Super moon power output

[Brian53713]

1019 p.m., supermoon pretty powerful voltage.

[bcroe]

Moonlight solar just isn't going to fly. That is more voltage than I measured. Bruce Roe

[Brian53713]

It actually went even higher and 1.15v.

[SunEagle]

I can chime in and ask you when was the last time that meter was calibrated and what is the +/- % accuracy rating on it?

Moon light (even a super moon) is not known to provide much more than a few foot candles even in the best of conditions so the light getting to those solar panels may have somehow been magnified for them to put out any voltage.

[inetdog]

I can chime in and ask you when was the last time that meter was calibrated and what is the +/- % accuracy rating on it?

Moon light (even a super moon) is not known to provide much more than a few foot candles even in the best of conditions so the light getting to those solar panels may have somehow been magnified for them to put out any voltage.

How much voltage is available from moonlight depends entirely on how much external load resistance was also on the panel and the magnitude of the internal leakage current within the semiconductor junctions. A really good (in terms of leakage) photocell could deliver close to its .5 per cell figure even in moonlight.
But practical design for maximum efficiency under sunlight and lowest cost per watt do not work together to allow really low internal leakage.

[Mike90250]

Panels will put out voltage with very little light, but there is very little current associated with it. Just enough to work a meter.

[SunEagle]

How much voltage is available from moonlight depends entirely on how much external load resistance was also on the panel and the magnitude of the internal leakage current within the semiconductor junctions. A really good (in terms of leakage) photocell could deliver close to its .5 per cell figure even in moonlight.
But practical design for maximum efficiency under sunlight and lowest cost per watt do not work together to allow really low internal leakage.

Hmm. I have to try that out with my Fluke sometime.

I just figured that there wasn't enough photons from moon light to excite enough electrons to jump out of the cells and add up to even 0.5 volts due to all that internal resistance in the panel.

But I learn something every day.

[inetdog]

Hmm. I have to try that out with my Fluke sometime.

I just figured that there wasn't enough photons from moon light to excite enough electrons to jump out of the cells and add up to even 0.5 volts due to all that internal resistance in the panel.

But I learn something every day.

The photoelectric effect is quantum phenomenon. All it takes to knock one electron loose is one photon at or above the right frequency. Where that electron ends up does not depend much on what is happening to other electrons around it until you build up an electric field that resists its motion. Series resistance within the cell does not play a role at that end of the curve. The internal shorting resistance (parallel) does.

PS: Strictly speaking the electrons jump from one area of the cell to another (other side of an N-P junction) rather than out of the cell.
From there they just walk to the metal electrodes.

[SunEagle]

The photoelectric effect is quantum phenomenon. All it takes to knock one electron loose is one photon at or above the right frequency. Where that electron ends up does not depend much on what is happening to other electrons around it until you build up an electric field that resists its motion. Series resistance within the cell does not play a role at that end of the curve.

But surface resistance will inhibit the number of electrons being harvested.

Although at the low end it probably does not matter so you still collect enough to get 1 volt on a 60 or 72 cell panel.

[bcroe]

OK Checking my notes, with all circuit breakers open under decent moonlight I got less than 10V on a string of 720 cells. Different
source panels showed some even much less than that; Isc was infinitesimal. Since these PVs are optimized for operation under
strong sun, there should be no expectation that they will be perfectly linear (V but at reduced I) over some 5 orders of magnitude.
There is a minimum sun threshold where they start behaving the way we like. Bruce Roe

[inetdog]

But surface resistance will inhibit the number of electrons being harvested.

Although at the low end it probably does not matter so you still collect enough to get 1 volt on a 60 or 72 cell panel.

Uh, not really. It is the number of electrons available that limits the current at the high output end (Isc). It is the series resistance that makes Vmp lower than Voc.
It is the parallel (leakage) resistance that limits the voltage under low light.

[SunEagle]

Uh, not really. It is the number of electrons available that limits the current at the high output end (Isc). It is the series resistance that makes Vmp lower than Voc.
It is the parallel (leakage) resistance that limits the voltage under low light.

Yeah. I realized that after I made my post. It has been a few years since I was in the research of that stuff. Thanks for keeping me honest.

[inetdog]

You're welcome.

[Brian53713]

So that voltage came from the Moonlight, and other City light sources. I always have some sort of reading on that, though it's obviously not making power. Four 100 watt 12-volt renogy panels in series making that reading.

[PNjunction]

Want to really trip out? Let's start at the beginning at how the photon is created in the first place.

* Pick up your mouse a few inches and drop it. Notice the gravitational force that keeps it (and you) firmly planted so you don't float away.
* The sun's gravitational force is part of the nuclear fusion process that emits a gamma ray at the center of the sun. 10-ton gorilla.
* That gamma ray bounces around for a million years in pachinko-machine like fashion off other elements, losing energy as it bounces around to only make it to the middle layers of the sun.
* That loss of energy to only get to the middle layer of the sun turns it into an x-ray. Think dentist chair.
* From the middle layer of the sun it is a relatively brisk one week trip riding magnetic currents to the surface.
* That trip to the surface weakens the x-ray to the point it is now what we call a photon.
* From there, it is the canonical 8-minute trip at light-speed to the surface of the earth. Maybe a little more or less to reach the moon, where it is then reflected to us at night.

(off topic: depending on eyesight and atmospheric conditions, I can visually pick out planets from stars by noting that direct energy sources like a star twinkle, whereas planets and other objects that reflect light are somewhat light-stable. Lots of squinting.

Thanks gravity!

Now you can tell people that you aren't solar-powered as such, but nuclear powered! Just 8-minutes (or a million-years + 8 minutes) light-speed away!

[Brian53713]

You guys are a fun bunch, and thanks for all the awesome help and advice at our disposal here. Kind of overwhelming when you first look at the website. But if you take a moment , you can get to the categories and help one needs before asking some of the silly questions. Thank you for not belittling me so far . In defense of some of the dumb questions, some people want up-to-date recent advice. Or don't know how to interpret some of the old info that's out there, and have to ask to get to the bottom of their not being able to explain.