Solar panel glossary


Alternating Current (AC) - A type of electrical current, the direction of which is reversed at regular intervals or cycles. In the North America, the standard is 120 reversals or 60 cycles per second. For solar systems an Inverter is required to take stored DC power to normal AC power.

Ampere (amp) - A unit of electrical current or rate of flow of electrons. One volt across one ohm of resistance causes a current flow of one ampere.

Ampere-Hour (Ah/AH) - A measure of the flow of current (in amperes) over one hour; used to measure battery capacity.

Angle of Incidence - The angle that a ray of sun makes with a line perpendicular to the surface. For example, a surface that directly faces the sun has a solar angle of incidence of zero, but if the surface is parallel to the sun (for example, sunrise striking a horizontal rooftop), the angle of incidence is 90°.

Antireflection Coating - A thin coating of a material applied to a solar cell surface that reduces the light reflection and increases light transmission.

Array Current - The electrical current produced by a photovoltaic array when it is exposed to sunlight.

Balance of System - Represents all components and costs other than the photovoltaic modules/array.

Charge Controller - A component of a photovoltaic system that controls the flow of current to and from the battery to protect it from over-charge and over-discharge. The charge controller may also indicate the system operational status.

Charge Rate - The current applied to a cell or battery to restore its available capacity. This rate is commonly normalized by a charge control device with respect to the rated capacity of the cell or battery.

Crystalline Silicon - A type of photovoltaic cell made from a slice of single-crystal silicon or polycrystalline silicon.

Current at Maximum Power (Imp) - The current at which maximum power is available from a module.

Cutoff Voltage - The voltage levels (activation) at which the charge controller disconnects the photovoltaic array from the battery or the load from the battery.

Days of Storage - The number of consecutive days the stand-alone system will meet a defined load without solar energy input. This term is related to system availability.

Deep-Cycle Battery - A battery with large plates that can withstand many discharges to a low state-of-charge. Solar systems work with deep cycle batteries, Flooded, AGM or Gell

Depth of Discharge (DOD) - The ampere-hours removed from a fully charged cell or battery, expressed as a percentage of rated capacity. For example, the removal of 25 ampere-hours from a fully charged 100 ampere-hours rated cell results in a 25% depth of discharge. Under certain conditions, such as discharge rates lower than that used to rate the cell, depth of discharge can exceed 100%.

Diode - An electronic device that allows current to flow in one direction only. See blocking diode and bypass diode. Diodes are built in to the solar module and charge controller to stop a reverse current from the battery through to the solar module during night time.

Direct Current (DC) - A type of electricity transmission and distribution by which electricity flows in one direction through the conductor, usually relatively low voltage and high current. All solar modules produce DC current.

Discharge Rate - The rate, usually expressed in amperes or time, at which electrical current is taken from the battery.

Electric Current - The flow of electrical energy (electricity) in a conductor, measured in amperes.

Equalization - The process of restoring all cells in a battery to an equal state-of-charge. Some battery types may require a complete discharge as a part of the equalization process.

Equalization Charge - The process of mixing the electrolyte in batteries by periodically overcharging the batteries for a short time in order to provide cell equalization within a battery.

Float Charge - The voltage required to counteract the self-discharge of the battery at a certain temperature.

Grid-Connected System - A solar electric or photovoltaic (PV) system in which the PV array acts like a central generating plant, supplying power to the grid.

High Voltage Disconnect - The voltage at which a charge controller will disconnect the photovoltaic array from the batteries to prevent overcharging.

Hybrid System - A solar electric or photovoltaic system that includes other sources of electricity generation, such as wind or diesel generators.

Insolation - The solar power density incident on a surface of stated area and orientation, usually expressed as Watts per square meter or Btu per square foot per hour.

Inverter - A device that converts direct current electricity to alternating current either for stand-alone systems or to supply power to an electricity grid.

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 characterizes cell performance.

