Absorber: A material that readily absorbs
photons to generate charge carriers (free electrons or holes).
Absorbers: Dark-colored objects that soak up
heat in solar collectors.
Absorption coefficient: The factor by which
photons are absorbed as they travel a unit distance through a material.
Acceptor: A dopant material, such as boron,
which has fewer outer shell electrons than required in an otherwise
balanced crystal structure, providing a hole, which can accept a free
Accessible: (As applied to wiring methods)
Capable of being removed or exposed without damaging the building
structure or finish, or not permanently closed in by the structure or
finish of the building.
Accessible: (as applied to equipment) Admitting
close approach: not guarded by locked doors, elevation, or other effective
means. (see Accessible, Readily)
Accessible, Readily: (Readily Accessible)
Capable of being reached quickly for operation, renewal, or inspections,
without requiring those to whom ready access is requisite to climb over or
remove obstacles or to resort to portable ladders, chairs, etc.
Actinide: an element with atomic number of 89
(actinium) or above.
Activation product: A radioactive isotope of an
element (e.g., in the steel of a reactor core) which has been created by
Active solar heater: A solar water or
space-heating system that moves heated air or water using pumps or fans.
Affected employee: An employee whose job
requires him or her to operate or use a machine or equipment on which
servicing or maintenance is being performed under lockout or tagout, or
whose job requires him or her to work in an area in which such servicing
or maintenance is being performed.
Air Circuit Breakers:
These are used to interrupt circuits while current flows through
them. Compressed air is used to quench the arc when the connection
Air mass: The ratio of the
mass of atmosphere in the actual observer-sun path to the mass that would
exist if the observer was at sea level, at standard barometric pressure,
and the sun was directly overhead. Note: (sometimes called air mass
Air mass 1.5 (AM1.5) standard reference spectrum:
The solar spectral irradiance distribution (diffuse and direct) incident
at sea level on a sun-facing 37-degree tilted surface. The atmospheric
conditions for AM1.5 are: precipitable water vapor, 14.2 mm; total ozone,
3.4 mm; turbidity (base e, lambda=0.5 mm), 0.27. [ASTM E 892, Table 2]
Alternating current: Electric current in which
the direction of flow is reversed at frequent intervals: usually 100 or
120 times per second (50 or 60 cycles per second or 50//60 Hz).
ALARA: As Low As Reasonably Achievable, economic
and social factors being taken into account. This is the optimization
principle of radiation protection.
Alpha particle: A positively-charged particle
from the nucleus of an atom, emitted during radioactive decay. Alpha
particles are helium nuclei, with 2 protons and 2 neutrons.
Alternative fuels: Solid fuels such as municipal
solid waste (MSW), refuse derived fuel (RDF), biomass, rubber tires, and
other combustibles that are used instead of fossil fuels (gas, oil, or
coal) in a boiler to produce steam for the generation of electrical
Ambient Temperature: The temperature of the air,
water, or surrounding earth. Conductor ampacity is corrected for changes
in ambient temperature including temperatures below 86°F. The cooling
effect can increase the current carrying capacity of the conductor.
(Review Section 310-10 of the Electrical Code for more understanding)
Ammeter: An electric meter used to measure
current, calibrated in amperes.
Ampacity: The current-carrying capacity of
conductors or equipment, expressed in amperes.
Ampere (A) or amp: The basic SI unit measuring
the quantity of electricity. The unit for the electric current; the flow
of electrons. One amp is 1 coulomb passing in one second. One amp is
produced by an electric force of 1 volt acting across a resistance of 1
Ampere-hour (Ah): Quantity of electricity or
measure of charge. (1 Ah = 3600 C [Coulomb])
Amorphous semiconductor: A non-crystalline
semiconductor material that has no long-range order.
Annual solar savings: The annual solar savings
of a solar building is the energy savings attributable to a solar feature
relative to the energy requirements of a non-solar building.
Anthropogenic: Referring to alterations in the
environment due to the presence or activities of humans.
Antireflection coating: A thin coating of a
material, which reduces the light reflection and increases light
transmission, applied to a photovoltaic cell surface.
Armored Cable: A cable provided with a wrapping
of metal, usually steel wires or tapes, primarily for the purpose of
Arc-over Voltage: The minimum voltage required
to cause an arc between electrodes separated by a gas or liquid
Array: Any number of photovoltaic modules
connected together to provide a single electrical output. Arrays are often
designed to produce significant amounts of electricity.
Atom: A particle of matter which cannot be
broken up by chemical means. Atoms have a nucleus consisting of
positively-charged protons and uncharged neutrons of the same mass. The
positive charges on the protons are balanced by a number of
negatively-charged electrons in motion around the nucleus.
Attendant: An employee assigned to remain
immediately outside the entrance to an enclosed or other space to render
assistance as needed to employees inside the space.
Attenuation: (l) The ratio of the input to
output power levels in a network (transmission line) when it is excited by
a matched source and terminated in a matched load. (2) Power loss in an
Authorized employee: An employee who locks out
or tags out machines or equipment in order to perform servicing or
maintenance on that machine or equipment. An affected employee becomes an
authorized employee when that employee's duties include performing
servicing or maintenance covered under this section.
Automatic circuit re-closer: A self-controlled
device for interrupting and re-closing an alternating current circuit with
a predetermined sequence of opening and re-closing followed by resetting,
hold-closed, or lockout operation.
Autonomous system: A stand-alone Photovoltaic
system that has no back-up generating source. May or may not include
Availability: Describes the reliability of power
plants. It refers to the number of hours the turbines are available to
produce power divided by the total hours in a year.
Avoided cost: The minimum amount an electric
utility is required to pay an independent power producer, under the PURPA
regulations of 1978, equal to the costs the utility calculates it avoids
in not having to produce that power (usually substantially less than the
retail price charged by the utility for power it sells to customers).
Background radiation: The naturally-occurring
ionizing radiation which every person is exposed to, arising from the
earth's crust (including radon) and from cosmic radiation.
Balance of system: Represents all components and
costs other than the Photovoltaic modules. It includes design costs, land,
site preparation, system installation, support structures, power
conditioning, operation and maintenance costs, indirect storage, and
Band gap: In a semiconductor, the energy
difference between the highest valence band and the lowest conduction
Band gap energy (EG):
The amount of energy (in electron volts) required to free an outer shell
electron from its orbit about the nucleus to a free state and, thus, to
promote it from the valence level to the conduction level.
Band-to-band Auger recombination: Recombination
of an electron and a hole occurring between bands of the same energy in
which no magnetic radiation is emitted.
Bare Conductor: A conductor not covered with
Barricade: A physical obstruction such as tapes,
cones, or A-frame type wood or metal structures intended to provide a
warning about and to limit access to a hazardous area.
Barrier: A physical obstruction which is
intended to prevent contact with energized lines or equipment or to
prevent unauthorized access to a work area.
Barrier energy: The energy given up by an
electron in penetrating the cell barrier; a measure of the electrostatic
potential of the barrier.
Barrier, fire: A continuous membrane, either
vertical or horizontal, such as a wall or floor assembly, that is designed
and constructed with specified fire resistance rating to limit the spread
of fire and that will also restrict the movement of smoke. Such barriers
can have protected openings.
Base load: That part of electricity demand which
is continuous, and does not vary over a 24-hour period. Approximately
equivalent to the minimum daily load.
Base power: Power generated by a utility unit
that operates at a very high capacity factor.
Baseline performance value: Initial values of
short-circuit current, open-circuit voltage, and current at maximum power
measured by the accredited laboratory and corrected to Standard Test
Conditions, used to validate the manufacturer's performance measurements
provided with the qualification modules per IEEE 1262.
These are used in the substation control house as a backup to
power the control systems in case of a power blackout.
Battery energy storage:
The three main applications for battery energy storage systems include
spinning reserve at generating stations, load leveling at substations, and
peak shaving on the customer side of the meter. Battery storage has also
been suggested for holding down air emissions at the power plant by
shifting the time of day of the emission or shifting the location of
Bayonet Coupling: A quick coupling device for
plug and receptacle connectors, accomplished by rotation of a cam
operating device designed to bring the connector halves together.
Becquerel: The SI unit of intrinsic
radioactivity in a material. One Bq measures one disintegration per second
and is thus the activity of a quantity of radioactive material which
averages one decay per second. (In practice, GBq or TBq are the common
Beryllium Copper (BeCu): A relatively expensive
contact material with properties superior to brass and phosphor bronze. It
is recommended for contact applications requiring repeated extraction and
reinsertion because of its resistance to fatigue at high operating
Beta particle: A particle emitted from an atom
during radioactive decay. Beta particles may be either electrons (with
negative charge) or positrons.
BIPV (Building-Integrated Photovoltaic): A term
for the design and integration of Photovoltaic into the building envelope,
typically replacing conventional building materials. This integration may
be in vertical facades, replacing view glass, spandrel glass, or other
facade material; into semitransparent skylight systems; into roofing
systems, replacing traditional roofing materials; into shading
"eyebrows" over windows; or other building envelope systems.
Biological shield: A mass of absorbing material
(e.g., thick concrete walls) placed around a reactor or radioactive
material to reduce the radiation (especially neutrons and gamma rays
respectively) to a level safe for humans.
Blocking diode: A diode used to restrict or
block reverse current from flowing backward through a module. [UL 1703]
Alternatively, diode connected in series to a Photovoltaic string; it
protects its modules from a reverse power flow and, thus, against the risk
of thermal destruction of solar cells.
Boiling water reactor (BWR): A common type of
light water reactor (LWR), where water is allowed to boil in the core thus
generating steam directly in the reactor vessel. (cf PWR)
Bonding Jumper: A bare or insulated conductor
used to ensure the required electrical conductivity between metal parts
required to be electrically connected. Frequently used from a bonding
bushing to the service equipment enclosure to provide a path around
concentric knockouts in an enclosure wall - also used to bond one raceway
Boron (B): A chemical element, atomic number 5,
semi-metallic in nature, used as a dopant to make p-semiconductor layers.
Boule: A sausage-shaped synthetic single-crystal
mass grown in a special furnace, pulled and turned at a rate necessary to
maintain the single-crystal structure during growth.
Breakdown Voltage: The voltage at which an
insulator or dielectric ruptures, or at which ionization and conduction
take place in a gas or vapor.
Breed: To form fissile nuclei, usually as a
result of neutron capture, possibly followed by radioactive decay.
Breeder reactor: see Fast Breeder Reactor and
Fast Neutron Reactor.
British thermal unit (Btu): The amount of heat
energy required to raise the temperature of one pound of water from 60
degrees F to 61 degrees F at one atmosphere pressure.
Burnable poison: A neutron absorber included in
the fuel which progressively disappears and compensates for the loss of
reactivity as the fuel is consumed. Gadolinium is commonly used.
Burnup: Measure of thermal energy released by
nuclear fuel relative to its mass, typically Gigawatt days per tonne (GWd/tU).
Bushing: An insulating structure, including a
through conductor or providing a passageway for such a conductor, with
provision for mounting on a barrier, conducting or otherwise, for the
purposes of insulating the conductor from the barrier and conducting
current from one side of the barrier to the other.
Bus Support Insulators:
These are porcelain or fiberglass insulators that serve to isolate
the bus bar switches and other support structures and to prevent
leakage current from flowing through the structure. These
insulators are similar in function of other insulators used in
substations and transmission poles and towers.
Bypass diode: A diode
connected across one or more solar cells in a photovoltaic module such
that the diode will conduct if the cell(s) become reverse biased. [UL
1703] Alternatively, diode connected anti-parallel across a part of the
solar cells of a Photovoltaic module. It protects these solar cells from
thermal destruction in case of total or partial shading of individual
solar cells while other cells are exposed to full light.
