Prof. Abdennaceur Karoui

Energy autonomy is a primary concern for many emerging machines, such as Unmanned Aerial Vehicles (UAVs). We developed a set of new technologies necessary for making a photovoltaic power supply capable of powering a UAV and enabling more functionalities. These technologies can be ported to many other machines such as mobile robots, humanoids, unattended sensors,... as well as manned vehicles and lightweight cars.

The main R&D components of the project were: design of a lightweight and high efficiency PV module of 120W and integrate it on the wings of a mid-size UAV that has 2.3m wingspan, shown in Fig. 1, development of special polymer materials that allow the integration of the high efficiency PV module on UAV, development of an automaton and strategies for standalone on-board energy management, and designing methods for optimally managing the energy generation and consumption in a multi-source and multi-load network, a topic of interest for engineering new micro-grids.

Fig. 1: UAV equipped with PV power supply and energy management system.

High performance silicon PV modules were an absolute requirement for this special PV project. We used the best silicon monocrystalline cells for they were the only that can provide high energy density at acceptable cost. Multi-junction PV cells were not cost-effective for this application, where the illumination is only 1 sun. The additional 8% efficiency did not justify the use of such costly cells. Thin film PV cells were excluded form the start as they have lower efficiency and are not robust. However, integration of monocrystalline silicon cells on UAV was challenging. With silicon cells being not flexible and brittle, their encapsulation on the UAV curved surfaces brought several complex issues. In addition, silicon cells are heavy compared to thin film cells, for instance CIGS cells; along with the encapsulant materials they add significant weight to the UAV. Moreover, the integrity of the aerodynamics of the UAV, conformal coverage of curved surfaces, minimization of added weight, degradation of cell efficiency when bent, limitation in the bending, increase of the adhesion of bent cells on the wings, etc. These critical issues were tackled on several fronts.

This work led to a lightweight PV system, fully integrated to a UAV. It has extended the mission time by 170%, increased the payload, and has allowed significant enhancement of the UAV functionalities.

Click this link to read more about his project (or copy this link and past it in your browser https://www.akaroui.net/Joomla2018/research-dissemination/solar-cells/19-experimental-techniques)