Active area: The surface area of the photovoltaic module responsible for the conversion of light into electricity Adhesive: A material used to bond two surfaces together Amorphous silicon cell (a-Si): A classification of thin-film photovoltaic cells composed of noncrystalline silicon that lacks long-range order and uniform lattice structure; typical Eg = 1.7 eV Antireflective coating: Typically an inorganic coating formulated to decrease the reflection and increase the transmission of specific wavelengths of light
Backsheet: A material typically composed of a polymer used as a primary barrier to the backside of a photovoltaic module Balance of Systems (BOS): Components of the installation used to mount the array to the roof and electrically connect it to the home or business
Band gap (Eg): The energy difference between the valence and conduction bands of a semiconductor material, more commonly referred to as the light energy required for a photovoltaic module to generate energy
Cadmium telluride (CdTe): A thin-film photovoltaic cell composed of a semiconductor constructed of the elements of cadmium and tellurium; typical Eg = 1.44 eV
Casting: Common processing technique used for elastomers and thermosets; an enclosure is used to give the polymer shape, and it is removed after the cure reaction is complete Cell degradation: Chemical and physical processes that decrease the photovoltaic cell’s electrical performance over time Cell interconnects: Electrical connections between cells Cell string: A series of cells connected together in order to increase electrical output
Circular Fresnel lens: Visually appears similar to a planar Fresnel lens but focuses light onto a spot
Compression: A mode of mechanical deformation defined by pressing the specimen between two plates
Concentrated photovoltaics: The use of mirrors, lenses, or both to concentrate light on a small area of photovoltaic cells and generate electricity
Copper indium diselenide (CIS): A thin-film photovoltaic cell made from a semiconductor composed of the elements copper, indium, and selenium; typical Eg = 1.04 eV
Copper indium gallium diselenide (CIGS): A thin-film photovoltaic cell made from a semiconductor composed of the elements of copper, indium, gallium, and selenium; typical Eg = 1.67 eV
Dielectric material: Electrical insulator that creates charge separation when an electric field is applied
Dielectric strength: The minimum electric field that causes polymeric breakdown
Directional hemispherical reflectance: The amount of reflected light from a surface when only irradiated with direct light
Elastic modulus: The slope of the stress versus strain curve in the elastic deformation region
Elastomer: A classification of polymers known for their rubbery mechanical behavior and chemical cross-links
Electrical insulator: A material used to separate and stabilize electrical charges
Electromagnetic spectrum: Categorization of the various wavelengths of electromagnetic radiation, also known as the light spectrum
Encapsulant: An intermittent polymer layer used to encase the photovoltaic cells in a photovoltaic module
Engineering strain: Change in length divided by the initial length
Engineering stress: Deformation force divided by the specimen’s initial area
Ethylene vinyl acetate copolymer (EVA): A copolymer composed of ethylene and vinyl acetate monomers
Fill factor: The peak maximum power divided by the power that would be generated if the device could simultaneously produce at open circuit voltage and short circuit current
Fluorinated polyolefin: A thermoplastic polymer with at least one fluorine atom in its hydrocarbon chain
Free radical: A highly reactive chemical species with an unpaired electron in its atomic orbital
Grid lines: Electrical contacts on photovoltaic cells
Hydrolytic degradation: A chemical mechanism requiring the presence of water which changes the polymer’s chemical composition and physical properties
Injection molding: A method of polymer processing used to convert polymer pellets into a new shape. It involves both heat and pressure created by a reciprocating screw and requires the molten polymer to be injected into a mold carved into the customer’s desired shape.
Insolation: Electromagnetic radiation on an area in a specified geographic location, time of day, and angle of orientation to the sun
Inverter: Electrical components required to covert the panel’s direct current (DC) to the alternating current (AC) output required by the home or business outlets
Ionomer: A classification of polymers that have a pendant ionic group along the backbone of the polymer chain
Irradiance: The power of the radiant electromagnetic light incident on an area per wavelength of light
Junction box: A container used to house electrical wires and connections Lamination: A processing technique used in photovoltaic packaging requiring heat and pressure to melt and encapsulate the photovoltaic cells Lap shear test: An adhesive test that requires pulling two substrates simultaneously in opposite directions
Mechanical strength: The peak stress a specimen experiences before it breaks
Mechanical toughness: A material’s resistance to fracture when under stress
Mole: A unit of measure equivalent to Avogadro’s number (6.022137 x 1023) Multijunction cell: A single solar cell composed of multiple thin-film semiconductor chemistries
Open circuit voltage: The voltage at zero current
Organic cell: A photovoltaic cell composed of polymers responsible for converting light into electricity, also known as a polymeric photovoltaic cell
Oxidative degradation: A chemical mechanism requiring the presence of oxygen that alters both the polymer’s chemical composition and its physical properties
Packaging factor: The effect of the packaging on the maximum power produced by the photovoltaic cells
Peak maximum power: The maximum power produced on a voltage-current curve of a photovoltaic cell or module Peel test: An adhesive test that requires pulling one substrate while holding the second stationary. The direction of force is either 90o or 180o relative to the stationary substrate.
