Solar power from Earth's orbit

16 January 2025

Imagine kilometre-long solar satellites that tap into the inexhaustible energy of the sun from orbit and transmit it to Earth using microwaves: What may sound like science fiction is being considered by governments, tested by researchers and actively driven forward by companies. And this technology might in the future end up supplying Iceland, the United Kingdom and the EU with solar power from space.

Photovoltaic systems are amazing. They convert the sun’s energy into electricity and are cheaper than any other form of energy generation. On Earth, however, they labour under a natural disadvantage: As is well known, the sun does not shine at night or from behind cloudy skies, and its rays are weaker in the winter. But even on summer days with bright blue skies, not all the solar energy actually gets to the panels: More than half of the radiated energy is absorbed or reflected by the Earth’s atmosphere.

So why not simply capture the sunlight where it shines around the clock and even more intensely than on Earth: in space? This would also provide renewable baseload energy throughout the year to stabilise the electricity grids.

While the concept of space-based solar energy may not be new, it has always been considered almost impossible to implement. However, increasing demand for renewable energies and falling prices for solar panels and space flights might now bring its realisation within reach. The British government, for example, announced in 2022 that it would invest around 15 billion pounds (about 18 billion euros) in this technology. A first test satellite is to be launched in 2030, and from the early 2040s onwards, large solar power plants in orbit might then cover 15 percent of the UK’s energy needs and replace ever larger numbers of fossil fuel power plants. That, at least, is the plan behind the “Space Energy Initiative”, in which British ministries, research institutions and aerospace companies have joined forces.

In November 2024, the Space Solar start-up publicly announced a particularly ambitious plan: The British company intends to supply Iceland with electricity via satellites as early as 2030. According to this plan, the project will start with a “smaller” prototype with a diameter of 400 metres which, if all goes well, will then supply electricity to around 3,000 Icelandic households from an altitude of some 37 kilometres. This would make the satellite almost four times as big as the largest man-made object ever launched into space, the ISS.

The start-up, which is cooperating with an Icelandic energy company, plans to send more solar modules into geostationary orbit by 2036. Once in situ, they will be assembled by drones and connected to each other to create a final diameter of 1,700 metres with the aim of sending many gigawatts of electricity to Earth. This would correspond to the capacity of a medium-sized nuclear power plant.

To fulfil this ambition, radiation from the sun will first be directed onto the solar panels by movable reflectors. The electricity thus generated will be converted into microwaves and transmitted to Earth. Here, the microwaves will be picked up by huge arrays of antennae and converted back into electricity. And the brilliance of this idea is that microwaves can theoretically be sent to any place on Earth where electricity is needed – provided that the right kind of receiving station is installed there.

With a calculated area of 78 square kilometres, these arrays of antennae would take up almost as much space as a small city like Würzburg. According to Space Solar, they could therefore be installed in sparsely populated areas, for example, and the land could be used for agriculture at the same time. But installation at sea, for example in offshore wind farms where they could then be connected directly to the existing power grid, would also be feasible.

Researchers at the California Institute of Technology (Caltech) have tested and demonstrated in practice that the principle is workable. In June 2023, the team succeeded for the first time in transmitting solar power to Earth in the form of microwaves. The researchers also tested various photovoltaic cells and a fold-out structure that will later serve as a solar power plant. All three test series were successful, although not everything went according to plan. For example, the deployment mechanism caused problems, but the researchers were able to remedy them.

This is a far cry from clarifying all the technical questions, of course: After all, kilometre-sized satellites have never been assembled in space using drones. Electricity transmission via microwave has also not yet been realised at the required scale – even if, as Space Solar emphasises, experiments on Earth have repeatedly confirmed the workability of the principle behind it. And what would happen if space debris were to punch holes in the solar sails, which are as huge as they are expensive, and render them unusable? According to the British start-up, this risk would be manageable. This is because in geostationary orbit, where the satellites are to be used, there is comparatively little junk floating around. If a collision were to occur, Space Solar promises that the satellites’ modular design would prevent a total failure and ensure that the collision would have only an insignificant impact on the overall performance of the plant.

As things stand, the cost of the technology is still considered a critical factor: To be able to withstand the adverse conditions, solar cells for use in space require much more elaborate processing and are therefore currently a hundred times more expensive than those destined for roofs, balconies and fields. And they age faster than they would on Earth, into the bargain. And then you also have the costs of carrying the modules into space, maintenance flights and spare parts. All told, according to a study by NASA, electricity from space could be 12 to 80 times more expensive than that generated by solar or wind power plants on Earth.

But things would not necessarily have to stay that way, according to the researchers: If the components were to become even more durable, the solar satellites be produced efficiently in large quantities and transport costs fall at the same time, electricity from space could catch up economically with that generated by terrestrial renewables. Space Solar is pinning great hopes on reusable rocket systems, such as those being developed by SpaceX with its Starship. For the consulting firm Frazer-Nash, these are also considered a key factor for the economic viability of the technology.

Concept studies by the European Space Agency ESA, which is exploring the possibilities of universal current in its Solaris project, come to a similar conclusion: Although the investment costs for electricity from space are high, they are likely to be offset by the long-term economic benefits.According to the study’s authors, however, further research and consistent international cooperation in the development of the regulatory framework and the strategic planning of the projects are crucial to “exploit the full potential of this innovative approach”. If all these were to be in place, “space-based solar energy could play an essential role in tackling the energy challenge as early as the 2030s,” says Sanjay Vijendran, head of the Solaris project.

Based on Solaris’ preliminary work, the EU is expected to decide at the end of 2025 whether a development programme for such satellite systems should be launched with the ultimate aim of supplying the European continent with green electricity from orbit.