Solargis Glossary

Solar resource terms

Acronym	Full Name	Units	Description
ALB	Ground surface albedo	-	The fraction of solar irradiance reflected by the surface is calculated as the ratio of upwelling to downwelling radiative fluxes at the surface.
D2G	Ratio of diffuse to global irradiation	-	Ratio of diffuse horizontal irradiation (DIF) to global horizontal irradiation (GHI).
DFN	Diffuse Normal Irradiance or Irradiation	W/m2, kWh/m2, Wh/m2	Solar radiation received from the sky (excluding direct sunlight) on a surface that is perpendicular to the direction of the sun’s rays.
DHI	Direct Horizontal Irradiance or Irradiation	W/m2, kWh/m2, Wh/m2	Solar radiation received directly from the sun on a horizontal surface.
DIF	Diffuse horizontal irradiation	W/m2, kWh/m2, Wh/m2	Solar radiation received from the sky (excluding direct sunlight) on a horizontal surface.
DNI	Direct normal irradiation	W/m2, kWh/m2, Wh/m2	Solar radiation received directly from the sun on a surface perpendicular to the sun’s rays.
DNI season	DNI seasonality	-	The ratio of maximum to minimum monthly averages of direct normal irradiation, indicating seasonal variability.
ETR_horizontal	Horizontal Extraterrestrial Radiation	W/m2	The amount of solar energy received per unit time on a horizontal surface at the top of the atmosphere of the Earth, assuming no atmospheric interference. It varies slightly throughout the year due to changes in the Earth-Sun distance.
ETR_normal	Normal Incidence Extraterrestrial Radiation	W/m2	The amount of solar energy received per unit time on a surface normal to the sun (perpendicular to the direction of propagation of the radiation) at the top of the atmosphere of the Earth. It varies slightly throughout the year due to changes in the Earth-Sun distance.
GHI	Global horizontal irradiation	W/m2, kWh/m2, Wh/m2	Total solar radiation on a horizontal surface (DIF + direct component projected onto horizontal).
GHI season	GHI seasonality	-	The ratio of maximum to minimum monthly averages of global horizontal irradiation, indicating seasonal variability.
GTI	Global Tilted Irradiance or Irradiation	W/m2, kWh/m2, Wh/m2	Total solar radiation received on a surface that is tilted at a specific angle from the horizontal.
GTI opta	Global tilted irradiation at the optimum angle	kWh/m²	AThe radiative flux integrated over a period of time from the sun falling on a tilted plane of PV modules mounted at the optimum angle.
GHI_C, DNI_C, GTI_C	Calculated Clear Sky GHI, DNI or GTI	W/m2, kWh/m2, Wh/m2	These are theoretical estimates of solar irradiance which represents the location in ideal clear sky conditions - meaning no clouds, minimal aerosols, and standard atmospheric clarity.
LWR	Longwave Irradiance or Irradiation	W/m2, kWh/m2, Wh/m2	The thermal radiation emitted by Earth’s surface, atmosphere, and clouds, primarily in the infrared portion of the electromagnetic spectrum.
PAR	Photo-Synthetically Active Irradiance or Irradiation	W/m2, kWh/m2, Wh/m2	Photo-synthetically active irradiation refers to the spectral range of solar irradiation that supports the growth of photosynthetic organisms.
RHI	Reflected Horizontal Irradiance or Irradiation	W/m2, kWh/m2, Wh/m2	The portion of solar radiation that is reflected from the ground or nearby surfaces and received on a horizontal plane.
Solar constant	Solar constant	W/m2	The amount of solar energy per unit time, at the mean distance of the earth from the sun, received on a unit area of a surface normal to the sun (perpendicular to the direction of propagation of the radiation) outside the atmosphere. The generally accepted value of the solar constant is approximately: 1,361 W/m²
Solar irradiance	Solar irradiance	W/m2	Solar power (instantaneous energy) falling on a unit area per unit time. Solar resource or solar radiation is used when considering both irradiance and irradiation. Used if solar power values are discussed
Solar irradiation	Solar irradiation	Wh/m2	Amount of solar energy falling on a unit area over a stated time interval. Solar resource or solar radiation is used when considering both irradiance and irradiation.
Solar resource	Solar resource	-	Encompasses information on the availability and intensity of solar radiation at a specific location, used to assess solar energy generation potential.
Solar spectrum	Solar spectrum	-	The total distribution of electromagnetic radiation emitted by the sun.

