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  Mar 23, 2021   

Solar Energy Glossary – A to Z Guide

Solar Energy Glossary – A to Z Guide

Solar energy seems to be full of technical jargon, so we’ve defined some basic terms which are frequently used in the solar energy field.



Alternating current (AC): Alternating current (AC) denotes the flow of charge that periodically changes its direction. It is a sinusoidal wave i.e.; it moves in a positive as well as negative direction. In a residential area in India, we get 220 or 230 V, 50Hz AC supply.

Alternating current distribution board (ACDB): ACDB is used for distributing electric current from solar inverter to the electric loads through the energy meter.

Air mass (AM) ratio: AM is defined as the angle between the vertical line and the sun. It is expressed as 1/Cosz (Cosine of zenith angle). It is used to measure solar cell performance i.e.; it defines how much solar radiation travels through the atmosphere at standard test conditions.

AM 1 denotes that the sun is directly at the head and it passes through 1 atmosphere condition.

Ambient temperature: The temperature of the surrounding atmosphere is termed ambient temperature.

Ampere: Ampere is the unit for measuring electric current. One ampere is defined as the one coulomb of charge flowing for one second.

Ampere hour meter(A-h): A-h meter is used to measure and record the total amount of electric energy consumed at a residential and commercial location.

Amorphous silicon: Amorphous silicon is a non-crystalline material and is widely used in designing solar cells due to its low manufacturing cost and non-toxic nature.

Anode:  Anode is the positive electrode or plate or wire in an electrolytic cell or battery through which charge flows into the circuit. Negative charges are attracted towards the anode.

Angle of incidence: The Angle between the sun’s ray and the surface is known as the angle of incidence. It is a 0-degree angle when the surface is directly facing the sun and a 90-degree angle when the surface is parallel to the sun.

Array: An array or photovoltaic array is a group of solar modules (a group of solar cells) that converts photovoltaic energy into electrical energy in the form of direct current. The number of arrays connected depends on the individual’s power requirement.

Array junction box (AJB): Array junction box is placed between the solar panel and the inverter. It helps in electrically connecting the solar panel in parallel and also to protect the inverter against overvoltage and overcurrent.

Azimuth angle:  Azimuth angle is the compass direction of solar radiation and generally defined from true north in a clockwise direction. It is the azimuth (measurement of angle in a spherical coordinate system) angle of the sun.


Balance of system:  In a photovoltaic system, the balance of system or BOS consists of types of equipment or components responsible for the transmission of DC energy generated by the solar panel into the AC supply. These components consist of cables/wires, fuses, fault detectors, switches, monitoring system and other protective equipment in addition to inverters, racking and other mounting systems.

Battery:  Battery plays an important role in energy storage especially when it isanoff-grid solar energy system. 

Battery lifespan: Battery lifespan is the total number of charge discharge cycle batteries undergo without affecting the performance efficiency. The battery life cycle depends on the depth of the discharge cycle.

Bill of material (BOM): BOM includes a list of all the ingredients and the specifications in hierarchy order from raw material to small parts like nuts, bolts etc. In the solar energy system BOM consists of solar panels, support structures, cables, junction boxes, batteries, inverters, etc. on the higher levels, and minor components like screws, nuts and bolts in the lowest level.

Building integrated photovoltaics (BIPV): BIPV is the photovoltaic materials used in building envelopes such as in roofs, skylights and facades, thus replacing the traditional building materials. BIPV helps in reducing the cost and electricity bills by initially integrating photovoltaic material into the building envelopes.


Cathode: Cathode is a negatively charged electrode through which charges enter into the circuit. Cathode and anode are the main elements of the electrochemical cell.

Cell (Photovoltaic Cell): Photovoltaic (PV) cell is the main element in the conversion of photon energy into electrical DC energy. Series of solar cells are connected to form the solar module to achieve the required voltage. Solar cells are generally made up of silicon material.

Central inverter: It is the type of grid connected inverter. Central inverter is similar to string inverter with a high-capacity range, needing only 1 large inverter for the entire plant / section of plant.

Charge controller: The charge controller is the component of the solar energy system; it is responsible for controlling the flow of the incoming and outgoing current of the battery to protect the overcharging of the battery.

