Strictly speaking, solar panels depend on direct sunlight in order to produce electricity. Raw sunlight contains a number of energized particles, including the all-important photon. When photons from the sun strike one side of an array of solar panels, they essentially cause electrons to break off from one panel, cross a thin membrane and attach themselves to another panel. The crossing of the freed electrons is what generates a usable electrical current.

If there were no photons striking the solar panels, the electrons would remain in place and no electricity would be generated. This is why dark clouds or nightfall are so problematic when generating solar power on a commercially viable scale. When the sunlight disappears, so does the electricity. The electricity produced during daylight hours is not lost forever, however. The excess electricity is stored in large batteries, and can provide power during overnight hours.

The main reason standard solar panels cannot charge in the moonlight is the nature of the moon's light. Unlike the sun, the moon does not generate its own light energy. What we see on Earth is the sun's light energy reflecting off the moon's surface. A solar panel array placed on the moon would generate electricity during our nighttime hours because it is receiving direct sunlight containing photons. The reflected light we see from Earth does not contain a significant number of photons, so even a full moon could not cause solar panels to generate electricity.

This is not to say that the power of the stars could not be used to generate electricity on Earth. A material sensitive to stellar energy, visible or invisible, could be used to create "stellar panels," which would supplement the output of traditional solar panels by generating electricity at night or on cloudy days. The current limitations of such an alternative energy source are financial and technological in nature. A material capable of converting stellar energy into electricity has yet to be perfected, and the initial cost of building a usable array would be prohibitive.

There are reports claiming Russian scientists may have developed a proprietary material which could indeed convert stellar energy into electricity 24 hours a day. This so-called "heteroelectric" material is said to be less expensive to produce than standard solar cells, and has an efficiency rating of 90%, compared to the 10-12% efficiency rating of silicon-based solar panels currently in use. The research scientists who developed this heteroelectric material have largely avoided the public spotlight, however, and there are other scientists who have expressed doubts about this apparent energy breakthrough.