System-Level Solar Module Optimization

Concentrated photovoltaic (CPV) systems achieve the highest level of solar conversion efficiency of all photovoltaic (PV) technologies by combining solar concentration, sun tracking, and high-efficiency multi-junction PV cells. Although these design features increase the overall efficiency of the device, they also dramatically increase the cost and physical volume of the system and make the system fragile and unwieldy. In this paper, we present recent progress towards the development of a robust, reduced form-factor CPV system. The CPV system is designed for portable applications and utilizes a series of low profile optical and optomechanical components to concentrate the solar spectrum, enhance energy absorption, and track the sun throughout the diurnal cycle. Based on commercial off-the-shelf (COTS) single-junction PV cells, the system exploits the efficiency gains associated with tuning the wavelength of the incoming light to the band-gap of a PV material. This is accomplished by spectrally splitting the concentrated incident beam into multiple wavelength bands via a series of custom optical elements. Additional energy is harvested by the system through the use of scavenger PV cells, thermoelectric generators, and biologically inspired anti-reflective materials. The system's compact, low-profile active solar tracking module minimizes the effects of wind-induced loads and reduces the overall size of the system, thus enabling future ruggedization of the system for defense applications. Designed from a systems engineering approach, the CPV system has been optimized to maximize efficiency while reducing system size and cost per kilowatt-hour. Results from system tests will be presented and design trade-offs will be discussed.