Glossary 2017-09-22T18:08:35+00:00

A | B | C | D | E | F | G | H | I | J | K | L | M
N | O | P | Q | R | S | T | U | V | W | X | Y | Z


Angle of Incidence (Degrees) = It refers to the angle between the direct solar beam and the normal (90 degrees) to a line perpendicual to the surface. Eg. a surface directly facing the sun has anangle of incidence of zero, and a surface parallel to the sun (such as a sunrise striking a horizontal rooftop) has an angle of incidence of 90°.

Air mass = The Air Mass is the path length which light takes through the atmosphere normalized to the shortest possible path length (that is, when the sun is directly overhead). The Air Mass quantifies the reduction in the power of light as it passes through the atmosphere and is absorbed by air and dust. When the sun is directly overhead, the Air Mass is 1.

Ambient temperature = The temperature of the surrounding area. Can be measured in Celsius or Fahrenheit by use of commonly available equipments such as RTD / Pt /etc.

Auxillary power = In case of larger solar power systems, there maybe requirement for auxillary power supply to various equipment such as monitoring, SCADA, safety, lighting, airconditioning, etc.

Annual solar savings = The annual solar savings of a solar building is the energy savings attributable to a solar feature relative to the energy requirements of a non-solar building.

Antireflection coating (ARC) = A thin coating of a material applied to a solar cell surface that reduces the light reflection and increases light transmission. Also known as ARC in solar modules. Is beneficial during low light periods such as morning, evening, cloudy weather. Usually delivers about 2 to 5% more energy output

Azimuth angle = The azimuth angle is the compass direction from which the sunlight is coming. At solar noon, the sun is always directly south in the northern hemisphere and directly north in the southern hemisphere. The azimuth angle varies throughout the day as shown in the animation below. At the equinoxes, the sun rises directly east and sets directly west regardless of the latitude, thus making the azimuth angles 90° at sunrise and 270° at sunset. In general however, the azimuth angle varies with the latitude and time of year



Balance of system (BOS) = Represents all components and items other than the photovoltaic modules / panels. It includes various items such as inverters, DC cables, AC cables, AJB, protection systems, earthing, etc.

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

Battery cycle life = The number of cycles, to a specified depth of discharge, that a cell or battery can undergo before failing to meet its specified capacity or efficiency performance criteria.

Bidirectional meter = It is commonly used in solar grid interactive (grid tie) systems for net metering. The difference between a bidirectional meter and a traditional meter is that the bidirectional meter has three readings for export, import and Net; whereas the traditional meter only has one reading Import. Import is the energy drawn from the grid and export refers to the energy fed to the grid during periods when solar power generation is higher than the consumption. Usually bidirectional meters require a prior approval or testing by the concerned electric utility or DISCOM.

Blocking diode = A semiconductor connected in series with a solar cell or cells and a storage battery to keep the battery from discharging through the cell when there is no output, or low output, from the solar cell. It can be thought of as a one-way valve that allows electrons to flow forwards, but not backwards.

Building integrated photovoltaics (BIPV) = A term for the design and integration of photovoltaic (PV) technology into the building envelope, typically replacing conventional building materials. This integration may be in vertical facades, replacing view glass, spandrel glass, or other facade material; into semitransparent skylight systems; into roofing systems, replacing traditional roofing materials; into shading “eyebrows” over windows; or other building envelope systems.

Busbar (Solar cells) = Crystalline silicon solar cells are metallized with thin rectangular shaped strips printed on front and rear of a solar cell. These front and rear contact strips are referred to as busbars. Solar busbars have a significant purpose of conducting the direct current produced by the solar cell from the incoming photons.

Bypass diode = A diode connected across one or more solar cells in a photovoltaic module such that the diode will conduct if the cell(s) become reverse biased. It protects these solar cells from thermal destruction in case of total or partial shading of individual solar cells while other cells are exposed to full light.


