Design and experimental investigation on a solar concentrating photovoltaic underwater

This paper presents a special concentrating photovoltaic that works underwater. A tri-junction GaAs solar cell and a deformable concentrator which is specially designed to converge sunlight underwater are applied to it. The concentrator is composed of a transparent membrane and a hollow cylinder with one sealed transparent end. When the membrane is perfectly cover onto the other end of the cylinder and put into water, the membrane will deform as a spherical lens due to the water pressure. A concentrator model with membrane radius of 100 mm is investigated. The effects of membrane's deformation ratio α and length of the cylinder t on its optical characteristics were analyzed via the theoretical and simulative methods. The theoretical result indicates that f varies from about 4 m to 0.45 m when α rises from 0.05 to 0.45. The optical simulation shows that a small t is beneficial to concentrate the energy density on the focus. Finally, testing platform with a solar cell of 20∗20 mm was set up. The results illustrate that the maximum output power and efficiency can be obtained about 2 W and 15% when α is 0.3 during the normal incidence. The increase of water depth and turbidity will obviously reduce the PV efficiency.