Which numbers should a reader keep in mind when judging any claim about space solar power?
The short answer. about a dozen. Sunlight above the atmosphere carries about 1,361 W/m². A collector in geostationary orbit is lit about 99% of the year, against about 20–25% capacity for good ground solar. The chain from sunlight to grid keeps about 18% of collected energy with microwaves and about 5.5% with lasers in Setcoin's reference. A 1 km transmitter at 5.8 GHz makes a spot about 4.5 km across from geostationary orbit. At 10 kg/kW, a 2 GW plant weighs about 20,000 tonnes and needs about 200 launches of 100 tonnes. At $1,000/kg to low orbit, launch makes up 92% of capital cost and electricity costs about $357/MWh; at $200/kg it is about $95/MWh. Firm power on Earth costs roughly $48–251/MWh, depending on technology. The table collects these numbers with the chapters that explain them.
The numbers
| Quantity | Value | Chapter |
|---|---|---|
| Sunlight above the atmosphere | ~1,361 W/m² | 9 |
| Time in sunlight, GEO | ~99% of the year | 9 |
| Capacity factor assumed for SBSP | 95% | 53 |
| Microwave chain efficiency, sunlight to grid | ~18% | 27 |
| Laser chain efficiency, sunlight to grid | ~5.5% | 29 |
| Spot diameter from GEO, 5.8 GHz, 1 km transmitter | ~4.5 km | 25 |
| Spot diameter from GEO, 2.45 GHz, 1 km transmitter | ~10.7 km | 25 |
| Average intensity, 2 GW over 4.5 km | ~125 W/m² | 25 |
| Public exposure guidance (summarised) | ~10 W/m² | 35 |
| Mass of a 2 GW plant at 10 kg/kW | ~20,000 t | 43 |
| Launches at 100 t each | ~200 | 43 |
| Capital cost, reference case | ~$27.3/W (~$54.6 billion for 2 GW) | 53 |
| Launch share of capital, reference case | ~92% | 53 |
| Cost of electricity, reference case | ~$357/MWh | 53 |
| Cost of electricity at $200/kg launch | ~$95/MWh | 53 |
| Annual output of 2 GW at 95% | ~16.6 TWh | 5 |
| Firm power on Earth (Lazard 2025 ranges) | ~$48–251/MWh | 57 |
| Rectenna land, 2 GW | ~25–40 km² | 33 |
How to use them
When a developer or report quotes a cost of electricity, check four inputs against these numbers: mass per kilowatt, launch price, hardware cost per watt and cost of capital. Most published differences come from these four (Chapter 55).
What would change this view
These numbers are Setcoin's reference values as of October 2026. Measured results from orbital demonstrations would replace several of them.