Capacity utilization factor (CUF) = the performance of a solar system in percentage terms over the total possible generation. For Example a 100kw system with a 15% CUF would deliver (100 x 365 x 24 x 0.15) KWh per annum = 131,400 KWh. Can be interchangeably used with PLF.

Cathodic protection = A method of preventing oxidation of the exposed metal in structures by imposing a small electrical voltage between the structure and the ground. Solar systems are commonly deployed for meeting cathodic protection power requirements in oil pipelines.

Cell junction = The area of immediate contact between two layers (positive and negative) of a photovoltaic cell. The junction lies at the center of the cell barrier or depletion zone.

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.

Chemical vapor deposition (CVD) = A method of depositing thin semiconductor films used to make certain types of photovoltaic devices. With this method, a substrate is exposed to one or more vaporized compounds, one or more of which contain desirable constituents. A chemical reaction is initiated, at or near the substrate surface, to produce the desired material that will condense on the substrate.

Concentrating photovoltaics (CPV) = A solar technology that uses lenses or mirrors to concentrate sunlight onto high-efficiency solar cells.

Concentrating solar power (CSP) = A solar technology that use mirrors to reflect and concentrate sunlight onto receivers that convert solar energy to heat. This thermal energy is then used to produce electricity with a steam turbine or heat engine driving a generator.

Crystalline silicon solar cell = A type of photovoltaic cell made from a wafer of either monocrystalline (Single crystalline) or multicrystalline (polycrystalline) silicon ingots.

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

Czochralski process = A method of growing large size, high quality semiconductor crystal by slowly lifting a seed crystal from a molten bath of the material under careful cooling conditions.


Deep-cycle battery = A battery with large plates that can withstand many discharges to a low state-of-charge.

Deep discharge = Discharging a battery to 20% or less of its full charge capacity.

Degradation (Solar) = Solar modules by default have a property of having a reduction in their output power rating when installed outdoor. Usually the degradation is slightly higher in the first 6 months and then follows a pattern of typically 0.67& to 1% per annum. However many solar panels show far higher degradations in field due to poor quality of product.

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. DOD is an important design parameter while designing battery bank capacity for off grid and battery based systems.

Diffuse insolation = Sunlight received indirectly as a result of scattering due to clouds, fog, haze, dust, or other obstructions in the atmosphere. Opposite of direct insolation.

Diffuse radiation = Radiation received from the sun after reflection and scattering by the atmosphere and ground.

Diffusion furnace = Furnace used to make junctions in semiconductors by diffusing dopant atoms into the surface of the material.

Diode = An electronic device that allows current to flow in one direction only.

Direct insolation = Sunlight falling directly upon a solar panel.

DISCOM = The electricity distribution company or the utility provider.

Declination angle = The declination angle, denoted by δ, varies seasonally due to the tilt of the Earth on its axis of rotation and the rotation of the Earth around the sun. If the Earth were not tilted on its axis of rotation, the declination would always be 0°. However, the Earth is tilted by 23.45° and the declination angle varies plus or minus this amount. Only at the spring and fall equinoxes is the declination angle equal to 0°

Discharge factor = A number equivalent to the time in hours during which a battery is discharged at constant current usually expressed as a percentage of the total battery capacity, i.e., C/5 indicates a
discharge factor of 5 hours. Related to discharge rate.

Distributed energy resources (DER) = A variety of small, modular power-generating technologies that can be combined with energy management and storage systems and used to improve the operation of the electricity delivery system, whether or not those technologies are connected to an electricity grid.

Distributed power = Generic term for any power supply source located near the point of power consumption.

DHI (Diffuse Horizontal Irradiation) = It is the amount of radiation received per unit area by a surface (no subject to any shade or shadow) that does not arrive on a direct path from the sun, but has been scattered by molecules and particles in the atmosphere and comes equally from all directions.

