Flying towards 10,000 m… and beyond
You might think solar energy with its infinite potential has become second nature, woven seamlessly into our habits, political decisions and new developments. Yet the reactions and comments on our social media remind us there is still work to be done! There are still sceptics who question the purpose of the challenges our electric solar aircraft takes on. This is exactly why our mission remains so important. Each flight by HB-SXA – like those in June preparing for this summer’s 10,000m flight over the Swiss Alps – is another symbolic step forward. Fulfilling the dream of Icarus: flying ever higher, without burning fossil fuels – or our wings. A powerful statement that a decarbonised future is already in motion. We invite you to join us for what promises to be an exhilarating summer!
Performance flights
Around 10 flights this month enabled us to perfect the variable-pitch settings of our new propeller and confirm the performance gains. The news is promising as we prepare to reach FL330 this summer: HB-SXA is climbing faster than ever. The test campaign ended with a performance flight on 25 June, when our test pilot reached FL170 – over 5,000 metres. This was also a chance to test the automatic power cut-off protection system – vital for optimising battery use and solar energy at high altitude. Now we head to Sion Airport, where the team will settle in to prepare for the 10,000 m attempt!
Truck vs. plane
It was like a scene from an action film on 23 June at Payerne Airport. An electric articulated lorry, the Volvo FH Electric T from our partner Planzer, sped along at 80km/h as our aircraft flew overhead and accelerated to 120km/h to win this ‘electric race’! The high-speed choreography was captured by helicopter. The goal – to raise awareness about switching to clean mobility to protect the planet – was achieved in full: numerous media outlets picked up the Keystone-ATS photo of the SolarStratos-liveried lorry, capable of carrying up to 20 tonnes of cargo with minimal CO2 emissions, being buzzed by our featherweight solar-powered aircraft.
Read the full story on Watson.ch.
Special Stratostime
To (re)experience the challenge with the Planzer electric truck, take a look at the special Stratostime edited by Stéphane Chopard, in charge of the videos and films documenting the SolarStratos mission. In one minute, this clip captures the intensity of the moment and the power of the image in promoting low-carbon transport for a more sustainable world
Flying with Fred To
A wonderful return to the future. In early June Raphaël Domjan and Fred To shared a flight rich in symbolism. To, a pioneer of the first solar adventure in 1978, took to the skies once more with today’s pioneer Domjan for an electric flight over Switzerland. A few days earlier, To – the co-designer of the world’s first solar aircraft – had also joined remotely from England for the opening of the PlanetSolar Foundation exhibition, which runs until 23 October at the Kosmos space of Primeo Energie in Münchenstein (BL).
The winner’s flight
Our online game – where you collect suns while avoiding clouds – culminates each year in a contest. This month the 2024 winner enjoyed his prize: an electric flight in a Pipistrel with Raphaël Domjan. Congratulations to Daryl, who achieved several top-10 finishes, including the current record of 17,900 points. For his flight from Ecuvillens he was joined by his sister Chloé, who also excelled in the game. Now it’s your turn! Enter the 2025 edition – it’s an unforgettable thrill to chase the sun across the sky.
Join the fun here: www.solarstratos.com/aventure/game.html
Worthy of an action film! On Tuesday 23 June, a spectacular demonstration took place at Payerne airport: an ultra-modern Planzer electric semi-trailer (the Volvo FH Electric T) rolled along the taxi-way, while the experimental electric and solar-powered SolarStratos aircraft flew alongside at 80 km/h, before accelerating to 120 km/h. A feat of synchronisation with a clear objective: to raise public awareness of the need to move towards clean mobility that preserves our planet, its climate and its biosphere.
There’s no better way to get the message across than this duo show of electric vehicles – one capable of carrying up to 20 tonnes of freight with very low CO2 emissions, the other flying on solar power, and this summer aiming for the highest flight ever made by a manned electric aircraft over the Alps. Then the ultimate flight to the stratosphere!
The media have covered this challenge for the future: https://www.swissinfo.ch/fre/payerne%3A-duel-in%C3%A9dit-entre-un-avion-solaire-et-un-camion-%C3%A9lectrique/89572474
HB-SXA finds its voice again
Latest news: Like the rest of the SolarStratos team, HB-SXA had been eager to return to the skies. Since 19 May, the aircraft has been flight-ready — and keen to make itself heard, its new variable-pitch propeller bringing a noticeable change in tone, with a deeper, more resonant sound! With the official Permit to Fly from the Federal Office of Civil Aviation in hand, Raphaël Domjan and our test pilot remained on standby, awaiting the first favourable weather window.
