# Which type of star is most effective for solar power?

I'm working on a worldbuilding game, and the subject of stars has come up. Imagine you're a species, chilling in the Goldilocks zone of some alien planet, orbiting an alien star. Your people stumble upon solar power, just as we did, and send a satellite with a 1m x 1m panel into space.

Which family of star will provide that satellite with the most energy, on average? The luminosity of a blue supergiant may be up to 1E6 x Sol's, for example, but that's being emitted by a much larger area, so does that mean that the brightness per square metre would actually be lower?

• Does this answer your question: worldbuilding.stackexchange.com
– hft
May 5, 2022 at 19:26
• Even if the star is not ideal, It probably would cost you less to build a bigger solar collector than it would cost to find a better star. May 5, 2022 at 19:57
• For the relationship between brightness per unit area and red vs. blue stars, search for "blackbody radiation" and the Stefan-Boltzmann law.
– rob
May 5, 2022 at 20:28

## 3 Answers

If you are using photovoltaic cells then all you care about is the flux of energy above the band gap in your photovoltaic devices. Even for sunlight, about 50% falls below this (wavelengths above about 1 $$\mu$$m). That would favour a luminous star (at a given distance) and a star hotter than the Sun.

However, there are other ways to collect stellar energy, just from its thermal effects. This doesn't really depend on the spectrum (if collected in space) so you just want your star to be as luminous as possible.

Only the luminosity of star and the distance to it go into your problem (the power collected would be proportional to the luminosity and inversely proportional to the square of the distance).

If you want to get into real detail, you would have to factor in the spectral response of the solar panel as well. This would tend to reduce the effect of blue radiation compared to red, but it would only be a minor correction to the enhanced luminosity of massive stars.

• The spectrum contributes as well, since you are concerned about getting photons above the band gap of your semiconductor. May 5, 2022 at 18:36

In general, the more luminosity - the more energy - the more power. So, according to standard stellar classification, stars in class O have a effective temperature ≥ 30,000 K and a luminosity ≥ 30,000 L☉ (luminosity of our star) and luminosity can be considered the power release of a star. Although, is important to consider the distance to the star.