Global horizontal irradiance (GHI) is the measure of the total radiation that is incident on a plane horizontal to the surface of the earth. The units of GHI are in watts per meter squared. GHI is the sum of the direct normal (DNI) and diffuse (DIF) irradiance conditions. The direct normal irradiance component is adjusted by the geometric relationship of the sun's position in the sky relative to location of interest. The Irradiance and Weather Data API uses SolarAnywhere data as its source for GHI. SolarAnywhere generates GHI measurements from 1998 through the present, and forecast data out to 90-days in the forecast horizon. SolarAnywhere generates these measurements by using the latest and most advanced SUNY satellite-to-solar irradiance model developed in collaboration with Dr. Richard Perez from The State University of New York at Albany (SUNY-Albany).

Direct normal irradiance (DNI) is the measure of the solar radiation perpendicular (normal) to the sun. The units of DNI are in watts per meter squared. DNI can also be referred to as the direct beam radiation. The Irradiance and Weather API uses SolarAnywhere data as the source for DNI. SolarAnywhere generates DNI measurements from 1998 through the present, and forecast data out to 90-days in the forecast horizon. SolarAnywhere generates these measurements using the latest and most advanced SUNY satellite-to-solar irradiance model developed in collaboration with Dr. Richard Perez from The State University of New York at Albany (SUNY-Albany). SolarAnywhere DNI data is produced using Dr. Perez's DIR_INT model.

Diffuse irradiance (DIF) is the measure of the solar radiation that is incident on a horizontal surface to the earth, created by the sky. DIF contains scattered direct light from the sun. The units on DIF are in watts per meter squared. The Irradiance and Weather API uses SolarAnywhere data as the source for DNI. SolarAnywhere generates DNI measurements from 1998 through the present, and forecast data out to 90-days in the forecast horizon. SolarAnywhere generates these measurements using the latest and most advanced SUNY satellite-to-solar irradiance model developed in collaboration with Dr. Richard Perez from The State University of New York at Albany (SUNY-Albany). SolarAnywhere DIF data is produced by enforcing the geometric relationship between GHI and DNI, where DIF = GHI - DNI*cos(Z) and Z = the sun's zenith angle.

Wind speed is a measurement of the flow of air, typically caused by pressure differentials in the atmosphere. For PV applications, wind speed data can be used to assess cooling factors, which ultimately impact temperature derate and PV module efficiency. Data is available in all geographic regions where irradiance data is present in time-series, forecast and typical-year data types. Wind speed data is sourced from multiple forecast and reanalysis numerical weather models, and ranges in spatial resolution from 25-km down to 5-km grids depending on data version and geographic region. Wind speed data is predicted at 10-meters off of the surface. Wind speed data is in units of meters per second.

Dry bulb temperature is the measurement of the ambient air temperature with account of irradiance or moisture. For PV applications, the dry bulb temperature data is an input into the calculation of the module derate due to temperature. Higher temperatures cause the PV modules to produce less power for equivalent levels of incident irradiance. Data is available in all geographic regions where irradiance data is present in time-series, forecast and typical-year data types. Temperature data is sourced from multiple forecast and reanalysis numerical weather models, and ranges in spatial resolution from 10-km down to 5-km grids. Temperature is predicted at 2-meters off of the surface and has units of Celsius.

Relative humidity (RH) is the measurement of air moisture content as a ratio of the partial pressure of water to the vapor pressure at ambient temperature. For PV applications, RH can be used to better predict the energy output of PV modules through spectral impacts on the incident irradiance. Data is available in all geographic regions where irradiance data is present, currently in time-series and typical-year data types. Forecast RH is not currently available. RH data is sourced from multiple reanalysis numerical weather models, and ranges in spatial resolution from 10-km down to 5-km grids. Relative humidity is in percentage units.

Precipitation is a measurement of the volume of liquid or solid water (primarily) that condenses out of the atmosphere. For PV applications, precipitation information can help determine the operational performance of a PV system and help identify certain conditions such as soiling. Data is available in all geographic regions in the time-series data type. Forecast and typical-year precipitation is currently not available via the API. Precipitation is broken into two forms: solid and liquid precipitation. Each is denoted by a separate field, SolidPrecipitation and LiquidPrecipitation respectively, via the API. Precipitation is sourced from reanalysis models, and ranges in spatial resolution from 5-km down to 1-km. Both solid and liquid precipitation are in units of kilogram per meter squared. Daily totals are down sampled to the temporal resolution specified by the client.

Snow depth is the measurement of the height of solid precipitation accumulated on the ground. For PV applications, snow depth information can help determine the operational performance of a PV system, and help identify certain conditions such as snow accumulation as a cause of under-performance. Data is available in all geographic regions in the time-series data type. Forecast and typical-year precipitation is currently not available via the API. Snow depth is sourced from reanalysis models, and ranges in spatial resolution from 5-km down to 1-km. Snow depth is in units of meters. Daily totals are down sampled to the temporal resolution specified by the client.

Albedo is a measure of the fraction of the global horizontal irradiance that is reflected off the ground. Albedo is unitless and is expressed as a decimal, e.g., 0.20. The parameter is critical for estimating the gain from bifacial PV systems. Data is available in all geographic regions and can be requested as an output field with time-series and typical-year (TGY/TDY/average year) data types. Albedo data is limited to SolarAnywhere versions 3.5 and later and is not currently available for forecast time periods. Visit the albedo resource page to learn more about SolarAnywhere albedo data.

Particulate Matter- also known as particle pollution or PM- is a mixture of small particles and liquid droplets suspended in the air. Particulate Matter data has been shown to be highly correlated with soiling losses and has been incorporated by PV simulation models such as the Humboldt State University (HSU) model to estimate soiling losses. Particulate matter may include dust, dirt, soot, smoke as well as other organic and inorganic compounds. Depending on the size of the particles, particulate matter can be categorized into:

1. Particles with diameter less than or equal to 10 micrometers, known as PM₁₀
2. Particles with diameter less than or equal to 2.5 micrometers, known as PM_2.5

Data is available in all geographic regions and can be requested as an output field with time-series and typical-year (TGY/TDY/average year) data types. Particulate matter data is limited to SolarAnywhere versions 3.5 and later and is not currently available for forecast or real-time time periods. SolarAnywhere particulate matter data is expressed in units of micrograms per meter cubed (μg/m³). Visit the particulate matter resources page to learn more about SolarAnywhere particulate matter.