An interconnected system of PV modules that function as a single electricity-producing unit. In smaller systems, an array can consist of a single module.

Photonics is the physical science and application of light generation, detection, and manipulation through emission, transmission, modulation, signal processing, switching, amplification, and sensing.

Photon energy is the energy carried by a single photon.

A "photoelectrochemical cell" produces electrical energy similarly to a dye-sensitized photovoltaic cell, which meets the standard definition of a photovoltaic cell.

The photoelectric effect is the emission of electrons when electromagnetic radiation, such as light, hits a material.

A photodiode is a semiconductor p-n junction device that converts light into an electrical current.

A phasor measurement unit is a device used to estimate the magnitude and phase angle of an electrical phasor quantity (such as voltage or current) in the electricity grid using a common time source for synchronization.

In chemistry and thermodynamics phase transitions (or phase changes) are the physical processes of transition between the basic states of matter of solids, liquids, and gasses.

Phase change materials, commonly referred to as PCMs, are a technology that is used to store sensible and latent heat within a building structure at a higher storage capacity than standard building materials.

In the physical sciences, a phase is a region of space (a thermodynamic system), throughout which all physical properties of a material are essentially uniform.

Petrology is the branch of geology that studies rocks and the conditions under which they form.

In petroleum geology, a trap is a geological structure affecting the reservoir rock and caprock of a petroleum system allowing the accumulation of hydrocarbons in a reservoir.

Petroleum transport is the transportation of petroleum and derivatives such as gasoline (petrol). Petroleum is transported via rail cars, trucks, tanker vessels, and through pipelines.

A petroleum seep is a place where natural liquid or gaseous hydrocarbons escape to the earth's atmosphere and surface, normally under low pressure or flow.

A petroleum reservoir or oil and gas reservoir is a subsurface pool of hydrocarbons contained in porous or fractured rock formations.

An industrial process plant where crude oil is transformed and refined into useful products such as petroleum naphtha, gasoline, diesel fuel, asphalt base, heating oil, kerosene, liquefied petroleum gas, jet fuel and fuel oils.

Petroleum products are materials derived from crude oil (petroleum) as it is processed in oil refineries.

In geology, a petroleum play, or simply a play, is a group of oil fields or prospects in the same region that are controlled by the same set of geological circumstances.

Petroleum licensing or exploration license is the act of giving licenses (geographical areas at land or sea) to a company or a joint venture allowing them to search for commercially feasible deposits for the extraction of petroleum.

The petroleum industry, also known as the oil industry or the oil patch, includes the global processes of exploration, extraction, refining, transporting (often by oil tankers and pipelines), and marketing of petroleum products.