Cable: A conductor with insulation, or a
stranded conductor with or without insulation and other coverings
(single-conductor cable), or a combination of conductors insulated from
one another (multiple-conductor cable).
Cable Assembly: A cable with plugs or connectors
on each end.
Cable sheath: A conductive protective covering
applied to cables. Note: A cable sheath may consist of multiple layers of
which one or more is conductive.
Cadmium (Cd): A chemical element, atomic number
48, used in making certain types of solar cells and batteries.
Cadmium telluride (CdTe): A polycrystalline
thin-film photovoltaic material.
Calandria: (in a CANDU reactor) a cylindrical
reactor vessel which contains the heavy water moderator. It is penetrated
from end to end by hundreds of calandria tubes which accommodate the
pressure tubes containing the fuel and coolant.
CANDU: Canadian deuterium uranium reactor,
moderated and (usually) cooled by heavy water.
Capacitance: That property of a system of
conductors and dielectrics that permits the storage of electricity when
potential difference exists between the conductors. Its value is expressed
as the ratio of quantity of electricity to a potential difference. A
capacitance value is always positive.
An array of capacitors connected into a circuit. Capacitors are
used to control voltages supplied to the customer by eliminating
the voltage drop in the system caused by inductive reactive loads.
Capacity factor: The
amount of energy that the system produces at a particular site as a
percentage of the total amount that it would produce if it operated at
rated capacity during the entire year. For example, the capacity factor
for a wind farm ranges from 20% to 35%. Thirty-five percent is close to
the technology potential.
Cathodic protection: A method of preventing
oxidation (rusting) of exposed metal structures, such as bridges and
pipelines, by imposing between the structure and the ground a small
electrical voltage that opposes the flow of electrons and that is greater
than the voltage present during oxidation.
Cell: The basic unit of a photovoltaic system.
Cell barrier: A very thin region of static
electric charge along the interface of the positive and negative layers in
a photovoltaic cell. The barrier inhibits the movement of electrons from
one layer to the other, so that higher-energy electrons from one side
diffuse preferentially through it in one direction, creating a current and
thus a voltage across the cell. Also called depletion zone, cell junction,
or space charge.
Cell junction: The area of immediate contact
between two layers (positive and negative) of a photovoltaic cell. The
junction lies at the center of the cell barrier or depletion zone.
Central power: The generation of electricity in
large power plants with distribution through a network of transmission
lines (grid) for sale to a number of users. Opposite of distributed power.
Chain reaction: A reaction that stimulates its
own repetition, in particular where the neutrons originating from nuclear
fission cause an ongoing series of fission reactions.
Charge carrier: A free and mobile conduction
electron or hole in a semiconductor.
Chemical vapor deposition (CVD): A method of
depositing thin semiconductor films. With this method, a substrate is
exposed to one or more vaporized compounds, one or more of which contain
desirable constituents. A chemical reaction is initiated, at or near the
substrate surface, to produce the desired material that will condense on
Chlorofluorocarbon: A family of chemicals
composed primarily of carbon, hydrogen, chlorine, and fluorine whose
principal applications are that of refrigerants and industrial cleansers
and whose principal drawback is the tendency to destroy the Earth's
protective ozone layer.
Circuit: A conductor or system of conductors
through which an electric current is intended to flow.
Circuit switchers a a set of switches for redirecting current in a
substation. Circuit switchers provide equipment protection for
transformers, lines, cables, and capacitor banks. They also are
used to energize and deenergize capacitor banks and other
Cladding: The metal tubes
containing oxide fuel pellets in a reactor core.
Clearance (between objects): The clear distance
between two objects measured surface to surface.
Clearance (for work): Authorization to perform
specified work or permission to enter a restricted area.
Cleavage of lateral epitaxial films for transfer
(CLEFT): A process for making inexpensive GaAs photovoltaic cells
in which a thin film of GaAs is grown atop a thick, single-crystal GaAs
(or other suitable material) substrate and then is cleaved from the
substrate and incorporated into a cell, allowing the substrate to be
reused to grow more thin-film GaAs.
Closed Entry Contact: A female contact designed
to prevent the entry of a pin or probing device having a cross-sectional
dimension (diameter) greater than the mating pin.
Coal: A black, solid fossil fuel found in the
Earth. Coal is often burned to make electricity.
Coaxial Cable: A high-band width cable
consisting of two concentric cylindrical conductors with a common axis
that is used for high-speed data communication and video signals.
Cogeneration: The process in which fuel is used
to produce heat for a boiler-steam turbine or gas for a turbine. The
turbine drives a generator that produces electricity, with the excess heat
used for process steam.
Combined collector: A photovoltaic device or
module that provides useful heat energy in addition to electricity.
Compact fluorescent lights: Lights that use a
lot less energy than regular light bulbs. We can use compact fluorescent
lights for reading lights and ceiling lights.
Component Lead: The solid or stranded wire or
formed conductor that extends from a component and serves as a readily
formable mechanical or electrical connection or both.
Compressed-air energy storage (CAES): CAES
plants use off-peak electrical energy to compress air into underground
storage reservoirs for storage until times of peak or intermediate
electricity demand. Wind power offers a good opportunity for charging CAES
storage. The storage is typically underground in natural aquifers,
depleted oil or gas fields, mined salt caverns, or excavated or natural
rock caverns. To generate power, the compressed air is first heated by gas
burners, then passed through a turbine.
Concentrator: A Photovoltaic module that uses
optical elements to increase the amount of sunlight incident on a
Concentrating: arrays must track the sun and use
only the direct sunlight because the diffuse portion cannot be focused
onto the Photovoltaic cells.
Concentrate: See Uranium oxide concentrate (U3O8).
Concentrator (module, array, or collector): An
arrangement of photovoltaic cells that includes a lens to concentrate
sunlight onto small-area cells. Concentrators can increase the power flux
of sunlight hundreds of times.
Concentricity: In a wire or cable, the
measurement of the location of the center of the conductor with respect to
the geometric center of the surrounding insulation.
A platform made of concrete that provides a solid stable support
for large equipment. Concrete foundations or pads are laid for all
large equipment, support structures, and control buildings in a
reciprocal of resistance. It is the ratio of current passing through a
material to the potential difference at its ends.
Conduction band; Conduction level: Energy level
at which electrons are not bound to (orbiting) a specific atomic nucleus
but are free to wander among the atoms. An energy band in which electrons
can move freely in a solid, producing a net transport of charge.
Conductivity: The ability of a material to
conduct electric current. It is expressed in terms of the current per unit
of applied voltage. It is the reciprocal of resistivity.
Conductor: A wire or combination of wires not
insulated from one another, suitable for carrying electric current.
Conduits are hollow tubes running from manhole to manhole in an
underground transmission or distribution system.
Connection: That part of a
circuit that has negligible impedance and that joins components, devices,
Connector: A device providing electrical
connection/disconnections. It consists of a mating plug and receptacle.
Various types of connectors include DIP, card edge, two-piece,
hermaphroditic and wire-wrapping configurations. Multiple contact
connectors join two or more conductors with others in one mechanical
Connector Discontinuity: An ohmic change in
Connector Insert: For connectors with metal
shells, the insert holds contacts in proper arrangement while electrically
insulating them from each other and from the shell.
Connector Shell: The case that encloses the
connector insert and contact assembly. Shells of mating connectors can
protect projecting contacts and provide proper alignment.
Constant-speed wind turbines: Turbines that
operate at a constant rotor revolutions per minute (RPM) and are optimized
for energy capture at a given rotor diameter at a particular speed in the
wind power curve.
Contact, Female: A contact located in an insert
or body in such a manner that the mating contact is inserted into the
unit. It is similar in function to a socket contact.
Contact, Male: A contact located in an insert or
body in such a manner that the mating portion extends into the female
contact. It is similar in function to a pin contact.
Contact Plating: Plated-on metal applied to the
base contact metal to provide the required contact resistance and/or wear
Contact Resistance: Maximum permitted electrical
resistance of pin and socket contacts when assembled in a connector under
typical service use.
Contact Retainer: A device either on the contact
or in the insert to retain the contact.
Contact Size: Defines the largest size wire that
can be used with the specific contact. By specification dimensioning, it
also defines the diameter of the engagement end of the pin.
Contact resistance: The resistance between
metallic contacts and the semiconductor.
Continuity: The state of being whole, unbroken.
Continuous Load: A load where the maximum
current is expected to continue for three hours or more. Rating of the
branch circuit protection device shall not be less tan 125% of the
The substation control house contains switchboard panels,
batteries, battery chargers, supervisory control, power-line
carrier, meters, and relays. The control house provides all
weather protection and security for the control equipment. It is
also called a doghouse.
Control panels contain meters, control switches and recorders
located in the control building, also called a doghouse. These are
used to control the substation equipment, to send power from one
circuit to another or to open or shut down circuits when needed.
Control rods: Devices to
absorb neutrons so that the chain reaction in a reactor core may be slowed
or stopped by inserting them further, or accelerated by withdrawing them.
Control wires are installed connecting the control house control
panels to all the equipment in the substation. A typical
substation control house contains several thousand feet of conduit
and miles of control wire.
process turning U3O8 into UF6 preparatory
Conversion efficiency (cell or module): The
ratio of the electric energy produced by a photovoltaic device (under
one-sun conditions) to the energy from sunlight incident upon the cell.
Converter stations are located at the terminals of a DC
transmission line. Converter stations change alternating current
into direct current and invert direct current to alternating
Coolant: The liquid or gas
used to transfer heat from the reactor core to the steam generators or
directly to the turbines.
Copper indium diselenide (CuInSe2, or CIS):
A polycrystalline thin-film photovoltaic material (sometimes incorporating
gallium (CIGS) and/or sulfur).
Core: The central part of a nuclear reactor
containing the fuel elements and control devices.
Coupling capacitors are used to transmit communication signals to
transmission lines. Some are used to measure the voltage in
Critical mass: The
smallest mass of fissile material that will support a self-sustaining
chain reaction under specified conditions.
Criticality: Condition of being able to sustain
a nuclear chain reaction.
Current at maximum power (Imp): The current at
which maximum power is available from a module. [UL 1703]
Current transformers can be used to supply information for
measuring power flows and the electrical inputs for the operation
of protective relays associated with the transmission and
distribution circuits or for power transformers.
Cycle life: Number of
discharge-charge cycles that a battery can tolerate under specified
conditions before it fails to meet specified criteria as to performance
(e.g., capacity decreases to 80-percent of the nominal capacity).
Czochralski process: A method of growing large
size, high quality semiconductor crystal by slowly lifting a seed crystal
from a molten bath of the material under careful cooling conditions.
Dangling bonds: A chemical bond associated with
an atom on the surface layer of a crystal. The bond does not join with
another atom of the crystal, but extends in the direction of exterior of
dc to DC converter: Electronic circuit to
convert DC voltages (e.g., Photovoltaic module voltage) into other levels
(e.g., load voltage). Can be part of a maximum power point tracker (MPPT).
Decay: Disintegration of atomic nuclei resulting
in the emission of alpha or beta particles (usually with gamma radiation).
Also the exponential decrease in radioactivity of a material as nuclear
disintegrations take place and more stable nuclei are formed.
Decommissioning: Removal of a facility (e.g.,
reactor) from service, also the subsequent actions of safe storage,
dismantling and making the site available for unrestricted use.
De-energized: Free from any electrical
connection to a source of potential difference and from electric charge;
not having a potential different from that of the earth. Note: The term is
used only with reference to current-carrying parts, which are sometimes
Deep discharge: Discharging a battery to
20-percent or less of its full charge.
