# What is the average intensity of sunlight on the Venerean surface?

NASA writes to say about Venera 8

... measured the light level as being suitable for surface photography, finding it to be similar to the amount of light on Earth on an overcast day with roughly 1 km visibility.

• Was this corroborated by other probes to Venus?
• Is the average intensity of sunlight (even through the overcast) adequate for a PV cell to supply power, or did any instruments work off the charge stored in batteries during descent?

The Venera landers operated on batteries for an hour or two.

The spectrometer on Venera 11 provided direct data on the solar insolation at the surface as a function of wavelength. This paper by Landis and Vo provides a plot of the insolation as a ratio of the intensity at the surface to the intensity in space at Venus, i.e. just outside the atmosphere. Blue is gone completely, green is almost gone at about 0.02, red is better at 0.08 to 0.12, and infrared at about 0.1.

Yes, you can operate solar cells at very low intensities. For example the Juno spacecraft will use them at Jupiter with an insolation of about 0.04 (relative to at Earth). From the Landis paper, a single-junction cell panel at the surface of Venus would require $1.17\,{{\mathrm m}^2\over W}$. That's a lot of panel for not a lot of power. Also it would require a significant technology development to come up with cells that can survive the temperature at the surface.

• Correct me if I'm wrong but I've read the cloud-cover on Venus is so thick that it almost doesn't matter where said solar-panel was pointing, as the sunlight is completely scattered. Sep 25 '13 at 21:39
• Yes, it is. Solar cells don't need direct light. They can produce energy with scattered light just as well. Which is good, since you don't have to point the solar panel at the Sun. Just point it up. Sep 25 '13 at 22:05
• There are some challenges to operating PV junctions at high temperature though. In addition to some materials melting (ohmic contacts, solder...) the losses due to recombination will be greater. PVs loose efficiency at elevated temperatures. See this question and associated answer.
– uhoh
Jul 29 '16 at 9:27