Space-Based Solar Power:
Physics, Costs and the Path to Firm Power from Orbit

Fifty-Eight Years of an Idea

How has space-based solar power evolved since it was first proposed, and why did earlier efforts stop?

A Plant on One Page: a Worked 2 GW Example

What would a single 2-gigawatt space solar plant look like, end to end, on Setcoin's reference assumptions?

Why Now?

Why has space-based solar power returned to serious attention in the mid-2020s?

Lessons from the 1979 Reference System

What did the first full study of a solar power satellite conclude, and which of its lessons still hold?

Method: How Setcoin Assesses Space Solar Power

How does this study estimate costs and judge evidence, and how can readers test the conclusions?

Sunlight in Orbit: the Basic Advantage

What exactly does a solar array gain by being in orbit, and how large is the advantage?

Concepts Compared: CASSIOPeiA, SPS-ALPHA, Tiles and Mirrors

Which designs are being studied, and how do they differ in principle?

CASSIOPeiA in Detail

How does the UK's leading design work, and what are its strengths and open questions?

Europe: ESA's SOLARIS Programme

What has ESA done on space-based solar power, and where does the programme stand?

SPS-ALPHA and Modular Concentrators

How do concentrator designs such as SPS-ALPHA differ, and what do they trade?

The United Kingdom: Studies, Competitions and Space Solar

How has the UK approached space-based solar power, and how far has its leading company progressed?

The United States: NASA, Caltech, AFRL and DARPA

What has the US done on space-based solar power, and what did NASA's cost study conclude?

Caltech's Space Solar Power Project in Detail

What did Caltech's programme set out to do, what did its first flight show and why does it matter?

Japan: Decades of Research and OHISAMA

What has Japan contributed, and what is the status of its orbital demonstration?

Other National Programmes: Korea, India and Beyond

Which other countries are working on space solar power, and what are they doing?

China: a National Roadmap to Gigawatts

What is China planning, and how credible is its timeline?

Europe's Industry Base for Space Solar Power

Which European companies and research groups could build a space solar plant, and what have they done so far?

The Companies

Which private companies are pursuing space-based power, what are they building and how far along are they?

Case Study: the Meta–Overview Energy Agreement

What did Meta agree with Overview Energy, and what does it tell us about demand?

Demonstrations So Far

What has actually been demonstrated in power beaming and space solar, and how far is it from a power plant?

What a First Orbital Demonstrator Should Prove

What should the first serious orbit-to-ground demonstration measure, so that its results can be used to judge the economics?

Beam Physics: Why Antennas Must Be Large

How does the physics of diffraction set the size of transmitters and receivers?

The Ionosphere and the Upper Atmosphere

Does a powerful microwave beam passing through the ionosphere heat or disturb it?

The Efficiency Chain: Microwave Systems

How much of the sunlight collected in orbit reaches the grid, step by step?

Inside the Transmitter: Amplifiers, Antennas and Heat

Why is the transmitter often the hardest part of a microwave solar power satellite?

Laser Power Beaming

What do lasers offer compared with microwaves, and what do they cost in efficiency?

Laser Receivers: Photovoltaics Tuned to Light

How do laser power receivers work, and how efficient can they become?

Mirrors and Near-Infrared: Lighting Existing Solar Farms

Can sunlight or light beamed from orbit simply make existing solar farms produce at night?

Microwaves or Lasers? A Side-by-Side Comparison

Which way of sending power to Earth is better, and for whom?

Rectennas and Land Use

How large are the receivers for microwave systems, and how much land do they need?

Offshore Rectennas

Could microwave receivers be built at sea, and what would that solve?

Safety: Beams, Birds, Aircraft and Eyes

Is power beamed from orbit safe, and what would regulators require?

Health Evidence on Microwave Exposure

What does research say about the health effects of the microwave intensities that a space solar plant would produce?

Spectrum and the ITU

Which frequencies would SBSP use, and what international coordination does it need?

Radio Astronomy and Other Spectrum Users

Would space solar beams interfere with radio telescopes, communications and radar?

Weather and the Atmosphere

How does weather affect power beamed from orbit?

Beam Control: How a Phased Array Points Itself

How does a space solar transmitter aim a beam precisely at a receiver 36,000 km away, and keep it safe?

Mass and Specific Power

How heavy would a space solar plant be, and why does mass per kilowatt decide its economics?

Solar Cells for Space Solar Power

Which solar cells would a space solar plant use, and what does that mean for supply?

Launch Requirements: Building a Plant in Orbit

How many launches would a gigawatt-scale plant need, how long would it take and what would launch cost?

The Launch Market Space Solar Power Would Create

How would space solar power change the launch industry, and could it drive its own launch costs down?

Assembling Gigawatts in Orbit

How would kilometre-scale structures be built in space, and is assembly the hidden bottleneck?

Assembly in Orbit: What Has Been Done So Far

What experience exists of assembling large structures in space, and how far is it from what a space solar plant needs?

Hardware Cost: the Second Gap

How much would space solar hardware need to cost, and how far is that from today?

The Supply Chain for a Gigawatt

What would it take to manufacture a gigawatt-scale plant, and which parts would be scarce?

Geostationary or Low Orbit?

