Among novel technologies for producing electricity from renewable resources, a new class of wind
energy converters has been conceived under the name of Airborne Wind Energy Systems (AWESs). This
new generation of systems employs flying tethered wings or aircraft in order to reach winds blowing at
atmosphere layers that are inaccessible by traditional wind turbines. Research on AWESs started in the
mid seventies, with a rapid acceleration in the last decade. A number of systems based on radically
different concepts have been analyzed and tested. Several prototypes have been developed all over the
world and the results from early experiments are becoming available. This paper provides a review of the
different technologies that have been conceived to harvest the energy of high-altitude winds, specifically
including prototypes developed by universities and companies. A classification of such systems is
proposed on the basis of their general layout and architecture. The focus is set on the hardware
architecture of systems that have been demonstrated and tested in real scenarios. Promising solutions
that are likely to be implemented in the close future are also considered.
& 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license