Concentrated photovoltaics (CPV): CPV is the photovoltaic technology used for the generation of electrical energy using curved mirrors or lenses to concentrate solar radiation efficiently on smaller solar cells.

Concentrated solar power (CSP): CSP is the system that generates solar power using a lens or mirror, in this solar energy incident on the receiver is converted into heat energy which is further converted into electrical energy with the help of a thermally driven generator or steam turbine.

Cutoff voltage: The maximum allowed voltage is termed as cutoff voltage. In a solar energy system, cutoff voltage is the voltage level at which the charge controller disconnects the solar array or loads from the battery system.


DC-DC converter: DC to DC converter is the power electronic device, as the name indicates it is used to convert DC supply from one voltage into another.

Deep cycle battery: The term deep cycle battery is mostly used for a lead-acid battery, the battery is designed in a way that it gets discharged more than 80% regularly without affecting the battery performance.

Depth of discharge (DOD): Depth of discharge is the alternative method for measuring the state of charge of the battery. It is denoted in fraction or percentage and it is termed as the amount of battery that can be used from the total charging capacity of the battery.

Direct current (DC): Direct current is the unidirectional flow of electric charge with zero frequency. The output of a solar panel is in the form of DC energy which is further converted into an AC supply using an inverter.

Direct current distribution box (DCDB): DCDB is used for connecting the output power from the solar panel to the input of the inverter.

Direct beam radiation: It is also referred to as direct radiation or simply beam radiation. It is defined as the amount of solar radiation travelling in a straight line on the earth surface.

Duty cycle: The duty cycle is defined as the ratio of on-time to the off time of the load or any appliances. It is also termed as duty factor; 60% duty cycle is referred to as 60% on-time and 40% off-time.


Electric current : An electric current is termed as the flow of charged particles in the closed-loop.

Electrical grid: Electrical grid or power grid is the integrated network for connecting the generated electricity to the consumers. The system consists of generating station, substation and transmission system.

Electrochemical cell: An electrochemical cell generates electrical energy from a chemical reaction or generates chemical reaction using electrical energy. Two types of electrochemical cells are available i.e., Galvanic cell/voltaic cell that generates electrical energy using chemical reaction and electrolytic cell that generates chemical energy using electrolysis.

Electrode: An electrode is an electrical conductor connected to the non-metallic circuit through which the current enters and leaves the circuit.

Electrolyte: An electrolyte substance is a liquid or gel that consists of ions and is capable of generating an electrically conductive solution when dissolved in a polar solvent like water.

Energy : Energy is defined as the capability of an appliance to do work. Energy can be transformed from one form to another, we cannot create or destroy energy.

Energy density:  It is defined as the amount of energy stored per unit volume or mass in a given system or space.


Flat-plate collector:  A flat plate collector is a metal box with a dark absorber at the bottom and a plastic or glass cover at the top. It is the type of solar thermal panel that converts solar heat radiation into thermal energy.

Frequency: Frequency is defined as the number of cycles per unit of time. It is measured in Hertz (Hz). In India, we get an AC supply of frequency 50 Hz.

Full sun:  Full sun is termed as the amount of solar energy incident on the earth surface at noon. It is approximately 1000 Watts/square meter.


Gel type battery: It is the type of sealed lead-acid battery, with gel electrolyte that reacts with lead plates.

Grid-connected system: Grid-connected solar system is the electricity generating system connected to the power grid.

Grid based Inverter:  These inverters are connected to the power grid system and are the most common type of inverters used in residential applications.


Hybrid system: A hybrid system, in general, is termed as the combination of two or more different sources, it can be the combination of renewable and non-renewable sources. In a solar energy system, the hybrid system is defined as the combination of an on-grid and off-grid photovoltaic system.

Hybrid inverter: It is the type of inverter used in solar energy systems. Hybrid inverters are the combination of off-grid and on-grid systems. They offer a lot of flexibility for power delivery by choosing between solar power, battery backup and grid connectivity.


Incident light: The light that falls on the subject is termed incident light. It can be either from a direct or indirect source of light. Solar rays are an example of direct source that falls on the subject (solar module).

Insolation: It is the total amount of solar radiation that falls on the earth surface in a given time. Insolation is measured on a daily basis in terms of kilowatt-hours per square meter (kWh/m2) or yearly as watts per square meter (W/m2).

