The spectral on-demand data service provides solar irradiances on inclined PV panels for 2002 narrow-wavelength bands from 0.28 to 4.0 µm. Based on users’ selection of location, time period, and PV system (fixed or one-axis PV system), a dedicated high-performance server located at NREL computes the spectral data in real time using the Fast All-sky Radiation Model for Solar applications with Narrowband Irradiances on Tilted surfaces (FARMS-NIT) and broadband and ancillary data served by the NSRDB. As soon as the data have been generated and are available for download, a signal is sent back up the job queue, which triggers an email to the users.

FARMS-NIT is an innovative radiative transfer model developed at NREL to efficiently and simultaneously calculate the spatial distribution of solar energy (radiances) in narrow-wavelength bands which are integrated over inclined PV panels to infer the plane-of-array (POA) irradiances. For clear-sky conditions, the Simple Model of the Atmospheric Radiative Transfer of Sunshine (SMARTS) is employed to rapidly provide the optical properties of a given clear-sky atmosphere. The clear-sky radiances in the narrow-wavelength bands are computed by considering three paths of photon transmission and solving the radiative transfer equation with the single-scattering approximation. For cloudy-sky conditions, FARMS-NIT uses cloud reflectance of irradiance and bidirectional transmittance distribution function (BTDF) from a precomputed lookup table by the LibRadtran model with a 32-stream Discrete Ordinates Radiative Transfer (DISORT). The cloud reflectance and BTDF are combined with the clear-sky properties to efficiently compute spectral radiances on the land surface and POA irradiances. The validation analysis confirms that FARMS-NIT has better accuracy than TMYSPEC as evaluated by both surface observations and a state-of-the-art radiative transfer model. It also substantially improves computational efficiency compared to other radiative transfer models. More technical details of FARMS-NIT can be found from the references below.

References

Xie, Y., Sengupta, M., 2018. A Fast All-sky Radiation Model for Solar applications with Narrowband Irradiances on Tilted surfaces (FARMS-NIT): Part I. The clear-sky model. Sol. Energy 174, 691-702. Xie, Y., Sengupta, M., Dooraghi, M., 2018. Assessment of uncertainty in the numerical simulation of solar irradiance over inclined PV panels: New algorithms using measurements and modeling tools. Sol. Energy 165, 55-64. Xie, Y., Sengupta, M., Wang, C., submitted. A Fast All-sky Radiation Model for Solar applications with Narrowband Irradiances on Tilted surfaces (FARMS-NIT): Part II. The cloudy-sky model. Sol. Energy.

Gridded Spectral On-demand data header

ElementUnit or Description
Year 1998-2017
Month 1-12
Day 1-28, 1-30, 1-31
hour 1-23
Minute 0
PV Tilt Angle Degree
Wavelength Micron
Spectral GHI Watt per square meter per micron
Spectral POA Irradiance Watt per square meter per micron