Perfectly competitive market: A market described by no barriers to entry or exit, a high quantity of suppliers, and each supplier sells a homogenous product with no ability to set market prices Photoelectric effect: The phenomenon of converting light into electricity; specifically, the active material emits electrons due to incident light rays
Photovoltaic array: A group of electrically connected photovoltaic modules Photovoltaic cell: Smallest division of a photovoltaic array capable of generating power, typically composed of a semiconductor material that converts light into electricity
Photovoltaic module: A series of connected and encapsulated photovoltaic cells representing the smallest unit of energy generation available for consumer purchase, also known as a photovoltaic panel Photovoltaic thermal energy: Harnessing light energy to generate thermal energy; high-temperature collectors use parabolic mirrors to
concentrate light on a tube of heat transfer fluid used to power a turbine and generate electricity, also known as solar thermal Planar Fresnel lens: A type of Fresnel lens that focuses light into a beam Polar molecule: A molecule with a separation of partial charges into a slightly positive region and slightly negative region of the molecule Polyacetal: A classification of thermoplastic polymers with an acetal group in the chain and synthesized from monomers with an aldehyde or ketone functional group
Polyacrylates: A classification of thermoplastic polymers known for their optical transparency and mechanical strength and synthesized from monomers with an acryl group, also called acrylics, and polymethylmethacrylate is one example
Polycarbonate: A thermoplastic polymer with carbonate groups in the polymer backbone and composed of the monomers bisphenol A and phosgene
Polycrystalline silicon photovoltaic cell: A type of crystalline silicon photovoltaic cell composed of multiple silicon crystals characterized by multiple grain boundaries
Polyene: A polymer with multiple carbon double bonds in its backbone Polyester: A classification of thermoplastic polymers with an ester group in the chain; polyethylene terephthalate is one example Polyethylene naphthalate: A type of polyester known for its barrier properties synthesized from the monomers ethylene glycol and naphthalene dicarboxylic acids
Polyethylene terephthalate (PET): A type of thermoplastic polymer with an ester linkage in its backbone and composed from ethylene glycol and terephthalic acid monomers
Polylactic acid: A type of biodegradable polyester derived from corn starch Polymer: A large, long molecular chain
Polymer fines: Thin slivers of polymeric pellets known to have static attraction to the parts of an injection molding machine resulting in sliver decomposition and part discoloration
Polymer grade: A specific proprietary formulation provided by a manufacturer. It includes the polymer chains and additives.
Polymer laminate: A combination of polymeric layers, metallic layers, or both adhered together to form a single material structure Polymer processing: The study and methodology of converting a polymer from one shape into another
Polyolefin: A thermoplastic composed of olefin monomers (CnH2n)
Potting: A processing technique used with elastomers and thermosets—an enclosure is used to give the polymer shape, and it is left in place after the cure reaction is complete
Quantum efficiency curve: A curve that depicts the ratio of the total amount of electrons generated from the photovoltaic cell divided by the number of incident photons for each incident wavelength of light
Rheology: The study of material flow
Secant modulus: The slope, typically reported in pascal, of a line connecting the origin and a point on the stress-strain curve Semiconductor: A chemistry that can conduct electrons under certain circumstances; the chemistry is typically doped with impurities to form electron acceptors (p-type) and electron donors (n-type)
Short circuit current: The current produced when there is zero voltage Silicone: An elastomeric polymer composed of silicon and oxygen atoms in the backbone of the chain
Single crystalline silicon photovoltaic cell: The most common type of crystalline silicon photovoltaic cell composed of a single silicon crystal characterized by one long-range, uniform lattice structure with no grain boundaries; typical Eg = 1.1 eV
Single junction cell: A single cell composed of one semiconductor chemistry
Solar reflectance: The percentage of sunlight reflected from a surface, also known as albedo and measured in a scale from 0 to 1, with 1 indicating a 100% reflectance
Strain to break: The strain when the specimen macroscopically breaks Superstrate: A material, typically glass, that is the top surface of the photovoltaic module
Tensile: A mode of deformation commonly used in bulk polymer mechanical testing described as pulling the same substrate simultaneously in opposite directions
Thermoplastic: A classification of polymers known for their high modulus and irreversible yield during deformation, also known as plastics Thermoplastic elastomer: A classification of polymers which combines the rubbery properties of an elastomer and the thermoplastic’s ability to flow at elevated temperature
Thin-film cells: A classification of photovoltaic cells denoted by the thin deposition (between a few nanometers and a few microns) of semiconductor material required to generate electricity from sunlight Ultraviolet (UV) degradation: A chemical mechanism stimulated by ultraviolet (UV) radiation that causes a change in the polymer’s chemical composition and physical properties
Ultraviolet-Visible (UV-Vis) spectrum: The transmission or absorbance of electromagnetic radiation by a substrate over the visible and ultraviolet wavelengths of the electromagnetic spectrum Viscosity: The measure of a polymer’s resistance to flow at a specified temperature and pressure while under shear or tensile stress
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