This paper presents a theoretical and experimental analysis of a non-tracking, cylindrical solar concentrator with circular cross-section of radius R. The focal length of the concentrator oscillates between 0.5R and 0 with decreasing amplitude as the rim angle increases from 0 to 90°. The...

A graphical method to measure average and instantaneous efficiencies of a solar concentrator used for heating and boiling liquids and a flat plate collector is presented. The overall heat loss coefficient for the collectors and the optical loss factors: ϱγ(τa)b—the product for a...

Two new atmospheric transmittance models are proposed to calculate the diurnal profile of solar radiation intensity. These two, together with six other models proposed by earlier researchers, are used to obtain analytical formulae for the optimum tilt angle for a plane absorber plate at any...

Most of the diffuse fraction correlations are based on hourly or daily data. However, the performance of solar collectors depends on instantaneous solar radiation. Moreover, in most cases the diffuse fraction is defined as IdIg, or GdGg, where Ig and Gg are hourly, and daily global radiation....

The analytical method developed by Nijegorodov et al. [Renewable Energy, 4, 529–543 (1994)] in order to find the optimum slope of an absorber plate, variously oriented at any latitude, is applied to study the variation of daily optimum slope with latitude from the north to the south poles. For...

A new algorithm to simulate all solar components and optimum slopes, βopt, based on new models for direct normal beam and diffuse radiation and an analytical model to predict βopt, developed at the University of Botswana is applied for complete study of solar conditions in Mozambique. The...

In this paper, relative air mass is defined analytically and treated empirically, and a new formula is proposed. This formula takes into account not only the zenith angle, but also the Earth's curvature, altitude and temperature. The new formula and the old one (m = 1cos θz) are in good...

Daily global insolation on a horizontal surface in Botswana is recorded continuously at several synoptic stations and at the University of Botswana's Physics Department. Over a number of years, daily total insolation on a tilted surface (β = −30°) was recorded at the Botswana Technology...

The attenuation of solar radiation by the atmosphere is caused by two simultaneous processes: (a) scattering by air molecules and by the atmospheric turbidity; and (b) absorption by O3, H2O and CO2. Since the atmospheric turbidity is closely related to horizontal visibility, V (meteorological...

ASHRAE model empirical coefficients A, B and C are obtained for clear days in Botswana from analysis of different solar radiation components recorded at the University of Botswana, Botswana Technology Centre and some synoptic stations. Investigations show that the direct normal radiation in...