A Physics-Based DNI Model Assessing All-Sky Circumsolar Radiation

Area of Science:

• Atmospheric science
• Renewable energy systems

Background:

• Current methods for calculating direct normal irradiance (DNI) using the Beer-Bouguer-Lambert law and empirical models exhibit significant bias under cloudy-sky conditions.
• This bias introduces substantial uncertainty in estimating solar energy conversion system electricity generation.

Purpose of the Study:

• To address the bias in cloudy-sky DNI calculations.
• To propose a physically-based, all-sky DNI model that enhances accuracy for solar energy applications.

Main Methods:

• Utilized long-term observations from the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site.
• Developed a novel model computing solar radiation along the sun's direction and scattered circumsolar radiation using finite-surface integration in differential solid angles.

Main Results:

• The proposed physical model significantly reduces uncertainty in DNI calculations by a factor of 2-7 compared to existing methods.
• Demonstrated a substantial improvement in computing cloudy-sky DNI.

Conclusions:

• The new all-sky DNI model offers a more accurate and reliable method for solar radiation assessment.
• Reduced uncertainty in DNI estimation will lead to more precise solar electricity generation forecasts.