The third and second to last part of our lexicon is finally ready. Here are some more useful definitions from the field of photovoltaics! Feel free to comment if you feel like anything is missing.


NOCT (Nominal Operating Cell Temperature): Average temperature of a cell in a solar module under certain conditions. These certain conditions also apply in all the tests needed to determine the technical product characteristics.

NOMINAL CURRENT AC: Current the inverter transfers to the power grid.

NOMINAL CURRENT DC: Current the inverter needs to operate properly.

NOMINAL VOLTAGE: Voltage of a module when running at full capacity.


OPEN CIRCUIT VOLTAGE: The voltage between your solar installation’s two terminals (positive and negative) when the circuit is open (power off).


PEAK POWER: The maximum power te panels deliver under ideal operation conditions. Peak power is measured in peak watt (Wp).

PEAK WATT: Unit of measure for peak power (a solar system’s maximum power under test conditions). The full definition can be found here.

PEAK: Power rating of a solar panels, i.e. the optimum power a panel can provide under ideal conditions.

PERFORMANCE RATIO: The ratio of the actual and theoretically possible energy outputs depending on the panel’s surface and the incident solar irradiation of a solar plant.

PHOTON: Particle in sunlight that transmits the electromagnetic interaction and triggers the photovoltaic effet.

PHOTONIC BAND-GAP: In semiconductors, the valence band (with bound electrons) and the conduction band (with free electrons) overlap. In other materials, the electrons in the valence band are separated by a large band-gap from the conduction band. The width of the band-gap gives insight into the materials’ insulating or seminconducting properties. The width corresponds to the energy level needed by an electron to bridge the gap.

PHOTOVOLTAIC ARRAY: The complete power-generating unit (producing direct current), consisting of any number of PV modules and panels.

PHOTOVOLTAIC EFFECT: Conversion process which transforms the photons in sunlight to electricity using a semiconductor.

PHOTOVOLTAIC GENERATOR: Electricity generator which is powered by solar energy through photovoltaic conversion.

PHOTOVOLTAIC MODULE: The combination of a certain number of solar cells and a protective coating.

POLYCRISTALLIN: A type of silicon made up of a mosaic of cristalls which are the result of melting and cooling off the silicon repetedly. This material is the basis for the eponymous solar panels.

POWER RATING: Maximal power delivered under the normal test conditions applying when rating solar modules.

PRIMARY ENERGY: Energy found in nature, without any altering through a human engineered conversion process.

PRODUCTION METER: Measures the amount of electricity sold to the ErDF. It is located next to the consumption meter and enables you to verify whether your installation is operating properly.

PURCHASE CONTRACT: Governs the relationship between the PV production and the buyer by contract.

PV cell: The main element in every solar panel which transforms solar energy into electricity thanks to its semiconductor (mostly silicon).

PV CYCLE: Organisation that started a take-back and recycling programm for old solar panels. The solar panels of participating manufacturers are collected at different drop-off points in Europe.


QUALIWATT:A new subsidies scheme for photovoltaics in Wallonia, Belgium which replaces the Solwatt system.


REDUCED VAT RATE: If you decide to retrofit a house that is older than two years with solar panels, you benefit from a reduced VAT rate when purchasing all the necessary products.

ROOF ANGLE: The angle between the PV module and the horizontal plane.

RT 2012: Thermal regulation stating the energy standards for new buildings and buildings under construction. These standards also serve as a reference for energy efficiency retrofits and granting labels.

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