Abstract
SummaryBy investigating the long-term observations at Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP), we find that the routinely used Beer-Bouguer-Lambert law and the models that empirically separate direct normal irradiance (DNI) from measurements of global horizontal irradiance (GHI) have dramatic and unexpected bias in computing cloudy-sky DNI. This bias has led to tremendous uncertainty in estimating the electricity generation by solar energy conversion systems. To effectively reduce the bias, this study proposes a physical solution of all-sky DNI that computes solar radiation in the infinite-narrow beam along the sun direction and the scattered radiation falls within the circumsolar region. In sharp contrast with the other DNI models, this method uses a finite-surface integration algorithm that computes solar radiation in differential solid angles and efficiently infers its contribution to a surface perpendicular to the sun direction. The new model substantially reduces the uncertainty in DNI by a factor of 2–7.
Highlights
Direct normal irradiance (DNI) is one of the most used quantities to assess solar energy resource and is crucial in evaluating or forecasting the performance of concentrating solar power systems (Desai et al, 2014; Lovegrove and Stein, 2012; Sengupta et al, 2018; Zhang et al, 2013)
To effectively reduce the bias, this study proposes a physical solution of all-sky direct normal irradiance (DNI) that computes solar radiation in the infinite-narrow beam along the sun direction and the scattered radiation falls within the circumsolar region
For clear-sky conditions, the transmittance of direct radiation is affected by the atmospheric absorption, Rayleigh scattering, and the scattering by aerosols in the atmosphere, which can be computed by a clear-sky radiative transfer model, e.g., REST2 (Gueymard, 2008), and models developed by Bird and Hulstrom (1981) and Ineichen and Perez (2002), which is designed for simulating observations by a surface-based pyrheliometer
Summary
Direct normal irradiance (DNI) is one of the most used quantities to assess solar energy resource and is crucial in evaluating or forecasting the performance of concentrating solar power systems (Desai et al, 2014; Lovegrove and Stein, 2012; Sengupta et al, 2018; Zhang et al, 2013). DNI is often interpreted differently, in the study of solar energy or observation by surface-based pyrheliometers (Blanc et al, 2014; Raisanen and Lindfors, 2019). DNI is often associated with substantial amount of scattered solar radiation within the circumsolar region leading to distinct disagreements with the simulation/forecast based on the Beer-Bouguer-Lambert law. These disagreements have seriously affected the model performance in solar resource assessment and forecasting and test frameworks aimed at understanding the implementations of models
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