Some of you must be wondering how the HB-SIA actually flies with nothing but the power of the sun. Well, today is your lucky day because I’ll be giving a little explanation on how sunlight is converted into energy allowing this unique airplane to glide through the skies.

The upper part of the solar airplane’s wings is covered by solar panels. These are solar generators, meaning that they convert sunrays directly into electricity. The panels together are constituted of a total of 12’000 solar cells which, in turn, are all grouped into “strings” of 300 cells. At the extremities of each string, just like in a battery, there is the positive (+) and negative (-) pole. Each string has what’s called a Maximum Power Point Tracker (MPPT) which is responsible for extracting the maximum amount of power from the panels at any given solar intensity.

The energy is then either stored in the batteries (there are 4 total) or immediately converted into mechanical energy, triggering the propellers to move. There are 4 motors on the HB-SIA.

Wondering how the energy is channeled? Well, when the motors are not running, the energy that is processed is directly stored in the batteries. However, if the airplane is in flight, sunlight is used to fuel the motors. When the energy produced is more than what is needed to fly, the remainder flows into the batteries. The Battery Management System (BMS) controls this process automatically reducing the electric current into the battery according to its charging status. The BMS also monitors the battery temperature during flights, ensuring they are not too cold (lowering their productivity) or overheating (which can be dangerous).

In simple words, the entire process is run through a chain of conversion. The cells convert sunlight into electricity; this electricity is channeled through the MPPT to get the maximum power output. The electricity can either be stored in the batteries or transmitted to the motors. The motors take the electricity and transform it into mechanical power, enabling the propellers to move and consequently the aircraft to fly. In flight, the pilot determines how much energy he needs depending on the speed of flight and how fast he wants to reach the desired altitude. Depending on the time of day, energy used is:

• Only energy directly from the sun (day)
• Some sun and some stored energy from the batteries (morning/evening)
• Only energy from the batteries (night)

What is incredible in this process is that, while in flight, the HB-SIA can use direct sunlight to power the motors while simultaneously charging the batteries! It’s as if you left your home in the morning with a half-empty tank of gas and came back in the evening with a full one! Wouldn’t that be nice? Who knows, maybe one day it could become reality…