A solar powered drone is an unmanned aircraft with solar cells on its wings. By day the cells power the electric motors and charge batteries, and the batteries keep it flying overnight. The working examples are very light aircraft with huge wings that fly in the stratosphere for weeks at a time, mainly for connectivity and surveillance. The term “solar drone” is also used loosely for ordinary quadcopters fitted with small solar panels, which are a different thing.
The most common use of drones in renewable energy today is not stratospheric flight but inspection. Drones with thermal and visual cameras are used to find faults on solar farms and to inspect wind turbine blades. For small solar plants, a 2024 study found them cheaper than crewed aircraft; for large plants, the aircraft was cheaper.
How it works
A solar powered UAV relies on a simple daily cycle. During the day, solar cells on the upper wing surface generate electricity, which runs the motors and charges the onboard batteries. At night, the aircraft runs on its batteries until sunrise. The energy collected by day has to exceed what the aircraft uses overnight.
These aircraft are known as HAPS, short for high-altitude platform stations or high-altitude pseudo-satellites. They fly slowly in the stratosphere, above about 60,000 feet, where there are no clouds and little weather. They are used for mobile connectivity and Earth observation; AALTO also lists surveillance, disaster management, border protection and precision agriculture.
“Solar panel drones” sold for hobby use are different. A consumer drone such as the DJI Mini 4 Pro weighs under 249 grams and runs on an 18.96 Wh lithium-ion battery giving up to 34 minutes of flight. Such a small quadcopter has very little surface for solar cells, and we found no published performance data showing that an add-on panel meaningfully extends its flight. These are not solar aircraft in the engineering sense.
Real-world examples
Airbus/AALTO Zephyr (UK)
The Zephyr was run by Airbus Defence and Space for about a decade and is now being commercialised by AALTO, an Airbus subsidiary based in Farnborough, UK. The Zephyr S has a wingspan of 25 metres and weighs under 75 kilograms.
Its main endurance flights:
- 2018: the Zephyr S flew for almost 26 days (25 days and 23 hours) on its maiden flight from Arizona, launched on 11 July 2018.
- 2022: a Zephyr 8 flown for the US Army from Yuma Proving Ground, Arizona, stayed up for 64 days, 18 hours and 26 minutes before the flight “unexpectedly” ended over the proving ground on 18-19 August 2022. Media reported it as a crash; no injuries were reported.
- 2025: Zephyr flew for 67 days, 6 hours and 52 minutes. It launched from AALTOPORT in Kenya on 20 February 2025 and ended on 28 April over a designated area of the Indian Ocean, crossing seven flight information regions. AALTO says this broke a world record for the longest flight that had stood for half a century; we found no independent ratification by a record body.
AALTO says Zephyr has logged over 5,000 flying hours, which it calls the most for any uncrewed fixed-wing HAPS. As of October 2026, Zephyr is pre-commercial. In May 2025 AALTO said it was targeting initial entry into service in Japan during 2026; in February 2026 it named Australia as Zephyr’s next operating site; and in March 2026 it agreed with Telkomsel to work towards initial operations in Indonesia from 2027. We found no confirmation that paid commercial service has begun.
BAE Systems / Prismatic PHASA-35 (UK)
The PHASA-35 is built by Prismatic Ltd, a BAE Systems subsidiary in Alton, Hampshire, with development starting in 2018. It has a 35-metre wingspan and a 15-kilogram payload.
It completed its first stratospheric flight in June 2023 from Spaceport America, New Mexico, climbing above 66,000 feet and flying for about 24 hours before landing safely. In late 2024 it made another 24-hour flight above 66,000 feet, carrying a payload more than twice as heavy as before. BAE Systems aims to have PHASA-35 ready for operational activity as early as 2026, for uses including intelligence and surveillance, 4G/5G communications and disaster relief. We found no published results of 2025-2026 flights.
Solar Impulse 2 (Switzerland)
Solar Impulse 2 is often cited in this context, but it was a crewed aircraft. It completed the first solar-powered round-the-world flight in July 2016, covering more than 42,000 km. In 2019, Skydweller Aero bought it and converted it into an uncrewed aircraft for surveillance and reconnaissance development. On 4 May 2026, it crashed into the sea off Mississippi; the cause has not been published.
Other projects
- Facebook Aquila (USA) - cancelled: a solar-powered internet-delivery drone with a wingspan comparable to a Boeing 737. It made its first full-scale flight on 28 June 2016 but was damaged on landing, and the US NTSB investigated. In June 2018 Facebook stopped building its own aircraft and closed its drone factory, saying it would work with partners instead.
- NASA Helios (USA) - lost: a historic prototype that reached an unofficial world-record altitude of 96,863 feet in August 2001. Its structure failed during a flight from Kauai, Hawaii, in June 2003, and it fell into the Pacific.
- Kea Atmos (New Zealand) - testing: a solar-powered high-altitude aircraft, still in testing.
What the numbers say
Energy density: the best rechargeable batteries store under 500 Wh/kg, about 25 times less than aviation gasoline. This is why solar drones must be extremely light and carry small payloads; the PHASA-35 carries 15 kg.
