Estimating collectable solar energy by partially shaded collectors using custom-designed charts and tables: demonstration for typical Zimbabwe locations

Abstract

In this paper, an approach for the estimation of insolation available to a solar energy collector that may be shaded temporally by external horizon obstructions is described. This approach uses, in place of complicated mathematical expressions or sophisticated specialized computer software, a set of custom-designed charts and tables, and a simple equation, to evaluate the temporal radiation income to the solar collector. The solar position diagram or sun-chart is first used to determine shading status, and then a package of charts and tables is used to evaluate a suitable tilted-plane sky model for collectable insolation. The approach is convenient for use by the average solar energy designer who might not have background training in the intricacies of solar geometry and meteorology. Although in the present case, the charts and tables have been designed to be applicable in Zimbabwe and for the standard flat plate configuration – equator facing and tilt equal to latitude, they can also be produced for any other location and collector configuration. A major approximation in the procedure was to neglect the effects of shading on diffuse radiation availability. The resultant error was analysed and was concluded negligible for reasonably likely cases involving low-tilt collectors.