Deflagration: Propagation of a combustion zone
through a fuel-oxidizer mixture at a rate that is less than the speed of
sound in the un-reacted medium and capable of producing a significant
increase in pressure.
Demand Factor: For an electrical system or
feeder circuit, this is a ratio of the amount of connected load (in kva or
amperes) that will be operating at the same time to the total amount of
connected load on the circuit. An 80% demand factor, for instance,
indicates that only 80% of the connected load on a circuit will ever be
operating at the same time. Conductor capacity can be based on that amount
Dendrite: A slender threadlike spike of pure
crystalline material, such as silicon.
Dendritic web technique: A method for making
sheets of polycrystalline silicon in which silicon dendrites are slowly
withdrawn from a melt of silicon whereupon a web of silicon forms between
the dendrites and solidifies as it rises from the melt and cools.
Depletion zone: Same as cell barrier. The term
derives from the fact that this microscopically thin region is depleted of
charge carriers (free electrons and holes).
Depleted uranium: Uranium having less than the
natural 0.7% U-235. As a by-product of enrichment in the fuel cycle it
generally has 0.25-0.30% U-235, the rest being U-238. Can be blended with
highly-enriched uranium (e.g., from weapons) to make reactor fuel.
Designated employee (designated person): An
employee (or person) who is designated by the employer to perform specific
duties under the terms of this section and who is knowledgeable in the
construction and operation of the equipment and the hazards involved.
Detachment: The locating of a combustible
particulate solid process in the open air or in a separate building.
Deuterium: "Heavy hydrogen", a stable
isotope having one proton and one neutron in the nucleus. It occurs in
nature as 1 atom to 6500 atoms of normal hydrogen, (Hydrogen atoms contain
one proton and no neutrons).
Diallyl Phthalate (DAP): A thermosetting plastic
that offers outstanding dimensional stability and resistance to most
chemicals and chemical compounds. It is used in the production of
Dielectric: (l) Any insulating medium that
intervenes between two conductors. (2) A material that, having the
property required to establish an electric field, is recoverable in whole
or in part as electric energy.
Dielectric Constant: That property of a
dielectric that determines the electrostatic energy stored per unit volume
for a unit potential gradient. Permittivity is the preferred term.
Dielectric Strength: The maximum voltage that a
dielectric material can withstand, under specified conditions, without
rupturing. It is usually expressed as volts/unit thickness. Also called
Disruptive Gradient or Electric Strength.
Dielectric Withstanding Voltage: Maximum
potential gradient that a dielectric material can withstand without
Diffuse insulation: Sunlight received indirectly
as a result of scattering due to clouds, fog, haze, dust, or other
obstructions in the atmosphere. Opposite of direct insulation.
Diffusion furnace: Furnace used to make
junctions in semiconductors by diffusing dopant atoms into the surface of
Diffusion length: The mean distance a free
electron or hole moves before recombining with another hole or electron.
Direct current (dc): Electric current in which
electrons flow in one direction only. Opposite of alternating current.
Direct gain: In direct-gain buildings, sunlight
directly enters the home through the windows and is absorbed and stored in
massive floors or walls. These buildings are elongated in the east-west
direction, and most of their windows are on the south side. The area
devoted to south windows varies throughout the country. It could be as
much as 20% of the floor area in sunny cold climates, where advanced
glazings or moveable insulation are recommended to prevent heat loss at
night. These buildings have high insulation levels and added thermal mass
for heat storage.
Direct insulation: Sunlight falling directly
upon a collector. Opposite of diffuse insulation.
Discharge rate: The rate, usually expressed in
amperes or time, at which electrical current is taken from the battery.
Disconnect switches or circuit breakers are used to isolate
equipment or to redirect current in a substation.
Distributed power: Generic
term for any power supply located near the point where the power is used.
Opposite of central power. See 'stand-alone'; 'remote site.'
Distributed systems: Systems that are installed
at or near the location where the electricity is used, as opposed to
central systems that supply electricity to grids. A residential
photovoltaic system is a distributed system.
A distribution bus is a steel structure array of switches used to
route power out of a substation.
Circuits: These are the connections between the output
terminals of a distribution substation and the input terminals of
primary circuits. The distribution feeder circuit conductors leave
the substation from a circuit breaker or circuit recloser via
underground cables, called substation exit cables.
Transformers: Distribution transformers reduce the
voltage of the primary circuit to the voltage required by
DOD: 'Depth of Discharge,'
from 100-percent state of charge (SOC), in a battery or battery system.
Donor: An n-type dopant that puts an additional
electron into an energy level very near the conduction band; this electron
is easily exited into the conduction band where it increases the
electrical conductivity over than of an undoped semiconductor.
Donor level: The level that donates conduction
electrons to the system.
Dopant: A chemical element (impurity) added in
small amounts to an otherwise pure semiconductor material to modify the
electrical properties of the material. An n-dopant introduces more
electrons. A p-dopant creates electron vacancies (holes).
Doping: The addition of dopants to a
Duct Runs: Ducts
are hollow tubes running from manhole to manhole inside a conduit
in an underground system. They are of various sizes usually from 2
to 6 inches in diameter.
or protected so that dust will not interfere with its successful
Dusttight: Constructed so that dust will not
enter the enclosing case under specified test conditions.
Duty, continuous: A service requirement that
demands operation at a substantially constant load for an indefinitely
Duty, intermittent: A service requirement that
demands operation for alternate intervals of load and no load, load and
rest, or load, no load, and rest.
Duty, periodic: A type of intermittent duty in
which the load conditions regularly reoccur.
Duty, short time: A requirement of service that
demands operations at a substantially constant load for a short and
definitely specified time.
Duty, varying: A requirement of of service that
demands operation at loads, and for intervals of time, both of which may
be subject to wide variation.
Edge-defined film-fed growth (EFG): A method for
making sheets of polycrystalline silicon in which molten silicon is drawn
upward by capillary action through a mold.
Elastomer: A material that at room temperature
stretches under low stress to at least twice its length and snaps back to
original length upon release of stress.
Electric circuit: Path followed by electrons
from a power source (generator or battery) through an external line
(including devices that use the electricity) and returning through another
line to the source.
Electric current: A flow of electrons;
Electrical grid: An integrated system of
electricity distribution, usually covering a large area.
Electric line truck: A truck used to transport
personnel, tools, and material for electric supply line work.
Electric Strength: The maximum potential
gradient that a material can withstand without rupture. Also called
Dielectric Strength and Disruptive Gradient.
Electric supply: Conductors used to transmit
electric energy and their necessary supporting or containing structures.
Signal lines of more than 400 volts are always supply lines within this
section, and those of less than 400 volts are considered as supply lines,
if so run and operated throughout.
Electric supply equipment: Equipment that
produces, modifies, regulates, controls, or safeguards a supply of
Electric utility: An organization responsible
for the installation, operation, or maintenance of an electric supply
Electrodeposition: Electrolytic process in which
a metal is deposited at the cathode from a solution of its ions.
Electrolyte: A liquid conductor of electricity.
Electron volt: An energy unit equal to the
energy an electron acquires when it passes through a potential difference
of one volt; it is equal to 1.602 x 10-19 volt.
Element: A chemical substance that cannot be
divided into simple substances by chemical means; atomic species with same
number of protons.
Emc: Electromagnetic compatibility.
Emi: Electromagnetic interference.
Enclosed space: A working space, such as a
manhole, vault, tunnel, or shaft, that has a limited means of egress or
entry, that is designed for periodic employee entry under normal operating
conditions, and that under normal conditions does not contain a hazardous
atmosphere, but that may contain a hazardous atmosphere under abnormal
Note: Spaces that are enclosed but not designed for employee entry
under normal operating conditions are not considered to be enclosed
spaces for the purposes of this definition. Similarly, spaces that are
enclosed and that are expected to contain a hazardous atmosphere are not
considered to be enclosed spaces for the purposes of this definition.
Such spaces meet the definition of permit spaces in 1910.146, and entry
into them must be performed in accordance with that standard.
Energized (alive, live): Electrically
connected to a source of potential difference, or electrically charged so
as to have a potential significantly different from that of earth in the
Energy audit: A survey that shows how much
energy you use in your house or apartment. It will help you find ways to
use less energy.
Energy contribution potential: Recombination
occurring in the emitter region of a photovoltaic cell.
Energy density: The ratio of energy available
from a battery to its volume (Wh/1) or mass (Wh/kg).
Energy isolating device: A physical device that
prevents the transmission or release of energy, including, but not limited
to, the following: a manually operated electric circuit breaker, a
disconnect switch, a manually operated switch, a slide gate, a slip blind,
a line valve, blocks, and any similar device with a visible indication of
the position of the device. (Push buttons, selector switches, and other
control-circuit-type devices are not energy isolating devices.)
Energy levels: The energy represented by an
electron in the band model of a substance.
Energy source: Any electrical, mechanical,
hydraulic, pneumatic, chemical, nuclear, thermal, or other energy source
that could cause injury to personnel.
Enriched uranium: Uranium in which the
proportion of U-235 (to U-238) has been increased above the natural 0.7%.
Reactor-grade uranium is usually enriched to about 3.5% U-235,
weapons-grade uranium is more than 90% U-235.
Enrichment: Physical process of increasing the
proportion of U-235 to U-238.
Environment: All the natural and living things
around us. The earth, air, weather, plants, and animals all make up our
Epitaxial growth: The growth of one crystal on
the surface of another crystal. The growth of the deposited crystal is
oriented by the lattice structure of the original crystal.
A zone of equal potential used to protect workers from hazardous step and
Extrinsic semiconductor: The product of doping a
Explosionproof: Designed and constructed to
withstand and internal explosion without creating an external explosion or
Exposed: Not isolated or guarded.
Fast breeder reactor (FBR): A fast neutron
reactor configured to produce more fissile material than it consumes,
using fertile material such as depleted uranium in a blanket around the
Fast neutron reactor: A reactor with little or
no moderator and hence utilizing fast neutrons. It normally burns
plutonium while producing fissile isotopes in fertile material such as
depleted uranium (or thorium).
Feeder: A circuit, such as conductors in conduit
or a busway run, which carries a large block of power from the service
equipment to a sub-feeder panel or a branch circuit panel or to some point
at which the block power is broken into smaller circuits.
Fermi level: Energy level at which the
probability of finding an electron is one-half. In a metal, the Fermi
level is very near the top of the filled levels in the partially filled
valance band. In a semiconductor, the Fermi level is in the band gap.
Fertile (of an isotope): Capable of becoming
fissile, by capturing neutrons, possibly followed by radioactive decay;
e.g., U-238, Pu-240.
Fill factor: The ratio of a photovoltaic cell's
actual power to its power if both current and voltage were at their maxima.
A key characteristic in evaluating cell performance.
Fire Barrier Wall: A wall separating buildings
or subdividing a building to prevent the spread of fire and having a fire
resistance rating and structural stability.
Fire loading: The amount of combustibles present
in a given area, expressed in Btu/ft2 (kJ/m2).
Fire point: The lowest temperature at which a
liquid in an open container will give off sufficient vapors to burn once
ignited. It generally is slightly above the flash point.
Fire protection rating: The time, in minutes or
hours, that materials and assemblies used as opening protection have
withstood a fire exposure as established in accordance with test
procedures of NFPA 252, Standard Methods of Fire
Tests of Door Assemblies, and NFPA 257, Standard on Fire Test for Window
and Glass Block assemblies, as applicable.
