Optical characteristic investigation on an underwater adjustable focus solar concentrator with single-layer membrane

This paper presents an underwater adjustable focus solar concentrator, which is composed of a piece of transparent elastic membrane and a hollow cylindrical-like structure. The deformation characteristic of the membrane is simulated in this study. It is found that the membrane is deformed into a sphere under the action of pressure difference. Optical simulation of the concentrator with different deformation ratios is carried out. The results illustrate that both the f-number and the concentration ratio are decreased when the membrane deformation is enlarged. For instance, if the deformation ratio changes from 0.1 to 0.4, the f-number ranges from 20 to 5.6, and the concentration ratio is changed from 440 to 40. The variation of the light receiving rate with the tracking error is also analyzed. The results show that the receiver captures 73% light within the tracking error of 0.6°. Experiments are performed to investigate the energy distribution on the focus and the performance of the underwater photovoltaic system. As a result, when the solar radiation of 590 W/m² is achieved, the maximum energy density on the focus decreases from 40 kW/m² to about 35.4 kW/m² with the deformation ratio ranges from 0.1 to 0.3. In addition, the average output power of about 1.3 W of the gallium arsenide solar cell, having a size of 10×10 mm², is achieved.