Definition of Terms - Solar Glossary

Please see below our list of definitions that you may find on our quotations etc

AC
Alternating Current – Electric current in which the direction of flow is reversed at frequent intervals.

AC cables
A cabling system suitable for conducting the AC produced by the inverter and connecting it in parallel with the main supply.

AC isolator
Electrical device capable of isolating the inverter from the 230v mains supply.

Ampere (A)
Unit of electric current. The rate of flow of electrons in a conductor equal to one coulomb per second.

Anti-reflection coating
A thin coating of a material, which reduces the light reflection and increases light transmission, applied to a photvoltaic cell surface.

Array
A collection of electrically connected photovoltaic (PV) modules.

Array current
The electrical current produced by a PV array when it is exposed to sunlight.

Azimuth
Horizontal angle measured clockwise from true north; 180 degrees is true south.

Base load
The average amount of electric power that a utility must provide in any period.

Blocking diode
A diode used to resist or block reverse current from flowing backward through a module. Alternatively, diode connected in series to a PV string; it protects its modules from a reverse power flow and thus against the risk of thermal destruction of solar cells.

Bypass diode
A diode connected across one or more solar cells within a photvoltaic module such that the diode will conduct if the cell(s) become reverse biased. Alternatively, diose connected anti-parallel across part of the solar cells of a PV module. It protects these solar cells from thermal destrucution in case of toatal or partial shading of individual solar cells while other cells are exposed to full light.

Current
The flow of electric charge in a conductor between two points having a difference in potential (voltage).

Diode
Electronic component that allows curent flow in one direction only.

DC
Direct current- Electric current flowing in one direction only.

DC cables
A cabling system suitable for conducting the DC current produced by the PV module.

DC isolator
A means of isolating the PV module output from the inverter.

Duty cycle
The ratio of active time to total time. Used to describe the operating regime of appliances or loads in PV systems.

Efficiency
The ration of output power (or energy) in input power (or energy). Expressed as a percentage.

Electric current
A flow of electrons; electricity.

Energy meter
A meter which indicates the amount of electricity produced by the PV array.

Export meter
A meter which indicates the amount of energy exported out into the national grid and not consumed within the property.

Grid
Term used to describe an electrical utility distribution network.

Instantaneous short circuit (Isc)
The amount of current produced by an illuminated PV cell, module or array when it’s positive and negative output connections are shorted.

Incident light
Light that shines onto the facade of a solar cell or module.

Inverter
In a PV system the inverter converts DC power from the PV array to Ac power compatible with the AC load of the building.

Inverter parallel connection
The AC output from the inverter is connected side by side with the incoming AC supply. The inverter must automatically disconnect from the mains if there is mains power failure. The PV system cannot work standalone to produce electricity in the event of a mains power failure.

Irradiance
The solar power incident on a surface. Usually expressed in kilowatts per square meter.

Joule (J)
Unit of energy equal to 1/3600 kilowatt hours.

Kilowatt (kW)
One thousand watts. A unit of power.

Kilowatt hour (kWh)
One thousand watt-hours. A unit of energy. Power multiplied by time = energy.

Kilowatt peak (kWp)
The value of power generated by a PV panel under full solar radiation. Solar radiation of 1000 watts per square metre is used to define standard conditions

Load
The amount of electric power used by any electrical unit or appliance at any given time.

Load current
The current required by the electrical device.

Maximum module reverse current
The maximum current a module can withstand in the wrong direction without damage occurring to the module. Each module is designed to withstand at least twice its Instantaneous short circuit current (Isc)

Module
The smallest replaceable unit in a PV array. An integral, encapsulated unit containing a number of PV cells.

MPP
Maximum Power Point; the point on the current-voltage (I-V) curve of a module under illumination, where the current and voltage is maximum.

NOCT
Nominal Operating Cell Temperature – The estimates temperature of a PV module when operating under 800 W/m2 irradiance, 20°C ambient temperature and wind speed of 1 meter per second. NOCT is used to estimate the nominal operating temperature of a module in its working environment.

Nominal voltage
A reference voltage used to describe modules or systems.

Open circuit voltage (Voc)
The maximum voltage produced by an illuminated photvoltaic cell, module or array with no load connected, measured across the positive and negative connections. This value will increase as the temperature of the PV material decreases.

Peak load
The maximum load demand on a system.

Photovoltaic system
An installation of PV modules and other components designed to produce power from sunlight and meet the power demand for a designated load.

Rated module current
The current output of a PV module measured at standard test conditions.

Resistance
The property of a conductor which opposes the flow of an electric current resulting in the generation of heat in the conductive material. The measure of resistance of a given conductor is the electromotive force needed for a unit current flow. The unit of resistance is ohms.

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 elevation angle
The angle made between ground level and the suns height above the horizon (0° when the sun is at the horizon and 90° when directly above)

Standard test conditions
Conditions under which a module is typically tested in a laboratory: Irradiance intensity of 1000 watts per meter square, AM1.5 solar reference spectrum and a cell or module temperature of 25°C, plus or minus 2°C.

String
A number of modules or panels interconnected electrically in series to produce the operating voltage required by the load.

Sun path diagram
Graphical representation of the sun’s height and azimuth.

Tilt angle
The angle of inclination of a solar collector measured from the horizontal.

Volt
The unit of electromotive force that will force a current of one ampere through a resistance of one ohm.

Voltage at maximum power
The voltage at which maximum power is available from a module.

Watt
The unit of electrical power. The power developed when a current of one ampere flows through a potential difference of one volt.

Watt hour (Wh)
A unit of energy equal to one watt of power connected for one hour.

Zenith angle
The angle between directly overhead and the line intersecting the sun ( 90° – zenith is the elevation angle of the sun above the horizon).