Solar farm inspection costs: in a University of Genoa and Wesii study of two roughly 1 MW solar plants in northern Italy (reported in 2024), a drone and a crewed aircraft both detected 99.6% of the most critical defects. The drone cost about EUR 800 a day and covered up to about 20 MW per working day. The aircraft cost about EUR 2,700 a day plus EUR 120 for the camera, and covered up to about 300 MW a day. For plants needing more than two working days of inspection, the aircraft was cheaper.
Wind farm inspection time: Ørsted reported in 2018 that automated drones from SkySpecs at its Burbo Bank Extension offshore wind farm cut blade inspection time from about 2 hours to about 20 minutes per turbine, and claimed downtime could be cut by up to 85%. In January 2026, RWE and partners demonstrated what they call the first autonomous drone inspection of offshore turbine blades while they keep rotating, at Rødsand 2 in Denmark, using a camera and an AI model to detect surface damage. Blade inspections are normally done with the turbine stopped, so the stated benefit is less lost generation; this was a demonstration, not routine practice.
Limitations
Despite the records, solar drones remain a niche technology.
Latitude and seasons: the energy budget is easiest to balance when days are long and nights short. SoftBank says long flight demonstrations have been done “mainly in low-latitude regions”, and that shorter winter days at higher latitudes make year-round flight difficult. Its NEDO-funded project is developing lighter, higher-energy batteries and stratosphere-optimised solar cells, aiming for a stratospheric demonstration in fiscal 2028. The UK lies at a higher latitude than Japan, so, by our reading, year-round solar HAPS flight over Britain has not been demonstrated; Zephyr’s record flight was flown from Kenya, near the equator.
Fragility: solar aircraft are light with large wings, which makes them vulnerable to turbulence. NASA’s mishap board blamed the Helios break-up on an inability to predict the reconfigured aircraft’s increased sensitivity to turbulence. The Zephyr loss after 64 days (2022), Aquila’s damaged first landing (2016) and the Solar Impulse 2 crash (2026) show the risks, although not all causes have been published.
Payload: because weight is critical, these aircraft carry small payloads, such as the PHASA-35’s 15 kg.
Regulation: Zephyr’s 2025 flight had to cross seven flight information regions, which shows that airspace coordination is part of the job.
The UK angle
Two of the best-known solar HAPS programmes are British: AALTO’s Zephyr, based in Farnborough, and BAE Systems’ PHASA-35, built in Hampshire. Both are aimed at connectivity and surveillance, and neither is confirmed in routine commercial service as of October 2026.
For renewable energy, the clearer UK example of drone use is inspection. Ørsted’s 2018 automated blade inspections took place at Burbo Bank Extension in Liverpool Bay, with 32 turbines of 8 MW and 80-metre blades. Drone inspection that uses AI to spot damage is part of a wider move towards data-driven operation of renewable energy systems, though the rotating-blade method is still at demonstration stage.
Frequently asked questions
How are drones used in renewable energy?
Mainly for inspection. On solar farms, drones with thermal cameras find faults such as hotspots, defective substrings and failed modules. On wind farms, they inspect turbine blades for surface damage. Ørsted reported cutting blade inspection time from about 2 hours to 20 minutes per turbine, and RWE has demonstrated inspecting offshore blades while they keep turning.
Can a drone fly forever on solar power?
No. The longest flight so far is Zephyr’s 67 days in 2025, according to AALTO. Each night the aircraft must survive on stored battery energy, so flights depend on long days, light batteries and good weather, and several aircraft have been lost. Year-round flight at high latitudes has not yet been demonstrated.
What is the longest a solar-powered drone has stayed in the air?
As of October 2026, AALTO says Zephyr holds the record with 67 days, 6 hours and 52 minutes of continuous flight, achieved in 2025; we found no independent ratification. Zephyr’s previous longest flight was 64 days and 18 hours in 2022, which ended in a crash.
Why don’t solar drones work well in UK winters?
Solar drones rely on sunlight to recharge their batteries for night flight. In winter, days are shorter at higher latitudes, so there is less time to collect energy and longer nights to survive. SoftBank says lighter batteries and more efficient solar cells are needed for year-round flight at latitudes such as Japan’s, and the UK lies further north.
What happened to Facebook’s Aquila solar drone?
Aquila made its first full-scale flight on 28 June 2016 over Arizona but was damaged on landing, and the NTSB investigated. In June 2018 Facebook closed its drone factory and stopped building its own aircraft, saying it would work with partners instead. The project was cancelled.
What are normal drones powered by, and can you add a solar panel?
Most consumer drones, such as the DJI Mini 4 Pro, run on rechargeable lithium-ion batteries; the Mini 4 Pro’s gives up to 34 minutes of flight. A small quadcopter has very little surface for solar cells, and we found no published data showing an add-on panel meaningfully extends flight time. Working solar aircraft have very large wings, from 25 metres on Zephyr S to 35 metres on PHASA-35.