Solar power runs most spacecraft near Earth, from satellites to the International Space Station. Above the atmosphere there is no weather, sunlight is stronger than at the ground, and some orbits see little or no night. Further out, the picture changes: Mars dust and the dim light around Jupiter set hard limits, and NASA’s two largest Mars rovers, Curiosity and Perseverance, are nuclear-powered, not solar.
The idea of beaming solar power down to Earth from orbit is still at the study and demonstration stage. The UK has been one of the more active countries in studying it. Here is how space solar works today, where it falls short and how close space-based solar power really is.
Why solar dominates near Earth
Spacecraft near Earth pair solar arrays with batteries, which keep systems running while the craft passes through Earth’s shadow.
Space arrays usually use high-efficiency multi-junction cells made from III-V semiconductors rather than the silicon found on roofs. For illustration: the best III-V multi-junction research cell without a light concentrator reached 39.46%, made in 2021 by the US National Renewable Energy Laboratory (now the National Laboratory of the Rockies), against about 27-28% for the best silicon cells. Those are records measured under sunlight at the Earth’s surface, not ratings for space cells, but they show why space agencies choose III-V cells. For how solar cells work on the ground, see our guide to solar energy.
Sunlight weakens with the square of distance from the Sun. At Jupiter, about five times further from the Sun than Earth, it is about 25 times weaker, which shapes the design of every solar-powered spacecraft sent that far.
The International Space Station
The ISS’s eight original solar array wings can generate up to 160 kW in orbital daylight, with about half of that stored in batteries for the dark part of each orbit.
Since 2021 NASA has added six ISS Roll-Out Solar Arrays (iROSAs), each producing more than 20 kW. They were installed in pairs in June 2021, December 2022 and June 2023, partly covering the older arrays. A roll-out array unrolls like a carpet from a compact drum, saving space at launch. NASA’s figures for the upgraded total vary, but with all six new arrays the station can generate more than 200 kW.
Mars: solar versus nuclear
Not every Mars rover runs on sunlight.
Curiosity (landed 2012) and Perseverance (2021) are nuclear-powered. Each carries a Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), which turns heat from decaying plutonium-238 into about 110 W of electricity at the start of a mission. It is designed to last 14 years, and its waste heat helps keep the rover warm. Neither rover has main solar panels. NASA notes that solar power “always runs the risk of not receiving enough sunlight”.
Spirit and Opportunity were solar-powered. Opportunity was designed for 90 days and worked for more than 15 years, from 2004 to 2019, driving 28.06 miles (45.16 km). In June 2018 a planet-wide dust storm starved its panels of light. Its last contact was on 10 June 2018, and NASA declared the mission over on 13 February 2019 after sending more than a thousand recovery commands. Over the years, Opportunity’s panels were cleaned from time to time by gusts of wind.
InSight, a solar-powered lander, shows the same problem. Dust cut its energy production by about 90% by mid-2022. Engineers improvised by trickling soil from the robotic arm’s scoop so that wind-blown grains would sweep dust off the panels. NASA retired the mission on 21 December 2022, after last contact on 15 December.
The lesson: dust is the main limit on solar power on Mars, which is a large part of why NASA’s biggest rovers went nuclear.
Deep space: Juno and Europa Clipper
The further a mission travels from the Sun, the larger its arrays must be.
Juno, which orbits Jupiter, carries three 9-metre (30 ft) solar arrays with 18,698 cells. They produce about 14 kW at Earth’s distance from the Sun, but around 500 W at Jupiter. On 13 January 2016 Juno became the most distant solar-powered spacecraft yet, about 793 million km from the Sun, beating the European Space Agency’s Rosetta (792 million km, 2012).
Europa Clipper, launched on 14 October 2024, spans more than 30 metres (100 ft) with its arrays deployed. Each array is about 14.2 m by 4.1 m, and together they will provide about 700 W at Jupiter.
Missions beyond Jupiter, such as Voyager, Cassini and New Horizons, use radioisotope power instead, because sunlight there is too weak for practical arrays. Solar sails, sometimes mentioned in the same breath, are different again: they use the pressure of sunlight for propulsion and do not generate electricity.