Fissile (of an isotope): Capable of capturing a
slow (thermal) neutron and undergoing nuclear fission, e.g., U-235, U-233,
Fissionable (of an isotope): Capable of
undergoing fission: If fissile, by slow neutrons; if fertile, by fast
Fission: The splitting of a heavy nucleus into
two, accompanied by the release of a relatively large amount of energy and
usually one or more neutrons. It may be spontaneous but usually is due to
a nucleus absorbing a neutron and thus becoming unstable.
Fission products: Daughter nuclei resulting
either from the fission of heavy elements such as uranium, or the
radioactive decay of those primary daughters. Usually highly radioactive.
Flammable liquid: Any liquid having a flash
point below 100°F (37.8°C) and having a vapor pressure not exceeding an
absolute pressure of 40 psi (276 kPa) at 100°F (37.8°C).
Flat-plate photovoltaic module: An arrangement
of photovoltaic cells mounted on a rigid flat surface with the cells
exposed freely to incoming sunlight.
Flat-plate Photovoltaic: Refers to a
Photovoltaic array or module that consists of non-concentrating elements.
Flat-plate arrays and modules use direct and diffuse sunlight, but if the
array is fixed in position, some portion of the direct sunlight is lost
because of oblique sun-angles in relation to the array.
Float charge: Float charge is the voltage
required to counteract the self-discharge of the battery at a certain
Float life: Number of years that a battery can
keep its stated capacity when it is kept at float charge (see float
Float-zone process: A method of growing a
large-size, high-quality crystal whereby coils heat a polycrystalline
ingot placed atop a single-crystal seed. As the coils are slowly raised
the molten interface beneath the coils becomes single crystal.
Fossil fuel: A fuel based on carbon presumed to
be originally from living matter, e.g., coal, oil, gas. Burned with oxygen
to yield energy, used in a boiler to produce steam for the generation of
Fresnel lens: An optical device that focuses
light like a magnifying glass; concentric rings are faced at slightly
different angles so that light falling on any ring is focused to the same
point. Fresnel lenses are flat rather than thick in the center and can be
stamped out in a mold.
A frequency changer is a motor-generator set that changes power of
an alternating current system from one frequency to one or more
different frequencies, with or without a change in the number of
phases, or in voltage.
Fuel: Any material that
can be burned to make energy.
Fuel assembly: Structured collection of fuel
rods or elements, the unit of fuel in a reactor.
Fuel cell: A device that converts the energy of
a fuel directly to electricity and heat, without combustion. Because there
is no combustion, fuel cells give off few emissions; because there are no
moving parts, fuel cells are quiet.
Fuel fabrication: Making reactor fuel
assemblies, usually from sintered UO2 pellets which are
inserted into zircalloy tubes, comprising the fuel rods or elements.
Gallium (Ga): A chemical element, atomic number
31, metallic in nature, used in making certain kinds of solar cells and
Gallium arsenide (GaAs): A crystalline
high-efficiency semiconductor/photovoltaic material.
Gamma rays: High energy electro-magnetic
radiation from the atomic nucleus, virtually identical to X-rays.
Gassing current: Portion of charge current that
goes into electrolytic production of hydrogen and oxygen from the
electrolytic liquid. This current increases with increasing voltage and
Gel-type battery: Lead-acid battery in which the
electrolyte is composed of a silica gel matrix.
Genetic mutation: Sudden change in the
chromosomal DNA of an individual gene. It may produce inherited changes in
descendants. Mutation in some organisms can be made more frequent by
irradiation (though this has never been demonstrated in humans).
Gigawatt (GW): One billion watts. One million
kilowatts. One thousand megawatts.
Glazings: Clear materials (such as glass or
plastic) that allow sunlight to pass into solar collectors and solar
buildings, trapping heat inside.
Grain boundaries: The boundaries where
crystallites in a polycrystalline material meet.
Graphite: Crystalline carbon used in very pure
form as a moderator, principally in gas-cooled reactors, but also in
Soviet-designed RBMK reactors.
Gray: The SI unit of absorbed radiation dose,
one joule per kilogram of tissue.
Greenhouse effect: The effect of the Earth's
atmosphere, due to certain gases, in trapping heat from the sun; the
atmosphere acts like a greenhouse.
Greenhouse gases: Gases that trap the heat of
the sun in the Earth's atmosphere, producing the greenhouse effect; the
two major greenhouse gases are water vapor and carbon dioxide; lesser
greenhouse gases include methane, ozone, chlorofluorocarbons, and nitrogen
Grid-connected (Photovoltaic system):
A Photovoltaic system in which the Photovoltaic array acts like a central
generating plant, supplying power to the grid.
Grid-interactive (Photovoltaic system):
See 'Grid-connected (Photovoltaic system).'
Ground: A large conducting body (such as the
earth) used as a common return for an electric circuit and as an arbitrary
zero of potential.
Grounded, effectively: Intentionally connected
to earth through a ground connection or connections of sufficiently low
impedance and having sufficient current-carrying capacity to prevent the
buildup of voltages that may result in undue hazards to connect equipment
or to persons.
Grounded Conductor: A system or circuit
conductor that is intentionally grounded, usually gray or white in color.
Grounding Conductor: A conductor used to connect
metal equipment enclosures and/or the system grounded conductor to a
grounding electrode, such as the ground wire run to the water pipe at a
service; also may be a bare or insulated conductor used to ground motor
frames, panel boxes, and other metal equipment enclosures used throughout
electrical systems. In most conduit systems, the conduit is used as the
Grounding Equipment Conductor: The conductor
used to connect the noncurrent-carrying metal parts of equipment,
raceways, and other enclosures to the system grounded conductor, the
grounding electrode conductor, or both, of the circuit at the service
equipment or at the source of a separately derived system.
Grounding Electrode: The conductor used to
connect the grounding electrode to the equipment grounding conductor, to
the grounded conductor, or to both, of the circuit at the service
equipment or at the source of a separately derived system.
Grounding Resistors are designed to provide added safety to
industrial distribution systems by limiting ground fault current
to reasonable levels.
Transformers: A grounding transformer intended
primarily to provide a neutral point for grounding purposes.
Ground Fault Circuit Interrupter: A device intended for the
protection of personal that functions to de-energize a circuit or portion
thereof within an established period of time when a current to ground
exceeds some predetermined value that is less than required to operate the
overcurrent protection device of the supply circuit.
Ground Fault Protection of Equipment: A system
intended to provide protection of equipment from damaging line to ground
fault currents by operating to cause a disconnecting means to open all
ungrounded conductors of the faulted circuit. This protection is provided
at current levels less than those required to protect conductors from
damage through the operations of a supply circuit overcurrent device.
Guarded: Covered, fenced, enclosed, or otherwise
protected, by means of suitable covers or casings, barrier rails or
screens, mats, or platforms, designed to minimize the possibility, under
normal conditions, of approach or accidental contact by persons or
objects. Note: Wires which are insulated, but not otherwise protected, are
not considered as guarded.
Half-life: The period required for half of the
atoms of a particular radioactive isotope to decay and become an isotope
of another element.
Hazardous atmosphere: An atmosphere that may
expose employees to the risk of death, incapacitation, impairment of
ability to self-rescue (that is, escape unaided from an enclosed space),
injury, or acute illness from one or more of the following causes:
Flammable gas, vapor, or mist in excess of 10 percent of its lower
flammable limit (LFL);
Airborne combustible dust at a concentration that meets or exceeds
its LFL; Note: This concentration may be approximated as a condition
in which the dust obscures vision at a distance of 5 feet (1.52 m) or
Atmospheric oxygen concentration below 19.5 percent or above 23.5
Atmospheric concentration of any substance for which a dose or a
permissible exposure limit is published and which could result in
employee exposure in excess of its dose or permissible exposure limit;
Note: An atmospheric concentration of any substance that is
not capable of causing death, incapacitation, impairment of
ability to self-rescue, injury, or acute illness due to its health
effects is not covered by this definition.
Any other atmospheric condition that is immediately dangerous to
life or health.
Note: For air contaminants for which OSHA has not determined a
dose or permissible exposure limit, other sources of information,
such as Material Safety Data Sheets that comply with the Hazard
Communication Standard, 1910.1200, published information, and
internal documents can provide guidance in establishing acceptable
Heat pump: Like an air
conditioner or refrigerator, a heat pump moves heat from one location to
another. In the cooling mode, heat pumps reduce indoor temperatures in the
summer by transferring heat to the ground. Unlike an air conditioning
unit, however, a heat pump's cycle is reversible. In winter, a heat pump
can extract heat from the ground and transfer it inside. The energy value
of the heat thus moved can be more than three times the cost of the
electricity required to perform the transfer process.
Heavy water: Water containing an elevated
concentration of molecules with deuterium ("heavy hydrogen")
Heavy water reactor (HWR): A reactor which uses
heavy water as its moderator, e.g., Canadian CANDU (pressurized HWR or
Heterojunction: A region of electrical contact
between two different semiconductor materials.
High-level wastes: Extremely radioactive fission
products and transuranic elements (usually other than plutonium) in spent
nuclear fuel. They may be separated by reprocessing the spent fuel, or the
spent fuel containing them may be regarded as high-level waste.
Highly (or High)-enriched uranium (HEU): Uranium
enriched to at least 20% U-235. (In weapons it is about 90% U-235.)
High-power tests: Tests in which fault currents,
load currents, magnetizing currents, and line-dropping currents are used
to test equipment, either at the equipment's rated voltage or at lower
Underground Cables: High voltage cables are designed to
carry high voltage current and are constructed in many different
ways, but are usually shielded cables. They are made with a
conductor, conductor-strand shielding, insulation, semi-conducting
insulation shielding, metallic insulation shielding, and a sheath.
High voltage direct current (HVDC)
converter station: A facility that functions as an electrical
rectifier (ac-dc) to control and transmit power in a high voltage network.
There are two types of HVDC valves: the mercury arc valve and the
present-day technology solid state thyristor valve. Both types of valves
present a fire risk due to high voltage equipment that consists of
oil-filled converter transformers, wall bushings, and capacitors in
addition to various polymeric components.
High Voltage Fuses:
High voltage fuses are used to protect the electrical system in a
substation from power transformer faults. They are switched for
maintenance and safety.
Tests in which voltages of approximately 1000 volts are used as a
practical minimum and in which the voltage source has sufficient energy to
High wind: A wind of such velocity that the
following hazards would be present:
An employee would be exposed to being blown from elevated
an employee or material handling equipment could lose control of
material being handled, or
an employee would be exposed to other hazards not controlled by
the standard involved.
Note: Winds exceeding 40 miles per hour (64.4 kilometers per
hour), or 30 miles per hour (48.3 kilometers per hour) if material
handling is involved, are normally considered as meeting this
criteria unless precautions are taken to protect employees from
the hazardous effects of the wind.
Hole: The vacancy
where an electron would normally exist in a solid; behaves like a
positively charged particle.
Homojunction: The region between an n-layer and
a p-layer in a single material photovoltaic cell.
Hybrid system: A Photovoltaic system that
includes other sources of electricity generation, such as wind or diesel
Hydrogenated amorphous silicon: Amorphous
silicon with a small amount of incorporated hydrogen. The hydrogen
neutralizes dangling bonds in the amorphous silicon, allowing charge
carriers to flow more freely.
Impedance: The total opposition that a circuit
offers to the flow of alternating current or any other varying current at
a particular frequency.
Incident light: Light that shines onto the face
of a solar cell or module.
Indium oxide: A wide band gap semiconductor that
can be heavily doped with tin to make a highly conductive, transparent
thin film. Often used as a front contact or one component of a
heterojunction solar cell.
