SEM subteam’s main responsibilities are solar panels design, analysis and implementation, battery charging circuit design and construction and rechargeable batteries research and selection.

Photovoltaic System(PV)

Photovoltaics selection for our solar-powered UAV is very important. Not only should they meet UAV’s energy requirements, but they must also be suitable in order to be integrated to the construction of the aircraft. For this purpose, they should be flexible.  High efficiency PV cells selection is crucial to achieve the biggest possible autonomy for our UAV.

The nominal characteristics of our photovoltaics as well as other important parameters and coefficients, are of high value for the subteam’s members as they provide a full image of the photovoltaic’s properties and behavior . They are also used to simulate the photovoltaics’ behavior in various wheather conditions using professional software.

SEM subteam’s members are also responsible for Photovoltaics connection and implementation on our UAV.

Energy Flow Diagram

Specific battery charging circuit has to be constructed in order to achieve battery charging via PV cells. After choosing appropriate hardware components, careful connection has to be done. Our goal is to convert the changing voltage from PV
cells to a constant voltage so as to supply the battery and the UAV’s electric motor. In addition, maximum utilization of generated energy from solar panels must be achieved.  

Experimental charging circuit

Energy Management System Hardware Design

Maximizing generated energy from solar panels is implemented with the use of a microcontroller, on which the entire Maximum Power Point Tracking system is based. The microcontroller decides constantly the maximum power point on which the solar panels operate, thus resulting in better utilization of the power produced. Τhe microcontroller accepts as inputs the Voltage and Current produced by the photovoltaic system and controls the duty cycle adjusting the voltage and current on the output of the buck converter. The voltage and current on the output are then supplied to the rest of the UAV’s systems (propulsion, avionics) as well as stored in rechargeable batteries during flight.

Rechargeable Batteries

After UAV energy balance analysis is made, rechargeable batteries are selected. Initially, appropriate battery type must be chosen. Βatteries must provide the proper voltage in order to power our electric motor. They must be durable, light weight and their energy density has to be as high as possible so as to achieve great autonomy.

Their charging and discharging characteristics as well as their nominal characteristics are taken into account when simulating the charging circuit with the use of software tools.