A standard solar array is a flat panel configured of many individual solar cells, wired in series or parallel, depending on their junction configuration and material. Since the solar flux is constant depending on the distance from the Sun, the maximum energy conversion for a given solar panel depends upon the capability to absorb as many spectral peaks as possible (different materials) across the total solar spectrum. If the radiative source is a man-made device such as a laser, parked in a different orbit or on Earth, then the impinging intensity is narrow spectrally, coherent and accurately pointed, and capable of very high intensities. Thus, the materials can be tailored to match the incoming radiation for maximum absorption.

A three-dimensional solar panel structure has been designed to maximize laser-based energy capture for maximum electrical production with minimal heat production and near 100% conversion efficiency from photons to electrons. Furthermore, the solar cell configuration scheme minimizes sensitivity to its orientation to the laser source.

When using a simple laser transmitter as an optical source, light can be used as a means of power transfer between two remote locations. The solar cell structure can be configured in a 3D fashion in order to capture the incoming light through multiple reflections, increase solar cell total area for a given 2D equivalent panel area, and hold the relatively high incoming power to manageable intensities striking the cells to maintain safe operation, yet produce high electrical powers. The use of 3D structures on a solar panel can increase the active surface area 2 to 3 times, and help to capture off-nadir light to hold the absorption efficiency at near peak levels.

Specifically, this innovation uses lightweight cylindrical, hexagonal, or rectangular tubes, mounted vertically on a given panel structure area. Each tube is approximately 3 to 5 in. (≈7.6 to 13 cm) in diameter, and anywhere from 2 to10 in. (≈5 to 25 cm) in height. When arranged in a close-packed manner, the interior walls of each tube hold solar cells where maximum coverage is achieved. The floor or bottom of the tube could readily be a solar cell as well, but the design plans for a lightweight, reflective center structure. This center cone has a concave parabolic shape that directs incoming light from above to the respective wall. For example, should a hexagonal tube be employed, a hexagonal parabolic cone is installed inside.

The 3D structure of vertical tubes acts as temporary optical traps of the incoming light and produces reflective paths that enable multiple reflections within each tube, as opposed to a simple single surface reflection typical of a flat solar panel. These parameters must be further modeled and studied, but initial estimates show a significant increase in surface area, multiple reflections, less sensitivity to incident angle due to semi-captured light within each tube, and multiple reflections of unabsorbed light.

This work was done by Barry Coyle of Goddard Space Flight Center. GSC-16821-1


NASA Tech Briefs Magazine

This article first appeared in the June, 2015 issue of NASA Tech Briefs Magazine.

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