Citation: Dinca, L.; Corcau, J.-I.; Voinea, D.-G. Solar UAVs—More Aerodynamic Efﬁciency or More Electrical Power? Energies 2023, 16, 3778. https://doi.org/10.3390/ en16093778 Academic Editor: Abu-Siada Ahmed Received: 31 March 2023 Revised: 22 April 2023 Accepted: 23 April 2023 Published: 28 April 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). energies Article Solar UAVs—More Aerodynamic Efﬁciency or More Electrical Power? Liviu Dinca, Jenica-Ileana Corcau * and Daniel-Gabriel Voinea Department of Electrical, Energetic and Aerospace Engineering, Faculty of Electrical Engineering, University of Craiova, 200585 Craiova, Romania; ldinca@elth.ucv.ro (L.D.); voinea.daniel.s4a@student.ucv.ro (D.-G.V.) * Correspondence: jcorcau@elth.ucv.ro Abstract: Solar UAVs (unmanned aerial vehicles) have experienced important development in recent years. The use of solar free energy is not neglected in the present energy crisis, with the intention to move toward green energies. However, an important problem arises concerning the limited amount of solar energy available on board UAVs. Until now, high-aerodynamic-efﬁciency conﬁgurations have been used. These conﬁgurations use high-aspect-ratio wings. However, high-aspect-ratio wings have some disadvantages regarding their excessive elasticity and weak bending resistance in the housing section. Additionally, the aircraft maneuverability is reduced. In this work, a study is proposed on a solar UAV conﬁguration that sacriﬁces high aerodynamic efﬁciency for a higher surface area available for solar cells. In this manner, the amount of energy available on board the UAV is increased, and the UAV structure becomes more rigid and robust. The presented UAV ﬁts better with more complex evolutions, is more maneuverable and the wingspan is much reduced. This UAV is more compact, can maneuver better in the take-off and landing phases, and the necessary storage space is considerably reduced. This paper highlights the performances that can be achieved using this kind of UAV and explores whether these performances are enough for some applications. Using an on-board energy balance, the possible performances of this new conﬁguration is studied. As this is a preliminary study, the precision level is not very high, but it offers an image concerning the possibilities of this new conﬁguration. Keywords: UAV; aerodynamic efﬁciency; electrical power 1. Introduction It is well known at present that society needs to move away from fossils fuel energy toward green energies. One of these energies is solar energy, and its implementation in aviation is an interesting research topic currently. However, there are some problems concerning solar energy in UAVs. The greatest problem is the very limited amount of energy possible to be obtained on a UAV using solar cells. It is well known the maximum solar radiation on the ground is around 1000 W/m 2 , and it increases by several percent at higher altitudes. The energetic efﬁciency of the best performing solar cells is around 25–30%, and this is obtained using silicon mono-crystalline solar cells. Optimistically speaking, the amount of energy possible to be obtained is around 250–300 W/m 2 . A light airplane such as a Cessna 172 has a 16.17 m 2 wing surface and 134 kW engine power. Taking into account the previous data and supposing that the entire wing is covered with solar cells, it is possible to obtain a maximum of 4.84 kW of electrical power. With 25% supplementary energy using fuselage- and empennage-mounted solar cells, this comes to 6.06 kW in total. This represents only 4.5% of a Cessna 172’s engine power. Additionally, this power can be obtained only at maximum solar radiation. Solar radiation changes signiﬁcantly throughout the day, from dark in the night to the maximum at noon. In conclusion, it can be said that the solar energy available is not enough for commercial applications in aviation. Energies 2023, 16, 3778. https://doi.org/10.3390/en16093778 https://www.mdpi.com/journal/energies