Space-based solar power

In plain language

Space-based solar power is the idea of building very large solar collectors in orbit, where sunlight can be collected for longer than on the ground. The collected energy would be turned into a radio beam or a laser and aimed at a receiver on Earth, which would turn it back into electricity.

The idea is simple to state but hard to build. The structures would need to be enormous, the beam would need to be aimed very precisely, and the system would need to compete on cost with ground solar farms, wind and batteries. In 2023 a small Caltech experiment sent microwave power to receivers about 30 centimetres away, in orbit. That showed the basic link can work in space, but it was far short of a power station.

Technical explanation

A complete system has four stages. Photovoltaic cells on a large collector turn sunlight into electricity. Power electronics drive a phased microwave array or a laser transmitter, and the array changes the timing of many small emitters so the combined beam can be steered without moving the whole structure. A ground rectenna converts the microwave beam back into electricity. The system also needs assembly, station-keeping, fault response, repair and end-of-life disposal. Losses occur at every stage, so performance has to be measured across the whole chain, from sunlight at the collector to net electricity at the grid connection.

The 2023 Caltech demonstrator, SSPD-1, carried three experiments: DOLCE, a deployable structure; ALBA, a set of solar cell types; and MAPLE, a flexible array of microwave transmitters. In orbit, MAPLE directed energy to two receiver arrays about 30 centimetres away, which converted it to direct current and lit LEDs. Caltech also reported a signal detected on a rooftop on Earth, but its announcement does not report useful grid power. After deliberate stress testing late in the mission, MAPLE's total transmitted power fell, and lab tests linked this to degraded transmitter elements and electrical-thermal interactions.

NASA's 2024 lifecycle assessment modelled two reference designs, each normalised to 2 GW to the grid from 2050, assembled in geostationary orbit. In its baseline, launch and manufacturing dominate cost and emissions. The heliostat-swarm design produced power for 99% of the year in the model, and the planar-array design for 60%, because it could reposition less. The results depend heavily on assumptions about launch prices, hardware lifetime and manufacturing, so they should be read as scenarios rather than forecasts.

What the evidence says

Each statement is typed by the strength of its evidence and linked to the source that supports it.

Limitations and open problems

• The only in-space power link so far is a small hosted test with receivers about 30 centimetres away. The published account gives no power levels or end-to-end energy balance, and it did not deliver grid electricity.
• NASA's cost and emissions figures are scenario outputs for first-of-a-kind systems in 2050. They are not a forecast, and they depend on assumed launch prices, hardware lifetimes and manufacturing learning curves.
• Launch drives most of the modelled cost and emissions. NASA's baseline needed 2,321 and 3,960 launches, and its emissions figures do not include upper-atmosphere effects of launch emissions, which are still under study.
• Lightweight arrays face deployment, radiation, thermal cycling and debris risks. SSPD-1 had a snagged deployment and a later drop in transmitted power.
• The sources reviewed do not report tests of beam containment, automatic shutdown, exposure limits or spectrum coordination at relevant power and scale.
• Microwave and laser designs face different constraints, such as atmospheric absorption and eye safety for lasers, and should be assessed separately.

Possible future uses

Timeline

1. 3 Jan 2023Caltech's Space Solar Power Demonstrator 1 (SSPD-1) launches as a hosted experiment carrying the DOLCE, ALBA and MAPLE payloads. Sources: [2]
2. 22 May 2023A receiver on a Caltech building roof detects the MAPLE signal from orbit, as reported by Caltech. Sources: [1]
3. 1 Jun 2023Caltech announces that MAPLE transmitted power in orbit to receivers about 30 centimetres away. Sources: [1]
4. 11 Nov 2023SSPD-1 stops communicating with Earth, ending the mission. Sources: [2]
5. 11 Jan 2024NASA's Office of Technology, Policy and Strategy publishes a lifecycle assessment of two reference space-based solar power designs. Sources: [3]
6. 13 May 2025A Caltech-led team publishes online a distributed space solar power architecture and technoeconomic analysis in Joule. Sources: [4]

Futures this could help bring about

How far away?

A space elevator

Science unproven · 2 of 9 steps done

Glossary

Rectenna

A rectifying antenna that converts received microwave energy into direct current electricity.

Phased array

A set of emitters whose timing is adjusted so that their combined beam can be steered electronically.

Geostationary orbit

An orbit above the equator in which a satellite keeps pace with Earth's rotation and stays over roughly the same longitude.

Levelised cost of energy

The average cost of each unit of electricity over a plant's lifetime, including build, operation and disposal costs.

Sources

1. university press release
   In a First, Caltech's Space Solar Power Demonstrator Wirelessly Transmits Power in Space
   California Institute of Technology, 1 Jun 2023. Accessed 21 Oct 2026.
2. university press release
   Space Solar Power Project Ends First In-Space Mission with Successes and Lessons
   California Institute of Technology, 16 Jan 2024. Accessed 21 Oct 2026.
3. government report
   Space Based Solar Power
   Erica Rodgers, Ellen Gertsen, Jordan Sotudeh et al.. NASA Office of Technology, Policy, and Strategy, 11 Jan 2024. Accessed 21 Oct 2026.
4. peer reviewed paper
   Space solar power generation: A viable system proposal and technoeconomic analysis
   Oren S. Mizrahi, Phillip Jahelka, Eleftherios Gdoutos et al.. Joule, 13 May 2025. DOI: 10.1016/j.joule.2025.101928. Accessed 21 Oct 2026.
5. company announcement
   ESA chooses Thales Alenia Space for SOLARIS feasibility study
   Thales Alenia Space, 24 Jul 2023. Accessed 21 Oct 2026.

Revision history

3 changes since this profile was created.