Solar Energy Glossary

With the increasing use and relevance of solar energy, you might find yourself encountering a lot of terms that are unique to the field. Here’s a quick guide to some of the most important common and technical terms you will encounter our in solar energy glossary.


This refers to a device that absorbs light particles to generate charge carriers in a solar power system.

Antireflection coating:
An antireflection coating is a thin layer of a substance that decreases the amount of light that is lost to reflection by the solar cell.

An array is essentially a collection of solar panels linked together as a system in order to generate a target amount of electrical energy. the higher the number of arrays, the higher the energy output.

Since the function of the solar panels depends on the ability of the sun to hit them, the Azimuth angle helps to determine the direction in which the panels should face, relative to the sun.


Balance of system:
This consists of all the components of the solar electricity generating system excluding the photovoltaic modules/array various. It also includes every other cost involved in the production process.

An important part of a solar energy electricity generating system, the battery helps to store electricity generated by the system from solar energy.

Blocking diode:
A semiconductor that serves as a one-way valve allowing the flow of electrons from the solar cell to the battery and blocking the current flow back, thus preventing the discharge of the battery.

Bypass diode:
This is a diode which is connected in parallel to multiple solar cells within a module in order  to provide an alternative current path in cases where there might  be a  reverse biasing of the cell(s)


This is the smallest unit of an electro-chemical device that is capable of converting chemical energy into electrical energy.

Cell barrier:
A cell barrier is a narrow region of electric charge which is static, lying along the interfacial layer of the positive layers in a solar cell, as well as the negative layers, designed to generate a voltage across the cell.

Charge controller:
This is an element  in a solar power system that serves to regulate the current that flows to the battery and from it, hence protecting it from being overcharged or conversely, from over discharging.

Combined collector:
This is a solar power system that is capable of generating heat energy alongside the electricity it produces.

A unit that can perform the conversion of one direct current (DC) voltage to another.

Cutoff voltage:
This is the level of voltage at which the charge controlling element stops current flow to the battery in order to protect it.


Days of storage:
This refers to the duration (number of days) for which a solar energy system will continuously meet a defined load without solar energy input.

DC-to-DC converter:
This is an electric circuit that is used to convert direct current voltages, like the one produced in a photovoltaic system into other voltage levels such as the load voltage.

Diffuse insolation:
As opposed to direct insolation, this is the sunlight received indirectly, either due to fog, haze, dust or even clouds scattering the direct light from the sun.

Direct current (DC):
Direct current refers to a type of transmission and distribution of electricity, usually with a relatively low voltage and high current, that only flows through the conductor in a single direction. For it to be utilised for normal, everyday household appliances, Direct current has to be converted into an alternating current.

Direct insolation:
This happens when sunlight falls upon a collector directly. This is contrary to the diffuse insolation.

Like the term implies, this refers to a period during which  the PV system cannot supply power for its load and it is often measured in hours per year, or a percentage of that.


Electrical grid:
This is an interconnected system that distributes electricity to a large region. it begins at the point of electricity generation, linking up until the point of electricity consumption.

Energy is defined as the capability of an appliance to do work. Energy is transformed from one form to another and can neither be created nor destroyed.

This, in essence, is a period in the year when night and day are of equal length because the sun appears to cross the equator of the Earth. It occurs twice in a year, around March 20 or 21 (spring equinox) and September 22 or 23 (fall equinox).


Fill factor:
This is defined as the ratio of a PV cell`s functioning power to its potential power, if its current and its voltage are theoretically at their maximum.

Fixed tilt array:
This is a solar power system array that is placed relative to the horizontal, at a fixed angle.

Flat-plate array:
A flat-plate solar power system array is an array that consists of non-concentrating PV modules.

Flat-plate module:
This is an arrangement of PV cells or material where it is mounted on a rigid flat surface in order for its cells to be directly facing incoming sunlight and be exposed to it.

Full sun:
This is a measure of the level of density of power received at the surface of the earth from the sun on a clear noon (the value is 1,000 Watts/square meter).


Gallium (Ga):
A metallic, naturally occurring chemical element, that is utilised in the production of some solar cells as well as semiconductor devices.

Grid-connected system:
This is a photovoltaic (PV) system in which the PV array acts as the generating source of the electrical grid, and thus, supplies the power  it generates to the grid.

Grid lines:
This refers to metallic contacts that are fused to the surface of the solar cell in order to create a path is low resistance path through which the electrons can flow out to the cell’s interconnect wires.


