Photovoltaic glossary


Amorphous Solar Cell

Solar cell made from amorphous silicon. Technology used for production is similar to the one for thin-film panels.


This is the time the PV system needs to produced an equivalent amount of power to cover its initial cost. Depending on the price for electricity in a country, this period can be longer or shorter

Angle of Inclination

This angle is measured between a tilted surface (i.e. a roof) and the horizontal. Depending on the local latitude, the ideal angle of inclination for a PV generator might vary.


Backside Ventilation

The backside ventilation of panels is important to cools down the panels and maximise the efficiency.


Alexandre-Edmond Becquerel, a French physisist, discovered together with his father in 1839 the photovoltaic effect.He proved that a batteries charge last longer if the battery was stored in sunlight. He also proved that, if a silver electrode in an electrolyte is illuminated by sunlight, an electrical voltage can be measured.

Bypass Diode

A bypass diode is parallell connected to a string of cells and -in case of clouding on that particular string- the diode redirects the power from other strings away from the clouded one.


Cell String

A cell string is a number of cells in a series connection.

Charge Controller

These items are mainly used with Off-grid or Back-up systems, where batteries are used. A charge controller prevents batteries from being overcharged.


Clouding in general is what has to be avoided on PV generators, as it lowers the effectivity of the whole system. Clouding can be caused by chimneys, walls, antennas, trees or other obstacles


Data Logger

A data logger records all data from an inverter and the generated power of a PV generator over a period of time.


Degradation specifies the loss of efficiency in a cristalline PV cell. Antaris guarantees for its panels 80% efficiency after 30 years in use.

Diffuse Radiation

Diffuse sky radiation is solar radiation reaching the Earth's surface after having been scattered from the direct solar beam by molecules or suspensoids in the atmosphere.

Direct Current (DC)

Direct current (DC) is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also be through semiconductors, insulators, or even through a vacuum as in electron or ion beams. The electric charge flows in a constant direction, distinguishing it from alternating current (AC).

Direct Radiation

When the direct solar radiation is not blocked by clouds, it is experienced as sunshine, a combination of bright light and radiant heat. The World Meteorological Organization uses the term "sunshine duration" to mean the cumulative time during which an area receives direct irradiance from the Sun of at least 120 watts per square meter.

Diurnal Cycle

A diurnal cycle in PV is the power output of a PV generator in connection with the season and the solar altitude.


Global Radiation

Global radiation is the total radiation energy of the sun that is measured on y certain levelled area on the earths surface. In Central Europe the global radiation on a sunny, non cloudy day is about 1.000W per square meter. On cloudy days the radiation goes down to 100W/m².

Grid Connection

A PV system gets connected to the public grid by using an inverter. Depending on the country feed-in tariffs paid per kWh of electricity put into the grid are varying.


Hot Spot

Hot Spot is a certain area on a PV panel that -under diffuse light or in shadow- changes its polarity while the current of the remaining cells is running through it. This area than reacts like a resistor and gets hot. Depending on the power that runs through it, it can even catch fire. To prevent this most panels come with Bypass-Diodes today.



An inverter is an electrical device that converts direct current (DC) to alternating current (AC); the converted AC can be at any required voltage and frequency with the use of appropriate transformers, switching, and control circuits.


The amount of money paid for a PV system, including installation and connection to the grid is called investment. Prices today, depending on the country and the used products are between 2.500,00 Euro and 3.500,00 Euro. Smaller systems installed on residential buildings are usually hogher in price than large scale systems installed on the ground.


Kilowatt Hour

A Kilowatt Hour (kWh) means 1000W power used for one hour. The kilowatt hour is most commonly known as a billing unit for energy delivered to consumers by electric utilities.


Maximum Power Point (MPP)

PV cells have a single operating point where the values of the current (I) and Voltage (V) of the cell result in a maximum power output. These values correspond to a particular resistance, which is equal to V/I as specified by Ohm's Law. A PV cell has an exponential relationship between current and voltage, and the maximum power point (MPP) occurs at the knee of the curve, where the resistance is equal to the negative of the differential resistance (V/I = -dV/dI). Maximum power point trackers utilize some type of control circuit or logic to search for this point and thus to allow the converter circuit to extract the maximum power available from a cell.

