What is a solar aircraft?
The principle behind solar aircraft is the use of photovoltaic panels to power the electric motors and on-board systems, enabling environmentally-friendly, sustainable flight.
- Estimating energy consumption: The energy consumption of a solar aircraft depends mainly on aerodynamic drag, aircraft weight and cruising speed. To estimate energy consumption, we first need to determine the power required to keep the plane in flight at the desired cruising speed.
- Calculatingsolar energy production: To estimate solar energy production, you need to take into account the total surface area of the solar panels installed on the aircraft, the efficiency of the solar cells and the average solar irradiance. Solar energy production (in watts) can be calculated using the following formula:
Solar output = Panel area × Cell efficiency × Solar irradiance
- Estimating the storage capacity required: The storage capacity required for the solar aircraft depends on the desired autonomy and the difference between solar energy production and energy consumption. Storage capacity (in watt-hours) can be estimated using the following formula:
Storage capacity = (Energy consumption – Solar production) × Desired flight time
- Factor in losses and inefficiencies: It’s important to factor in energy losses due to reverse current, internal battery resistance and other system inefficiencies. A safety factor must also be added to account for variations in solar irradiance, temperature fluctuations and component wear.
Types of solar aircraft
- Experimental solar aircraft: These aircraft are designed to test and demonstrate the feasibility of solar energy in aviation. They are generally small and equipped with solar panels covering a large part of their surface area to maximize energy production. Solar panel and battery requirements depend on aircraft size and flight objectives, ranging from a few kilowatts to several tens of kilowatts.
- Solar drones: Solar drones are unmanned aircraft that use solar energy for surveillance, communication or scientific research missions. They are generally fitted with solar panels on their wings and fuselage, with capacities ranging from a few hundred watts to several kilowatts. Batteries for these drones generally range from a few kilowatt-hours to several tens of kilowatt-hours.
- Solar pseudo-satellites: Solar pseudo-satellites are unmanned solar aircraft designed to fly at high altitudes for long periods, offering services similar to satellites. These aircraft are equipped with high-efficiency solar panels and lightweight batteries to provide power during the day and night. Solar panel requirements typically range from 1 to 10 kW, and batteries from 10 to 100 kWh.
Solar aircraft projects
Here are a few notable examples of solar aircraft:
- The Solar Impulse 2 is an experimental solar airplane that completed the first round-the-world solar flight in 2016. Piloted by Bertrand Piccard and André Borschberg, the plane covered 43,000 km in 17 stages without using a single drop of fossil fuel. It is equipped with 17,248 solar cells on its wings, which power four electric motors and charge batteries for night flight.
- The Sunseeker Duo is a two-seater solar aircraft developed by Solar Flight. It features solar panels on its wings and tail, which generate up to 2.5 kW of energy to power the electric motor and charge the batteries. The Sunseeker Duo made its maiden flight in 2014.
- SolarStratos is an experimental solar aircraft developed by the Swiss company SolarXplorers. This aircraft is designed to reach an altitude of 25,000 meters using only solar energy. It features 22 m² of solar panels on its wings, powering a 32 kW electric motor and lithium-polymer batteries.
- Zephyr is an unmanned solar aircraft developed by Airbus Defence and Space. It is a high-altitude pseudo-satellite system (HAPS) designed for surveillance and communication missions. Zephyr uses solar panels to power its electric motors during the day and batteries to fly at night. It holds the endurance flight record for an unmanned aircraft, having flown for 25 consecutive days in 2018.