Meteorological resource terms

Acronym	Full Name	Units	Description
AOD	Aerosol Optical Depth	-	Aerosol Optical Depth (AOD) is the measure of aerosols (e.g. urban haze, smoke particles, desert dust, sea salt) distributed within a column of air from the instrument (or Earth's surface) to the top of the atmosphere.
AP	Atmospheric Pressure	hPa	Also known as air pressure or barometric pressure, is the force exerted by the weight of the air above a given point on Earth's surface.
CDD	Cooling degree days	degree days	Measures energy demand needed to cool a building by quantifying how much and for how long outside air temperature exceeds a base temperature (18°C)2.
HDD	Heating degree days	degree days	Measures energy demand needed to heat a building by quantifying how much and for how long outside air temperature is below a base temperature (18°C).
MOR	Meteorological Optical Range	m	Defines visibility conditions. The distance over which a beam of light is reduced to 5% of its original intensity due to scattering and absorption by particles in the atmosphere (like fog, dust, smoke, or pollution).
PM	Particulate Matter	µg/m3	A complex mixture of tiny solid particles and liquid droplets suspended in the air. These particles vary in size, composition, and origin, and they can have significant effects on both human health and the environment. PM10 refers to Particulate Matter with a diameter of 10 µm or less. PM2P5 refers to Particulate Matter with a diameter of 2.5 µm or less.
PREC	Precipitation (rainfall)	mm	Average yearly and monthly sums of precipitation.
PWAT	Precipitable water	kg/m²	Depth of water vapor in the atmosphere if precipitated as rain, indicating atmospheric moisture.
RH	Relative humidity	%	Average yearly or monthly relative humidity at 2 m above ground.
SDWE	Snow depth water equivalent	mm, cm, inch	Measures liquid water content in a snowpack if melted.
SFWE	Water Equivalent of Fresh Snowfall Rate	kg/m2/hour	The amount of liquid water contained in freshly fallen snow per unit of time. It’s a key metric in hydrology and meteorology for estimating how much water is being added to the snowpack or watershed during a snowfall event.
SDENS	Snow density	kg/m3	A measure of how much mass (mostly ice and some liquid water) is packed into a given volume of snow.
TEMP	Air temperature	°C, °F	Average yearly, monthly, and daily air temperature at 2 m above ground.
TD	Dew point temperature	°C, °F	The temperature at which air becomes saturated with moisture and dew begins to form. It is used to assess the risk of condensation, accelerated corrosion, and degradation of PV components.
TMOD	Module Temperature	°C, °F	Module temperature is the operating temperature of a module determined by the equilibrium between the heat produced by the PV module, the heat lost to the environment and the ambient operating temperature.
TS	Surface Temperature	°C, °F	The temperature at the surface of the photovoltaic module.
TSD	True Accumulated Snow Depth	°C, °F	True accumulated snow depth refers to the actual vertical thickness of the snowpack that has built up on the ground over time. It’s measured from the ground surface to the top of the snow layer, and accounts for all snowfall events, compaction, melting, and settling that have occurred.
WBT	Wet bulb temperature	°C, °F	The lowest temperature to which air can be cooled by the evaporation of water at constant pressure. It is an indicator of thermal comfort and is used to assess the cooling efficiency of PV modules in humid environments.
WD	Wind Direction	deg	The direction from which the wind is blowing. Typically measured at 10 m above the ground.
WG	Wind gust	m/s	A sudden, brief increase in the speed of the wind. Wind gust is typically measured as the maximum value of the 3-second running average wind speed over an observing cycle.
WS	Wind speed	m/s	Average yearly, monthly, and daily wind speed at 10 m above ground.