DNI (Direct Normal Irradiance) = It is the amount ofsolar radiation received per unit area by a surface that is always held perpendicular (or normal) to the rays that come in a straight line from the direction of the sun at its current position in the sky.

Downtime = Time when the photovoltaic system cannot provide power for the load. Usually expressed in percentage or days.

Dual axis tracking = A photovoltaic array tracking system capable of rotating independently about two axis. It is basically a mechanical structure having other devices such as motors, drives, sensors, actuators, etc.


Elevation angle = The elevation angle (used interchangeably with altitude angle) is the angular height of the sun in the sky measured from the horizontal. Confusingly, both altitude and elevation are also used to describe the height in meters above sea level. The elevation is 0° at sunrise and 90° when the sun is directly overhead (which occurs for example at the equator on the spring and fall equinoxes). The elevation angle varies throughout the day. It also depends on the latitude of a particular location and the day of the year.

Energy audit = A detailed technical survey usually done by qualified personnel in industries , offices, etc to identify ways to reduce energy consumption and reduce any energy wastages.

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.

Equinox = The two times of the year when the sun crosses the equator and night and day are of equal length; occurring around March 20 or 21 (spring equinox) and September 22 or 23 (fall equinox).


Feed in tariff = It is an energy supply policy that promotes the rapid deployment of renewable energy resources. A FIT offers a guarantee of payments to solar energy developers or rooftop solar system owners for the electricity they produce. Payments can be composed of electricity alone or of electricity bundled with renewable energy certificates. These payments are generally awarded as long-term contracts set over a period of 15 to 30 years.

Fill factor (FF) = It is a parameter which, in conjunction with Voc and Isc, determines the maximum power from a solar cell. The FF is defined as the ratio of the maximum power from the solar cell to the product of Voc and Isc. Graphically, the FF is a measure of the “squareness” of the solar cell and is also the area of the largest rectangle which will fit in the IV curve. A good quality solar module should have a fill factor of 0.7 or higher.

Fixed tilt array = A photovoltaic array set in at a fixed angle with respect to horizontal.

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

Float life = The number of years that a battery can keep its stated capacity when it is kept at float charge.

Float service = A battery operation in which the battery is normally connected to an external current source; for instance, a battery charger which supplies the battery load< under normal conditions, while also providing enough energy input to the battery to make up for its internal quiescent losses, thus keeping the battery always up to full power and ready for service.


Gallium arsenide (GaAs) = A crystalline, high-efficiency compound used to make certain types of solar cells and semiconductor material.

Gel battery = Lead-acid battery with a silica gel electrolyte. It is a maintenance free type of battery suitable for deep discharge applications

GHI (Global Horizontal Irradiance) = It is the total amount of radiation received from above by a horizontal surface. This value includes both Direct Normal Irradiation (DNI) and Diffuse Horizontal Irradiation (DHI) and hence is a sum of the two.

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. Also referred as Grid-interactive system.

Grid lines (Solar cell) = Metallic contacts fused to the surface of the solar cell to provide a low resistance path for electrons to flow out to the cell interconnect wires.

Gross metering = The solar power generated is directly fed to the grid at a Feed in Tariff (FiT).


Harmonic content = The number of frequencies in the output waveform in addition to the primary frequency (50 or 60 Hz.). Energy in these harmonic frequencies is lost and may cause excessive heating of the load.

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.


IGPB Inverter = A range of grid-tie solar inverters from Novergy which are available in different power ratings and different voltage ratings. Also known as on-grid or grid tie inverters. Sometimes also referred to as Solar PCU.

Imp (current at maximum power) = The output current of a solar photovoltaic module at which maximum power is available.

Isc (Current at short circuit) = The output current of a solar module in short-circuit condition.

Ingot = A casting of material, usually crystalline silicon, from which slices or wafers can be cut for use in a solar cell.

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 efficiency = The ratio of DC input to AC output power of an inverter. Measured in percentage. It is an indicator of the technological capability of an inverter and also shows how much power an inverter is losing in converting the DC power to utilizable AC power.