Module (Panel)

A solar module converts sunlight into electrical energy. Major components of a solar modules are solar cells. The characteristics of a solar module are found in ist electrical connection load. Those values are dependings on the types of cells used.

Module Efficiency

Module efficiency is the ratio between energy input (sunlight) and energy output (DC power). Standard efficiency values for thin film panels are from 6 - 9% and for crystalline panels from 14 - 18%.

Monocrystalline Silicon

A single crystal solid is a material in which the crystal lattice of the entire sample is continuous and unbroken to the edges of the sample, with no grain boundaries. Because grain boundaries can have significant effects on the physical and electrical properties of a material, single crystals are of interest to industry, and have important industrial applications.

Multicrystalline (Poly) Silicon

Polycrystalline materials are solids that are composed of many crystallites of varying size and orientation. The variation in direction can be random (called random texture) or directed, possibly due to growth and processing conditions. Fiber texture is an example of the latter. Polycrystalline is the structure of a solid material that, when cooled, form crystallite grains at different points within it. The areas where these crystallite grains meet are known as grain boundaries.


Nominal Power

The nominal power of a PV module is the maximum power this module can generate. It is measured in Watt peak (Wp) under Standard Test Conditions (STC).


Off-Grid System

The so called Off-Grid or Island system is a stand alone power supply, based on any type of generator (Wind-Turbine, PV, Diesel Engine, etc.). The generated power is stored in batteries and can be used at any time during 24h. Off-Grid systems are mainly used in areas without proper or no grid connectibility. They can also be used as a back-up where the grid is not reliable.


The annual output of a PV system with a nominal power of 1kWp is in Southern Germany 930 - 1.100kWh, depending on type of cells, direction, inclination, temperature and sun radiation. As the weather changes from year to year, an average result from the last ten years is used to calculate the output.


Performance Ratio

Performance ratio is an evaluation criterion for PV systems that does not depend on the direction or the global radiation. It is the ratio between real generated energy vs. the theoretically possible power generation. It specifies the degree of utilization between irradiation and generated power and therewith the quality of the whole PV system.

Photoelectric Effect

The photoelectric effect is a phenomenon in which electrons are emitted from matter (metals and non-metallic solids, liquids or gases) as a consequence of their absorption of energy from electromagnetic radiation of very short wavelength, such as visible or ultraviolet light. Electrons emitted in this manner may be referred to as "photoelectrons".


In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic "unit" of light and all other forms of electromagnetic radiation.


Photovoltaics are best known as a method for generating electric power by using solar cells to convert energy from the sun into electricity. The photovoltaic effect refers to photons of light knocking electrons into a higher state of energy to create electricity. The term photovoltaic denotes the unbiased operating mode of a photodiode in which current through the device is entirely due to the transduced light energy. Virtually all photovoltaic devices are some type of photodiode.

Potential of PV

The total solar energy absorbed by Earth's atmosphere, oceans and land masses is approximately 3,850,000 exajoules (EJ) per year. In 2002, this was more energy in one hour than the world used in one year. Photosynthesis captures approximately 3,000 EJ per year in biomass. The amount of solar energy reaching the surface of the planet is so vast that in one year it is about twice as much as will ever be obtained from all of the Earth's non-renewable resources of coal, oil, natural gas, and mined uranium combined. From the table of resources it would appear that solar, wind or biomass would be sufficient to supply all of our energy needs.

PV System

A photovoltaic system is a system which uses solar cells to convert light into electricity. A photovoltaic system consists of multiple components, including cells, mechanical and electrical connections and mountings and means of regulating and/or modifying the electrical output. Due to the low voltage of an individual solar cell (typically ca. 0.5V), several cells are combined into photovoltaic modules, which are in turn connected together into an array. The electricity generated can be either stored, used directly (island/standalone plant)or fed into a large electricity grid powered by central generation plants (grid-connected/grid-tied plant) or combined with one or many domestic electricity generators to feed into a small grid (hybrid plant). Depending on the type of application, the rest of the system ("balance of system" or "BOS") consists of different components. The BOS depends on the load profile and the system type. Systems are generally designed in order to ensure the highest energy yield for a given investment.