Environmental resource terms

Acronym	Full Name	Units	Description
Elevation	Elevation	m	Geographical position; it refers to the height of a point on Earth's surface above mean sea level.
Horizontal shading	Horizontal shading	-	Refers to distant objects blocking sunlight and creating shading on solar panels or surfaces.
INC	Incidence Angle of Direct Irradiance	deg	The incidence angle is defined as the angle of the sun's rays, with respect to the normal to the collector plane. Incidence angle is zero for rays perpendicular to the plane, and 90° for rays parallel to the plane.
KC	Clear-Sky Index	-	Clear sky index is the ratio of irradiance measured at ground level compared to the theoretical irradiance at ground level in clear sky conditions.
KT	Clearness Index	-	Clearness index is the ratio of irradiance measured at ground level compared to the irradiance at the top of the atmosphere. It typically acquires values in range (0, 1.1), during the night -9.
KTM	Modified Clearness Index	-	Modified clearness index takes into account the relative width of the atmosphere.
Latitude, φ	Latitude	deg	Geographical position; angle from the equatorial plane to the perpendicular to the ellipsoid through a given point, northwards treated as positive.
Longitude, λ	Longitude	deg	Geographical position; angle from the prime meridian plane to the meridian plane of a given point, eastward treated as positive.
Maintenance event	Maintenance event or log	-	A maintenance log is a structured record used to document all maintenance activities performed on an instrument or system. It helps track the history of cleaning, repairs, inspections, calibrations, and any other upkeep tasks to ensure the equipment remains in optimal working condition.
SNOWD	Snow days	days	Days with snow water depth equivalent to or higher than 5 mm.
SUN_ASPECT	Sun aspect	deg	The sun aspect angle is the compass direction from which the sunlight is coming. South = 0 deg, East = -90 deg, West = 90 deg, North = 180 (-180) deg
SUN_AZIMUTH	Sun azimuth angle	deg	The azimuth angle is the compass direction from which the sunlight is coming. North = 0 (360) deg, East = 90 deg, South = 180 deg, West = 270 deg. Northern hemisphere: Southern hemisphere:
SUN_ELEVATION	Sun elevation	deg	The elevation angle is the angular height of the sun in the sky measured from the horizon.
ZENITH_ANGLE	Zenith angle	deg	The solar zenith angle is the angle between the direction of solar radiation and the vertical direction. It is a complementary angle of sun elevation.

