The audacious plan to harvest sunlight in orbit — 24 hours a day
Solar panels on Earth face an unavoidable problem: night. For roughly half of every 24-hour period, the sun is below the horizon, and even during daylight, clouds, atmosphere, and angles reduce the energy reaching ground-level panels. In space, none of these limitations apply. A solar array in a geostationary orbit 35,786 km above the equator experiences sunlight 24 hours a day, unimpeded by atmosphere or weather, with intensities roughly 8 times higher than the average received at Earth’s surface. Space-Based Solar Power (SBSP) has been discussed since physicist Peter Glaser proposed it in 1968, but it is only in the past five years that government programs, falling launch costs, and advances in wireless power transmission have moved it from science fiction toward engineering feasibility.
How SBSP Would Work
A SBSP system has three main components: a large solar array in orbit that collects sunlight and converts it to electricity; a microwave or laser transmitter that beams the energy to Earth; and a ground-based receiver (called a ‘rectenna’ for microwave systems) that converts the beam back to electricity. The microwave approach, operating at 2.45 GHz or 5.8 GHz, is favored for long-term systems because microwave radiation passes through clouds and rain with minimal attenuation, does not interfere with living organisms at the power densities proposed, and can be steered electronically. A rectenna can be a relatively lightweight mesh of receiving elements that would allow crops and other uses beneath it.
Technical Challenges
The challenges are formidable. A commercial SBSP plant might require a solar array several kilometers across in orbit — vastly larger than any structure ever built in space. Launch costs have historically made this economically impossible: placing 1 kg in geostationary orbit has cost $15,000–30,000 historically. SpaceX’s Starship, which targets costs below $100/kg to low Earth orbit with full reusability, would dramatically change this equation if it achieves its targets. In-space assembly or deployment of large structures using robotics is another key challenge. Microwave transmission over 35,000 km with sufficient efficiency and safety is technically demonstrated at small scale but never at commercial power levels.
National Programs
Several governments are now funding serious SBSP development. The European Space Agency launched its SOLARIS initiative in 2022, beginning preparatory studies for a potential SBSP demonstration. The UK Space Energy Initiative, backed by both government and industry, is developing the Cassiopeia satellite concept targeting a 2035 demonstration of a small-scale SBSP system. Japan’s JAXA demonstrated wireless power transmission of 1.8 kW at 50 meters in 2015 and has a long-running SBSP research program. China’s CAST institute announced plans in 2020 for a 1 MW demonstration in the 2030s and a commercial MW-scale system by 2050. The U.S. Naval Research Laboratory demonstrated DC-to-DC wireless power transmission in space on the X-37B orbital test vehicle in 2020.
The Cost Trajectory
A 2021 study by Frazer-Nash Consultancy for the UK government concluded that SBSP could be cost-competitive with other forms of low-carbon electricity by the mid-2030s under optimistic assumptions about launch cost reductions and in-space manufacturing. The critical enablers are achieving Starship-class launch economics, advancing in-space robotic assembly, and improving photovoltaic and wireless transmission efficiency. The same study estimated a commercial-scale 2 GW SBSP system could supply electricity at £50/MWh — competitive with offshore wind — if these enablers materialize.
Space-based solar power is simultaneously one of the most technically challenging and potentially most transformative energy concepts ever seriously proposed. If launch costs fall as dramatically as Starship’s developers project, and in-space manufacturing and assembly capabilities develop as the robotics industry evolves, it becomes a genuinely viable path to truly abundant clean energy — continuous, weather-independent, and potentially available anywhere on Earth with a suitable rectenna.