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Title: Model for Deriving the Direct Normal and Diffuse Horizontal Irradiance from the Global Tilted Irradiance

Journal Article · · Solar Energy
 [1]
  1. National Renewable Energy Lab. (NREL), Golden, CO (United States)
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We developed a separation model for deriving the direct normal irradiance (DNI) and the diffuse horizontal irradiance (DHI) from the global tilted irradiance (GTI). The model is based on the DIRINT model, but substitutes the use of the GTI in place of the global horizontal irradiance (GHI) for determining the global clearness index (Kt). Additionally, an iterative method is used to adjust Kt to improve the derived values of the DNI and the DHI. The model is referred to as the GTI-DIRINT model. When using for model input the GTI measured with a pyranometer tilted at a small angle from the horizontal (10°), the deviations between the measured DNI and DHI and the GTI-DIRINT-modeled DNI and DHI were essentially the same as those for the DIRINT model when using the GHI for model input. Increasing the tilt angle from horizontal (as great as 44° for Eugene, Oregon) increased the deviations between the modeled and measured DNI and DHI, but our results were still reasonable. The GTI-DIRINT model provides reasonable values of DNI and DHI from the GTI, and if they are subsequently used with the Perez tilted surface model to model the GTI for orientations within 30° of the azimuth and tilt of the GTI used for model input, the result is as good or better than may be obtained when using a measured DNI and DHI, and without their significant instrumentation cost.

Research Organization:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Organization:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Renewable Power Office. Solar Energy Technologies Office
Grant/Contract Number:
AC36-08GO28308; AC36-08-GO28308
OSTI ID:
1227196
Alternate ID(s):
OSTI ID: 1245236
Report Number(s):
NREL/JA-5J00-65165
Journal Information:
Solar Energy, Vol. 122; ISSN 0038-092X
Publisher:
ElsevierCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 28 works
Citation information provided by
Web of Science

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14 SOLAR ENERGY
36 MATERIALS SCIENCE
Direct and diffuse irradiance
Global tilted irradiance
Model