A handful of aviation pioneers are breathing life into solar plane technology. The jury is still out on whether they will remain prototypes forever.
According to the International Energy Agency (IEA), in 2023, aviation accounted for 2,5% of global energy-related CO2 emissions, having grown faster between 2000 and 2019 than rail, road or shipping. In late 2022, ICAO member states adopted a long-term aspirational goal to achieve net zero carbon emissions from international aviation by 2050.
While this effort is expected to mostly rely on hydrogen and sustainable aviation fuels, pioneering work in other areas is highlighting the role that could be played by solar energy. Solar-powered aircraft, while still only prototypes, could offer a promising solution in the long run. These aircraft rely on a combination of advanced technologies designed to maximize energy efficiency, minimize weight and ensure stable performance.
Key to this is the use of high-efficiency solar panels or modules, often integrated directly into the aircraft’s wings to capture maximum sunlight. These lightweight cells, combined with lithium-ion batteries, store excess energy for nighttime or cloudy conditions. Special systems are also needed to carefully manage this energy to make sure none goes to waste.
Engineering innovation based in Switzerland
To stay light and efficient, these planes are built using strong but featherweight materials like carbon fiber. Their electric motors are designed to use as little energy as possible, while smart autopilot systems help manage long flights.
With its strong tradition of engineering excellence, especially in precision industries, and as a nation committed to sustainability, Switzerland appears to be leading the way with solar aviation. The Solar Impulse project is a clear case in point – one that was about engineering innovation as well as inspiring global awareness about clean technologies and sustainable solutions.
Led by Swiss pioneers Bertrand Piccard and André Borschberg, the project successfully developed a series of solar-powered aircraft that achieved impressive milestones in sustainable flight. The duo built a prototype aircraft and completed a 26-hour non-stop flight in 2010, marking the first-ever night flight powered only by solar energy. This demonstrated the aircraft’s ability to generate and store enough power to operate round the clock.
The second leg of this project, in 2016, resulted in an improved model of the craft that achieved a historic circumnavigation of the globe using only solar energy. The journey covered over 40,000 km across multiple continents in 17 legs, showcasing the potential of solar photovoltaic energy in aviation.
The latest project in this vein has been SolarStratos, a solar-powered aircraft designed to fly in the stratosphere (the edge of space) using only energy from the sun to push the boundaries of what is possible with renewable energy. Its aim is to inspire broader applications of sustainable technology worldwide. The project is the brainchild of Raphaël Domjan, a former mechanic, paramedic and Swiss mountain guide who has dedicated the last 20 years of his life to exploring and promoting clean technologies. In 2012, the explorer completed the first circumnavigation of the globe in a solar-powered boat PlanetSolar.
The 52-year-old is also friends with Solar Impulse’s Piccard and admits to being heavily influenced by this project, which, he says, taught him some important lessons. “We saw that the size of the plane is important. If the plane is too big, the costs are very high and it’s difficult to manage. You then need a huge team and it’s very expensive,” he explained to Wired magazine in 2016.
Solar Impulse cost around CHF 178 million ($187 million), while the cost of the SolarStratos plane, he told the tech magazine, would be “closer to $ 10 million.” Domjan’s two-seater aircraft features 22 m2 of PV cells on its wings, providing approximately 6 kW of energy. This setup, he claims, allows the plane to operate solely on solar power during typical flights.
Speaking to Aerospace Global News, Domjan explained how the power worked: “We have the solar panels always connected to the engine, so we use what we get from the sun, and if we need more energy at take-off for example, we also use the battery, but when we land, we don’t need power, so we stop the engine and we just recharge the battery.”
Asked how long the plane could cruise the stratosphere, Domjan said that this was not the point of the project: “The aim is to go as high as possible and with a good sun we can fly between 2-6 h. The goal for 2025 will be to fly above 10,000 m, which will be the first manned aircraft to go above this altitude. If this flight is a success, he added, the plan would then be to fly to the stratosphere in an ultra-lightweight spacesuit powered by solar energy (another world first!) designed by the Russian firm Zvezda, which created suits for Yuri Gagarin, the first man in space.
Challenges and solutions
Controlling the plane while wearing the suit in the cramped cockpit and with restricted views will require special training, he acknowledged, highlighting one of the many challenges Domjan and his team face. Some have also questioned the feasibility and practicality of the project. Concerns include the project's ambitious goals, technological limitations, and potential risks associated with a high-altitude, solar-powered flight. “The batteries are a big challenge,” Domjan has admitted. “The batteries for the record flight are not ready yet. We must also change the propeller for the high-altitude flight. It’s a big challenge to have the best, lightest battery.”
In other areas, however, SolarStratos has made notable progress. Last year the aircraft achieved a significant milestone by reaching an altitude of 5,993 m during a flight over the Matterhorn, demonstrating the aircraft's capability to operate at high altitudes.
This followed a series of test flights over the last five years, which have been crucial in validating design improvements and system functionalities. Next, the team plans to attempt a 10,000 m altitude flight over the Swiss Alps this summer, marking a critical step towards reaching the stratosphere.
Are there any commercial implications?
Domjan's vision extends beyond piloted flights, with the development of high-altitude solar drones. In a 2024 interview, he expressed hope that the expertise gained from the SolarStratos project could contribute to advances in electric aviation and facilitate the creation of solar-powered stratospheric drones.
Although it will be a long time before solar planes can carry heavier loads or fly as fast as traditional aircraft, developments in solar technology and batteries may one day make this more practical. In the future, they could play an important role in areas like environmental research, communications or even eco-friendly tourism. Ultimately, Domjan envisions a future where solar-powered aviation becomes commercially viable. As the Swiss pioneer asserts on the project’s website, “The aim of SolarStratos is to show what can be achieved through solar energy with the hope that the aviation industry takes notice and steers away from fossil fuels to more sustainable sources of power.”
Standards and conformity assessment could help
An IEC technical committee, IEC TC 82, prepares standards for solar PV energy systems. For the time being, these standards are used for land-based PV systems, whether large installations or small roof-mounted systems. The TC has also embarked on developing standards for floating PV systems. (For more information on this, read The bright future for floating solar tech). While solar panels or modules for planes or drones would require specific standards, much could be derived from the large body of work already published in the IEC.
The IEC also has two TCs specifically dealing with the aviation industry, IEC TC 107: Process management for avionics, and IEC TC 97: Electrical installations for lighting and beaconing of aerodromes. Any electronics going into aircrafts must meet TC 107 standards. One of the main concerns is to prevent the use of counterfeit or recycled electronic components that do not meet the expected safety and performance requirements for aircraft. IEC 62668-1 is an example of such standards. The IEC Quality Assessment System, IECQ, offers third-party assessment and certification of compliance with IEC 62239-1 and IEC 62239-2.
While solar planes are far from becoming commercially viable, if they do one day reach wider market appeal, IEC International Standards will be there to ensure they meet the appropriate safety and performance requirements.
Author: Ann-Marie Corvin
The International Electrotechnical Commission (IEC) is a global, not-for-profit membership organization that brings together 174 countries and coordinates the work of 30.000 experts globally. IEC International Standards and conformity assessment underpin international trade in electrical and electronic goods. They facilitate electricity access and verify the safety, performance and interoperability of electric and electronic devices and systems, including for example, consumer devices such as mobile phones or refrigerators, office and medical equipment, information technology, electricity generation, and much more.
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