Inductive reactance: Electrical
current produces heat and/or a magnetic field (such as in the windings of
a motor). We refer to the tendency for current flow and changes in flow to
be influenced by magnetic fields as inductance. An AC circuit that
contains only inductance, capacitance or a combination of the two is
defined by the total opposition to current flow expressed in reactance.
Inductance only affects current flow when the current is changing.
Inductance produces a self-induced voltage (called a counter emf) that
opposes changes in current. Obviously, the current changes constantly in
an AC circuit. Inductance in an AC circuit, therefore, causes a continual
opposition. This opposition to current flow is called inductive reactance.
Infrared radiation: Electromagnetic radiation
whose wavelengths lie in the range from 0.75 micrometer to 1000
Insertion Force: The effort, usually measured in
ounces, required to engage mating components.
Insulation: A material that offers high electric
resistance making it suitable for covering components, terminals and wires
to prevent the possible future contact of adjacent conductors resulting in
a short circuit.
Insolation: Sunlight, direct or diffuse; from
'incident solar radiation.' Not to be confused with insulation.
Insulation: Materials that prevent or slow down
the movement of heat.
In situ leaching (ISL): The recovery by chemical
leaching of minerals from porous ore bodies without physical excavation.
Also known as solution mining.
In Sight From: (within sight from, within sight)
Where it is specified that one equipment shall be "in sight
from", "within sight from" or "within sight",
etc. of another equipment, the specified equipment is to be visible and
not more that 50´ distant from the other
Insulated: Separated from other conducting
surfaces by a dielectric (including air space) offering a high resistance
to the passage of current.
Note: When any object is said to be insulated, it is understood to
be insulated for the conditions to which it is normally subjected.
Otherwise, it is, within the purpose of this section, uninsulated.
That which is relied upon to insulate the conductor from other conductors
or conducting parts or from ground.
Interconnect: A conductor within a module or
other means of connection which provides an electrical interconnection
between the solar cells. [UL 1703]
Interfacial Seal: Sealing of a two-piece,
multiple contact connector over the whole area of the interface to provide
sealing around each contact.
Interrupter Rating: The highest current at rated
voltage that a device is intended to interrupt under standard test
Intrinsic semiconductor: An undoped
Inverters: Devices that convert DC electricity
into AC electricity (single or multiphase), either for stand-alone systems
(not connected to the grid) or for utility-interactive systems.
Ion: An atom that is electrically-charged
because of loss or gain of electrons.
Ionizing radiation: Radiation (including alpha
particles) capable of breaking chemical bonds, thus causing ionization of
the matter through which it passes and damage to living tissue.
Irradiate: Material subjected to ionizing
radiation. Irradiated reactor fuel and components have been subjected to
neutron irradiation and hence become radioactive themselves.
Isotope: An atomic form of an element having a
particular number of neutrons. Different isotopes of an element have the
same number of protons but different numbers of neutrons and hence
different atomic mass, e.g.,. U-235, U-238. Some isotopes are unstable and
decay to form isotopes of other elements.
ISPRA guidelines: Guidelines for the assessment
of Photovoltaic Plants, published by the Joint Research Centre of the
Commission of the European Communities, Ispra, Italy.
I-type semiconductor: Semiconductor material
that is left intrinsic, or undoped so that the concentration of charge
carriers is characteristic of the material itself rather than of added
I-V curve: A graphical presentation of the
current versus the voltage from a photovoltaic device as the load is
increased from the short circuit (no load) condition to the open circuit
(maximum voltage) condition. The shape of the curve characterized cell
I-V data: The relationship between current and
voltage of a photovoltaic device in the power-producing quadrant, as a set
of ordered pairs of current and voltage readings in a table, or as a curve
plotted in a suitable coordinate system (e.g., Cartesian). [ASTM E 1036]
Jacket: Outermost layer of insulating material
of a cable or wire.
Junction: A region of transition between
semiconductor layers, such as a p/n junction, which goes from a region
that has a high concentration of acceptors (p-type) to one that has a high
concentration of donors (n-type).
Junction box: A Photovoltaic generator junction
box is an enclosure on the module where Photovoltaic strings are
electrically connected and where protection devices can be located, if
Junction diode: A semiconductor device with a
junction and a built-in potential that passes current better in one
direction than the other. All solar cells are junction diodes.
Kilowatt (kW): 1000 watts.
Kilowatt-hour (kWh): One thousand watts acting
over a period of 1 hour. The kWh is a unit of energy. 1 kWh=3600 kJ.
Labeled: Items to which a label, trademark, or
other identifying mark of nationally recognized testing labs has been
attached to identify the items as having been tested and meeting
Lattice: The regular periodic arrangement of
atoms or molecules in a crystal.
Light-induced defects: Defects, such as dangling
bonds, induced in an amorphous silicon semiconductor upon initial exposure
Lightning arresters are devices for protecting many different
pieces of equipment such as, power poles and towers, power
transformers, circuit breakers, bus structures, and steel
superstructures, from damage from lightning strikes.
Light trapping: The
trapping of light inside a semiconductor material by refracting and
reflecting the light at critical angles; trapped light will travel further
in the material, greatly increasing the probability of absorption and
hence of producing charge carriers.
Light water: Ordinary water (H20) as
distinct from heavy water.
Light water reactor (LWR): A common nuclear
reactor cooled and usually moderated by ordinary water.
Lines, Communication: The conductors and their
supporting or containing structures which are used for public or private
signal or communication service, and which operate at potentials not
exceeding 400 volts to ground or 750 volts between any two points of the
circuit, and the transmitted power of which does not exceed 150 watts. If
the lines are operating at less than 150 volts, no limit is placed on the
transmitted power of the system. Under certain conditions, communication
cables may include communication circuits exceeding these limitations
where such circuits are also used to supply power solely to communication
Note: Telephone, telegraph, railroad signal, data, clock, fire,
police alarm, cable television, and other systems conforming to this
definition are included. Lines used for signaling purposes, but not
included under this definition, are considered as electric supply lines
of the same voltage.
An inverter that is tied to a power grid or line. The commutation of power
(conversion from DC to AC) is controlled by the power line, so that, if
there is a failure in the power grid, the Photovoltaic system cannot feed
power into the line.
Listed: Equipment or materials included in a
list published by an organization acceptable to the authority having
jurisdiction and concerned with product evaluation, that maintains
periodic inspection of production of listed equipment or materials, and
whose listing states either that the equipment or material meets
appropriate designated standards or has been tested and found suitable for
use in specified manner.
Load: Anything in an electrical circuit that,
when the circuit is turned on, draws power from that circuit.
Location, damp: A location subject to moderate
amount of moisture such as some basements, barns, cold storage, warehouse
and the like.
Location, dry: A location not normally subject
to dampness or wetness: a location classified as dry may be temporarily
subject to dampness or wetness, as in case of a building under
Location, wet: A location subject to saturation
with water or other liquids.
Low-enriched uranium: Uranium enriched to less
than 20% U-235. (That in power reactors is usually 3.5: 5.0% U-235.)
Lower Flammable Limit (LFL): The lowest
concentration of material that will propagate a flame from an ignition
source through a mixture of flammable gas or combustible dust dispersion
with a gaseous oxidizer.
Majority carrier: Current carriers (either free
electrons or holes) that are in excess in a specific layer of a
semiconductor material (electrons in the n-layer, holes in the p-layer) of
manhole is the opening in the underground duct system which houses
cables plices and which cablemen enter to pull in cable and to
make splices and tests. Also called a splicing chamber or cable
Marginal cost: The cost of
one additional unit within a group of like units.
Maximum power point (MPP): The point on the
current-voltage (I-V) curve of a module under illumination, where the
product of current and voltage is maximum. [UL 1703] For a typical silicon
cell, this is at about 0.45 V.
Maximum power point tracker (MPPT): Means of a
power conditioning unit that automatically operates the
Photovoltaic-generator at its MPP under all conditions.
Megaohm: A unit of electrical resistance equal
to one million ohms.
Megaohmmeter: An instrument for measuring
extremely high resistance.
Megawatt (MW): A unit of power, = 106
watts. MWe refers to electric output from a generator, MWt to thermal
output from a reactor or heat source (e.g., the gross heat output of a
reactor itself, typically three times the MWe figure).
Megger: A test instrument for measuring the
insulation resistance of conductors and other electrical equipment;
specifically, a megaohm (million ohms) meter; this is a registered trade
mark of the James Biddle Co.
An outdoor metal-clad switchgear is a weatherproof housing for
circuit breakers, protective relays, meters, current transformers,
potential transformers, bus conductors, and other equipment. An
indoor switchgear must be protected from the environment and
contains the same types of equipment as the outdoor type.
Metal fuels: Natural
uranium metal as used in a gas-cooled reactor.
are measuring devices and can be an indicating meter or a
recording meter. An indicating meter shows on a dial the quantity
being measured. A recording meter makes a permanent record of the
quantity being measured, usually by tracing a line on a chart or
Micro: one millionth of a
unit (e.g., microsievert is 10-6 Sv).
Microgroove: A small groove scribed into the
surface of a cell which is filled with metal for contacts.
Substations commonly use microwave communication equipment for
communication with local and regional electric power system
control centers. This system allows for rapid communication and
signaling for controlling the routing of power.
Milling: Process by which
minerals are extracted from ore, usually at the mine site.
Minority carrier: A current carrier, either an
electron or a hole, that is in the minority in a specific layer of a
semiconductor material; the diffusion of minority carriers under the
action of the cell junction voltage is the current in a photovoltaic
Minority carrier lifetime: The average time a
minority carrier exists before recombination.
Mixed oxide fuel (MOX): Reactor fuel which
consists of both uranium and plutonium oxides, usually about 5% Pu, which
is the main fissile component.
Moderator: A material such as light or heavy
water or graphite used in a reactor to slow down fast neutrons by
collision with lighter nuclei so as to expedite further fission.
Module: See 'Photovoltaic Module.'
Monolithic: Fabricated as a single structure.
Multicrystalline: Material that is solidified at
such as rate that many small crystals (crystallites) form. The atoms
within a single crystallite are symmetrically arranged, whereas
crystallites are jumbled together. These numerous grain boundaries reduce
the device efficiency. A material composed of variously oriented, small
individual crystals. (Sometimes referred to as polycrystalline or
Multijunction device: A photovoltaic device
containing two or more cell junctions, each of which is optimized for a
particular part of the solar spectrum, to achieve greater overall
Natural uranium: Uranium with an isotopic
composition as found in nature, containing 99.3% U-238, 0.7% U-235 and a
trace of U-234. Can be used as fuel in heavy water-moderated reactors.
Neutron: An uncharged elementary particle found
in the nucleus of every atom except hydrogen. Solitary mobile neutrons
traveling at various speeds originate from fission reactions. Slow
(thermal) neutrons can in turn readily cause fission in nuclei of
"fissile" isotopes, e.g., U-235, Pu-239, U-233; and fast
neutrons can cause fission in nuclei of "fertile" isotopes such
as U-238, Pu-239. Sometimes atomic nuclei simply capture neutrons.
Noninductive Circuit: A circuit in which the
magnetic effect of the current flowing has been reduced by one several
methods to a minimum or to zero.
Nonlinear Load: A load where the wave shape of
the steady state current does not follow the wave shape of the applied
Nonrenewable fuels: Fuels that cannot be easily
made or "renewed." We can use up nonrenewable fuels. Oil,
natural gas, and coal are nonrenewable fuels.
N-type semiconductor: A semiconductor produced
by doping an intrinsic semiconductor with an electron-donor impurity
(e.g., phosphorous in silicon).
Nuclear energy: Energy that comes from splitting
atoms of radioactive materials, such as uranium.
