Equations for potential annual direct incident radiation and heat load

TLDR

Estimation of potential annual direct incident radiation has traditionally required numerical integration with simulation models. The authors present convenient equations for estimating potential annual direct incident radiation in spreadsheet, GIS, and database applications. The equations use latitude, slope, and aspect as inputs, apply to 0–60° north latitude and slopes 0–90°, and can be transformed to serve as a heat load index symmetric about a northeast–southwest axis. Abstract.

Abstract

Abstract. Estimation of potential annual direct incident radiation has traditionally required numerical integration with simulation models. As an alternative, we present convenient equations for use in spreadsheet, GIS, and database applications. Input variables are latitude, slope, and aspect. The equations apply to 0–60° north latitude, slopes from 0–90°, and all aspects. By transforming aspect, the equations can also be applied as an index of heat load, symmetrical about a northeast to southwest axis.