Irradiance = The direct, diffuse, and reflected solar radiation that strikes a surface. Usually expressed in kilowatts per square meter. Irradiance multiplied by time equals insolation.

IPCL Inverter = A range of Solar inverters from Novergy for battery based solar systems. They are having an in-built solar charge controller and Grid chargers. They are available in different power ratings starting from 1KW onwards and going upto 100kw. They have advanced features such as MPPT technology, LCD display, USB port, higher efficiency, etc. Many times also referred to as Solar PCU.

IPCT Inverter = A range of smaller power rating Solar inverters from Novergy for battery based solar systems. They are having an in-built solar charge controller and Grid chargers with an LCD display. They are available in different power ratings starting from 1KW onwards and going upto 5kw. Many times also referred to as Solar PCU.

IPCV Inverter = Solar inverters from Novergy having the capability to operate in multiple modes based on different scenarios of solar power input, battery charge status, Grid availability, Load conditions, etc. They are having an in-built solar MPPT charge controller, AC Grid chargers, Inverter, Battery charger, synchronizing capability with an LCD display. They are available in different power ratings starting from 3KW onwards and going upto 10kw. Can also be used as either a string inverter or a purely battery based inverter.

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 (Solar cell junction) = A region of transition between semiconductor layers, such as a p/n junction, which goes from a region that has a high concentration of acceptors (p-type) to one that has a high concentration of donors (n-type).

Junction box (Solar module) = A photovoltaic (PV) generator junction box is an enclosure on the module where PV strings are electrically connected and where protection devices such as bypass diodes can be located. Nowadays most solar modules come with junction boxes that contain in-built bypass diodes. Most Junction boxes are now available in IP65 or higher ingress protection ratings.


K Factor = K-factor is a weighting of the harmonic load currents according to their effects on transformer heating, as derived from ANSI/IEEE C57.110. The higher the K-factor, the greater the harmonic heating effects. There are many different loads such as computers, solidstate devices and motors which cause a non linear load. These type of loads generate harmonic currents that cause transformers and system neutrals to overheat, which can destroy the transformer. When a non-linear load is supplied from a transformer, K-factor transformers withstand the heating effects of harmonic currents created by these type of loads.

Kit = See Solar Kit.


Levelized cost of energy (LCOE) = The cost of energy of a solar system that is based on the system’s installed price, its total lifetime cost, and its lifetime electricity production.

Life-cycle cost = The estimated cost of owning and operating a photovoltaic system for the period of its useful life.

Light-induced defects = Defects, such as dangling bonds, induced in an amorphous siliconsemiconductor upon initial exposure to light.

Light trapping = The trapping of light inside a semiconductor material by refracting and reflecting the light at critical angles; trapped light will travel further in the material, greatly increasing the probability of absorption and hence of producing charge carriers.

Linear warranty = An advanced warranty version for solar modules where the warranty offered follows a linear degradation pattern of the maximum permissible degradation being 0.67% from the 2nd year onwards. It is more beneficial for the customer as it ensures a very reliable performance of the product over time.

Load forecast = Predictions of future demand. For normal operations, daily and weekly forecasts of the hour-by-hour demand are used to help develop generation schedules to ensure that sufficient quantities and types of generation are available when needed.

Low voltage disconnect = The voltage at which a charge controller will disconnect the load from the batteries to prevent over-discharging.


Maintenance-free battery = A sealed battery to which water cannot be added to maintain electrolyte level.

MCA and MCAL = A range of Monocrystalline silicon cell based solar modules from Novergy which are available in different wattages and cell configurations such as 350W, 275W, 100W, etc.

MC4 = A type of connector very commonly used in solar modules and solar systems to provide a weatherproof and safe connection.

