Langley (L) — Unit of solar irradiance. One gram calorie per square centimeter. 1 L = 85.93 kwh/m2.
Lattice — The regular periodic arrangement of atoms or molecules in a crystal of semiconductor material.
Lead-Acid Battery — A general category that includes batteries with plates made of pure lead, lead-antimony, or
lead-calcium immersed in an acid electrolyte.
Life — The period during which a system is capable of operating above a specified performance level.
Life-Cycle Cost — The estimated cost of owning and operating a photovoltaic system for the period of its useful
life.
Light-Induced Defects — Defects, such as dangling bonds, induced in an amorphous silicon semiconductor upon
initial exposure to light.
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.
Line-Commutated Inverter — An inverter that is tied to a power grid or line. The commutation of power
(conversion from direct current to alternating current) 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.
Liquid Electrolyte Battery — A battery containing a liquid solution of acid and water. Distilled water may be added
to these batteries to replenish the electrolyte as necessary. Also called a flooded battery because the plates are
covered with the electrolyte.
Load — The demand on an energy producing system; the energy consumption or requirement of a piece or
group of equipment. Usually expressed in terms of amperes or watts in reference to electricity.
Load Circuit — The wire, switches, fuses, etc. that connect the load to the power source.
Load Current (A) — The current required by the electrical device.
Load Resistance — The resistance presented by the load. See resistance.
Low Voltage Cutoff (LVC) — The voltage level at which a charge controller will disconnect the load from the
battery.
Low Voltage Disconnect — The voltage at which a charge controller will disconnect the load from the batteries to
prevent over-discharging.
Low Voltage Disconnect Hysteresis — The voltage difference between the low voltage disconnect set point and
the voltage at which the load will be reconnected.
Low Voltage Warning — A warning buzzer or light that indicates the low battery voltage set point has been
reached.
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M
Maintenance-Free Battery — A sealed battery to which water cannot be added to maintain electrolyte level.
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 a cell.
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. For a typical silicon cell, this is at about 0.45 volts.
Maximum Power Point Tracker (MPPT) — Means of a power conditioning unit that automatically operates the
photovoltaic generator at its maximum power point under all conditions.
Maximum Power Tracking — Operating a photovoltaic array at the peak power point of the array's I-V curve
where maximum power is obtained. Also called peak power tracking.
Megawatt (MW) — 1,000 kilowatts, or 1 million watts; standard measure of electric power plant generating
capacity.
Megawatt-Hour — 1,000 kilowatt-hours or 1 million watt-hours.
Microgroove — A small groove scribed into the surface of a solar cell, which is filled with metal for contacts.
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 device.
Minority Carrier Lifetime — The average time a minority carrier exists before recombination.
Modified Sine Wave — A waveform that has at least three states (i.e., positive, off, and negative). Has less
harmonic content than a square wave.
Modularity — The use of multiple inverters connected in parallel to service different loads.
Module — See photovoltaic (PV) module.
Module Derate Factor — A factor that lowers the photovoltaic module current to account for field operating
conditions such as dirt accumulation on the module.
Monolithic — Fabricated as a single structure.
Movistor — Metal Oxide Varistor. Used to protect electronic circuits from surge currents such as those produced
by lightning.
Multicrystalline — A semiconductor (photovoltaic) material composed of variously oriented, small, individual
crystals. Sometimes referred to as polycrystalline or semicrystalline.
Multijunction Device — A high-efficiency photovoltaic device containing two or more cell junctions, each of which
is optimized for a particular part of the solar spectrum.
Multi-Stage Controller — A charging controller unit that allows different charging currents as the battery nears
full state_of_charge.
Lattice — The regular periodic arrangement of atoms or molecules in a crystal of semiconductor material.
Lead-Acid Battery — A general category that includes batteries with plates made of pure lead, lead-antimony, or
lead-calcium immersed in an acid electrolyte.
Life — The period during which a system is capable of operating above a specified performance level.
Life-Cycle Cost — The estimated cost of owning and operating a photovoltaic system for the period of its useful
life.
Light-Induced Defects — Defects, such as dangling bonds, induced in an amorphous silicon semiconductor upon
initial exposure to light.
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.
Line-Commutated Inverter — An inverter that is tied to a power grid or line. The commutation of power
(conversion from direct current to alternating current) 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.
Liquid Electrolyte Battery — A battery containing a liquid solution of acid and water. Distilled water may be added
to these batteries to replenish the electrolyte as necessary. Also called a flooded battery because the plates are
covered with the electrolyte.
Load — The demand on an energy producing system; the energy consumption or requirement of a piece or
group of equipment. Usually expressed in terms of amperes or watts in reference to electricity.
Load Circuit — The wire, switches, fuses, etc. that connect the load to the power source.
Load Current (A) — The current required by the electrical device.
Load Resistance — The resistance presented by the load. See resistance.
Low Voltage Cutoff (LVC) — The voltage level at which a charge controller will disconnect the load from the
battery.
Low Voltage Disconnect — The voltage at which a charge controller will disconnect the load from the batteries to
prevent over-discharging.
Low Voltage Disconnect Hysteresis — The voltage difference between the low voltage disconnect set point and
the voltage at which the load will be reconnected.
Low Voltage Warning — A warning buzzer or light that indicates the low battery voltage set point has been
reached.
Back to Top
M
Maintenance-Free Battery — A sealed battery to which water cannot be added to maintain electrolyte level.
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 a cell.
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. For a typical silicon cell, this is at about 0.45 volts.
Maximum Power Point Tracker (MPPT) — Means of a power conditioning unit that automatically operates the
photovoltaic generator at its maximum power point under all conditions.
Maximum Power Tracking — Operating a photovoltaic array at the peak power point of the array's I-V curve
where maximum power is obtained. Also called peak power tracking.
Megawatt (MW) — 1,000 kilowatts, or 1 million watts; standard measure of electric power plant generating
capacity.
Megawatt-Hour — 1,000 kilowatt-hours or 1 million watt-hours.
Microgroove — A small groove scribed into the surface of a solar cell, which is filled with metal for contacts.
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 device.
Minority Carrier Lifetime — The average time a minority carrier exists before recombination.
Modified Sine Wave — A waveform that has at least three states (i.e., positive, off, and negative). Has less
harmonic content than a square wave.
Modularity — The use of multiple inverters connected in parallel to service different loads.
Module — See photovoltaic (PV) module.
Module Derate Factor — A factor that lowers the photovoltaic module current to account for field operating
conditions such as dirt accumulation on the module.
Monolithic — Fabricated as a single structure.
Movistor — Metal Oxide Varistor. Used to protect electronic circuits from surge currents such as those produced
by lightning.
Multicrystalline — A semiconductor (photovoltaic) material composed of variously oriented, small, individual
crystals. Sometimes referred to as polycrystalline or semicrystalline.
Multijunction Device — A high-efficiency photovoltaic device containing two or more cell junctions, each of which
is optimized for a particular part of the solar spectrum.
Multi-Stage Controller — A charging controller unit that allows different charging currents as the battery nears
full state_of_charge.
GLOSSARY OF TERMS
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