| |
**Simple Solar Spectral Model for
Direct and Diffuse Irradiance
on Horizontal and Tilted Planes at the Earth's Surface for
Cloudless Atmospheres** |

Table of Contents
List of Tables

**SECTION 1.0**

**INTRODUCTION**

In previous work (Bird), we presented a simple model to
calculate direct normal and
diffuse horizontal spectral irradiance at the earth's surface for clear days. In
this report, we present a new simple model that incorporates improvements in
methodology as well as an algorithm to produce spectra for tilted surfaces. The
goal of this work is to give researchers the capability to produce accurate
terrestrial spectra using only a microcomputer.

The first model (Bird) was based on models
developed by
Leckner and Brine and
Iqbal. Since that work was completed, Justus and Paris
have made
improvements to the simple model approach. In the model presented here, we
refined the Justus and Paris model and extended it to calculate spectra for
tilted surfaces using methods developed by Hay and Davies.
Refinements to the Justus and Paris model were based on comparisons with results
of rigorous radiative transfer codes and with measured spectra.

The new simple model and results are presented in the sections that follow.
Sections 2.0 and 3.0
describe methods for calculating direct normal and diffuse
spectral irradiance, respectively. Section 4.0 gives
comparisons of the simple model results with rigorous model results and
measurements. Examples of the application of the new model are given in
Section 5.0.

2.0 Direct Normal Irradiance
Table of Contents

Return to RReDC Homepage *( http://www.nrel.gov/rredc )*