Magnet Alternator

A generating device with permanent magnets (usually ferrite or NdFeB material) in its rotating part (magnet rotor). The changing pattern of magnetism through its fixed coils (stator) creates electricity as the rotor spins.

Permanent Magnet Alternator

A generating device with permanent magnets (usually ferrite or NdFeB material) in its rotating part (magnet rotor). The changing pattern of magnetism through its fixed coils (stator) creates electricity as the rotor spins. The speed (for a given voltage) can only be adjusted by adjusting the magnet rotors while stationary.

Personal Electric Vehicle

Refers to a single-user, battery-powered electric vehicle for short-range use. It can include small, inexpensive battery-powered scooters, electric-assist bicycles, and larger, more expensive products such as motorcycles, Segways, and NEV products.

Personal Fall Arrest System

Consists of a harness, a rope or cable, anchor point(s), and specific attachment hardware, and is one way workers who are exposed to vertical drops of 6 feet or more can meet OSHA fall-protection requirements.

Personal Protective Equipment

Clothing, hats, goggles, gloves, or other equipment designed to reduce exposure to hazards in the workplace.

PEV

PEV can refer to either a personal electric vehicle or, more commonly, a plug-in electric vehicle. Personal electric vehicles are generally small, low-speed single-user products; plug-in electric vehicles can include full-sized, full-featured cars and motorcycles.

PFAS

A personal fall arrest system (PFAS) consists of a harness, a rope or cable, anchor point(s), and specific attachment hardware, and is one way workers who are exposed to vertical drops of 6 feet or more can meet OSHA fall protection requirements.

pH

A measure used to determine the acidity, neutrality, or alkalinity of a solution--a measurement used for testing propylene glycol.

Phantom Loads

Small electric loads that constantly draw power, even when they're turned off. Some examples of traditional appliances that can have a phantom load are televisions, computers, and anything with a remote control or a built-in digital clock, such as microwaves and coffee makers.

PHEV

A plug-in hybrid (PHEV) is a hybrid drive system that allows recharging of the batteries by conventional plug-in charging (rather than exclusively being charged by the gasoline motor, or regenerative braking).

Photovoltaic Cell

A cell that produces electricity from sunlight. Each crystalline cell operates at about one-half a volt; the amount of current produced is dependent on the surface area. Also known as a PV cell.

Photovoltaic Effect

The basic physical process through which a PV cell converts sunlight into electricity.

Photovoltaic Power Source Disconnect

A device that opens the ungrounded PV source and/or output circuits and may also function as an equipment disconnect.

Photovoltaic System

Systems that transform light from the sun directly into electricity, without any moving parts; also known as solar electric or PV systems.

Photovoltaic System Disconnect

A device that disconnects the ungrounded inverter output circuits from the building wiring.

Photovoltaics

A method of generating electrical power by converting solar radiation into DC electricity using semiconductors that exhibit the photovoltaic effect.

Pipe Loss

Lost energy due to friction. For a given size of pipe, friction loss rises rapidly with increased flow. (It varies roughly with the square of the flow.) There will also be friction losses in belt drive systems.

Pitch Control

A method of governing that relies on changing the pitch angle of the blades to reduce their aerodynamic effectiveness and reduce efficiency, and thus to limit speed and production. Blades can be pitched toward feather or stall, reducing or increasing the angle of attack of the blade.

Pitched-Roof PV Array

An array in which the racking structure is attached to an angled roof, generally one with a 3:12 (14-degree) or greater slope.

Plug-In Electric Vehicle

Refers to any car with an electric drivetrain, full electric, or gasoline-electric hybrid. It is most often used to distinguish between hybrids that do and do not allow plug-in recharging, or for vehicles like the Chevy Volt--branded as primarily an electric vehicle, rather than a hybrid.

Plug-In Hybrid Electric Vehicle

A hybrid system that allows the user to recharge the battery system by plugging into a household current or charging station. It's distinguished from a more common hybrid that recharges only from the gasoline motor, or regenerative braking.

Polarity

Testing for polarity means confirming that the positive and negative conductors are in the correct locations; a polarity check needs to be done at each electrical box with all DC sources before commissioning a system.

Pole Mount

A mounting system consisting of a steel pipe placed in a foundation in the ground to provide a support structure for a PV array.

Polycrystalline

PV cells made by a casting silicon in a mold; once solidified, it creates many crystals within the ingot.

Polystyrene Insulation

A common rigid foam insulation that is typically used in below-grade applications.

Potable

Water that is drinkable; domestic water.

