Solar glossary

Solar glossary

A: Abbreviation for ampere, unit of electrical current

Shade: The amount of sun that hits the surface of the PV system is affected by objects like, for example, chimneys, satellite dishes or trees. The amount of shadow cast can lead to a loss in energy production from the solar panel system.

Ageing: also referred to as degradation, performance reduction: decrease in the efficiency of the solar cells after long-term exposure to the sun’s rays. Generally only occurs in amorphous solar cells. It is known that an amorphous solar cell reaches a stable level of efficiency after around 1,000 hours of sunshine and then achieves the nominal power output quoted by the manufacturer.

Anti-reflection layer: A thin transparent layer, a few millionths of a millimetre thick, which reduces solar cells‘ reflection loss, thereby increasing the amount of light captured and the efficiency.

Bypass diode: Connected in parallel to a diode, diverts the current from individual solar cells past cells (connected in series) which are shaded.

Degradation: Ageing

Diffuse radiation: Sunlight diffused by clouds and other atmospheric particles that has no defined direction from the sun to the observation point on the ground.

Direct radiation: Sun’s rays that fall directly from the sun to the observation point on the ground. At the observation point these are joined by diffuse radiation.

Thin-film technology: Manufacturing process for (thin) amorphous solar cells. In this, several semi-conductor layers are evaporated onto a substrate (usually glass). The manufacturing process is therefore done without wafers (crystalline silicon). The advantage of thin-film technology is the significantly reduced energy requirements and the lower manufacturing costs compared to crystalline silicon.

EEG: Abbreviation for the renewable energy law in Germany.

Energy return time: The time it takes for a solar panel system to produce the same amount of power through electricity generation as was needed for its manufacture.

EVU: Abbreviation for utility company

Global radiation: The total amount of solar energy that falls per unit of time on a horizontal surface on the earth. Global radiation is made up of diffuse radation and direct radiation. It is around 1,000 W/m2 when the sun’s rays hit the ground vertically. When the geographic location and the different number of hours of sunlight per year are taken into account, the annual amount of radiated energy in Germany is around 1,000kWh/m2 and 2,200kWh/m2 at the equator.

Island system: A solar electricity system that uses the electricity it produces itself, saves it, and doesn’t feed it into the public electricity grid. Useful in remote areas, like in the mountains.

MPP tracking: Readjusting the power conversion so that a solar system always operates at the Maximum Power Point and avoids a loss of performance. Included with the regulator and the inverter.

Monocrystalline solar cells: The atoms in the crystal in monocrystalline solar cells have a perfect, regular arrangement across the whole block of material. The efficiency levels of monocrystalline solar cells are higher than those of polycrystalline solar cells.

Repositioning: A mounting system that constantly repositions the orientation of the solar modules so that the sun’s rays fall vertically onto the solar cells and thereby guarantees a maximum energy yield.

Angle of inclination: Angle between the solar cell and the horizontal. According to the latitude of the solar system’s location there are different optimum angles of inclination.

Nominal power: maximum nominal power output of a module, measured using the vertical radiation of the surface and Standard Test Conditions (STC). Given in watts peak (abbreviation Wp or kWp for kilowatt-peak).

Grid coupling: Connection of the solar electricity system via an inverter to the electricity supplier’s grid for the purpose of complete or partial feed-in of the electricity produced by the photovoltaic system that hasn’t been used. Solar electricity systems that are coupled to the grid do not need an energy store.

Photovoltaic principle: This describes the creation of an electrical charge in a semi-conductor, a dye molecule or similar, when the charge carrier is stimulated by light. When you extract these charge carriers you can produce electrical energy in the form of electricity. The photovoltaic principle was discovered in 1839 by Becquerel.

Polycrystalline silicon: Term for silicon that is in the form of individual, small crystals that are firmly linked together.

Polycrystalline (or multicrystalline) solar cells: These consist of individual, small crystals firmly linked together that range from a few millimetres to a few centimetres wide. These are simpler and cheaper to manufacture than monocrystalline solar cells.

Photovoltaics (abbreviation PV): The technology that enables the sun’s energy to be turned into electrical energy (electricity) using solar cells.

Reflection loss: Light that is reflected off the surface of the solar cell and cannot be collected to produce electricity.

Silicon, Si: Chemical element in the 4th main group in the periodic table. Silicon is the most-used semi-conductor in the semi-conductor industry and photovoltaics. The raw material, silicon dioxide,(SiO2, silica) is available in practically unlimited quantities. Silicon can be processed into monocrystalline, polycrystalline or amorphous silicon.

Solar module: A solar or PV module consists of several interconnected solar cells, embedded between two sheets of glass or in sheets made from a combination of glass and plastic, protected from the weather. PV modules are mounted on the roof using a frame and sub-structure developed by Ra Lux or integrated into glass roof structures and façades.

TAB: Abbreviation for technical connection requirements

V: Abbreviation for volt, unit of electrical current.

W: Abbreviation for watt, unit of (e.g. electrical) power

Wafer: Term for a thin sheet of semi-conductor material. It is used as a charge carrier in the production of computer chips and solar cells. The sheets are generally sawn from semi-conductor blocks and are 0.2 to 0.3mm thick.

Watt-Peak: (Abbreviation Wp), measurement for the power of solar cells and modules (cf. Nominal power). This measures the maximum electrical power produced when sunlight hits the panels vertically with a solar spectrum of AM 1.5.

Module prices are usually given in €/Wp.

Inverter: Turns the solar cells‘ direct current into alternating current so that it can be fed into the public electricity grid. The inverter extracts the power from the solar electricity system at the Maximum Power Point.