Solar Glossary
Clear definitions of all important photovoltaic and solar energy terms.
AC/DC (Alternating Current/Direct Current)
AC (Alternating Current) is the mains electricity from the grid, DC (Direct Current) is produced by solar modules and batteries.
Agri-PV
Dual use of agricultural land by combining photovoltaics with crop farming or livestock husbandry.
Amortisation
The period until a PV system's investment costs are recouped through electricity savings and feed-in tariff revenue.
Azimuth
Compass direction of the module orientation in degrees -- 0° = South, -90° = East, +90° = West, +/-180° = North.
Balcony Solar System
Small plug-in solar device (up to 800 W) mounted on a balcony or facade that feeds electricity directly into the home grid.
Battery Storage
Energy storage for PV systems that stores surplus solar electricity and releases it on demand.
Bypass Diode
Protective component in a solar module that routes current around shaded cells to prevent power loss and hot spots.
Degradation
Gradual power loss of solar modules over their operating lifetime, typically 0.3--0.5% per year.
Dynamic Electricity Tariff
Electricity tariff with variable pricing that changes hourly based on the wholesale electricity price -- ideal with PV and storage.
EEG (Renewable Energy Sources Act)
German law promoting renewable energies -- governs the feed-in tariff for solar electricity, among other things.
Efficiency
Ratio of usable electrical energy to incident solar energy -- indicates the effectiveness of a solar cell or system.
Feed-in Tariff
Legally guaranteed remuneration for solar electricity fed into the public grid, governed by the EEG.
Full Feed-in
Operating model where all generated solar electricity is fed into the public grid -- with a higher tariff per kWh.
Global Irradiance
Total solar radiation hitting a horizontal surface -- the sum of direct and diffuse radiation.
Grid Operator
Company that operates the local electricity grid and is responsible for grid connection and feed-in tariff payments.
HJT (Heterojunction)
Heterojunction cell technology combining crystalline and amorphous silicon, achieving very high efficiencies.
Hybrid Inverter
Inverter that combines PV electricity generation, battery storage, and grid feed-in in a single device.
Inverter
Converts the direct current (DC) generated by solar modules into grid-compliant alternating current (AC).
KfW
KfW Development Bank -- German promotional bank offering low-interest loans and grants for PV systems and storage.
kWh (Kilowatt-Hour)
Unit of electrical energy -- one kWh equals the energy converted at a power of 1 kW over one hour.
kWp (Kilowatt Peak)
Unit for the maximum power output of a solar module or PV system under Standard Test Conditions (STC).
Levelised Cost of Electricity (LCOE)
Total cost of electricity generation per kWh over the lifetime of a system -- for PV currently 5--10 cents/kWh.
Lithium Iron Phosphate (LiFePO4)
Safe and long-lasting lithium-ion battery chemistry that is the standard for residential solar storage systems.
Market Master Data Register
Official register of the Federal Network Agency where all electricity generating systems in Germany must be registered.
Microinverter
Small inverter mounted directly on a single solar module, converting DC to AC on a per-module basis.
Monocrystalline
Solar cell type made from single-crystal silicon with high efficiency and a characteristically dark, uniform surface.
MPP Tracker
Electronic control in the inverter that continuously finds and optimises the Maximum Power Point of the solar modules.
NMC (Nickel Manganese Cobalt)
Lithium-ion battery chemistry with high energy density, used in compact solar storage systems and electric vehicles.
NOCT
Nominal Operating Cell Temperature -- cell temperature under realistic operating conditions (800 W/m², 20 °C, 1 m/s wind).
PERC
Passivated Emitter and Rear Cell -- cell technology with an additional passivation layer on the rear side for higher efficiency.
Perovskite
Novel semiconductor material class for solar cells with high efficiency potential and simple manufacturing.
Photoelectric Effect
Physical effect where light photons release electrons from a material -- the fundamental principle behind photovoltaics.
Photovoltaics
Technology for the direct conversion of sunlight into electrical power using solar cells made from semiconductor material.
Polycrystalline
Solar cell type made from multi-crystalline silicon with a bluish appearance and slightly lower efficiency than monocrystalline cells.
PVGIS
Free EU online tool for calculating solar yields based on location, orientation, and tilt angle.
Roof Pitch
Angle of the roof relative to the horizontal -- affects solar yield and optimal module orientation.
Self-Consumption
Share of self-generated solar electricity consumed directly in the household rather than fed into the grid.
Self-Sufficiency Rate
Share of electricity consumption covered by the own PV system -- indicates independence from the electricity grid.
Semiconductor
Material with electrical conductivity between a conductor and an insulator -- the base material for solar cells, usually silicon.
Shading
Partial or complete shading of solar modules by trees, buildings, or other obstacles.
Smart Meter
Intelligent metering system that digitally records electricity consumption and transmits data to the grid operator and consumer.
Solar Cell
Semiconductor device that converts sunlight directly into electrical current through the photoelectric effect.
Solar Constant
Radiant power of the sun per square metre at the top of Earth's atmosphere -- approximately 1,361 W/m².
Solar Module
Assembly of multiple solar cells in a weatherproof housing for generating electricity from sunlight.
Solar Obligation
Legal requirement to install a solar system on new buildings or during roof renovations -- in effect in several German states.
Solar Thermal
Technology that uses solar heat for hot water preparation and space heating support via solar collectors.
STC (Standard Test Conditions)
Standardised test conditions (1,000 W/m², 25 °C, AM 1.5) under which the rated power of solar modules is measured.
String Inverter
Central inverter that converts the direct current from one or more series-connected module strings into alternating current.
Surplus Feed-in
Operating model where solar electricity is primarily self-consumed and only the surplus is fed into the grid.
Tandem Solar Cell
Multi-layer solar cell combining two semiconductor materials to utilise different light spectra and achieve higher efficiencies.
Temperature Coefficient
Metric indicating how much a solar module's power decreases per degree Celsius of temperature rise (typical: -0.3%/°C).
Tenant Electricity
Solar electricity generated on a multi-family building's roof and sold directly to the tenants in the building.
Thin-Film
Solar cell technology in which extremely thin semiconductor layers are deposited onto a substrate material.
Tilt Mounting
Mounting system that positions solar modules at an optimal tilt angle on flat roofs or open ground.
TOPCon
Tunnel Oxide Passivated Contact -- advanced cell technology with a tunnel oxide layer achieving efficiencies above 24%.
Wp (Watt Peak)
Unit for the peak power of a single solar module under Standard Test Conditions (STC).