Microgrid = a small network of electricity users with a local source of supply that is usually attached to a centralized national grid but is able to function independently. It is usually achieved through a combination of various power sources such as Solar, Genset, Battery, etc. Microgrids involve a very elaborate design and engineering requirements and invole an intelligent controller which communicates with all the power sources, loads, storage, etc.

Modified sine wave = A waveform that has at least three states (i.e., positive, off, and negative). Has less harmonic content than a square wave. But not suitable for inductive loads such as fans, motors, etc.

Module derate factor = A factor that lowers the photovoltaic module current to account for field operating conditions such as dirt accumulation on the module.

MPPT (maximum power point tracking) = Means of a power conditioning unit that automatically operates the photovoltaic generator at its maximum power point under all conditions.

Multicrystalline = A semiconductor (photovoltaic) material composed of variously oriented, small, individual crystals. Also referred to as polycrystalline.


Net metering = It is a billing mechanism that credits solar energy system owners for the electricity they add to the grid. For example, if an industrial customer has a PV system on the their rooftop, it may generate more electricity than it uses during daylight hours. If the industry is net-metered, the electricity meter will run backwards to provide a credit against what electricity is consumed at night or other periods where the industry’s electricity use exceeds the system’s output. Customers are only billed for their “net” energy use.

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

NOCT (normal operating cell temperature) = The estimated temperature of a photovoltaic modulewhen 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.

n-type = Negative semiconductor material in which there are more electrons than holes; current is carried through it by the flow of electrons.
n-type semiconductor = A semiconductor produced by doping an intrinsic semiconductor with an electron-donor impurity (e.g., phosphorus in silicon).

NSMPPT = A range of solar controllers from Novergy with MPPT technology suitable for various battery voltages such as 12v, 24v, 48v, etc. Models start from current rating of 20Amps onwards. They are having various features including protection of battery from overcharging or deep discharge and have an in-built LCD display in most models.

NSP = A range of solar pumps from Novergy suitable for different applications such as surface, borewell, openwell, etc. They are available in different power ratings and head configurations.

NSPWM = A range of PWM solar controllers from Novergy available in various battery voltages such as 12v, 24v, 48v, etc. They are having various features including protection of battery from overcharging or deep discharge.


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

Operating point = The current and voltage that a photovoltaic module or array produces when connected to a load. The operating point is dependent on the load or the batteries connected to the output terminals of the array.

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.

PCA and PCAL = A range of Polycrystalline (multicrystalline) silicon cell based solar modules from Novergy which are available in different wattages and cell configurations such as 330W, 250W, 150W, etc.

Peak demand / Peak load = The maximum energy demand or load in a specified time period.

Peak sun hours = The equivalent number of hours per day when solar irradiance averages 1,000 w/m2. For example, six peak sun hours means that the energy received during total daylight hours equals the energy that would have been received had the irradiance for six hours been 1,000 w/m2.

Photoelectric cell = A device for measuring light intensity that works by converting light falling on, or reach it, to electricity, and then measuring the current; used in photometers.

Photovoltaic(s) (PV) = A device which converts solar radiation (photons) into electrical current. It is a solid-state electrical device that converts light directly into direct current electricity of voltage-current characteristics that are a function of the characteristics of the light source and the materials in and design of the device. Solar photovoltaic devices are made of various semiconductor materials including silicon, cadmium sulfide, cadmium telluride, and gallium arsenide, and in single crystalline, multicrystalline, or amorphous forms.

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) efficiency = See Solar Efficiency.

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 unconcentrated sunlight. The structural (load carrying) member of a module can either be the top layer (superstrate) or the back layer (substrate).

Physical vapor deposition = A method of depositing thin semiconductor photovoltaic films. With this method, physical processes, such as thermal evaporation or bombardment of ions, are used to deposit elemental semiconductor material on a substrate.

PID (Potential induced degradation) = It is a phenomenon that negatively affects the solar PV modules. It is a process which occurs a few years after installation of the solar modules in field. PID causes an accelerated degradation in performance which expands exponentially. In general, the Performance Ratio (PR) of a solar photovoltaic system will decrease by 15 to 50% when PID occurs.