That window finally opened on Friday 23 May, when the first flight of the year was successfully completed — just ahead of an approaching thunderstorm. This 107th flight took place under the attentive gaze of a special guest: Mark Rocket, space enthusiast and CEO of Kea Aerospace, who is soon to become the first New Zealander in space as part of Blue Origin’s next mission. The result of this inaugural flight of 2025? Several performance enhancements — a promising beginning as the team looks ahead to the planned 10,000-metre flight this summer.
Ground thrust tests: a propeller that packs a punch!
Optimisation. Since 13 May, our home base in Payerne has been alive with activity. One major advantage of ground-based thrust testing? It can continue regardless of the weather — grey skies and rain included. A full sequence of tests was conducted according to a precise protocol, including fine-tuning the pitch of the variable propeller to optimise climb rate in relation to energy consumption.
The outcome confirmed the aircraft’s impressive performance: with HB-SXA securely anchored to the ground, the dynamometer recorded nearly 200 kilograms of thrust. And yes — thrust is the technically correct term, even if, like one of our online followers who raised the question, we tend to picture the propeller as ‘pulling’ the aircraft. Propeller thrust even has its own equation — in newtons, thrust (N) = mass (kg) × acceleration (m/s²).
We can even hear the birds sing!
Almost completely silent. One of the standout benefits of a solar-electric aircraft like SolarStratos — though several of you have rightly noted it isn’t entirely noise free — is just how much quieter it is compared to conventional aircraft (especially when set against the roar of FA/18 jets ripping through the skies above Payerne). While reviewing footage from recent ground tests, we were delighted to hear birdsong in the background — a gentle reminder of the aircraft’s near-silent operation.
Beyond offering a decarbonised way to experience the joy of flight, SolarStratos brings with it the added advantage of remarkably low noise emissions.
A curious new bird aboard: welcome Baptistou!
Team update. If you’ve been following us on social media or through our website, you may have spotted a new addition to the SolarStratos team. Jean-Baptiste Loiselet (whose surname translates as ‘little bird’) — better known as Baptistou — has joined us to support the technical operations around this summer’s preparatory flight campaigns, first in Payerne and then in Sion, ahead of our planned attempt to reach 10,000 metres. Armed with the insights gained last year, the team is more determined than ever to achieve this milestone — and Baptistou brings valuable expertise. A seasoned figure in solar aviation, he has spent the past several years developing a remarkable self-launching solar glider capable of autonomous flight. In 2022, he completed a fully solar-powered, solo tour of France in his aircraft, Sol.Ex. Find out more about his pioneering work at https://www.desailespourlaplanete.fr.
The final tests and adjustments are underway this week at the Swiss Aeropole in Payerne to kick off the preparatory flight campaign for the altitude record attempt scheduled this summer in Sion — and which the whole team is convinced will be a success!
The “song” of HB-SXA once again echoed through its home base. On Monday, various thrust tests were carried out with the aircraft secured to the ground, at different engine speeds and with various settings of the new variable-pitch propeller. The results were (very) conclusive: a thrust of around 200 kg was measured.
To the ear, one noticeable difference: the propeller’s sound is now one or two tones lower than before! But what beautiful solar music it is.
Ground tests, including taxiing, are continuing. We can’t wait to hear HB-SXA soaring through the skies again. It’s just around the corner…
When Solar Power Reaches New Heights
In Paris, the Avant-Garde Foundation brought together adventurer-author Sylvain Tesson and solar pioneer Raphaël Domjan for a breakfast event titled Collisions — and the ideas certainly soared. With both speakers deeply committed to sustainability and the future of our planet, the exchange inspired attendees like explorer Gauthier Toulemonde and left a powerful message: when visionaries meet, altitude is more than just physical.
Meanwhile, back on the ground — or rather, back in the air — the HB-SXA solar aircraft has returned from its maintenance in Germany. It’s now back at its home base in Payerne, fully restored and ready for flight. Test flights are scheduled from mid-May, aiming to assess new performance benchmarks — including altitude capabilities. A full weigh-in, à la professional boxing, is also on the schedule.
The sky’s the limit, once again.
Balanced to Perform
The HB-SXA didn’t just come back refurbished — it came back upgraded. A brand-new variable-pitch propeller now allows for more efficient climb performance. Ground tests have confirmed the precision of its balance and function, and early listeners report a subtly different, more electric hum from its engine.
This May’s flight tests will also include assessments of two new half-batteries, integrated to boost the aircraft’s overall energy potential.
