Ilaria Rosella Pagliaro The ESA's SOLARIS project and the Japanese OHISAMA initiative are opening new frontiers in transmitting solar energy from space to Earth, utilizing advanced technologies to improve energy efficiency and global sustainability.
©ESA
In 1958, the United States’ Vanguard 1 satellite became the first spacecraft to use a solar panel to power a radio transmitter. Although it ceased to function after a few years, it remains in orbit as the oldest artificial object orbiting Earth. Vanguard 1 paved the way for the use of solar energy in space. Today, the International Space Station is equipped with over 4,300 square feet of panels, generating 240,000 times more energy than Vanguard 1’s modest setup.
Could this renewable energy be continuously and efficiently transmitted to Earth, irrespective of weather conditions? This is the goal of the SOLARIS project, which the European Space Agency (ESA) will focus on in the coming years.
The SOLARIS project
Launched in 2023, the SOLARIS project aims to generate energy in space for use on Earth. Experts in photovoltaic technologies, grids, and storage are participating in this initiative. Initial contributions include preliminary identification of potential business models and determining the size of orbital solar power plants, along with basic guidelines for installing ground-based energy reception stations.
The idea is to install space solar power plants 22,400 miles from Earth‘s surface in geostationary orbit. Here, the solar panels would be exposed to the Sun almost all day, producing energy consistently, except for a few days a year during equinoxes due to Earth’s conical shadow. These space solar panels are lighter and multi-junction compared to those used on Earth, comprising multiple layers of semiconductor materials capable of absorbing different parts of the solar spectrum, increasing the energy extracted from the same surface area. Using materials like indium arsenide or gallium arsenide, these panels currently have an efficiency of 30%, expected to reach 40% within a decade (compared to 21-22% for terrestrial panels).
The first significant date for the SOLARIS project is set for 2025, when the actual efficiency of transmission will need to be assessed: how much of the energy produced in orbit will reach Earth. Transmission will occur wirelessly, not via a giant cable or space elevator. Energy will be transmitted as microwaves and “captured” by a series of antennas converting it into electricity for the grid. The first space-to-Earth energy transmission occurred in 2023 with technology developed by the California Institute of Technology and used by the Space Solar Power Demonstrator (SSPD-1) satellite, which lit two LED lights, proving the technical feasibility.
The current challenge is the industrial and economic feasibility of the process. A one-gigawatt plant would weigh around 11,000 tons and require 100 launches to deliver all the materials to orbit. For economic sustainability, transmission efficiency must exceed 90%. If all goes well, the next step around 2030 will be sending a 1 MW solar farm into orbit, pre-assembled and capable of automatic extension.
After 2030, increasingly powerful plants will be developed, reaching a gigawatt of installed capacity between 2040 and 2045, to start a real commercial application of the new technology. Standard 1 GW space solar plants will be metal structures with photovoltaic panels mounted in parallel over an area of about two square miles, with a large transmission antenna. On Earth, other antennas, spread over about ten square miles, will receive the microwaves. An installed capacity of one gigawatt in space can produce six to seven times more energy than one on Earth, operating nearly 24/7.
The OHISAMA project
Japan is also exploring the potential of space solar power. The OHISAMA project, slated for launch in 2025, aims to demonstrate the feasibility of solar energy transmission from space to Earth. Japanese scientists have already demonstrated wireless transmission of solar energy to the ground from a stationary source and plan to conduct a transmission from an aircraft in December 2024. The aircraft will be equipped with a photovoltaic panel identical to the one that will fly in space and will transmit energy over a distance of 3-4 miles (5-7 km). The project aims to use a 21.5 square foot photovoltaic panel aboard a spacecraft to charge a battery, which will then convert the accumulated energy into microwaves for transmission to a receiving antenna on Earth.
The SOLARIS project and initiatives like OHISAMA are pushing the boundaries of solar technology, serving as catalysts for the development of increasingly efficient photovoltaic cells for terrestrial use as well. Currently, solar cells for space applications are produced using complex and expensive microelectronic processes. The project’s goals include increasing solar panel efficiency to 40% and reducing production costs. Achieving high efficiency at a low cost could enable the development of a new generation of solar panels for domestic use and large terrestrial plants, solidifying solar energy as a cornerstone of the energy transition and helping to produce nearly 90% of the world’s energy from renewable sources by 2050.
