Preliminary Study And Experiments On Energy Management Of Solar Powered Aircraft

Solar powered aircraft is an unpiloted vehicle which utilizes solar power and canfly continuously for more than weeks at high altitude. For it can perform much workdone by satellites, it is also called "atmosphere satellite". Its unique characteristic hasaroused the concerns and interests of US and European Union. The bottleneck ofcurrent solar powered aircraft is rechargeable battery. If a battery with a specificenergy up to 600Wh/kg and efficiency up to 60% was obtained the craft could hoverover North latitude 40 for a complete year at an altitude of 20 km . US Air Force willdevelop a solar powered aircraft with flight altitude 18 km and endurance time morethan 30 days in a few years to come. It can carry a payload of 150 kg.This dissertation mainly conducts preliminary study and experiments on energymanagement of solar powered aircraft. A ground test-bed has been constructed withsolar arrays and lead acid batteries as its key components. It is found that thetemperature difference between solar arrays in inclined planes is small when the Sunelevation angle is in a large value. The relationship between comparative magnitudeof solar array's output power and azimuth angle is also revealed.The output current/voltage of solar array and its working temperature could bederived by combining solar cell I-V curve formulation and energy balancemodel.Bi-section method is utilized for solution. For solar arrays which are located at20 km altitude over North 40 degree,daily variations of current/voltage and workingtemperature has been worked out on Mar 22nd/Jun 22nd and Dec 22nd respectively.One type of solar cell with conversion efficiency of 28% is taken as example .Itsoperating temperature ranges from 210 to 335 K at 20 km altitude.Radiation heattransfer shares the same magnitude with convection heat transfer and output power ofsolar array.Improvements has been made on the base of the popular design method nowdays.The improvement considers the influence of wind speed and could be used todeal with energy balance during a period of time. In addition,a viable flow chart forsolution is presented in detail. The design flight speed is the larger one of wind speedand flight velocity at minimum power. Comparisons has been conducted on energybalance during a year and on Dec 22nd. The ratio of energy should be stored towing area for the former is 100 time in magnitude as that for the latter, which is thecause of unsolvability. It accounts for why no workable solution is found for theformer. Among many combinations between the area of solar cell and the weight offuel cell, which can sustain nonstop flight during a year at high altitude, the designresult for the latter is the combination with the largest weight of fuel cell and thelargest area of solar cell. This combination leads to the most surplus energy in a year.The more surplus energy the aircraft produces, the higher degree where it flies over.