Flying with the Sun
PV Magazine Spotlights SolarStratos: SolarStratos earned top billing in PV Magazine this month with an in-depth article by Ann-Marie Corvin, highlighting the project’s commitment to pushing the boundaries of solar-powered aviation. The centerpiece? A bold attempt this summer to reach 10,000 meters over the Swiss Alps — a potential world record in solar flight. A human-scaled mission, with sky-high ambitions. https://www.pv-magazine.com/2025/04/07/flying-with-the-sun/
To the Land of the sun god Inti
PlanetSolar II Reaches Lake Titicaca
While SolarStratos climbs the sky, PlanetSolar II sets sail — this time on Lake Titicaca, the world’s highest navigable lake, and a place deeply rooted in the sun-worshiping traditions of the Inca and their god Inti. The solar-electric boat, operated by the PlanetSolar Foundation, reached the Bolivian shores in late April to begin a scientific and promotional mission focused on solar-powered navigation.
In a touching ceremony in Puno, the Swiss Ambassador to Bolivia officially handed over the vessel to the Binational Authority of Lake Titicaca. Full story and images at www.planetsolar.org.
P.S. Even the trailer got a touch of sunshine! Back from Germany, it was time for a little refresh — and Raphaël Domjan himself took to the task with good humor and a pressure washer in hand. A fresh coat of paint, a bit of elbow grease, and voilà: ready for the next adventure.
Podcasts are in full bloom this spring!
A podcast can tackle weighty issues and major challenges — AND retain a sense of humour. Beacause joy matters. Because conversation brings us together. While HB-SXA has been undergoing a full winter maintenance programme — now successfully completed in Germany — Raphaël Domjan had the honour this month of being the second guest on the #GettingSerious podcast hosted by Greater Geneva Bern area (GGBa) and Woody Wade.
The episode aired on March 10 and was shared across SolarStratos social channels. And because podcasts seem to be setting the tone for early 2025, you can also catch the SolarStratos team and Raphaël on the podcast Inspirez – from Thursday 27 March – where they share their vision and aspirations for a greener, more sustainable sky — and planet. Listen now at www.inspirez.co.
“Another cup of iced tea, Woody?”
The #GettingSerious podcast took a deep dive into the bold and optimistic mission behind SolarStratos and the PlanetSolar Foundation. The conversation centred on the upcoming record-breaking flight planned for this summer – aiming to reach 10,000 metres above the Alps in a solar-powered aircraft — a key milestone towards the ultimate goal of reaching the stratosphere, powered entirely by the sun.
A delightfully British moment added levity to the discussion when host Woody Wade asked Raphaël about the drink he had in front of him during the interview. It turns out that our eco-adventurer’s fuel of choice is… Migros iced tea! Raphaël even joked that it might just become a global sensation! Full episode: https://ggba.swiss/en/category/getting-serious/. ‘Cup of tea’ moment here.
Coming up: A meeting of minds with Sylvain Tesson
Following his live appearance on ARTE on February 6, Raphaël Domjan is preparing for another high-profile encounter. On April 8, he will join acclaimed author and adventurer Sylvain Tesson for a special edition of the Avant-Garde Foundation’s breakfast talks. The theme is Modern explorers: when innovation charts a course to a sustainable world. This exchange promises to be rich in ideas and inspiration, as two explorers — one of words the other of the skies — reflect on how we can rethink our relationship with the planet. Tesson’s latest book, Les Piliers de la mer, is both a tribute to Earth’s last untouched landscapes and a powerful call to action for the protection of our planet.
Bon voyage PlanetSolar II!
While SolarStratos sets its course for the stratosphere, the PlanetSolar Foundation continues to explore both oceans and lakes. The PlanetSolar II expedition on Lake Titicaca is now underway, and you can follow the progress of this scientific mission here: www.planetsolar.org.
As of late March 2025, as Raphaël Domjan was collecting customs documents at the Peruvian Embassy in Berne, PlanetSolar II has successfully passed through the Panama Canal — exactly 14 years after the MS PlanetSolar solar-powered catamaran crossed the same waters during its historic round-the-world voyage.
It’s a moment rich with memory, emotion and renewed purpose — as we look to the future and the next chapter of our solar-powered journey. A shared pursuit continues for a decarbonised, sustainable world where dreaming and flying remain possible.
Are you coming along? Thank you for following us — and for your continued support!