PLF = See CUF (Capacity Utilization Factor)

Plug-and-play PV system = A commercial, off-the-shelf photovoltaic system that is fully inclusive with little need for individual customization. The system can be installed without special training and using few tools. The homeowner plugs the system into a PV-ready circuit and an automatic PV discovery process initiates communication between the system and the utility. The system and grid are automatically configured for optimal operation.

Polycrystalline silicon = A material used to make photovoltaic cells, which consist of many crystals unlike single-crystal silicon.

Power conditioning Unit (PCU) = Electrical equipment, or power electronics, used to convert power from a photovoltaic array into a form suitable for subsequent use. A collective term for inverter, converter, battery charge regulator, and blocking diode.

Power conversion efficiency = The ratio of output power to input power of the inverter.

Power factor (PF) = The ratio of actual power being used in a circuit, expressed in watts or kilowatts, to the power that is apparently being drawn from a power source, expressed in volt-amperes or kilovolt-amperes.

P-N junction = P-n junctions are formed by joining n-type and p-type semiconductor materials, as shown below. Since the n-type region has a high electron concentration and the p-type a high hole concentration, electrons diffuse from the n-type side to the p-type side. Similarly, holes flow by diffusion from the p-type side to the n-type side. If the electrons and holes were not charged, this diffusion process would continue until the concentration of electrons and holes on the two sides were the same, as happens if two gasses come into contact with each other.

PR = Performance ratio is the ratio of AC power generated by the solar photovoltaic system to the Solar radiation falling on a solar photovoltaic system. Measured in percentage. Typically most solar systems have PR of 75% or higher.

PWM = It is a modulation process or technique used in solar controllers and inverters systems for encoding the amplitude of a signal right into a pulse width or duration of another signal. The average value of voltage (and current) fed to the load is controlled by turning the switch between supply and load on and off at a fast rate. The longer the switch is on compared to the off periods, the higher the total power supplied to the load. The main advantage of PWM is that power loss in the switching devices is very low. When a switch is off there is practically no current, and when it is on and power is being transferred to the load, there is almost no voltage drop across the switch. Power loss, being the product of voltage and current, is thus in both cases close to zero. PWM also works well with digital controls, which, because of their on/off nature, can easily set the needed duty cycle.

Pyranometer = An instrument used for measuring solar irradiance. Used in solar systems to measure the Performance ratio or the quality of the solar system installation.


Quantum Efficiency (QE) = The ratio of the number of charge carriers collected by a photovoltaic cell to the number of photons of a given energy shining on the cell. Quantum efficiency relates to the response of a solar cell to the different wavelengths in the spectrum of light shining on the cell. QE is given as a function of either wavelength or energy. Optimally, a solar cell should generate considerable electrical current for wavelengths that are most abundant in sunlight.


Reactive power = The sine of the phase angle between the current and voltage waveforms in an alternating current system.

Reverse current protection = Any method of preventing unwanted current flow from the battery to the photovoltaic array (usually at night). See also blocking diode.


Solar array = Any number of Photovoltaic modules connected together electrically in a combination of series and parallel installed on a mechanical structure. The output from

Solar Efficiency = The ratio of the electric power produced by a photovoltaic device to the power of the sunlight incident on the device. Measured in Percentage.

Spectral irradiance = The spectral irradiance as a function of photon wavelength (or energy), denoted by F, is the most common way of characterising a light source. It gives the power density at a particular wavelength. The units of spectral irradiance are in Wm-2µm-1. The Wm-2 term is the power density at the wavelength λ(µm). Therefore, the m-2 refers to the surface area of the light emitter and the µm-1 refers to the wavelength of interest.
In the analysis of solar cells, the photon flux is often needed as well as the spectral irradiance. The spectral irradiance can be determined from the photon flux by converting the photon flux at a given wavelength to W/m2

Scheduling = The general practice of ensuring that a generator is committed and available when needed. It also can refer to scheduling of imports or exports of energy into or out of a balancing area.

