# Space-based solar power: Efficiency

Eight conversion steps, and why orbit might still pay off

Source page: https://www.materialinsights.org/energy/e_space_solar/efficiency/

What this tab covers How much of the energy available is actually captured or extracted, in per cent: theoretical limits, laboratory records, typical new equipment and in-service averages, each with exactly what is being measured.

Space-based solar power collects sunlight in orbit, where there is almost no night or cloud, then beams it to Earth as microwaves or laser light. Every conversion step loses energy, so NASA's 2024 reference designs deliver only about 13% of the sunlight hitting the panels to the grid (calculated).

Chart: Efficiency ranges
 Commercial

#### Efficiency by measure

| Measure | Range | Type | What is measured |
|---|---|---|---|
| **Space solar cells assumed in NASA reference designs** | 35%^[1](https://www.nasa.gov/wp-content/uploads/2024/01/otps-sbsp-report-final-tagged-approved-1-8-24-tagged-v2.pdf) | Commercial | Sunlight to DC electricity in orbit; a design assumption |
| **DC electricity to microwave beam** | 70%^[1](https://www.nasa.gov/wp-content/uploads/2024/01/otps-sbsp-report-final-tagged-approved-1-8-24-tagged-v2.pdf) | Commercial | Conversion in the transmitter (DC to RF), design assumption |
| **Ground rectenna, microwave to DC** | 78%^[1](https://www.nasa.gov/wp-content/uploads/2024/01/otps-sbsp-report-final-tagged-approved-1-8-24-tagged-v2.pdf) | Commercial | Rectifying antenna on the ground, design assumption |
| **End to end, sunlight on panels to grid electricity** | 13%^[1](https://www.nasa.gov/wp-content/uploads/2024/01/otps-sbsp-report-final-tagged-approved-1-8-24-tagged-v2.pdf) | Commercial | Product of NASA's stage efficiencies (35, 90, 70, 90, 98, 95, 78 and 90%) (calculated) |

#### Where the energy is lost

| Step | Loss |
|---|---|
| **Solar cells (sunlight not converted)** | 65%^[1](https://www.nasa.gov/wp-content/uploads/2024/01/otps-sbsp-report-final-tagged-approved-1-8-24-tagged-v2.pdf) |
| **DC to microwave conversion** | 30%^[1](https://www.nasa.gov/wp-content/uploads/2024/01/otps-sbsp-report-final-tagged-approved-1-8-24-tagged-v2.pdf) |
| **Rectenna conversion back to DC** | 22%^[1](https://www.nasa.gov/wp-content/uploads/2024/01/otps-sbsp-report-final-tagged-approved-1-8-24-tagged-v2.pdf) |
| **Power conditioning in space and on the ground (two DC-DC stages)** | 10% each^[1](https://www.nasa.gov/wp-content/uploads/2024/01/otps-sbsp-report-final-tagged-approved-1-8-24-tagged-v2.pdf) |
| **Beam emission, atmosphere and collection** | 10%, 2% and 5%^[1](https://www.nasa.gov/wp-content/uploads/2024/01/otps-sbsp-report-final-tagged-approved-1-8-24-tagged-v2.pdf) |

The case for going to orbit is utilisation, not conversion efficiency. NASA's reflector design (RD1) would run at a 99.7% capacity factor, against 60% for its simpler planar design (RD2). The cost is a long chain of conversions: light to DC, DC to microwaves, microwaves through the air, and back to DC.

No full system has been built, so all values are design assumptions rather than measurements.

#### Sources

1. [Space-Based Solar Power (Office of Technology, Policy, and Strategy)](https://www.nasa.gov/wp-content/uploads/2024/01/otps-sbsp-report-final-tagged-approved-1-8-24-tagged-v2.pdf) NASA, 2024

## Other sections

- [Summary](https://www.materialinsights.org/energy/e_space_solar/index.md)
- [Overview](https://www.materialinsights.org/energy/e_space_solar/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_space_solar/correlation/index.md)
- [Techniques](https://www.materialinsights.org/energy/e_space_solar/techniques/index.md)
- [Resources and labour](https://www.materialinsights.org/energy/e_space_solar/resources/index.md)
- [Impact on the biosphere](https://www.materialinsights.org/energy/e_space_solar/biosphere/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_space_solar/links/index.md)