Junction Box - A photovoltaic (PV) generator junction box is an enclosure on the module where PV strings are electrically connected and where protection devices can be located, if necessary.

Kilowatt (kW) - A standard unit of electrical power equal to 1000 watts.

Kilowatt-Hour (kWh) - 1,000 thousand watts acting over a period of 1 hour. The kWh is a unit of energy.

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 Current (A) - The current required by the electrical device. Re Draw Rate

Low Voltage Disconnect - The voltage at which a charge controller will disconnect the load from the batteries to prevent over-discharging. This feature is available on specific charge controllers.

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. MPPT controllers can increase solar production by as much as 30% by managing the volt / amp relationship to maximize output.

Multicrystalline - A semiconductor (photovoltaic) material composed of variously oriented, small, individual crystals. Sometimes referred to as multi crystalline.

Nominal Voltage - A reference voltage used to describe batteries, modules, or systems (i.e., a 12-volt or 24-volt battery, module, or system).

Open-Circuit Voltage (Voc) - The maximum possible voltage across a photovoltaic cell; the voltage across the cell in sunlight when no current is flowing.

Orientation - Placement with respect to the cardinal directions, N, S, E, W; azimuth is the measure of orientation from north

Overcharge - Forcing current into a fully charged battery. The battery will be damaged if overcharged for a long period.

Parallel Connection - A way of joining solar cells or photovoltaic modules by connecting positive leads together and negative leads together; such a configuration increases the current, but not the voltage.

Photovoltaic(s) (PV) - Pertaining to the direct conversion of light into electricity.

Photovoltaic (PV) Array - An interconnected system of PV 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 (PV) Effect - The phenomenon that occurs when photons, the "particles" in a beam of light, knock electrons loose from the atoms they strike. When this property of light is combined with the properties of semiconductors, electrons flow in one direction across a junction, setting up a voltage. With the addition of circuitry, current will flow and electric power will be available.

Photovoltaic (PV) 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 direct current power under un-concentrated sunlight. The structural (load carrying) member of a module can either be the top layer (superstrate) or the back layer (substrate).

Photovoltaic (PV) Panel - often used interchangeably with PV 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 (PV) System - A complete set of components for converting sunlight into electricity by the photovoltaic process, including the array and balance of system components.

Rated Battery Capacity - The term used by battery manufacturers to indicate the maximum amount of energy that can be withdrawn from a battery under specified discharge rate and temperature.

Rated Module Current (A) - The current output of a photovoltaic module measured in Amps.

Regulator - Also called a Charge Controller - Prevents overcharging of batteries by controlling charge cycle-usually adjustable to conform to specific battery needs.

Reverse Current Protection - Any method of preventing unwanted current flow from the battery to the photovoltaic array (usually at night). See blocking diode.

Series Connection - A way of joining photovoltaic cells by connecting positive leads to negative leads; such a configuration increases the voltage.

Short-Circuit Current (Isc) - The current flowing freely through an external circuit that has no load or resistance; the maximum current possible.

Sine Wave Inverter - An inverter that produces utility-quality, sine wave power forms.

Single-Crystal Silicon - Material with a single crystalline formation. Many photovoltaic cells are made from single-crystal silicon

Stand-Alone System - An autonomous or hybrid photovoltaic system not connected to a grid. Most stand-alone systems require batteries or some other form of storage.

System Operating Voltage - The photovoltaic array output voltage under load. The system operating voltage is dependent on the load or batteries connected to the output terminals.

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.

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.

Total AC Load Demand - The sum of the alternating current loads. This value is important when selecting an inverter.

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.

Trickle Charge - A charge at a low rate, balancing through self-discharge losses, to maintain a cell or battery in a fully charged condition.

Voltage at Maximum Power (Vmp) - The voltage at which maximum power is available from a photovoltaic module.

Watt - The rate of energy transfer equivalent to one ampere under an electrical pressure of one volt. One watt equals 1/746 horsepower, or one joule per second. It is the product of voltage and current (amperage).