Solar Glossary

Solar Term


AGM (Adsorbed Glass Mat)

Type of battery construction which uses saturated adsorbant glass mats instead of liquid or gelled electrolyte; typically more reliable compared to flooded (liquid), but also more expensive.

Alternating current (AC)

An electrical current that continually reverses direction of flow; powers electronic devices or appliances in your home.


A device for producing alternating current electricity.

Amorphous silicon

A thin-film solar PV cell material with a glassy structure instead of crystalline structure.

Ampere (A) or amp

Unit of electric current; flow of electrons.


A number of solar modules connected together in a single structure.

Array current

Electrical current output of a PV array when exposed to sunlight.


System in which stored chemical energy is converted directly into electrical energy.

Battery capacity

The total number of ampere-hours (Ah) that a fully charged battery can output.

Battery cell

Individual unit of a battery that can store electrical energy; capable of furnishing a current to an external load.

Battery charger

Device used to charge a battery by converting AC voltage to DC voltage.

Battery cycle life

The number of times a battery can undergo a cycle of discharge and recharge before failing.

Battery self-discharge

Energy loss by a battery that is not under load.


Maximum volume (of c-Si or TF cells) that could be produced at a given time.


Basic unit of a PV module or battery; contains electrodes and electrolyte in a battery, to produce electricity.

Cell efficiency

Ratio of electrical energy produced by a photovoltaic cell (under full sun conditions) to the energy from sunlight falling upon the photovoltaic cell.


Process of inputting electrical energy to a battery.

Charge controller

A component that controls the flow of current to and from the battery subsystem to protect it from overcharge and over discharge; necessary to guarantee that the battery gets maximum state of charge and longest life; may also monitor system performance and provide system protection; also called regulators.

Charge rate

Measure of current used to charge a battery as a proportion of its capacity.

Crystalline silicon

Type of PV cell material made from a single crystal or polycrystalline ingot of silicon.


Flow of electric charge in a conductor between two points having a difference in electrical potential (voltage) and is measured in Amps.

Deep cycle battery

Battery designed to regularly discharge 80% of its capacity before recharging.

Direct radiation

Light that has traveled in a straight path from the sun (also referred to as beam radiation). An object in the path of direct radiation casts a shadow on a clear day.


Withdrawal of electrical energy from a battery.


A wholesaler of PV products.


The ratio of output power or energy to input power or energy, expressed as a percentage.

Electric current

The flow of electrons measured in Amps.

Electrical grid

A network for electricity distribution across a large area.


The movement of electrons (a sub-atomic particle), produced by a voltage, through a conductor.


An electrically conductive material forming part of an electrical device. Often used to lead current into or out of a liquid or gas. In a battery, the electrodes are also known as plates.


Power consumed multiplied by the duration of use. For example, 1000 Watts used for four hours is 4000 Watt hours.

Energy density

The ratio of the energy available from an energy storage device such as a battery to its volume (Wh/m3) or weight (Wh/kg).

Fixed tilt array

A solar PV array set at a fixed angle to the horizontal.

Flooded cell battery

A form of rechargeable battery in which the plates are completely immersed in a liquid electrolyte. Most cars use flooded cell batteries. Flooded cell batteries are the most commonly used type for independent and remote area power supplies.

Gel-type battery

Lead-acid battery in which the electrolyte is immobilized in a gel. Usually used for mobile installations and when batteries will be subject to high levels of shock or vibration.


A mechanical device used to produce DC electricity. Power is produced by coils of wire passing through magnetic fields inside the generator. Most alternating current generating sets are also referred to as generators.


An electrical utility distribution network.


An energy producing system connected to the utility transmission grid. Also called Grid-tied.

High voltage disconnect

Voltage at which the charge controller will disconnect the array to prevent overcharging the batteries.

Incentive programs

Incentive program the project is entitled to.

Install date

Refers to manufacturing equipment installation timing for a fab or a fab phase.


Markets and customizes PV systems for installation.


An inverter converts DC power from the PV array/battery to AC power. Used either for stand-alone systems or grid-connected systems.


The solar power incident on a surface, usually expressed in kilowatts per square meter. Irradiance multiplied by time gives insolation.


A unit of electrical power equal to 1000 Watts.

Kilowatt-hour (kWh)

A unit that describes the amount of energy that derives from a power of 1000 Watts acting over a period of 1 hour. 1 kWh equals 3600 kJ.

kWh Output

Estimated first year kilowatt hour output of the PV system. Often the output on which the PPA price is paid.

Liquid electrolyte battery

A battery containing a liquid solution of an electrolyte in a solvent (e.g. sulfuric acid in water). Also called a flooded battery because the plates are covered with the electrolyte solution.

Maintenance free battery

A sealed battery to which water cannot be added to maintain the level of the

Maximum power point tracker (MPPT)

A power conditioning unit that automatically operates the PV generator at its MPP under all conditions. An MPPT will typically increase power delivered to the system by 10% to 40%, depending on climate conditions and battery state of charge.

Megawatt (MW)

A measurement of power equal to one million Watts.

Megawatt-hour (MWh)

A measurement of power with respect to time (i.e. energy). One megawatt-hour is equal to one megawatt being used for a period of one hour, or one kilowatt being used for 1000 hours.

Module supplier

Suppliers of modules.

Module type

Type of modules – c-Si:multi/mono; TF:a-Si/CdTe/CIGS; CPV.

Monocrystalline solar cell

A form of solar cell made from a thin slice of a single large crystal of silicon.