Join the mission
Want to join the adventure? Become part of the mission as a SolarFriend, SolarSupporter or SolarMember — or take the journey further as a SolarPilot, SolarNavigator or SolarVoyager! Our boarding gate is always open, and we look forward to welcoming you onboard!.
As storm clouds gather over the United States, one striking graph has caught Raphaël Domjan’s attention. The data underscores the critical role of solar energy in the fight to save our climate —whether or not Donald Trump cares to acknowledge it. Yes, “Sun is fun, Mr President!” SolarStratos has already been busy in the first few months of this year highlighting its potential – notably on ARTE on February 6. This newsletter announces another high-flying event — also cause for celebration: you are reading the 100th edition of our newsletter!
The sun is Mr Clean
The graph illustrating the rapid rise of solar energy — outpacing coal, gas, and oil — confirms that it is THE resource of the future and our best hope for saving the climate. Raphaël Domjan summarised this powerfully: “It is the cheapest, safest, least polluting, and least resource-intensive energy source. It also bridges the gap between the Global North and South, enabling developing countries to limit their reliance on polluting energy sources. Above all, it is the most inclusive energy — everyone can produce their own. The sun shines for everyone.” Yes, even Mr Trump can get sunburnt.
28 Minutes, down to the wire!
Precision timing saw Raphaël Domjan make it to ARTE’s studio just in time on February 6. A delayed TGV meant a last-minute motorbike taxi dash to reach the set of 28 Minutes, where the discussion centred on the 100% eco-friendly aircraft. Joined by engineer Laurent Castaignède and aerospace journalist Caroline Bruneau, Raphaël Domjan engaged with host Élisabeth Quin, delivering a crucial message: “We must face the challenges ahead with optimism! We need to offer young people a vision for the future — without it, we risk dragging our civilisation into despair, stagnation, and the status quo. It’s not just aeroplanes that need to go green; our world and our skies must too!”
Photovoltaic cells checked by the CSEM
As previously mentioned, HB-SXA underwent a comprehensive inspection this winter at ElektraSolar in Germany. Meanwhile, on 5 February, the solar cells on our aircraft were also checked by CSEM, a Swiss centre of excellence partnering the mission: visual inspection, performance measurement, thermography, bonding: everything is ok. With maintenance now successfully completed, our experimental solar-electric aircraft is set to return to its home base in Payerne in the coming days. It will be reassembled in March before taking to the skies for its first post-maintenance flights equipped with new enhancements, including two additional half-batteries. On the horizon this summer in Valais: a new 10,000m world record attempt.
100th newsletter!
Yes, you read that right—this is the 100th edition of the SolarStratos newsletter!
The very first issue was sent out on December 24, 2014, just in time for Christmas. It chronicled the first steps of our adventure, that already included the CSEM. Since then, over the course of these 100 newsletters and twenty news items, we’ve come a long way — including a year-long pause due to the Covid pandemic. Now, ten years and 100 flights later, we stand on the brink of a historic achievement: the world altitude record. With our variable-pitch propeller poised for action, the entire team is ready to make it happen for you this summer! Are you ready for take-off?
ARTE’s ‘28 Minutes’ magazine looked at the aviation of tomorrow on Thursday 6 February. Elisabeth Quin invited @Raphaël Domjan – in his pilot’s jacket, if you please! -, to join her, with engineer Laurent Castaignède and aviation journalist Caroline Bruneau.
Perspectives, hydrogen, 100% green aircraft, airships? The discussion – and the images on the screen, including HB-SXA from SolarStratros – was… showy.
“I hope my message was clear: we need to approach the challenges of the future with optimism! If we don’t give young people prospects, we risk creating a civilisation of despair, with stagnation and the status quo. It’s not aeroplanes that need to become green, but our world and our skies”, commented the pilot of the SolarStratos mission after the programme.
Taking part in this programme was great recognition of the work being done by SolarStratos and the PlanetSolar Foundation. It was also a great way of putting the spotlight on our partners. And for solar energy!
Missed this “28 Minutes”: here it is.
Three landmark moments
The entire SolarStratos team wishes you an inspiring and fulfilling 2025! Our year promises to be high-flying… and we have at least three landmark moments in store. First, the 10,000 m record attempt, which we hope will be successful this summer over the Swiss Alps. Then, PlanetSolar Foundation’s exhibition ‘Solar Pioneers’ which will be unveiled for the first time to the German-speaking public from April to October at Primeo Energie in Basel. And finally, the PlanetSolar II expedition, which will take on new heights at nearly 4,000 m above sea level on Lake Titicaca this summer. Ready to embark on the next chapter of our solar explorations? Let’s cast off!
