November 14, 2016 was the night of an extra-super supermoon. With voltmeter in hand, founder and owner of Independent Power systems, Tony Boniface, and I set out to answer the question: Does moonlight create a photoelectric effect on PV (photovoltaic, i.e. solar electric) panels?

For our test, we hooked up the volt meter to an array of nine 210 watt solar panels.

Einstein’s contribution to the solar industry

The photoelectric effect is a natural phenomenon that describes how photovoltaic cells embedded in solar panels generate electricity when exposed to sunlight. Albert Einstein, renowned for his theory of relativity, actually received his Nobel prize in physics in 1921 for explaining the photoelectric effect. Einstein was the first to suggest that light was both a wave and a particle. This duality of the behavior of light became fundamental to the fields of quantum mechanics and the development of solar cells.

Moon … light …

Moonlight is actually sunlight that is reflected off the moon’s surface. A full moon occurs when the moon’s orbit brings it between – actually slightly above or below – the Earth-sun plane so that we see its light reflected fully. That said, the moon reflects only about 3 – 12 percent of the sunlight that hits it depending on the particular phase of the moon as it orbits the Earth.

Electrical panel and inverter with voltage meter

Measuring voltage during the supermoon rising, the voltage increased as the moon rose directly above the array. Photo credit: Tony Boniface

Our Results

On this event of the biggest, closest, and brightest supermoon since January 26, 1948,  did we, as we had anticipated, generate any useful energy from our solar panel array?

No, we did not. And frankly, not even enough energy was generated to ‘wake up’ the inverter (that is normally dormant at night).

But there was this: We did observe a photoelectric effect – measuring 2.9 volts to be exact! This is about the voltage necessary to power an LED.

Relatively speaking, this is barley a blip on the radar compared to actual sun power.

But wait, if the moon reflects about 3 – 12 percent of sunlight, why wasn’t more voltage produced? Well, it turns out that it would take almost 400,000 moons to equal the brightness of the sun. (Which probably explains why you can stare at the moon directly and not fry your retinas!)

There are more technical reasons to explain the non-linear relationship of reflected sunlight from the moon and the amount of light which strikes the Earth, or in our case, the solar array. Tony suggested that light reflecting off the moon is scattered due to its spherical shape, so we get very little of it; most of it scatters into space.

Meanwhile, I was lost in imagination, trying to picture what nighttime on Earth would be like if our satellite were, say, the size of Earth. Then it hit me that astronaut Neil Armstrong would have observed that from the moon our Earth appears nearly four times larger than a full moon and can shine 45 – 100 times brighter than the full moon.

Supermoon, schmoopermoon … it still doesn’t hold a ‘candle power’ to the light of the Sun or even that of our planet!

Other cool Moon and Sun facts:  Did you know?

  • It takes 29.5 days for the moon to make one complete rotation around the Earth.
  • We always see the same side of the moon.
  • There really is no actual “dark side of the moon” since the moon is constantly rotating on its own axis. The only time the far side of the moon is completely dark is during a full moon when the Earth is between the moon and the sun.
  • The moon not only pulls on the Earth’s oceans but also the Earth’s crust, though this is essentially imperceptible.
  • The Earth (and moon) is closest to the sun in January—perihelion—and about 3 million miles further away in July—aphelion.
  • At its furthest distance, Earth is 94.5 million miles away from the sun.
  • It takes about 8 minutes for sunlight to reach the Earth’s surface.

To find out if your property—roof or grounds—might be suitable for a solar electric system, contact Independent Power Systems.

Yolanda Duperret is the general manager of Independent Power Systems.