Nuclear reactor: A device in which a nuclear
fission chain reaction occurs under controlled conditions so that the heat
yield can be harnessed or the neutron beams utilized. All commercial
reactors are thermal reactors, using a moderator to slow down the
"O" RING: A doughnut-shaped ring of
rubber used as a seal around the periphery of the mating insulator
interface of cylindrical connectors.
Ohm: The derived SI unit for electrical
resistance or impedance; one ohm equals one volt per ampere.
Ohmmeter: an instrument for measuring resistance
Oil: A black liquid fossil fuel found deep in
the Earth. Gasoline and most plastics are made from oil.
Oil Circuit Breakers:
Oil circuit breakers are used to switch circuits and equipment in
and out of a system in a substation. They are oil filled to
provide cooling and to prevent arcing when the switch is
One-axis tracking: A
system capable of rotating about one axis.
Open-circuit voltage (Voc): The maximum possible
voltage across a photovoltaic cell or module; the voltage across the cell
in sunlight when no current is flowing.
Overcurrent: Any current in excess of the rated
current of equipment or the ampacity of a conductor. It may result from
overload, short circuit or ground fault.
Overload: Load greater than the load for which
the system or mechanism was intended. A fault, such as a short circuit or
ground fault, is not an overload.
Oxide fuels: Enriched or natural uranium in the
form of the oxide UO2, used in many types of reactor.
Packing factor: The ratio of array area to
actual land area or building envelope area, for a system; or, the ratio of
total Photovoltaic cell area to the total module area, for a module.
Panelboard: A single panel or group of panel
units designed for assembly in the form of a single panel: includes buses
and may come with or without switches and/or automatic overcurrent
protective devices for the control of light, heat, or power circuits of
individual as well as aggregate capacity. It is designed to be placed in a
cabinet or cutout box that is in or against a wall or partition and is
accessible only from the front.
Parallel connection: A way of joining two or
more electricity-producing devices (i.e., Photovoltaic cells or modules)
by connecting positive leads together and negative leads together; such a
configuration increases the current.
Passivation: A chemical reaction that eliminates
the detrimental effect of electrically reactive atoms on a photovoltaic
Passive solar home: A house that uses a room or
another part of the building as a solar collector.
Peak load; Peak demand: The maximum load, or
usage, of electrical power occurring in a given period of time, typically
Peak power: Power generated by a utility unit
that operates at a very low capacity factor; generally used to meet
short-lived and variable high demand periods.
Peak watts (Wp): See 'Photovoltaic peak watt.'
Phosphorous (P): A chemical element, atomic
number 15, used as a dopant in making n-semiconductor layers.
Photocurrent: An electric current induced by
Photoelectrochemical cell: A special kind of
photovoltaic cell in which the electricity produced is used immediately
within the cell to produce a useful chemical product, such as hydrogen.
The product material is continuously withdrawn from the cell for direct
use as a fuel or as an ingredient in making other chemicals, or it may be
stored and used subsequently.
Photon: A particle of light that acts as an
individual unit of energy.
Photovoltaic (Photovoltaic): Pertaining to the
direct conversion of light into electricity.
Photovoltaic (Photovoltaic) array: An
interconnected system of Photovoltaic modules that function as a single
electricity-producing unit. The modules are assembled as a discrete
structure, with common support or mounting. In smaller systems, an array
can consist of a single module.
Photovoltaic (Photovoltaic) cell: The smallest
semiconductor element within a Photovoltaic module to perform the
immediate conversion of light into electrical energy (dc voltage and
Photovoltaic (Photovoltaic) conversion efficiency:
The ratio of the electric power produced by a photovoltaic device to the
power of the sunlight incident on the device.
Photovoltaic (Photovoltaic) device: A device
that converts light directly into DC electricity.
Photovoltaic (Photovoltaic) efficiency: The
ratio of electric power produced by a cell at any instant to the power of
the sunlight striking the cell.
Photovoltaic (Photovoltaic) generator: The total
of all Photovoltaic strings of a Photovoltaic power supply system, which
are electrically interconnected.
Photovoltaic (Photovoltaic) module: The smallest
environmentally protected, essentially planar assembly of solar cells and
ancillary parts, such as interconnections, terminals, [and protective
devices such as diodes] intended to generate DC power under unconcentrated
sunlight. The structural (load carrying) member of a module can either be
the top layer (superstrate) or the back layer (substrate). [UL 1703]
Photovoltaic (Photovoltaic) panel: often used
interchangeably with Photovoltaic module (especially in one-module
systems), but more accurately used to refer to a physically connected
collection of modules (i.e., a laminate string of modules used to achieve
a required voltage and current).
Photovoltaic (Photovoltaic) peak watt: Maximum
"rated" output of a cell, module, or system. Typical rating
conditions are 0.645 watts per square inch (1000 watts per square meter)
of sunlight, 68 degrees F (20 degrees C) ambient air temperature and 6.2 x
10-3 mi/s (1 m/s) wind speed.
Photovoltaic (Photovoltaic) system: A complete
set of components for converting sunlight into electricity by the
photovoltaic process, including the array and balance of system
Photovoltaic-thermal (Photovoltaic/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 films. With this method, physical processes,
such as thermal evaporation or bombardment of ions, are used to deposit
elemental semiconductor material on a substrate.
Plenum: Chamber or space forming a part of an
air conditioning system
Plutonium: A transuranic element, formed in a
nuclear reactor by neutron capture. It has several isotopes, some of which
are fissile and some of which undergo spontaneous fission, releasing
neutrons. Weapons-grade plutonium is produced in special reactors to give
>90% Pu-239, reactor-grade plutonium contains about 30% non-fissile
isotopes. About one third of the energy in a light water reactor comes
from the fission of Pu-239, and this is the main isotope of value
recovered from reprocessing spent fuel.
P-i-n: A semiconductor 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
P/n: A semiconductor device structure in which
the junction is formed between a p-type layer and an n-type layer.
Point-contact cell: A high efficiency silicon
concentrator cell that employs light trapping techniques and
point-diffused contacts on the rear surface for current collection.
Polycrystalline: See 'Multicrystalline.'
Potential transformers are required to provide accurate voltages
for meters used for billing industrial customers or utility
type of insulator with a bell or pot-like shape used to connect
underground electrical cables to overhead lines. It serves to
separate the bunched-up conductors from one another in the cable
to the much wider separation in the overhead line. It also seals
the cable end from the weather.
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
Power density: The ratio of the power available
from a battery to its mass (W/kg) or volume (W/l).
Power factor: The ratio of the average power and
the apparent volt-amperes.
Plants: A facility designed to produce electric energy
from another form of energy, such as fossil fuel, nuclear,
hydroelectric, geothermal, solar thermal, and wind.
Power Line Carrier:
A device for producing radio-frequency power for transmission on
Transformers raise or lower the voltage as needed to serve the
transmission or distribution circuits.
Pressurized water reactor (PWR):
The most common type of light water reactor (LWR), it uses water at very
high pressure in a primary circuit and steam is formed in a secondary
These are the distribution circuits that carry power from
substations to local load areas. They are also called express
feeders or distribution main feeders. The distribution feeder bay
routes power from the substation to the distribution primary
Projected area: The net
south-facing glazing area projected on a vertical plane.
Equipment in a distribution system such as protective relays,
cutout switches, disconnect switches, lightning arresters, and
fuses. These all work in concert to open circuits whenever a short
circuit, lightning strikes or other disruptive event occurs.
A semiconductor in which holes carry the current; produced by doping an
intrinsic semiconductor with an electron acceptor impurity (e.g., boron in
Pulse-width-modulated (pwm) wave inverter (PWM):
PWM inverters are the most expensive, but produce a high quality of output
signal at minimum current harmonics. The output voltage is very close to
Photovoltaic: Abbreviation for photovoltaic(s).
Quad: A measure of energy equal to one trillion
Btus; an energy equivalent to approximately 172 million barrels of oil.
Qualified employee (qualified person): One
knowledgeable in the construction and operation of the electric power
generation, transmission, and distribution equipment involved, along with
the associated hazards.
Note 1: An employee must have the training required by 1910.269 in order
to be considered a qualified employee.
Note 2: Except as provided in 1910.260, an employee who is undergoing
on-the-job training and who, in the course of such training, has
demonstrated an ability to perform duties safely at his or her level of
training and who is under the direct supervision of a qualified person
is considered to be a qualified person for the performance of those
Qualification test (Photovoltaic): A procedure
applied to a selected set of Photovoltaic modules involving the
application of defined electrical, mechanical, or thermal stress in a
prescribed manner and amount. Test results are subject to a list of
Quick Disconnect: A type of connector shell that
permits rapid locking and unlocking of two connector halves.
Quick Disconnect Coupling: A design feature,
apparent in the quick disconnect connector; it permits relatively rapid
joining and separation.
Radiation: The emission and propagation of
energy by means of electromagnetic waves or particles.
Radioactive waste: Radioactive materials left
over from making nuclear energy. Radioactive waste can harm people and the
environment if it is not stored safely.
Radioactivity: The spontaneous decay of an
unstable atomic nucleus, giving rise to the emission of radiation.
Radionuclide: A radioactive isotope of an
Radiotoxicity: The adverse health effect of a
radionuclide due to its radioactivity.
Radium: A radioactive decay product of uranium
often found in uranium ore. It has several radioactive isotopes.
Radium-226 decays to radon-222.
Radon (Rn): A heavy radioactive gas given off by
rocks containing radium (or thorium). Rn-222 is the main isotope.
Radon daughters: Short-lived decay products of
radon-222 (Po-218, Pb-214, Bi-214, Po-214).
Rainproof: So constructed, projected, or treated
as to prevent rain from interfering with the successful operation of the
apparatus under specified test conditions.
Raintight: So constructed or protected that
exposure to a beating rain will not result in the entrance of water.
Rated Voltage: The maximum voltage at which an
electric component can operate for extended periods without undue
degradation or safety hazard.
Recombination: The action of a free electron
falling back into a hole. Recombination processes are either radiative,
where the energy of recombination results in the emission of a photon, or
non-radiative, where the energy of recombination is given to a second
electron which then relaxes back to its original energy by emitting
phonons. Recombination can take place in the bulk of the semiconductor, at
the surfaces, in the junction region, at defects, or between interfaces.
A rectifier is a device used to convert alternating current to
Recycling: A way to reuse
materials instead of just throwing them away.
mark: A design of three arrows that make up a circle.
This mark tells you that you can recycle the product. It can also
mean that the material is made from recycled materials.
Relays: A relay
is a low-powered device used to activate a high-powered device.
Relays are used to trigger circuit breakers and other switches in
substations and transmission and distribution systems.
Remote systems: Systems
off of the utility grid.
Renewable fuels: Fuels that can be easily made
or "renewed." We can never use up renewable fuels. Types of
renewable fuels are solar, wind, and hydropower energy.
RES: Acronym for the Residential Experiment
Reserve capacity: The amount of generating
capacity a central power system must maintain to meet peak loads.
Resistive voltage drop: The voltage developed
across a cell by the current flow through the resistance of the cell.
Reactor pressure vessel: The main steel vessel
containing the reactor fuel, moderator and coolant under pressure.
Repository: A permanent disposal place for
Reprocessing: Chemical treatment of spent
reactor fuel to separate uranium and plutonium from the small quantity of
fission product, waste products and transuranic elements, leaving a much
reduced quantity of high-level waste.
Ribbon: A thin sheet of crystalline or
multi-crystalline material, such as silicon, produced in a continuous
process by withdrawal from a molten bath of the parent material.
Riser: A riser
is a power line pole that connects an overhead system to an
underground system. A riser has a conduit from the ground up the
pole where potheads are used to connect to the overhead lines.