Space-based solar power: beaming energy to Earth
Space-based solar power (SBSP) means collecting sunlight on very large satellites in high orbit, where they are in sunlight almost all the time, and beaming the energy to Earth, usually as microwaves, to large receiving antennas. As of October 2026, no country receives usable grid power from space.
The UK angle
A study by the engineering consultancy Frazer-Nash for the then Department for Business, Energy and Industrial Strategy, published on 27 September 2021, concluded that SBSP is “technically feasible” and could be cost-competitive. Its reference design, CASSIOPeiA from the UK firm International Electric, is a satellite of about 2,000 tonnes and 1.7 km across in geosynchronous orbit (35,786 km up). It would beam microwaves to a ground antenna (rectenna) measuring 6.7 km by 13 km, delivering about 2 GW to the grid.
The study projected an orbital demonstrator by 2031 and an operational system by 2040, with development costs of £16.3 billion (net present value) and electricity at about £50 per MWh (at a 20% hurdle rate, assuming commissioning in 2040). It said cheap, reusable launch would be essential. These are a consultancy’s projections, not government targets.
The Department for Energy Security and Net Zero’s SBSP Innovation Competition then made nine awards totalling about £5.5 million (as listed on GOV.UK in April 2024). They included about £1.2 million to Space Solar Engineering Ltd in Oxford for CASSIOPeiA design work; £999,513 to the Satellite Applications Catapult for the CASSIE antenna experiment, plus £424,989 for a concept study; £960,607 to Queen Mary University of London for wireless power transmission; and £770,666 to the University of Cambridge for concentrator solar cells. A further DESNZ-commissioned study in 2025 looked at smaller-scale systems that could be deployed in the 2030s.
In October 2024 a UK company, Space Solar, signed a memorandum of understanding with Transition Labs and Reykjavik Energy aiming at 30 MW of space-based solar for Iceland by 2030. That is a company target, not a binding commitment.
Rest of the world
Caltech (US) launched its Space Solar Power Demonstrator, SSPD-1, in January 2023. Its MAPLE experiment demonstrated wireless power transfer in space on 3 March 2023 and beamed detectable power to a receiver at Caltech in Pasadena, a first for the field. The power involved was tiny, and no usable electricity was delivered on the ground.
Japan has a JAXA-linked small-satellite project, OHISAMA, designed to beam microwaves at 5.8 GHz to a ground antenna.
The European Space Agency approved its SOLARIS preparatory programme in 2022 to inform a possible decision in 2025 on a full development programme.
The hurdles
The main obstacles are launch cost and mass (thousands of tonnes for a gigawatt-scale satellite), robotic assembly in orbit, beam safety and public acceptance, and the size of the ground antennas. For more on the idea, see our news report on solar power from space.
Frequently asked questions
Are Curiosity and Perseverance solar-powered?
No. Both run on a nuclear generator (MMRTG) that turns heat from decaying plutonium-238 into about 110 W of electricity at the start of the mission. Neither has main solar panels.
Which Mars rovers used solar panels?
NASA’s Spirit and Opportunity rovers were solar-powered, as was the InSight lander. Opportunity worked for more than 15 years, from 2004 to 2019, before a planet-wide dust storm cut off its power.
Why do missions to the outer planets use nuclear power?
Sunlight weakens with the square of distance from the Sun. At Jupiter it is about 25 times weaker than at Earth, so Juno needs three 9-metre arrays to make around 500 W. Beyond Jupiter, missions use radioisotope generators.
Is space-based solar power already supplying electricity?
No. As of October 2026 no country receives grid power from space. Caltech’s SSPD-1 showed wireless power transfer in space in 2023, but at tiny power levels.
What is the UK doing on space solar?
The government commissioned the 2021 Frazer-Nash feasibility study, which projected an operational system by 2040, and its innovation competition has awarded about £5.5 million to universities and companies. These are research steps, not plans to build a power station. Back on the ground, our guide to solar panels for your home in the UK covers what you can install today.
How efficient are space solar cells?
Space arrays use multi-junction III-V cells. The best research cell of this kind, without a concentrator, reached 39.46% in 2021 under surface sunlight conditions, compared with about 27-28% for the best silicon cells.