Sealed (SMF) battery = A sealed battery which does not require water topping up and hence making it maintenance free. Also called a valve regulated battery. Usually the popular version is a VRLA battery.

Self-discharge = The rate at which a battery, without a load, will lose its charge.

Semiconductor = Any material that has a limited capacity for conducting an electric current. Certain semiconductors, including silicon, gallium arsenide, copper indium diselenide, and cadmium telluride, are uniquely suited to the photovoltaic conversion process.

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 loador resistance; the maximum current possible.

Shunt controller = A charge controller that redirects or shunts the charging current away from the battery. The controller requires a large heat sink to dissipate the current from the short-circuited photovoltaic array. Most shunt controllers are for smaller systems producing 30 amperes or less.

Sine wave = A waveform corresponding to a single-frequency periodic oscillation that can be mathematically represented as a function of amplitude versus angle in which the value of the curve at any point is equal to the sine of that angle.

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

Single axis tracking = A photovoltaic array tracking system capable of rotating independently in a
single axis. It is basically a mechanical structure having other devices such as motors, drives, sensors, actuators, etc.

Smart grid = An intelligent electric power system that regulates the two-way flow of electricity and information between power plants and consumers to control grid activity.

Solar cell = The smallest semiconductor element within a PV module to perform the immediate conversion of light into electrical energy (direct current voltage and current).

Solar constant = The average amount of solar radiation that reaches the earth’s upper atmosphere on a surface perpendicular to the sun’s rays; equal to 1353 watts per square meter or 492 Btu per square foot.

Solar controller = See charge controller.

Solar-grade silicon = Intermediate-grade silicon used in the manufacture of solar cells. Less expensive than electronic-grade silicon.

Solar insolation = See insolation.

Solar irradiance = See irradiance.

Solar kit = A combination of the critical items in a solar system consisting of a pre-designed solar system which is ready to install at site. Available in different combinations to meet any kind of solar system requirement such as grid tied systems, battery based systems, hybrid systems, pumping systems, etc.

Solar mounting structure = This refers to the mechanical structure used in solar photovoltaic systems to hold the solar modules. The solar mounting structures should ideally be made of a weather resistant material like Galvanized Iron (GI) or Anodized aluminium or other similar weather resistant materials.

Solar resource = The amount of solar insolation a site receives, usually measured in kWh/m2/day, which is equivalent to the number of peak sun hours.

Solar spectrum = The total distribution of electromagnetic radiation emanating from the sun. The different regions of the solar spectrum are described by their wavelength range. The visible region extends from about 390 to 780 nanometers (a nanometer is one billionth of one meter). About 99 percent of solar radiation is contained in a wavelength region from 300 nm (ultraviolet) to 3,000 nm (near-infrared). The combined radiation in the wavelength region from 280 nm to 4,000 nm is called the broadband, or total, solar radiation.

Spinning reserve = Electric power plant or utility capacity on-line and running at low power in excess of actual load.

Sputtering = A process used to apply photovoltaic semiconductor material to a substrate by a physical vapor deposition process where high-energy ions are used to bombard elemental sources of semiconductor material, which eject vapors of atoms that are then deposited in thin layers on a substrate.

Square wave = A waveform that has only two states, (i.e., positive or negative). A square wave contains a large number of harmonics.

Square wave inverter = A type of inverter that produces square wave output. It consists of a direct current source, four switches, and the load. The switches are power semiconductors that can carry a large current and withstand a high voltage rating. The switches are turned on and off at a correct sequence, at a certain frequency.

