Abstract

High-concentration photovoltaic systems can provide power conversion efficiency that is nearly double that of conventional solar panels. Concentrating photovoltaics (CPV) cannot compete with fixed silicon panels for rooftop installations due to the complexity and cost of CPV two-axis pedestal tracking systems. Fixed optic designs have recently been proposed to have a transparent middle sheet with small, widely spaced, and highly efficient solar cells sandwiched between a fixed lenslet array on the top and a fixed reflector array on the bottom. Precision actuators position the middle sheet at the focal points of the lenslet/reflector array to microtrack the sun throughout the day. This paper discusses the kinematic design and control of shape memory alloy (SMA) actuators used for the first time in this solar microtracking application. SMA actuators have the potential to be less expensive, easier to integrate, and lower power than electric motors. The kinematic design maintains upper and lower bounds on wire tension to prevent failure and ensure reversible actuation, respectively. The SMA actuators under quasi-linearized proportional integral directive (PID) control can position the middle sheet with ± 7 mm of range in the vertical and horizontal directions while ensuring less than 1.9 µm of steady-state error in SMA actuator stroke. The middle sheet position and orientation errors, however, exceed 1 mm and 0.5 deg, respectively. These relatively large errors are due to flexibility in the suspension system, friction at wire supports, and large kinematic gains at extreme positions and indicate the need for middle sheet error measurement and feedback control.

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