A material that has solidified at a rate such that many small crystals (crystallites) form. The atoms within a single crystallite are symmetrically arranged with a particular orientation, whereas the crystallites themselves are differently oriented. The multitude of grain boundaries in the material (between the crystallites) reduce the cell efficiency. Multicrystalline is also referred to as polycrystalline.



Off-grid applications

use independent, or stand-alone, power generation systems, normally with a form of storage such as batteries, to provide a continuous power capability. They include rural applications where the system may power lighting, TV and radio, and industrial applications such as telecommunications, navigation aids and cathodic protection systems.

On-grid applications

Application characterized by connection of the PV system to the main electricity supply such that excess energy generated by the system can be exported to the grid, and electricity can be drawn from the grid in times of a shortfall in PV output, or to meet high daytime loads.


Applying current to a fully charged battery, which can damage the battery.


Used interchangeably with “module”.

Parallel connected

A method of connection in which positive terminals are connected together and negative terminals are connected together. Current output adds and voltage remains the same.

Peak sun hours

The equivalent number of hours per day when solar irradiance averages 1000 W/m2.

Photovoltaic (PV)

Any device which produces free electrons when exposed to light.

Photovoltaic (PV) array

A number of PV modules connected together in a single structure.

Photovoltaic (PV) cell

The smallest discrete element in a PV module that performs the conversion of light into electrical energy to produce a DC current and voltage.

Photovoltaic (PV) module

A single assembly of solar cells and ancillary parts, such as interconnections, terminals, (and protective devices such as diodes) intended to generate DC 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). [UL 1703]

Photovoltaic (PV) panel

Term often used interchangeably with PV module (especially in single module systems).

Photovoltaic cell

The semiconductor device that converts solar irradiance (light) into DC electricity.

Polycrystalline cell

A wafer of silicon with a multi-grained structure. All grains have the same atomic crystal lattice, however, each grain has a unique orientation in space thereby producing a unique reflection of light.

Polycrystalline silicon

A material used to make solar PV cells which consists of many crystals, compared to single crystal silicon.


The rate of doing work. Expressed as Watts (W). For example, a generator rated at 800 watts can provide that amount of power continuously. 1 Watt = 1 joule/sec.


Abbreviation for photovoltaics.

PV array

Two or more photovoltaic panels wired in series and or parallel.

PV components

The individual parts of a PV system. Includes batteries, inverters, regulators, wiring.

PV system

All the parts in combination required to generate solar electricity.

Renewable energy

Energy that is produced from a renewable source.

Series connected

A method of connection in which the positive terminal of one device is connected to the negative terminal of another. The voltages add and the current is limited to the least of any device in the string.

Silicon (Si)

A chemical element with atomic number 14, a dark gray semi-metal. Occurs in a wide range of silicate minerals and makes up approximately 28% of the earth’s crust (by weight). Silicon has a face-centered cubic lattice structure like diamond. The most common semiconductor material used in making PV cells either traditionally in its crystalline form or more recently as an amorphous thin film.

Solar energy

Energy from the sun.

Solar module

A device used to convert light from the sun directly into DC electricity by using the photovoltaic effect. Usually made of multiple solar cells bonded between glass and a backing material. A typical solar module has 100 Watts of power output (but module powers can range from 1 Watt to 300 Watts) and dimensions of 2 feet by 4 feet.

Solar power

Electricity generated by conversion of sunlight, either directly through the use of photovoltaic panels, or indirectly through solar-thermal processes.

Stand-alone (PV system)

A solar PV system that operates without connection to a grid supplying electricity.


Storing energy in a battery or battery stack. In water pumping, storage can be achieved by pumping water to a storage tank.

Storage density

The capacity of a battery, in amp-hours compared to its weight. Measured in Watt-hours per kilogram.

Thin film

A layer of semiconductor material, a few microns or less in thickness, used to make photovoltaic cells. Examples are copper indium diselenide, cadmium telluride, gallium arsenide, and amorphous silicon.


Any device used to direct a PV array towards the sun.

Tracking array

A PV array that is moved to follow the path of the sun in order to maintain the maximum incident solar radiation on its surface. The two most common methods are single-axis tracking in which the array tracks the sun from east to west, and two-axis tracking in which the array points directly at the sun all the time. Two-axis tracking arrays capture the maximum possible daily energy. Typically, a single axis tracker will give 15% to 25% more power per day, and dual axis tracking will add a further 5%.

Utility-interactive inverter

An inverter that can operate only when connected to the utility grid supply and an output voltage frequency fully synchronized with the utility power.


The unit of electric potential and potential difference. The amount of work done per unit charge in moving a charge from one place to another. The potential difference across a resistance of 1 Ohm when a current of 1 Amp is flowing.


Unit of measurement for the electrical pressure of electricity. Measured in Volts (V).

Voltage drop

The voltage lost along a length of wire or conductor due to the resistance of that conductor. Also applies to resistors. The voltage drop is calculated by using Ohm’s Law.

Voltage regulator

A device that controls the operating voltage of a photovoltaic array.

Watt (W)

The unit of electrical power commonly used to define the electricity consumption of an appliance. The power developed when a current of one ampere flows through a potential difference of one volt; 1/746 of a horsepower. 1 Watt = 1 Joule.

Watt hour (Wh)

A unit of energy equal to one Watt of power being used for one hour.


Units of electrical power (that is, the rate at which electrical energy is generated) increasing in scale by a factor of 1000.