Irradiance: Irradiance or flux density of radiation is the amount of power incident on a given surface area. It is expressed as watts per square centimeter or square meter.

Inverter: Inverter is the power electronic device responsible for the conversion of DC power into AC power. In solar energy systems, an inverter is considered the heart of the system as it converts the generated DC power of the solar panel into useful AC power.

I-V curve: I-V Curve stands for current flowing through the circuit versus the applied voltage. Graphical representation of the I-V characteristic curve denotes the solar cell or module performance.


Junction box: Photovoltaic junction box is usually pre-installed at the backside of the solar module. It is used for electrically interconnecting two or more solar panels and providing protection to these electrical units.


Kilowatt-hour: Kilowatt-hour is the unit for measuring the energy (give link of energy of the article on basic of electricity) consumed by the appliances.


Lead acid battery: The lead acid battery is the type of rechargeable battery commonly used in the solar energy system. The plates in the batteries are made up of lead sponge and lead peroxide for the conversion of chemical energy into electrical energy.

Line commutated inverter: The line commutated inverter is connected to the power grid. The conversion of DC power to AC power is controlled by the power line, so if the grid fails then the solar panel won’t be able to supply power to the line.

Load: In general load or electrical load is termed as the electrical appliance or components that consume active power for their functioning. Common examples of electrical loads include appliances such as light, fan, TV etc.


Maximum power point: Maximum power point on the I-V curve isdefined as the point where the product of current and voltage is maximum. For silicon solar cells, the maximum power point occurs generally at 0.45 volt.

Maximum power point tracker (MPPT): MPPT is the system generally used with wind or solar systems to optimize power extraction under all conditions.

Micro-inverter: It is the type of grid connected inverter used in the places where space is the factor. These inverters are placed on every solar panel, thus independently converting DC to AC supply.

Module: Solar module is defined as the group of solar cells connected. The number of solar cells connected to form a solar module depends on the power requirements. It is an alternative term for a solar panel.

Module mounting structure: Mounting structure in general is used to support the system. Module mounting structure helps in assembling the solar panel depending on the type of solar system i.e., rooftop or ground based.


National Electrical Code (NEC): NEC defines the guidelines for all types of electrical installations, “article 690” describes installation and protection guidelines for solar photovoltaic systems.

Normal operating cell temperature (NOCT): Normal or nominal operating cell temperature is defined as the solar cell temperature at 20°C ambient temperature and wind speed of 1m/ s with 800W/ m² irradiance, and solar module at an angle of 45°.


Off-grid solar system: This type of solar energy system is not connected to the power grid system.

Off-grid inverter: These inverters work independently and have no contact with the power grid system.

One-axis tracking: One-axis tracking systems have trackers mounted on photovoltaic systems that are capable of rotating only in one direction with the movement of solar radiation.

Overcharge: Charging the battery beyond the full charge limit of the battery is known as overcharging.


Photovoltaic: Photovoltaic is the conversion of light energy into electrical energy using semiconducting material that possesses the photoelectric property.

Photoelectric effect: The photoelectric effectis the emission or release of electrons when light energy is incident on the material surface.

Photovoltaic panel: Photovoltaic panel consists of a group of solar modules assembled for the conversion of photon energy into electrical energy.

Power factor: The Power factor (PF) of an AC circuit is defined as the ratio of real or active power to the apparent power of the particular load. It is in the range of +1 to -1. Power factor as unity is defined as an ideal condition. For DC circuits as the frequency is zero there is no power factor term involved.

Power : Electric Power is defined as the amount of work done in a per unit time or amount of energy consumed by the electrical circuit. It is measured in Watts.

Power density: Power density is defined as the amount of power per unit volume. It is expressed as.

Primary battery: Primary batteries are defined as non-rechargeable batteries. These batteries once discharged cannot be charged again.

Pyranometer: Pyranometer is the type of actinometer used for measuring solar irradiance, it is used for measuring the diffuse solar radiation.

Pyrheliometer: Pyrheliometer is used for measuring direct solar radiation incident on a location. Thermopile is used for converting the incident heat energy into the measurable electrical signals for recording solar radiations.


Quantum efficiency: Quantum efficiency is defined as the ratio of charge carriers collected by the solar cell to the number of photon energy incidents on the solar cell. Quantum efficiency is the function of energy or wavelength.