Electrical and technical terms

Acronym	Full Name	Units	Description
AC	Alternating Current	V (Volts)	An electric current that periodically reverses direction, typically at a frequency of 50 or 60 Hz.
A	Current	A (Amperes)	The unit for electric current; the flow of electrons. One ampere is 1 coulomb passing in one second.
Array	Photovoltaic Array	-	An interconnected system of PV modules that function as a single electricity-producing unit.
Azimuth	Azimuth Angle	Degrees	The angle between the north direction and the projection of the surface normal into the horizontal plane; measured clockwise from north.
Backtracking	Backtracking Strategy	-	A control strategy that adjusts the tilt angle of modules to minimize shading between rows, maximizing overall energy production.
BATT	Battery status	V	Refers to the current condition and charge level of a battery
Cell	Photovoltaic Cell	-	The smallest semiconductor element within a PV module that converts light into electrical energy (DC voltage and current).
DC	Direct Current	A (Amperes)	Electric current in which electrons flow in one direction only.
DC/AC ratio	DC/AC Ratio	-	Also known as the inverter loading ratio (ILR), it is the ratio of the total DC power output of a PV system's solar panels to the AC power rating of the system's inverter.
Distributed systems	Distributed Systems	-	Systems installed at or near the location where electricity is used, as opposed to central systems that supply electricity to grids.
Effective tilt	Effective tilt	degrees	An optimized angle at which solar panels are positioned to achieve maximum energy production accounting for specific conditions such as shading, snow accumulation, or seasonal variations in sunlight.
Electrical Grid	Electrical Grid	-	An integrated system of electricity distribution, usually covering a large area.
Fractional table	Fractional Table	-	A mounting structure designed to hold a specific fraction of the total number of PV modules in a string, allowing for modular and flexible array configurations.
Grid Connection	Grid Connection	-	A connection point where the PV array connects to the distribution grid, supplying power to the grid.
Inverter	Inverter	-	A device that converts DC electricity into AC electricity for stand-alone or utility-interactive systems.
kW	Kilowatt	-	A unit of power; 1 kW = 1000 watts.
kWh	Kilowatt-hour	-	A unit of energy; 1 kWh = 1000 watts acting over a period of 1 hour.
Load	Load	-	Anything in an electrical circuit that draws power when the circuit is turned on.
Module	Photovoltaic Module	-	The smallest environmentally protected assembly of solar cells and ancillary parts, intended to generate DC power under unconcentrated sunlight.
Ohm	Ohm	Ω (Ohms)	The unit of resistance to the flow of an electric current.
One-axis tracking	One-axis Tracking	-	A system capable of rotating about one axis, usually following the sun from East to West.
Parallel connection	Parallel Connection	-	A way of joining electricity-producing devices by connecting positive leads together and negative leads together; increases the current.
Peak load	Peak Load	-	The maximum load or usage of electrical power occurring in a given period of time, typically a day.
Performance variability	Performance Variability	-	Refers to the extent of fluctuation or deviation from a consistent level of performance, often measured by the dispersion of outcomes over time.
Photovoltaic (PV) array	PV Array	-	An interconnected system of PV modules that function as a single electricity-producing unit.
Photovoltaic (PV) cell	PV Cell	-	The smallest semiconductor element within a PV module that converts light into electrical energy (DC voltage and current).
Photovoltaic (PV) efficiency	PV Efficiency	%	The ratio of electric power produced by a cell at any instant to the power of the sunlight striking the cell.
Photovoltaic (PV) module	PV Module	-	The smallest environmentally protected assembly of solar cells and ancillary parts, intended to generate DC power under unconcentrated sunlight.
Photovoltaic (PV) panel	PV Panel	-	Often used interchangeably with PV module, but more accurately refers to a physically connected collection of modules.
Photovoltaic (PV) system	PV System	-	A complete set of components for converting sunlight into electricity by the photovoltaic process, including the array and balance of system components.
Power factor	Power Factor	-	The ratio of the average power and the apparent volt-amperes. Affected by the inductance and capacitance of the load.
PVOUT	Photovoltaic Power Output or Production	kW, kWh	The amount of electrical energy generated by a solar photovoltaic system over a specific period of time
Safe zone (inverters)	Safe Zone	-	Refers to the specific area or distance around the inverter that ensures proper ventilation, accessibility for maintenance, and protection from environmental hazards.
Series connection	Series Connection	-	A way of joining photovoltaic cells or batteries by connecting positive leads to negative leads; increases the voltage.
Soiling losses	Soiling Losses	-	Refer to the reduction in energy output caused by the accumulation of dirt, dust, pollution, or other contaminants on the surface of solar panels.
Solar energy	Solar Energy	-	Energy from the sun.
Stand-alone PV system	Stand-alone PV 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.
String size	String Size	-	Refers to the number of photovoltaic (PV) modules connected in series within a solar array, determining the overall voltage of the string.
tilt	tilt	degrees	The angle at which solar panels are installed relative to the horizontal plane. This angle is typically set to match the geographical latitude of the installation site to maximize sunlight exposure and energy production.
Transformer	Transformer	-	Steps AC voltage up or down, depending on the application.
Transformer class	Transformer Class	-	Refers to the classification of a transformer based on its voltage rating, application, insulation type, cooling method, and other specifications.
Two-axis tracking	Two-axis Tracking	-	A system capable of rotating independently about two axes (e.g., vertical and horizontal) and following the sun for maximum efficiency of the solar array.
Vac	Voltage of Alternating Current	V (Volts)	Refers to the voltage of alternating current (AC) in a PV system or electrical circuit, typically representing the output voltage from an inverter or the grid voltage to which the system is connected.
Voc	Open-circuit Voltage	V (Volts)	The maximum possible voltage across a photovoltaic cell or module when no current is flowing.
Watt	Watt	W (Watts)	The unit of electric power; 1 watt = 1 joule per second.
Wh	Watt-hour	Wh (Watt-hours)	A unit of energy; see kilowatt-hour for a larger unit.
WOUT	Wind Power Output or Production	kW, kWh	The amount of electrical energy generated by a wind turbines over a specific period of time

Other terms

Acronym	Full name	Unit	Explanation
FLAG	Flag	-	A flag is a marker or annotation used to identify data points that may be unreliable, erroneous, or require special attention. Flags help distinguish between valid measurements and those affected by potential issues, ensuring transparency and accuracy in data analysis.