Satellite power system (SPS): Concept for
providing large amounts of electricity for use on the Earth from one or
more satellites in geosynchronous Earth orbit. A very large array of solar
cells on each satellite would provide electricity, which would be
converted to microwave energy and beamed to a receiving antenna on the
ground. There, it would be reconverted into electricity and distributed
the same as any other centrally generated power, through a grid.
Saturation Temperature: The boiling point of a
liquid, or the temperature at which the liquid vapor pressure is equal to
the total local pressure. The saturation temperature for water at
atmospheric pressure is 212°F (100°C).
Schottky barrier: A cell barrier established as
the interface between a semiconductor, such as silicon, and a sheet of
Scribing: The cutting of a grid pattern of
grooves in a semiconductor material, generally for the purpose of making
Seasonal energy-efficiency ratio (SEER): The
ratio of the total seasonal cooling requirement (measured in Btu) to the
total seasonal watt-hours (Wh) of energy used, expressed in terms of Btu/Wh.
(The SEER rating equals 3.413 times the seasonal COP.)
These are the conductors originating at the low-voltage secondary
winding of a distribution transformer.
interposing of a fire and explosion-resistant barrier between the
combustible particulate solid process and other operations.
Semiconductor: Any material that has a limited
capacity for conducting an electric current. Certain semiconductors,
including silicon, gallium arsenide, copper indium diselenide, and cadmium
telluride, are uniquely suited to the photovoltaic conversion process.
Self discharge: The rate at which a battery,
without a load, will lose its charge.
Separation: The interposing of distance between
the combustible particulate solid process and other operations that are in
the same room.
Separately Derived System: A premises wiring
system whose power is derived from a battery, a solar photovoltaic system,
or from a generator, transformer, or converter windings, and that has no
direct electrical connection, including solidly connected grounded circuit
conductor, to supply conductors originating in another system.
Separative Work Unit (SWU): This is a complex
unit which is a function of the amount of uranium processed and the degree
to which it is enriched, i.e., the extent of increase in the concentration
of the U-235 isotope relative to the remainder. The unit is strictly:
Kilogram Separative Work Unit, and it measures the quantity of Separative
work (indicative of energy used in enrichment) when feed and product
quantities are expressed in kilograms, e.g., to produce one kilogram of
uranium enriched to 3.5% U-235 requires 4.3 SWU if the plant is operated
at a tails assay 0.30%, or 4.8 SWU if the tails assay is 0.25% (thereby
requiring only 7.0 kg instead of 7.8 kg of natural U feed).
About 100-120,000 SWU is required to enrich the annual fuel loading for a
typical 1000 MWe light water reactor. Enrichment costs are related to
electrical energy used. The gaseous diffusion process consumes some 2400
kWh per SWU, while gas centrifuge plants require only about 60 kWh/SWU.
Series connection: A way of joining circuits by
connecting positive leads to negative leads; such a configuration
increases the voltage.
Series regulator: Type of battery charge
regulator where the charging current is controlled by a switch connected
in series with the Photovoltaic module or array.
Series resistance: Parasitic resistance to
current flow in a cell due to mechanisms such as resistance from the bulk
of the semiconductor material, metallic contacts, and interconnections.
Service Drop: Run of cables from the power
company's aerial power lines to the point of connection to a customer's
Service Conductors: The supply conductors that
extend from the street main or transformers to the service equipment of
the premises being supplied.
Service Entrance Conductors: (Overhead) The
service conductors between the terminals of the service equipment and a
point usually outside the building, clear of building walls, where they
are joined by tap or splice to the service drop.
Service Entrance Conductors: (Underground) The
service conductors between the terminals of the service equipment and the
point of connection to the service lateral.
Service Equipment: The necessary equipment,
usually consisting of a circuit breaker or switch and fuses and their
accessories, located near the point entrance of supply conductors to a
building and intended to constitute the main control and cutoff means for
the supply to the building.
Service Lateral: The underground service
conductors between the street main, including any risers at a pole or
other structure or from transformers, and the first point of connection to
the service-entrance conductors in a terminal box, meter, or other
enclosure with adequate space, inside or outside the building wall. Where
there is no terminal box, meter, or other enclosure with adequate space,
the point of connection is the entrance point of the service conductors
into the building.
Service Point: The point of connection between
the facilities of the serving utility and the premises wiring.
wires extending from the secondaries or distribution transformer
to a customer's location are called a service. A service can be
above or below ground.
Breakers: These operate to switch electric circuits and
equipment in and out of the system. These circuit breakers are
filled with compressed sulfur-hexafluoride gas which acts to open
and close the switch contacts.
Shield: Device surrounding
that portion of a connector that is used for attaching wires or cables to
shield against electromagnetic interference, and/or protect connector
wires or cable from mechanical damage.
Shelf life of batteries: The length of time,
under specified conditions, that a battery can be stored so that it keeps
its guaranteed capacity.
Short-circuit current (Isc): The current flowing
freely from a photovoltaic cell through an external circuit that has no
load or resistance; the maximum current possible.
These are used in an extra high-voltage substation to neutralize
inductive reactance in long EHV transmission lines.
Shunt regulator: Type of a
battery charge regulator where the charging current is controlled by a
switch connected in parallel with the Photovoltaic generator. Overcharging
of the battery is prevented by shorting the Photovoltaic generator.
Siemens process: A commercial method of making
Silicon (Si): A chemical element, atomic number
14, semi-metallic in nature, dark gray, an excellent semiconductor
material. A common constituent of sand and quartz (as the oxide).
Crystallizes in face-centered cubic lattice like a diamond. The most
common semiconductor material used in making photovoltaic devices.
Sine wave inverter: An inverter that produces
utility-quality, sine wave power forms.
Single-crystal material: A material that is
composed of a single crystal or a few large crystals.
Sievert (Sv): Unit indicating the biological
damage caused by radiation. One Joule of beta or gamma radiation absorbed
per kilogram of tissue has 1 Sv of biological effect; 1 J/kg of alpha
radiation has 20 Sv effect and 1 J/kg of neutrons has 10 Sv effect.
Spent fuel: Fuel assemblies removed from a
reactor after use.
Stable: Incapable of spontaneous radioactive
Solar cell: See 'Photovoltaic cell.'
Solar constant: The strength of sunlight; 1353
watts per square meter in space and about 1000 watts per square meter at
sea level at the equator at solar noon.
Solar energy: Energy from the sun. The heat that
builds up in your car when it is parked in the sun is an example of solar
Solar-grade silicon: Intermediate-grade silicon
used in the manufacture of solar cells. Less expensive than
Solar noon: That moment of the day that divides
the daylight hours for that day exactly in half. To determine solar noon,
calculate the length of the day from the time of sunset and sunrise and
divide by two.
Solar spectrum: The total distribution of
electromagnetic radiation emanating from the sun.
Solar thermal electric: Method of producing
electricity from solar energy by using focused sunlight to heat a working
fluid, which in turn drives a turbogenerator.
Spinning reserve: Utility generating capacity
on-line and running at low power in excess of actual load.
Split-spectrum cell: A compound photovoltaic
device in which sunlight is first divided into spectral regions by optical
means. Each region is then directed to a different photovoltaic cell
optimized for converting that portion of the spectrum into electricity.
Such a device achieves significantly greater overall conversion of
incident sunlight into electricity. See 'mulitjunction device.'
Sputtering: A physical vapor deposition process
where high-energy ions are used to bombard elemental sources of
semiconductor material, which eject vapors of atoms that are then
deposited in thin layers on a substrate.
Square wave inverter: The inverter consists of a
DC source, four switches, and the load. The switches are power
semiconductors that can carry a large current and withstand a high voltage
rating. The switches are turned on and off at a correct sequence, at a
certain frequency. The square wave inverter is the simplest and the least
expensive to purchase, but it produces the lowest quality of power.
Staebler-Wronski effect: The tendency of
amorphous silicon photovoltaic devices to lose efficiency upon initial
exposure to light; named for Dr. David Staebler and Dr. Christopher
Wronski; work performed at RCA.
Standardized: For a lockout or tagout device to
be standardized they must all be similar in at least one of the following
ways: color, shape, size. Additionally, in the case of tagout devices,
print and format should also be similar.
Stand-alone (Photovoltaic system):
An autonomous or hybrid photovoltaic system not connected to a grid. May
or may not have storage, but most stand-alone systems require batteries or
some other form of storage.
Stand-off mounting: Technique for mounting a
photovoltaic array on a sloped roof, which involves mounting the modules a
short distance above the pitched roof and tilting them to the optimum
Standard reporting conditions (SRC): A fixed set
of conditions (including meteorological) to which the electrical
performance data of a photovoltaic module are translated from the set of
actual test conditions. [ASTM E 1036]
Standard test conditions (STC): Conditions under
which a module is typically tested in a laboratory: (1) Irradiance
intensity of 1000 W/square meter (0.645 watts per square inch), AM1.5
solar reference spectrum, and (3) a cell (module) temperature of 25
degrees C, plus or minus 2 degrees C (77 degrees F, plus or minus 3.6
degrees F). [IEC 1215]
State of charge (SOC): The available capacity
remaining in the battery, expressed as a percentage of the rated capacity.
Steel superstructures are used to support equipment, lines, and
switches in substations as well as transmission and distribution
line towers and poles.
Step bolt: A bolt or rung
attached at intervals along a structural member and used for foot
placement during climbing or standing.
Step Potential: The
voltage between the feet of a person standing near an energized grounded
object. It is equal to the difference in voltage, given by the voltage
distribution curve, between two points at different distances from the
"electrode". A person could be at risk of injury during a fault
simply by standing near the grounding point.
Substrate: The physical material upon which a
photovoltaic cell is made.
A high-voltage electric system facility. It is used to switch
generators, equipment, and circuits or lines in and out of a
system. It also is used to change AC voltages from one level to
another, and/or change alternating current to direct current or
direct current to alternating current.
Substation: Receives electric power from a nearby
generating facility and uses a large power transformer to
increase the voltage for transmission to distant locations.
Transmission Substation: These substations are
located at switching points in an electrical grid. They connect
different parts of a grid and are a source for subtransmission
Substation: These are located near to the end-users.
Distribution substation transformers change the subtransmission
voltage to lower levels for use by end-users.
Distribution Substation: These are also located near
to the end-users. Distribution substation transformers change
the subtransmission voltage to lower levels for use by
Sulfation: A condition
that afflicts unused and discharged batteries; large crystals of lead
sulfate grow on the plate, instead of the usual tiny crystals, making the
battery extremely difficult to recharge.
Sunspace: A room that faces south, or a small
structure attached to the south side of a house.
Sun tempering: A sun-tempered building is
elongated in the east-west direction, with the majority of the windows on
the south side. The area of the windows is generally limited to about 7%
of the total floor area. A sun-tempered design has no added thermal mass
beyond what is already in the framing, wall board, and so on. Insulation
levels are generally high.
Superconducting magnetic energy storage (SMES):
SMES technology uses the superconducting characteristics of
low-temperature materials to produce intense magnetic fields to store
energy. SMES has been proposed as a storage option to support large-scale
use of photovoltaics and wind as a means to smooth out fluctuations in
Superconductivity: The pairing of electrons in
certain materials when cooled below a critical temperature, causing the
material to lose all resistance to electricity flow. Superconductors can
carry electric current without any energy losses.
Superstrate: The covering on the sun side of a
photovoltaic module, providing protection for the photovoltaic materials
from impact and environmental degradation while allowing maximum
transmission of the appropriate wavelengths of the solar spectrum.
Supervisory control refers to equipment that allows for remote
control of a substation's functions from a system control center
or other point of control.