Potbox

A simple potentiometer (or rheostat) that is controlled with a cable or shaft from a throttle pedal (or twist-throttle). It is generally used to control the speed of a drive system by using low-voltage signals to the motor speed controller, which then sends high-voltage pulses to the drive motor.

Power

The instantaneous rate at which electricity is transferred by an electric circuit and is a measurement of work; expressed in watts (W). It can be derived from Ohm's Law by multiplying current and voltage (W = V x A).

Power Clipping

Occurs when the array wattage is greater than an inverter or charge controller can output, and the device will decrease the power output.

Power Density

The ratio of a module's wattage to its surface area; modules with a higher power density are more efficient.

Power Purchase Agreement

A contract between a producer and a purchaser, lasting between 15 and 20 years, where the purchaser buys energy, and sometimes capacity, from the producer.

Power Terms

1 kW = 1,000 W; 1 MW = 1,000 kW; 1 GW = 1,000 MW; 1 TW = 1,000 GW

Power Tolerance

The range of variance a manufacturer allows from a module's STC power rating.

PPA

A power purchase agreement (PPA) is a contract between a producer and a purchaser, lasting between 15 and 20 years, where the purchaser buys energy, and sometimes capacity, from the producer.

PPE

Personal protective equipment (PPE) refers to clothing, hats, goggles, gloves, or other equipment designed to reduce exposure to hazards in the workplace.

Pressure Gauge

A gauge in antifreeze systems used to monitor system pressure.

Pressure Gauge

An instrument that displays the pressure (usually close to the turbine itself). A low reading often indicates that reduced stream flow or a blockage at the intake has resulted in air being drawn into the pipe, which in turn has reduced the net head. Reducing the turbine flow or cleaning the nozzle restores normal pressure.

Propeller Turbine

A reaction hydro turbine that uses a propeller-type runner, through which the water flows axially. This is the type of turbine that can handle the largest flows and the lowest heads.

Propylene Glycol

A nontoxic antifreeze; heat transfer fluid that is circulated through IFC systems.

Public Utility Regulatory Policies Act

Requires utilities to purchase power from non-utility generators, including distributed generation such as roof-mounted grid-direct PV systems.

Pulse Width Modulated Devices

Devices that regulate battery charging by switching the PV array on and off hundreds or thousands of times a second to taper the array output current.

Pump Station

An assembly containing a system pump(s), control, valves, air relief, and sometimes a heat exchanger and expansion tank as a single unit.

Pump-as-Turbine

Using water pumps in reverse as turbines, a strategy that has wide applicability. Often the motor can also be used as a generator. This works very well as a low-cost solution, but can be a false economy on sites where the pipe and civil works are the major cost.

PURPA

The Public Utility Regulatory Policies Act (PURPA) requires utilities to purchase power from non-utility generators, including distributed generation such as roof-mounted grid-direct PV systems.

PV

Abbreviation for photovoltaics. A method of generating electrical power by converting solar radiation into DC electricity using semiconductors that exhibit the photovoltaic effect.

PV Array

A group of PV modules or panels wired and mounted together to produce specific levels of current and voltage.

PV Cell

A photovoltaic (PV) cell produces electricity from sunlight; each crystalline cell operates at about one-half a volt; the amount of current produced is dependent on the surface area.

PV Direct System

The simplest type of PV system, consisting of only a PV module and a DC load.

PV Maximum Circuit Current

The sum of parallel module or parallel source circuit STC-rated short-circuit current (Isc) multiplied by 125 percent.

PV Module

Consists of PV cells wired together to produce a desired voltage and current when exposed to sunlight.

PV Output Circuits

The paralleled PV source circuit conductors, which run between a combiner box and the inverter or DC utilization equipment.

PV Panel

According to the National Electrical Code: “a collection of modules mechanically fastened together, wired, and designed to provide a field-installable unit."

PV Source Circuit

The conductors used to wire modules in series, that continue on to an inverter or up to a point of parallel connection such as a DC combiner box; often referred to as series strings or homeruns.

PV Systems

Also known as photovoltaic systems or solar electric systems, transform light from the sun directly into electricity--without any moving parts.

PV Wire

Extra-insulated sunlight-resistant 90ºC wet or dry rated conductor with a non-standard outer diameter used for solar power applications.

PWM

Pulse width modulated (PWM) devices regulate battery charging by switching the PV array on and off hundreds or thousands of times a second to taper the array output current.

Pyronometer

A tool that measures the intensity of sunlight in watts per square meter.

1 A B C D E F G H I J K L M N O P Q R S T U V W Y

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