1st AUTOCOM Workshop on Preventive and Active Safety Systems for Road Vehicles Optimal Design of a Hybrid Electric Car with Solar Cells I.Arsie, M.Marotta, C.Pianese, G.Rizzo, M.Sorrentino Department of Mechanical Engineering, University of Salerno, 84084 Fisciano (SA), Italy ABSTRACT: A model for the optimal design of a solar hybrid vehicle is presented. The model can describe the effects of solar panels area and position, vehicle dimensions and propulsion system components on vehicle performance, weight, fuel savings and costs for different sites. It is shown that significant fuel savings can be achieved for intermittent use with limited average power, and that economic feasibility could be achieved in next future considering expected trends in costs and prices. Keywords: Hybrid Vehicle, Solar Energy, Photovoltaic Panel I. INTRODUCTION In the last years, increasing attention has been spent toward the applications of solar energy to cars. Various prototypes of solar cars have been built and tested, mainly for racing [1][2][3] and demonstrative purposes [4][5][6], also to stimulate young students toward energy saving and automotive applications [7]. Despite of a significant technological effort and some spectacular outcomes, the limitations due to low density and unpredictable availability of solar source, the weight associated to energy storage systems, the need of minimizing weight, friction and aerodynamic losses make these vehicles quite different from the current idea of a car (FIG. 1). But, while cars powered only by the sun seems still unfeasible for practical uses, the concept of an electric hybrid car assisted by solar cells appears more realistic [8][9][10][11]. In fact, in the last decades Hybrid Electric Vehicles (HEV) have evolved to industrial maturity, after a relevant research effort [12][13][14][15]. These vehicles now represent a realistic solution to the reduction of gaseous pollution in urban drive and to energy saving, thanks to the possibility of optimizing the recourse to two different engines and to perform regenerative braking. Nevertheless, the need of mounting on-board both thermal and electrical machines and a battery of significant capacity makes these vehicles heavier than the conventional ones, at the same power, while solar cars are characterized by very limited power and weight. Therefore, the feasibility of a hybrid vehicle where solar energy can provide a significant contribution to propulsion is of course questionable. On the other hand, there is a large number of users that utilizes daily their car for short trips with limited power. Some recent studies of the UK government report that about 71% of UK users reaches their office by car, and 46% of them have trips shorter than 20 min., mostly with only one person on board [16]. In spite of their potential interest, solar hybrid cars have received relatively little attention in literature. An innovative prototype (Viking 23) has been developed at Western Washington University [10][11] in the 90’s, adopting advanced solutions for materials, aerodynamic drag reduction and PV power maximization with peak power tracking. Another study on a solar hybrid vehicle has been presented by Japanese researchers [8], with PV panels located on the roof and on the windows of the car: fuel consumption savings up to 90% could be achieved in some conditions. A further prototype of solar hybrid car powered with a gasoline engine and an electric engine has been proposed and tested by other Japanese researchers [9]. In this case, a relevant amount of the solar energy was provided by PV panels located at the parking place, while only a small fraction was supplied by PV panels on the car. The hybridization lead to a significant weight increase (350 kg), due to the adoption of lead batteries. A very advanced prototype (Ultra Commuter) has been recently developed at the Queensland University, adopting a hybrid series structure [17]. Although these works demonstrate the general feasibility of this idea, a detailed presentation of results and performance and a systematic approach to the design of a solar hybrid vehicle seems still missing in literature. Such a model is particularly necessary since the technological scenario is rapidly changing, and new components and solutions are becoming available or will be available in the next future. Moreover, cost and prices are also subject to rapid variations, thus requiring the development of a