An insulator type usually made of porcelain that can be stacked in
a string and hangs from a cross arm on a tower or pole and
supports the line conductor.
Distribution systems have switches installed at strategic
locations to redirect power flows for load balancing or
Switchboard: A large
single panel, frame, or assembly of panels having switches, overcurrent,
and other protective devices, buses, and usually instruments mounted on
the face or back or both. Switchboards are generally accessible from the
rear and from the front and are not intended to be installed in cabinets.
Switch, general use: A switch intended for use
in general distribution and branch circuits. It is rated in amperes and is
capable of interrupting its rated voltage.
Switch, general-use snap: A type of general-use
switch so constructed that it can be installed in flush device boxes or on
outlet covers, or otherwise used in conjunction with wiring systems
recognized by the National Electric Code.
Switch, isolating: A switch intended for
isolating an electrical circuit from the source of power. It has no
interrupting rating and is intended to be operated only after the circuit
has been opened by some other means.
Switch, knife: A switch in which the circuit is
closed by a moving blade engaging contact clips.
Switch, motor-circuit: A switch, rated in
horsepower, capable of interrupting the maximum operating overload current
of a motor of the same horsepower rating as the switch at the rated
Switch, transfer: A transfer switch is an
automatic or non-automatic device for transferring one or more load
conductor connections from one power source to another.
Switch-Leg: That part of a circuit run from a
lighting outlet box where a luminaire or lampholder is installed down to
an outlet box that contains the wall switch that turns the light or other
load on or off: it is a control leg of the branch circuit.
A synchronous condenser is a synchronous machine running without
mechanical load and supplying or absorbing reactive power to or
from a power system. Also called a synchronous capacitor,
synchronous compensator or rotating machinery.
System operator: A
qualified person designated to operate the system or its parts.
Tails: Depleted uranium, with about 0.3% U-235.
Tailings: Ground rock remaining after particular
ore minerals (e.g., uranium oxides) are extracted.
Thermal electric: Electric energy derived from
heat energy, usually by heating a working fluid, which drives a
turbogenerator. See 'solar thermal electric.'
Thermal mass: Materials that store heat within a
sunspace or solar collector.
Thermal reactor: A reactor in which the fission
chain reaction is sustained primarily by slow neutrons, and hence
requiring a moderator (as distinct from Fast Neutron Reactor).
Thermal Shock: Thermal shock is the effect of
heat or cold applied at such a rate that non-uniform thermal expansion or
contraction occur within a given material or combination of materials. In
connectors, the effect can cause inserts and other insulation materials to
pull away from metal parts.
Thermal storage walls (masonry or water): A
thermal storage wall is a south-facing wall that is glazed on the outside.
Solar heat strikes the glazing and is absorbed into the wall, which
conducts the heat into the room over time. The walls are at least 8 in
thick. Generally, the thicker the wall, the less the indoor temperature
Thermophotovoltaic (TPV) device: A device that
converts secondary thermal radiation, re-emitted by an absorber or heat
source, into electricity; The device is designed for maximum efficiency at
the wavelength of the secondary radiation.
Thick-crystalline materials: Semiconductor
material, typically measuring from 200-400 microns thick, that is cut from
ingots or ribbons.
Thin film: A layer of semiconductor material,
such as copper indium diselenide, cadmium telluride, gallium arsenide, or
amorphous silicon, a few microns or less in thickness, used to make
III-V (three-five) materials: Elemental
materials that occupy groups III and V of the Periodic Table of the
Tin oxide: A wide band-gap semiconductor similar to indium oxide;
used in heterojunction solar cells or to make a transparent conductive
film, called NESA glass when deposited on glass.
The voltage between the energized object and the feet of a person in
contact with the object. It is equal to the difference in voltage between
the object and a point some distance away. It should be noted that the
touch potential could be nearly the full voltage across the grounded
object if that object is grounded at a point remote from the place where
the person is in contact with it. For example, a crane that was grounded
to the system neutral and that contacted an energized line would expose
any person in contact with the crane or its uninsulated load line to a
touch potential nearly equal to the full fault voltage.
Total energy system: See 'photovoltaic-thermal
Total harmonic distortion (thd): The measure of
closeness in shape between a waveform and its fundamental component.
Total internal reflection: The trapping of light
by refraction and reflection at critical angles inside a semiconductor
device so that it cannot escape the device and must eventually be absorbed
by the semiconductor.
Tracking Photovoltaic array:
Photovoltaic array that follows the path of the sun to maximize the solar
radiation incident on the Photovoltaic surface. The two most common
orientations are (1) one axis where the array tracks the sun east to west
and (2) two-axis tracking where the array points directly at the sun at
all times. Tracking arrays use both the direct and diffuse sunlight.
Two-axis tracking arrays capture the maximum possible daily energy.
Transformer: Converts the generator's
low-voltage electricity to higher voltage levels for transmission to the
load center, such as a city or factory.
Underground: An underground transformer is essentially
the same as an aboveground transformer, but is constructed for the
particular needs of underground installation.
A transformer vault is an underground structure or room in which
power transformers, network protectors, voltage regulators,
circuit breakers, meters, etc. are housed.
Transmission buses are steel structure arrays of switches used to
route power in a substation.
Transmit high-voltage electricity from the generation source or substation
to another substation in the electric distribution system.
Lines: Overhead AC transmission lines share one
characteristic; they carry 3-phase current. The voltages vary
according to the particular grid system they belong to.
Transmission voltages vary from 69 kv up to 765 kv.
Lines: These lines carry voltages reduced from the
major transmission line system, usually 69 kv.
Transmission Lines: These lines are becoming more
common, especially in highly populated area. They may be buried
with no protection, or placed in conduit, trenches, or tunnels.
Transmutation: Changing atoms of one element
into those of another by neutron bombardment, causing neutron capture.
Transuranic element: A very heavy element formed
artificially by neutron capture and possibly subsequent beta decay(s). Has
a higher atomic number than uranium (92). All are radioactive. Neptunium,
plutonium, americium and curium are the best-known.
Trickle charge: A charge at a low rate,
balancing through self-discharge losses, to maintain a cell or battery in
a fully charged condition.
Tunneling: Quantum mechanical concept whereby an
electron is found on the opposite side of an insulating barrier without
having passed through or around the barrier.
Two-axis tracking: A system capable of rotating
independently about two axes (e.g., vertical and horizontal).
Ultraviolet: Electromagnetic radiation in the
wavelength range of 4 to 400 nanometers.
Uranium (U): A mildly radioactive element with
two isotopes which are fissile (U-235 and U-233) and two which are fertile
(U-238 and U-234). Uranium is the basic fuel of nuclear energy.
Uranium hexafluoride (UF6): A
compound of uranium which is a gas above 56oC and is thus a
suitable form in which to enrich the uranium.
Uranium oxide concentrate (U3O8):
The mixture of uranium oxides produced after milling uranium ore from a
mine. Sometimes loosely called yellowcake. It is khaki in colour and is
usually represented by the empirical formula U3O8.
Uranium is sold in this form.
Utility-interactive inverter: An inverter that
can function only when tied to the utility grid, and uses the prevailing
line-voltage frequency on the utility line as a control parameter to
ensure that the Photovoltaic system's output is fully synchronized with
the utility power.
Vac: Volts ac
Vacuum evaporation: The deposition of thin films
of semiconductor material by the evaporation of elemental sources in a
Vdc: Volts DC
Vmp: Voltage at maximum power
Voc: Open-circuit voltage
Vacuum Circuit Breakers:
A vacuum circuit breaker utilizes a vacuum to extinguish arcing
when the circuit breaker is opened and to act as a dielectric to
insulate the contacts after the arc is interrupted.
Vacuum evaporation: Method
of depositing thin coatings of a substance by heating it in a vacuum
Vacuum zero: The energy of an electron at rest
in empty space; used as a reference level in energy band diagrams.
Valence band: The highest energy band in a
semiconductor that can be filled with electrons.
Valence state; Valence level energy, bound state:
Energy content of an electron in orbit about an atomic nucleus.
Vault: An enclosure, above or below ground,
which personnel may enter and which is used for the purpose of installing,
operating, or maintaining equipment or cable.
Vented vault: A vault that has provision for air
changes using exhaust flue stacks and low level air intakes operating on
differentials of pressure and temperature providing for airflow which
precludes a hazardous atmosphere from developing.
Vertical multijunction cell
(VMJ) : A compound
cell made of different semiconductor materials in layers, one above the
other. Sunlight entering the top passes through successive cell barriers,
each of which converts a separate portion of the spectrum into
electricity, thus achieving greater total conversion efficiency of the
incident light. Also called a multiple junction cell. See 'multijunction
device'; 'split-spectrum cell.'
Vitrification: The incorporation of high-level
wastes into borosilicate glass, to make up about 14% of it by mass. It is
designed to immobilise radionuclides in an insoluble matrix ready for
Volt (V): A unit of measure of the force, or
'push,' given the electrons in an electric circuit. One volt produces one
ampere of current when acting on a resistance of one ohm.
Voltage: The effective (rms) potential
difference between any two conductors or between a conductor and ground.
Voltages are expressed in nominal values unless otherwise indicated. The
nominal voltage of a system or circuit is the value assigned to a system
or circuit of a given voltage class for the purpose of convenient
designation. The operating voltage of the system may vary above or below
Voltage at maximum power (Vmp): The voltage at
which maximum power is available from a module.
Voltage Drop: The loss of voltage between the
input to a device and the output from a device due to the internal
impedance or resistance of the device. In all electrical systems, the
conductors should be sized so that the voltage drop never exceeds 3% for
power, heating, and lighting loads or combinations of these. Furthermore,
the maximum total voltage drop for conductors for feeders and branch
circuits combined should never exceed 5%.
Wafer: A thin sheet of semiconductor material
made by mechanically sawing it from a single-crystal or multi-crystal
ingot or casting.
Waste: Refers to radioactive wastes. High-level
waste (HLW) is highly radioactive material arising from nuclear fission.
It can be recovered from reprocessing spent fuel, though some countries
regard spent fuel itself as HLW. It requires very careful handling,
storage and disposal. Low-level waste (LLW) is mildly radioactive material
usually disposed of by incineration and burial.
Watertight: So constructed that water/moisture
will not enter the enclosure under specified test conditions.
Watt (W): The unit of electric power, or amount
of work (J), done in a unit of time. One ampere of current flowing at a
potential of one volt produces one watt of power.
Watt-hour (Wh): See 'Kilowatt-hour.'
Waveform: The shape of the curve graphically
representing the change in the ac signal voltage and current amplitude,
with respect to time.
Signs: Display signs warning unqualified persons to 'keep
out' at entrances to rooms and spaces where hazards of high voltage
Weatherproof: So constructed or protected that
exposure to the weather will not interfere with successful operation.
Window: A wide band gap material chosen for its
transparency to light. Generally used as the top layer of a photovoltaic
device, the window allows almost all of the light to reach the
semiconductor layers beneath.
Winston concentrator: A trough-type parabolic
collector with one-axis tracking, developed by Roland Winston.
Work function: The energy difference between the
Fermi level and vacuum zero. The minimum amount of energy it takes to
remove an electron from a substance into the vacuum.
Yellowcake: Ammonium diuranate, the penultimate
uranium compound in U3O8 production, but the form in
which mine product was sold until about 1970. See also Uranium oxide
Zircaloy: Zirconium alloy used as a tube to
contain uranium oxide fuel pellets in a reactor fuel assembly.
Zone refining: Method of purifying solid rods by
means of melting narrow zones through the rods. These zones are slowly
moved from one end of the rod to the other, sweeping out the impurities.