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 (5W) 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 non-standard 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 (0.1W). 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.