Electrowetting controlled liquid lenses have emerged as a useful technique for steering light. In this study, we report on a novel hexagonal cell design of an electrowetting device for two-axis solar tracking. This study proposes an array of these hexagonal electrowetting cell structures to facilitate a planar device that can steer sunlight coming from a range of directions. A proof of concept device is fabricated to demonstrate this design. The hexagonal cell is dosed with two immiscible liquids. The liquid-liquid interface is modulated by varying the voltage to different electrode faces in the cell. By deforming the liquid shape in an electrowetting cell, light can be steered and concentrated for solar energy applications. Here, the study demonstrates that the interface can be tilted vertically by applying a voltage to the side electrode faces. By sequentially applying a voltage to different electrode faces, the interface can be rotated 360° horizontally. Finally, the study demonstrates a 4.5° change of laser beam path with only a 0.2 refractive index difference of the liquids. The device has the potential to eliminate the disadvantages associated with bulky mechanical tracking devices. A thin array of electrowetting cells can be placed on a Fresnel lens and direct the sunlight towards the Fresnel lens for concentration without extra tracking. The electrowetting cell array can also be used to steer and concentrate solar energy onto a concentrated photovoltaic cell directly.
Electrowetting control of liquid lenses has emerged as a novel approach for solar tracking and concentration. Recent studies have demonstrated the concept of steering sunlight using thin electrowetting cells without the use of any bulky mechanical equipment. Effective application of this technique may facilitate designing thin and flat solar concentrators. Understanding the behavior of liquid-liquid and liquid-solid interface of the electrowetting cell through trial and error experimental processes is not efficient and is time consuming. In this paper, we present a simulation model to predict the liquid-liquid and liquid-solid interface behavior of electrowetting cell as a function of various parameters such as applied voltage, dielectric constant, cell size etc. We used Comsol Multiphysics simulations incorporating experimental data of different liquids. We have designed both two dimensional and three dimensional simulation models, which predict the shape of the liquid lenses. The model calculates the contact angle using the Young-Lippman equation and uses a moving mesh interface to solve the Navier-stokes equation with Navier slip wall boundary condition. Simulation of the electric field from the electrodes is coupled to the Young-Lippman equation. The model can also be used to determine operational characteristics of other MEMS electrowetting devices such as electrowetting display, optical switches, electronic paper, electrowetting Fresnel lens etc.
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