Full maintenance in Germany
This winter our prototype solar electric aircraft, which has notched up over 100 flights, is undergoing comprehensive maintenance in Germany. This check-up is also an opportunity to implement improvements identified after the 2024 campaign over the Alps. Next month, HB-SXA will return from its health retreat at Elektra Solar in Germany equipped with two additional half-batteries, a refined variable-pitch propeller, and an enhanced horizontal stabilizer – fully prepared for the 10,000 m record attempt in the summer.
First conference of the year
Founder and pilot of SolarStratos, Raphaël Domjan is also a renowned lecturer. He gave his first lecture of the year 2025 at ESSEC Business School in front of a thousand students. They gave him great feedback: “ Their energy, optimism and ideas gave me immense hope. It was one of the first highlights of my year. Let’s build a better future together. ”
Online competition: and the winner is…
Have you entered our ongoing online competition, available on our website ? Every year a winner receives a prize, and in 2024 that person was Daryl, who achieved several top-10 performances with a top score of 17,900 points. He wins an exclusive flight in an electric aircraft with mission pilot Raphaël Domjan. We are delighted to welcome Daryl onboard for this unique experience, combining innovation with respect for the environment. Don’t miss out – the 2025 edition of the competition is now open!
‘Solar Pioneers’ auf Deutsch bitte!
“ Die Solarpioniere ”: the PlanetSolar Foundation exhibition featuring SolarStratos, will be presented for the first time in German-speaking Switzerland from April 16 to October, at Primeo Energie in Basel. And of course, auf Deutsch bitte! The exhibition has been translated to German and features an additional module with exciting new exhibits, such as the first solar-powered FM radio and one of the first photovoltaic cells in history. So, if you’re in Basel this year drop in!
A tribute to pioneer Jacques Bonvin
The Swiss solar energy pioneer and visionary Jacques Bonvin died recently in a tragic accident. He was the very first sponsor of Raphaël Domjan and his brother Alexis. Raphaël Domjan paid tribute to the co-founder of Solstis, who had supported them early on in the SolarStratos project: “At a time when we only had ideas and dreams, he trusted us, seeing in solar energy the power of the future, long before many realised its potential,” he said. “Our heartfelt thoughts are with his family and loved ones.”
Infiltrated! An undercover spy
captures 2024 exploits on film
Have you been following our adventure this year? Did you experience the thrills and suspense alongside us from Payerne to Sion and back, in the Alpark hangars that made us so welcome, during the flights over the Alps and the great Matterhorn, soaring to 5,993 metres? Filmmaker Stéphane Chopard went undercover to capture our high-flying year, and it is a spine-tingling experience. Narrated by Raphaël Domjan this video is our Christmas gift to you, with shared hopes of reaching even greater heights in 2025. Together we aim to push the boundaries of solar energy and demonstrate its untapped potential. A decarbonized world is within reach!
Discover Stratostime 2024 here:
A visionary speaker, inspiring change
“To be a pioneer is to inspire future generations.” This quote resonated deeply with one attendee at Raphaël Domjan’s recent conference in Narbonne, France, hosted by AXA France. This video of the event captures the essence of SolarStratos’ mission and vision, and we’re delighted to share it with you:
As the founder and pilot of SolarStratos, Raphaël is not only an innovator but also an exceptional speaker. His passion and commitment to a sustainable, decarbonised world are contagious. Recently he also presented at Lakal in Saarlouis, Germany, and at the API Days Energy event in Angers, France, on December 12.
Four powerful moments from the AXA conference:
It’s winter maintenance time!
HB-SXA is on its way for a thorough winter check-up. Tucked up in its trailer, the plane is headed to Elektra Solar GmbH in Landsberg, Germany, for a full inspection that will include the engine, batteries, and more. The journey itself had its moments! The images of us crossing Lake Constance, for instance, prompted this amusing comment: “An electric, solar-powered plane… in a truck… on a boat? You SolarStratos people are mad!” Indeed, we are!
Season’s Greetings and shared hope!
As 2024 draws to a close against a backdrop of wars, uncertainty, and hesitation around urgent climate decisions, the SolarStratos team remains driven and optimistic. We are determined to seek out and promote solutions, proving through spectacular challenges that it’s possible to dream big and fly high – higher than the Matterhorn, even to the stratosphere – powered solely by solar energy. Thank you for joining us on this journey to explore new pathways toward a decarbonized and more sustainable world. We are proud to share this hope with you as we wish you a joyful holiday season and a radiant start to 2025.
