Measurements of Optical Performance and Alignment Error of a Manually-Positioned Line-Focus Concentrator

Abstract

We describe the construction and testing of a robust 2 m² manually-tracked concentrator, for a small-scale p.v. water pumping system. It uses Glaverbel mirrors bent into a cylindrical parabola, mounted perpendicular to a polar axis. The collector achieves 10 times concentration, yet requires only three positioning movements per day. Construction is straightforward, requiring only simple tools, and the alignment of the axes used only simple equipment.

Instantaneous optical performance tests found the combined reflectivity and intercept factor to be of the order of 90%. This high value is due to the quality of the mirrors and the mounting profile achieved. Measurement of collector and axis misalignment indicated that they gave an equivalent tracking error of ±1 degree. A computer program that combined this value with the sun’s movement throughout a year showed that a string of cells of 1/10 the aperture in width would intercept 95% of the reflected radiation, on an annual basis.

Cost of materials for the collector and mounting (but excluding cells) came to about $85/m² at retail prices. Four of these collectors, with grid-modified photovoltaic cells and a commercially available pump and motor set, could pump water for less than half the cost of an equivalent flat-array p.v. pumping system.