Range of Application of Photovoltaic

Solar cells produce direct current electricity from light, which can be used to power equipment or to recharge a battery. The first practical application of photovoltaics was to power orbiting satellites and other spacecraft, but today the majority of photovoltaic modules are used for grid connected power generation. In this case an inverter is required to convert the DC to AC. There is a smaller market for off-grid power for remote dwellings, boats, recreational vehicles, electric cars, roadside emergency telephones, remote sensing, and cathodic protection of pipelines.


A rectifier is an electrical device that converts alternating current (AC) to direct current (DC), a process known as rectification. Rectifiers have many uses including as components of power supplies and as detectors of radio signals.

Reflection Loss

PV panels lose efficiency by reflecting radation. To prevent this an anti-reflection coating on the surface of the panel is recommended.

Return of Energy

This means the period of time a PV panels takes to generate the wmount of energy beeing used in its manufacturing process.



Silicon is the most common metalloid. It is a chemical element, which has the symbol Si and atomic number 14. A tetravalent metalloid, silicon is less reactive than its chemical analog carbon. As the eighth most common element in the universe by mass, silicon very rarely occurs as the pure free element in nature, but is more widely distributed in dusts, planetoids and planets as various forms of silicon dioxide (silica) or silicates. In Earth's crust, silicon is the second most abundant element after oxygen, making up 25.7% of the crust by mass. Silicon has many industrial uses. It is the principal component of most semiconductor devices, most importantly integrated circuits or microchips. Silicon is widely used in semiconductors because it remains a semiconductor at higher temperatures than the semiconductor germanium and because its native oxide is easily grown in a furnace and forms a better semiconductor/dielectric interface than any other material.

Solar Thermal Collector

A solar thermal collector is a solar collector specifically intended to collect heat: that is, to absorb sunlight to provide heat. Flat plate collectors is the most common type of solar thermal collector. Generally all consist of a flat-plate absorber, which intercepts and absorbs the solar energy, a transparent cover(s) that allows solar energy to pass through but reduces heat loss from the absorber, a heat-transport fluid (oil, antifreeze or water) flowing through tubes to remove heat from the absorber, and a heat insulating backing.


Tedlar a plastic foil, mainly used in flammability-lowering coating of airplane interiors and photovoltaic module backsheets.
Temperature Coefficient The temperature coefficient is the relative change of a modules performance when the temperature is changed by 1 K. The higher this coefficient, the more important the back ventilation of the panel becomes.

Thin Film Panel

A thin film panel is made without crystalline solar wafers and the production process due to the low volume of required material is cheaper that standard cells. Today the efficieny of thin film panels is about 5 - 6% below standard crystalline cells.

Thin Film Technology

The various thin-film technologies currently being developed reduce the amount (or mass) of light absorbing material required in creating a solar cell. This can lead to reduced processing costs from that of bulk materials (in the case of silicon thin films) but also tends to reduce energy conversion efficiency (an average 7 to 10% efficiency).


A tracking system is a special carrier for PV panels that always position the panels in the ideal angle to the sun. Modern systems work with computerised calendar applications.



A wafer is a thin slice of semiconductor material, such as a silicon crystal, used in the fabrication of integrated circuits and other microdevices. Several types of solar cells are made from such wafers. Wafers are formed of highly pure (99.9999% purity), nearly defect-free single crystalline material. One process for forming crystalline wafers is known as Czochralski growth invented by the Polish chemist Jan Czochralski. In this process, a cylindrical ingot of high purity crystalline silicon is formed by pulling a seed crystal from a 'melt'. The ingot is then sliced with a wafer saw (wire saw) and polished to form wafers. The size of wafers for photovoltaics is 100 – 200 mm square and the thickness is 200 - 300 µm. In the future, 160 µm will be the standard.

Watt-Peak (Wp)

Watt Peak is (Wp) is a measure of power output, most often used in relation to photovoltaic solar energy devices. Related units such as kilowatt-peak (kWp) and megawatts-peak (MWp) are also used, and in the context of domestic installations kWp is the most common unit encountered.