Tare Loss — Loss caused by a charge controller. One minus tare loss, expressed as a percentage, is equal to
the controller efficiency.
Temperature Compensation — A circuit that adjusts the charge controller activation points depending on battery
temperature. This feature is recommended if the battery temperature is expected to vary more than ±5°C from
ambient temperature.
Temperature Factors — It is common for three elements in photovoltaic system sizing to have distinct
temperature corrections: a factor used to decrease battery capacity at cold temperatures; a factor used to
decrease PV module voltage at high temperatures; and a factor used to decrease the current carrying capability
of wire at high temperatures.
Thermophotovoltaic Cell (TPV) — A device where sunlight concentrated onto a absorber heats it to a high
temperature, and the thermal radiation emitted by the absorber is used as the energy source for a photovoltaic
cell that is designed to maximize conversion efficiency at the wavelength of the thermal 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 or gallium arsenide, a few
microns or less in thickness, used to make photovoltaic cells.
Thin Film Photovoltaic Module — A photovoltaic module constructed with sequential layers of thin film
semiconductor materials. See amorphous silicon.
Tilt Angle — The angle at which a photovoltaic array is set to face the sun relative to a horizontal position. The
tilt angle can be set or adjusted to maximize seasonal or annual energy collection.
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.
Total AC Load Demand — The sum of the alternating current loads. This value is important when selecting an
inverter.
Total Harmonic Distortion — The measure of closeness in shape between a waveform and it's 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 be eventually absorbed by the
semiconductor.
Tracking Array — A photovoltaic (PV) array that follows the path of the sun to maximize the solar radiation
incident on the PV 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 — An electromagnetic device that changes the voltage of alternating current electricity.
Tray Cable (TC) - may be used for interconnecting balance-of-systems.
Trickle Charge — A charge at a low rate, balancing through self-discharge losses, to maintain a cell or battery in
a fully charged condition.
Two-Axis Tracking — A photovoltaic array tracking system capable of rotating independently about two axes (e.
g., vertical and horizontal).
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.
U
Ultraviolet — Electromagnetic radiation in the wavelength range of 4 to 400 nanometers.
Underground Feeder (UF) — May be used for photovoltaic array wiring if sunlight resistant coating is specified;
can be used for interconnecting balance-of-system components but not recommended for use within battery
enclosures.
Underground Service Entrance (USE) — May be used within battery enclosures and for interconnecting balance-
of-systems.
Uninterruptible Power Supply (UPS) — The designation of a power supply providing continuous uninterruptible
service. The UPS will contain batteries.
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.
V
Vacuum Evaporation - The deposition of thin films of semiconductor material by the evaporation of elemental
sources 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 Level Energy/Valence State — Energy content of an electron in orbit about an atomic nucleus. Also
called bound state.
Varistor — A voltage-dependent variable resistor. Normally used to protect sensitive equipment from power
spikes or lightning strikes by shunting the energy to ground.
Vented Cell — A battery designed with a vent mechanism to expel gases generated during charging.
Vertical Multijunction (VMJ) Cell — 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 and split-spectrum cell.
Volt (V) — A unit of electrical force equal to that amount of electromotive force that will cause a steady current of
one ampere to flow through a resistance of one ohm.
Voltage — The amount of electromotive force, measured in volts, that exists between two points.
Voltage at Maximum Power (Vmp) — The voltage at which maximum power is available from a photovoltaic
module.
Voltage Protection — Many inverters have sensing circuits that will disconnect the unit from the battery if input
voltage limits are exceeded.
Voltage Regulation — This indicates the variability in the output voltage. Some loads will not tolerate voltage
variations greater than a few percent.
the controller efficiency.
Temperature Compensation — A circuit that adjusts the charge controller activation points depending on battery
temperature. This feature is recommended if the battery temperature is expected to vary more than ±5°C from
ambient temperature.
Temperature Factors — It is common for three elements in photovoltaic system sizing to have distinct
temperature corrections: a factor used to decrease battery capacity at cold temperatures; a factor used to
decrease PV module voltage at high temperatures; and a factor used to decrease the current carrying capability
of wire at high temperatures.
Thermophotovoltaic Cell (TPV) — A device where sunlight concentrated onto a absorber heats it to a high
temperature, and the thermal radiation emitted by the absorber is used as the energy source for a photovoltaic
cell that is designed to maximize conversion efficiency at the wavelength of the thermal 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 or gallium arsenide, a few
microns or less in thickness, used to make photovoltaic cells.
Thin Film Photovoltaic Module — A photovoltaic module constructed with sequential layers of thin film
semiconductor materials. See amorphous silicon.
Tilt Angle — The angle at which a photovoltaic array is set to face the sun relative to a horizontal position. The
tilt angle can be set or adjusted to maximize seasonal or annual energy collection.
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.
Total AC Load Demand — The sum of the alternating current loads. This value is important when selecting an
inverter.
Total Harmonic Distortion — The measure of closeness in shape between a waveform and it's 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 be eventually absorbed by the
semiconductor.
Tracking Array — A photovoltaic (PV) array that follows the path of the sun to maximize the solar radiation
incident on the PV 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 — An electromagnetic device that changes the voltage of alternating current electricity.
Tray Cable (TC) - may be used for interconnecting balance-of-systems.
Trickle Charge — A charge at a low rate, balancing through self-discharge losses, to maintain a cell or battery in
a fully charged condition.
Two-Axis Tracking — A photovoltaic array tracking system capable of rotating independently about two axes (e.
g., vertical and horizontal).
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.
U
Ultraviolet — Electromagnetic radiation in the wavelength range of 4 to 400 nanometers.
Underground Feeder (UF) — May be used for photovoltaic array wiring if sunlight resistant coating is specified;
can be used for interconnecting balance-of-system components but not recommended for use within battery
enclosures.
Underground Service Entrance (USE) — May be used within battery enclosures and for interconnecting balance-
of-systems.
Uninterruptible Power Supply (UPS) — The designation of a power supply providing continuous uninterruptible
service. The UPS will contain batteries.
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.
V
Vacuum Evaporation - The deposition of thin films of semiconductor material by the evaporation of elemental
sources 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 Level Energy/Valence State — Energy content of an electron in orbit about an atomic nucleus. Also
called bound state.
Varistor — A voltage-dependent variable resistor. Normally used to protect sensitive equipment from power
spikes or lightning strikes by shunting the energy to ground.
Vented Cell — A battery designed with a vent mechanism to expel gases generated during charging.
Vertical Multijunction (VMJ) Cell — 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 and split-spectrum cell.
Volt (V) — A unit of electrical force equal to that amount of electromotive force that will cause a steady current of
one ampere to flow through a resistance of one ohm.
Voltage — The amount of electromotive force, measured in volts, that exists between two points.
Voltage at Maximum Power (Vmp) — The voltage at which maximum power is available from a photovoltaic
module.
Voltage Protection — Many inverters have sensing circuits that will disconnect the unit from the battery if input
voltage limits are exceeded.
Voltage Regulation — This indicates the variability in the output voltage. Some loads will not tolerate voltage
variations greater than a few percent.
GLOSSARY OF TERMS
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