Hybrid system:
This is a solar electric or PV  system that also includes and is combined with other sources through which electricity can be generated, such as wind or diesel generators.


Interconnection agreement:
This is a contract between a solar power generating homeowner and the local utility that allows the homeowner to connect their solar power system to the electric grid

A solar inverter is a device which takes electricity from the solar energy system in DC from and uses it to create AC electricity.


Junction diode:
A junction diode is a device (semiconductor) that has a junction and potential causes it to pass its current more effectively through one direction than in the other.


Kilowatt (kW):
The Kilowatt is the standard unit of electrical power and it is equal to a thousand watts, or in other terms, to a rate at which energy is consumed at 1000joules per second.


Langley (L):
The unit of solar irradiance measured in one gram calorie per square centimeter. 1 L = 85.93 kWh/m2.

Light trapping:
This refers to the use of the reflection and refraction of light at critical angles in order to trap it within a semiconductor material.

This refers to a demand on an energy generation system. It is the level of energy that is consumed or required by a component and it is mostly expressed in the unit of amperes or watts as a reference to electricity.


This refers to a device that serves to monitor the level of energy that is produced in a home by its solar system.

Also called solar panels, a solar module refers to a single photovoltaic panel which is made up of solar cells that are connected together. These solar cells are what help to generate electricity by the absorption of the energy present in sunlight.

A multicrystalline is a semiconductor (photovoltaic) material that is composed of crystals that are small, individual and have various orientations.

Multijunction device:
This is a high-efficiency solar power system that contains multiple cell junctions, that are all optimised for different parts of the solar spectrum.


Net metering:
A net meter records the energy that is sent to the grid compared to the energy that is  received from it and credits or charges the user according to local rates and rules.


Open-circuit voltage (Voc):
This is the highest possible voltage that can be present across a photovoltaic cell. It is also the voltage present across the cell when it is in sunlight and there is no current flowing.


Packing factor:
The ratio of the area of the array to the land or building area on which it is.

Parallel connection:
A parallel connection is a way of joining PV modules where the positive leads are connected together, and the negative leads are connected together as well. Doing this has a positive effect (increase) on the current but a reverse effect (decrease) on the voltage.

This is a reaction that serves to eliminate the destructive effect of atoms which electrically react on the surface of a solar cell

Peak sun hours:
This is the number of hours in a day when the irradiance of the sun is an average of 1,000 w/m2.

This refers to an electric current that is induced as a result of radiant energy.

A particle of light that acts as an individual unit of energy.

This term is used to describe a state of producing a voltage (-voltaic) when exposed to light (photo-).


Ribbon (photovoltaic) cells:
This is a type of device made through a continuous process in which it is pulled from a molten bath of material capable of producing voltage on exposure to light such as silicon, to form a thin sheet of material.


Solar cooling:
Although something of an oxymoron, solar cooling refers to the use of solar energy to power a cooling appliance.

Solar energy:
As the name implies, this refers to energy transmitted from the sun, also referred to as solar radiation. Harnessing this energy forms the basis of using the sun to generate electricity.

Solar panel:
See Module

This is a number of PV panels that are electrically interconnected in order to produce the amount of voltage required by the load in order for it to operate.

This is a covering on the sunny side of a photovoltaic (PV) module, that provides protection for the PV materials from force, impact and degradation due to weather and other environmental factors while allowing maximum transmission of the appropriate wavelengths of the solar spectrum.


Total internal reflection:
Total internal reflection is the trapping of light through 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:
This is a photovoltaic (PV) array capable of following the direction in which the sun moves in order to maximise the amount of solar radiation it receives on its surface.

This is an electromagnetic device that is used to change the voltage of alternating current electricity.


Utility-interactive inverter:
This is an inverter that functions only when it is tied to the utility grid, and by making use of the prevailing line-voltage frequency on the utility line as a control parameter, ensures that the output of the photovoltaic system is fully synchronized with the utility power.


Also known as a voltage-dependent variable resistor, this device is used to shunt energy to the ground, thus protecting sensitive parts and equipment of machinery or devices from power spikes or lightning strikes.

This refers to the amount of electromotive force that exists between two points and it is measured in Volts.


This is a transparent material with a wide bandgap that is used as the surface top of a solar power system or photovoltaic device, in order to allow almost all of the light to reach the semiconductor layers beneath.