Fly around the World with a Solar Powered Airplane

Abstract

Quite a few manned and unmanned solar powered aircraft have been developed and flown in the last 30 years. Objectives and missions cover a wide spectrum ranging from a pure technological goal to “Fly with Solar Energy” to civil or military surveillance and reconnaissance missions. However, none of those aircraft was able to demonstrate a continuous day and night operation until 2005. An overview of the historic solar powered aircraft is provided and the basic challenges which have to be solved for a solar powered aircraft are being discussed: • Geographical area of operation, time windows during the year, mission profiles, payload • Energy collection and utilization • Typical design parameter for different missions Today’s technological status in the critical areas (solar cells, batteries, structure/materials) is discussed. It allows developing a solar powered aircraft with the capability not only to fly during the sunshine hours, but to save enough energy during the day to fly throughout the night and recollect energy after sunrise the next day for a perpetual continuation of flight. In 2001 the Swiss Bertrand Piccard, who together with Brian Jones (UK) circled the earth in a balloon in 1999, proposed to design a manned solar powered aircraft and to fly it around the world. Such an aircraft is now being developed by the Solar Impulse organization in Switzerland. The primary objective of this endeavor is to make people aware of the fact, that the conventional energy sources are limited and that renewable energy must and can be used to solve future demands. Development aspects of the Solar Impulse Program are described and a program status is provided. 1. Solar Power Collection, the Basics Today solar cells for power generation on houses have an efficiency of up to 17 %. For special purposes monocrystaline cells may convert more than 20 % of the incoming energy into electric energy. The trivial, however, for flying extremely important conclusion is: the electric energy collected is proportional to the solar cell area (Fig. 1-1). Energy (W) Collected Solar Cell Area (m2) Theoretical Limit of SC efficiency: ~28 %, monocristaline Silizium ~29 % Gallium Arsenid 20% for high tech application ~14 % for ground based systems (e.g.solar roof ) Energy collected is proportional to solar cell area! Solar Cell Cost Fig. 1-1: Solar energy collection The orientation and the inclination of the solar cell area relative to the horizon are very important parameters, in addition to the geographic location (latitude), the time of the year and the time of the day. Also the altitude and of course the weather (clouds, humidity, temperature) play an important role for the determination of the solar energy collection. Fig.1-2 illustrates these principal relationships and shows calculated and measured values for solar energy collected for a location near Munich (Germany) on a summer and winter day [Ref.1]. A maximum of 900W of beam energy can be collected with an area of 1 m2 on a summer day at noon. However, the electrical output of the solar cell is much lower because of the efficiency factor. Earth Rotational Axis