SSL = Solar LED based street lighting models from Novergy. They include the solar module, solar controller, battery, etc. They are having various features such as automatic dusk to dawn capabilities and many protection features such as battery deep discharge and overcharging protection
stand-alone system = An autonomous or hybrid photovoltaic system not connected to a grid. May or may not have storage, but most stand-alone systems require batteries or some other form of storage.

STC (standard test conditions) = Conditions under which a module is typically tested in a laboratory. Typical STC conditions are Solar radiation of 1000 W/m2, AM of 1 and temperature of 25 Deg C.
standby current = This is the amount of current (power) used by the inverter when no load is active (lost power). The efficiency of the inverter is lowest when the load demand is low.

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

String inverters = A term used to describe a category of solar grid-tie inverters in lower power ratings. Typically models with power rating lower than 80kw are called as string inverters.

Substrate = The physical material upon which a photovoltaic cell is applied.

Superstrate = The covering on the sunny side of a photovoltaic (PV) module, providing protection for the PV materials from impact and environmental degradation while allowing maximum transmission of the appropriate wavelengths of the solar spectrum.
Surge capacity = The maximum power, usually 1.5 to 3 times the rated power, that can be provided over a short time by a solar Inverter. Sometimes the inverter may have different surge ratings for different durations (eg. For 30sec, 5sec, 30 cycles, etc)

System availability = The percentage of time (usually expressed in hours per year) when a photovoltaic system will be able to fully meet the load demand.

System maximum 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. Usually on-grid systems operate on either 600VDC or 1000VDC. Nowadays systems are also available in higher voltages such as 1500VDC.


Temperature coefficient = Defined in % / Deg. C. The temperature of the solar cell has direct influence on the power output of a solar PV module. Being a semiconductor the solar cells have a negative relationship with the temperature. Hence for the same solar insolation, as the temperature rises there is a drop in the power output. Most commercially available Solar modules come with a temperature coefficient of about -0.5% / degree Celsius. However advanced products like Novergy modules come with a lower temperature coefficient of -0.37% / C. Hence resulting in a better output on higher temperatures as compared to other standard crystalline solar modules.

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.

Thin film photovoltaic module = A photovoltaic module constructed with sequential layers of thin film semiconductor materials. Examples of thin film solar modules are amorphous silicon , Cadmium telluride (CdTe), CIGS , etc.

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 harmonic distortion (THD) = The THD, of a signal is a measurement of the harmonic distortion present and is defined as the ratio of the sum of the powers of all harmonic components to the power of the fundamental frequency.

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.

Transparent conducting oxide (TCO) = A doped metal oxide used to coat and improve the performance of optoelectronic devices such as photovoltaics and flat panel displays. Most TCO films are fabricated with polycrystalline or amorphous microstructures and are deposited on glass. The current industry-standard TCO is indium tin oxide. Indium is relatively rare and expensive, so research is ongoing to develop improved TCOs based on alternative materials.


Utility-interactive inverter = An inverter that can function only when tied to the utility grid, and uses the prevailing line-voltage frequency on the utility line as a control parameter to ensure that the photovoltaic system’s output is fully synchronized with the utility power.


Vmp (voltage at maximum power) = The voltage at which maximum power is available from a photovoltaic module.

Voc (voltage at open circuit) = The voltage of a solar photovoltaic panel in open circuit state when it is not connected to any loads or inverter or charge controller, but exposed to solar insolation.

Voltage protection = Many inverters have sensing circuits that will disconnect the unit from the battery if input voltage limits are exceeded.

Voltage regulation = This indicates the variability in the output voltage. Some loads will not tolerate voltage variations greater than a few percent.


Wafer = A thin sheet of semiconductor (photovoltaic material) made by cutting it from a single crystal or ingot.

Weather Tuff = A range of weatherproof and waterproof solar controllers from Novergy available in various battery voltages such as 12v, 24v, etc. They are having various features including protection of battery from overcharging or deep discharge.


Zenith angle = the angle between the direction of interest (of the sun, for example) and the zenith (directly overhead).