Space, the new frontier of photovoltaics

This isn’t science fiction: producing photovoltaic energy directly in space and then beaming it down for use on Earth is the focus of the European Space Agency’s SOLARIS project, which we’re also involved in. The first major goal: to place a one-megawatt power plant in orbit by 2030. The results of the project will also be useful for “terrestrial” photovoltaic applications.

Space-based solar power has been around for more than 60 years: in fact, in 1958, the U.S. satellite Vanguard 1 was the first spacecraft to use a sub-one-watt power panel to operate a radio transmitter. The satellite stopped working a few years later, but it’s still in orbit: not only did it pave the way for the use of solar energy in space, it’s also the oldest human-made object orbiting the Earth. In the meantime, technology has advanced: today the International Space Station is equipped with more than 400 square meters of panels, which provide it with more than 240,000 times the energy of that first small installation on Vanguard 1.

But if it’s possible to supply solar power to spacecraft, can thisrenewable energyalso be beamed back to Earth, continuously and constantly, with greater efficiency, at all times of the day and without weather conditions interfering? That’s the challenge the SOLARIS project will be focusing on in the coming years.

Energy from space

The European Space Agency’s goal with the SOLARIS project, which started in 2023, is to generate energy in space to be used on Earth. The Enel Group is also taking part, thanks to our expertise in photovoltaic technology, grids and storage and, in general, in the creation of large-scale renewable energy generation plants and the subsequent management of the energy produced. In the SOLARIS project, Enel has made an important contribution in the preliminary identification of potential business models and in determining the size of the solar power plants that will be in orbit, as well as giving the basic guidelines for the installation of the stations that will receive energy from space.

The idea is to set up space-based solar power plants 36,000 km above the Earth’s surface, in a geostationary orbit: that is, a circular orbit around the equator which coincides with the Earth’s rotation period. The panels would be exposed to the Sun at all times, thus producing energy at practically all hours of the day and in all seasons, except for a few days a year, during the period of the equinoxes (the transition from winter to spring and from summer to fall), due to the conical shadow created by the Earth.

Space-based solar panels are not like those normally used in photovoltaic systems on Earth. They’re lighter and multi-junction, which means they’re made of several layers, each of a different semiconductor material and therefore able to absorb a different part of the solar spectrum, thus extracting more energy in the same amount of exposed surface area. They don’t use silicon, but rather materials such as indium arsenide or gallium arsenide, and they can reach higher levels of efficiency: they currently have an efficiency of 30%, but are expected to reach 40% within 10 years (those used for generation plants on Earth currently top out at 21-22%, while the HJT panel developed in our 3Sun factory in Catania reaches 24.5%).

Efficiency assessment in 2025, the first launch in 2030

The first important date for SOLARIS is set for next year, 2025. By then, it will be necessary to assess what the actual transmission efficiency is: that is, how much of the energy produced in orbit would reach Earth. Not through a giant cable or space elevator – for the moment, that’s still science fiction – but through a wireless system. Microwave energy will be beamed to Earth and “captured” by a series of antennas that will turn it into electricity and feed it onto the grid.

Power transmission from space was first accomplished in 2023, thanks to technology developed by the California Institute of Technology and used by the Space Solar Power Demonstrator (SSPD-1) satellite. It was an experiment that demonstrated technical feasibility by turning on two LED lights.

The question now, however, is the industrial and economic feasibility and sustainability of the process. A one-gigawatt power plant would have an approximate weight of about 11,000 tons, and it would take 100 launches to get all the material into orbit. To be an economically sustainable system, the transmission efficiency – that is, the share of the energy produced in orbit that would reach Earth, which to date is still unknown – would have to be more than 90%.

If all goes well, then the next step, around 2030, will be to send the first solar farm into orbit: a 1-MW power plant that’s already assembled and capable of automatic extension.

Solar farms of the future

After that, there will be more and more powerful plants, up to 1 gigawatt of installed capacity between 2040 and 2045, in order to start a real commercial application of the new technology. These standard 1 GW space-based solar power plants will be metal structures with photovoltaic panels mounted in parallel, over a total area of about five square kilometers, with a large transmitting antenna. On Earth, other antennas, arranged over an area of about 25 square kilometers, will receive the microwaves. A gigawatt of installed capacity in space can produce six or seven times more energy than one installed on Earth, virtually around the clock.  So, if all goes well, there’s also likely to be a rush to space photovoltaics by countries and companies.

The impact on “terrestrial” solar

The SOLARIS project also acts as a catalyst in the development of increasingly efficient photovoltaic cells that can also be used in power generation plants here on Earth. Today, solar cells for space applications are produced using complex microelectronic processes, and their cost is extremely high. So the project has two goals: to increase the efficiency of solar panels to 40% (which is very high) and to reduce the cost of production.

The goal of high efficiency at low cost could then enable the development of a whole new generation of solar panels for terrestrial uses: first for domestic applications only and then for the development of technology for large-scale, ground-based generation plants – thus confirming solar energy as an essential pillar of the energy transition and contributing to the goal of producing nearly 90% of the world’s energy from renewable sources by 2050.