Should a space solar system sit in geostationary orbit or in lower orbits, and what changes with the choice?

Other Orbits: Medium Orbit, Elliptical Orbits and Low-Orbit Constellations

Are there orbits other than geostationary orbit and low orbit that could work for space solar power?

Operations, Servicing, Life and Debris

What does it take to operate a space solar plant for decades, and what are the risks?

Thermal Management: Getting Rid of Waste Heat

How does a space solar plant get rid of the heat it produces, and why does that matter for mass?

The Cost of Electricity: Setcoin's Model

What would a megawatt-hour from orbit cost, and which inputs matter most?

Space Solar or Ground Solar with Wires and Storage?

Is beaming power from orbit better than building more ground solar, long transmission lines and storage?

Reconciling Published Cost Estimates

Why do published estimates for space solar power range from under $50 to more than $1,500 per megawatt-hour?

Learning Curves: What Solar Panels and Rockets Teach

How quickly could the cost of space solar power fall with experience, and what do other technologies suggest?

Firm Power on Earth: the Real Competition

What does space solar power compete with, and what would it need to cost?

The Cost of the First Plant

What would the first grid-scale space solar plant cost, as opposed to the tenth?

The Break-Even Map

Which combinations of launch price and hardware cost make space solar power competitive?

If Launch Became Almost Free

What would space solar power cost if launch prices fell to tens of dollars a kilogram?

What Drives Cost: Sensitivities and Learning

Which assumptions move the cost of space solar power most, and how fast could costs fall with experience?

Inside the Reference Plant's Costs

Where does the money go in Setcoin's 2 GW reference plant, and what does each year of operation cost?

The Value of Firm, Movable Power

Is the cost per megawatt-hour the right measure, or is space solar power worth more than its energy?

Public Money So Far

How much public money has gone into space solar power, and what has it bought?

Financing a First Plant

How could a first space solar plant be financed, and what does the cost of capital do to the economics?

Insurance and Risk Transfer

How would the risks of a space solar programme be insured and shared?

Carbon and Lifecycle Emissions

How clean is electricity from orbit once launches and manufacturing are counted?

Building with Lunar Materials

Could space solar plants be built from materials mined on the Moon rather than launched from Earth?

Defence and Remote Power: the First Paying Customers

Why are militaries likely to buy space-beamed power before utilities, and what would they pay?

Power Beaming for the Moon and Mars

Could the technologies of space solar power serve exploration before they serve Earth?

Data Centres and Round-the-Clock Clean Power

Why are data-centre operators interested in space-based solar power, and could they become anchor customers?

Mines, Industrial Sites and Off-Grid Industry

Could remote mines and industrial sites be early customers for beamed power?

Islands, Remote Grids and Disaster Relief

Where else could beamed power command a premium before grid parity?

Hydrogen and Fuels from Space Solar Power

Could space solar power produce hydrogen and synthetic fuels, and at what cost?

Power for Satellites: a Market in Orbit

Could beaming power to other spacecraft be the first commercial market for space power?

Grid Integration and Power Markets

How would a space solar plant connect to a grid and sell its power?

Regulation: Who Licenses a Power Beam?

Which regulators would have to approve space-based solar power, and what would they require?

International Law and Security Concerns

Does international law permit power beaming from orbit, and do security concerns pose an obstacle?

Environmental Effects Beyond Carbon

What environmental effects other than carbon emissions would space solar power have?

Public Acceptance

Would the public accept power beamed from space, and what would shape opinion?

Skills and Workforce

What skills would a space solar power industry need, and are they available?

Scenarios to 2050

How might space-based solar power develop over the next twenty-five years?

Three Plants: Pilot, Commercial and Mature

How would a pilot plant, a first commercial plant and a mature plant differ in size, cost and output?

Roadmap: Milestones from 2026 to 2040

What sequence of milestones would a credible programme follow, and where is the field on it?

Designing a Public Programme: Stage Gates

If a government decided to develop space solar power, how should it structure the programme to limit the money at risk?

What Would Have to Be True

What conditions must all hold for space-based solar power to supply grids competitively?

Common Misconceptions

What do people often get wrong about space solar power, in both directions?

The Case For and Against

Is space-based solar power a serious future energy source or a perennial dream?

A Timeline of Space Solar Power

What are the key events in the history of space solar power, from the first idea to October 2026?

Lessons from Other Energy Technologies

What can fusion, offshore wind, solar and nuclear teach space solar power?

Space Solar Power and Fusion: Two Long Bets Compared

How does space solar power compare with fusion as a long-term source of firm, clean power?

Due-Diligence Checklist

What should a buyer, government or capital provider check before backing a space solar programme?

Implications by Reader

What should each kind of reader do with this study?

Risk Register

What could go wrong for space-based solar power, how likely is it and how much would it matter?

How This Study Connects to the Space Research Programme

How does space solar power depend on the other sectors Setcoin studies?

Signals to Watch

Which events over the next few years will show whether space-based solar power is advancing?

Twenty Questions This Study Answers

What are the short answers to the questions readers most often ask about space-based solar power?

Methodology and Sources

How was this study built, and how reliable are its figures?

Appendix A: Programme and Demonstration Reference Table

Appendix B: Glossary

Appendix C: Setcoin Reference Data