Rated power:  Rated power is mentioned on the power appliances, it is defined as the maximum allowable power of the particular equipment under the normal condition.

Reactive power(Q): Reactive power of the circuit is defined as the power that moves back and forth in the circuit. It is given in volt ampere-reactive (VAR).

Rectifier: Rectifier is the power electronic device that converts alternating current into direct current.

Rechargeable battery: A battery that can be refilled with charges once discharged is termed as a rechargeable battery or secondary battery. These batteries are generally used in the solar energy system.

Resistance: Resistance is defined as the power to oppose the flow of current in the circuit. According to Ohm’s law, the current is inversely proportional to the amount of resistance in the circuit.


Semiconductor: Semiconductor material has a conductivity between conductors and insulators. Compounds such as gallium arsenide, germanium or silicon are termed semiconductors.

Sealed battery: Sealed batteries also termed valve-regulated batteries are the type of lead acid batteries; they are sealed to protect against spilling or overflow of electrolytes.

Secondary battery: Secondary battery is also known as a rechargeable battery, once discharged it can be recharged again. These batteries are used in applications like solar energy systems, electric vehicles etc.

Silicon: Silicon (Si) is a hard, brittle crystalline solid material with a blue-grey metallic luster, it is a semiconductor material used in manufacturing of solar cells.

Smart grid: Smart grid is an intelligent electrical power grid that is integrated with digitally operated meters.

Solar energy: Solar energy is the heat and light energy received from the sun which is converted into usable electrical energy using various technologies such as photovoltaic technology. The amount of solar radiation that reaches the earth is almost one billionth of total solar energy generated.

Solar spectrum: Solar spectrum consists of various wavelengths from ultraviolet to deep infrared rays. It is not uniform; it changes with location and time-zone.

Standalone system: Standalone solar energy system is also referred to as an off-grid system, it utilizes only solar energy as the main source of energy. As these systems are not connected to the power grid, energy storage batteries play an important role in storing energy when solar radiations are not available i.e., during the night and cloudy days.

Standard test conditions (STC) — Standard test conditions are defined as solar radiations of one kilowatt per square meter at 25°C at an angle of 45 degrees. Generally, output ratings of solar panels are defined at standard test conditions.

State-of-charge (SoC): SoC of the battery is defined as the amount of energy available in the battery, it is expressed in percentage. For example, 60% SoC is defined as the 60% full battery at that point of time.

String: Photovoltaic modules are to be connected in series or parallel to achieve the required voltage, solar modules or panels connected in series are termed as String.

String inverter: It is the type of grid connected inverter. In this bunch of strings is attached to form a single string inverter, every string receives solar power in the form of DC energy and it is converted into required AC power.


Thin film: Thin film solar cells are made up of depositing one or many layers of thin film photovoltaic material on glass, plastic or metal. They are second-generation solar cell with a wide variety of thickness from nanometer to micrometer

Tilt angle: Tilt angle is the angle at which the solar panel is placed to get optimum solar radiations.

Transformer: A transformer is an electrical device that transfers electrical energy from one circuit into another using the electromagnetic induction principle. It converts voltage at one level to another level.

Two-axis tracking:  Solar photovoltaic system capable of rotating along two axes i.e., at the horizontal or vertical axis is known as two- axis tracking system. This system is able to optimize solar performance by almost 25%.


Utility-interactive inverter: The inverter that can operate only when connected to a grid is known as a utility-interactive inverter. In case the grid fails, the inverter ceases the AC supply.


Vented cell batteries: They are also termed wet cell or flooded cell batteries. It consists of a pressure release valve to vent out the gases produced during the normal operation. They are mostly used in the application where charging-discharging rate is high.

Voltage: Voltage is defined as the amount of potential energy between two points in the circuit. It is the pressure applied in the circuit to allow the flow of charges; it is measured in volts.

Voltage regulation: Voltage regulation is defined as the difference between the magnitude of sending and receiving end voltage, it is usually expressed in percentage.


Wafer: In an electronic circuit wafer is also known as slice, it is the thin semiconductor structure used in designing of solar silicon cells.


Zenith angle: Zenith angle is defined as the angle between solar radiation and vertical. The higher the sun is in the sky lower is the zenith angle i.e., solar zenith angle is minimum at noon.

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