Portable Photo-voltaic Stand-alone System, Operating at Very Low Power Conditions

A new approach to mobile photo-voltaic systems is proposed; the system described in this paper is of very low power (5 W) and is intended mainly for recharging or powering small portable electronics devices. The objects of this study are: (i) the optimization of photo-voltaic cells connection with regard to mobile conditions; a nonstandard topology is adopted, to compensate shadowing or non-optimal orientation; (ii) the introduction of a novel topology for battery and DC/DC converter, in which the battery voltage is optimized for photo-voltaic operation and a buck-boost converter can provide any voltage to the load. A good efficiency is achieved also in marginal condition of illumination (0.1 W). A prototype has been built with thin film photo-voltaic cells mounted on a flexible plastic support and integrated in a jacket. A series of measurements have been performed in a real-life situation, and the system has been characterized. The efficiency of the proposed system has been compared with a conventional system, in the same operating conditions.