Theoretical question on series panels used at night

[Hogheavenfarm]

I have noticed during a full moon that my SCC registers around 2 volts coming in from the panels, which led my friend asking an interesting question, Why not have a large series of panels, enough to bring that voltage up into the charging range (lets say 12v system for simplicity). Obviously that amount of panels would fry a controller in daylight, so a voltage monitoring relay could essentially shut down the panels when the voltage exceeds some preset value. This would (in theory) just shut down the strings that did the "night collecting" and leave the "day collecting" strings engaged.
What are the arguments against something along these lines working? Is the theory tenable?
I know this would entail a vast amount of panels, that goes without saying, but wouldn't 7 panels in series collect 14 volts (probably zero to minimal amps I assume)?
Inquiring minds would like to know.

 

[BentleyJ]

I would say the basic premise may work with enough panels in series but rather than having 2 sets of panels, day and night, I would think some kind of switching network would be more practical.
Lets say there are 20 panels, 2 strings of 10 connected to separate MPPT controllers. At night there would be an automatic set of switches that turns the array into a 20S string connected to only one MPPT input. Would be an interesting test.

Sorry to go slightly off topic, have to mention that several YouTubers have measured the effect of direct moonlight on Black metal sheets vs. the same sheet shielded from direct moonlight but exposed to the same ambient temp. They found moonlight to be a "cold" light thus the panel with direct exposure actually got a little cooler than ambient temp. Have not tried to duplicate the test, just saying if there is any truth to it, the amount of energy in moonlight may turn out to be useless.

 

[squowse]

As soon as the mppt starts to draw current the voltage will drop away fast. Any level of illumination will produce some power but whats the point when its tiny? Just to prove its possible?

 

[Hogheavenfarm]

Just a theoretical idea, I don't have enough panels to experiment with, but sounds like an interesting idea. If it was practical, I would expect solar farms to employ some of it, and I don't see that happening, but they sure have enough panels to play with.

 

[squowse]

Just a theoretical idea, I don't have enough panels to experiment with, but sounds like an interesting idea. If it was practical, I would expect solar farms to employ some of it, and I don't see that happening, but they sure have enough panels to play with.

The reason they don't do it will be the same as why they don't use tracking systems. Not economic.

 

[12VoltInstalls]

The reason they don't do it will be the same as why they don't use tracking systems. Not economic.

The reason they don’t do it is because the lumens/sunpressure/irradiance/bandwidth of moonlight is (can’t remember, guessing here) 0.002% of the light required to create a current.
It just doesn’t work.

 

[squowse]

The reason they don’t do it is because the lumens/sunpressure/irradiance/bandwidth of moonlight is (can’t remember, guessing here) 0.002% of the light required to create a current.
It just doesn’t work.

I think any amount of light could cause (tiny) current to flow if you had it set up right. In theory. But the OP has just seen 2V and assumed that if you multiply that up you will get current out of the controller. Which you wont.

 

[Hedges]

Your SCC may put significant (compared to night time yield) load on the array.
Try measuring a panel with 10 Meg ohm DMM for Voc. With milliamp or microamp meter for Isc.
Perhaps many strings in parallel, rather than excessive series string. Easier to deal with, too.

A second possible source is radio waves or more like 60 Hz fields from powerlines coupling in.

And finally, backfeed through the charge controller from AC. One of my GT PV inverters registered power production at night; the others did not. A quick calculation ruled out yard light illumination.

 

[OzSolar]

I know this would entail a vast amount of panels, that goes without saying, but wouldn't 7 panels in series collect 14 volts (probably zero to minimal amps I assume)?

Fun question!

Let's play with the math and assume that you could get .1 amps. Realistically you probably can't even get .01 amps but for fun we will continue.

V x A = Watts

14 x .1 = 1.4 watts which I don't think will even power up a charge controller let alone be any sort of usable wattage.

Continuing with the exercise let's take it up by a factor of 10 and put 70 panels in series. 140 x .1 = 14 watts and realistically it's probably worse than 140 x .01.

FWIW: I have a numerous solar array's ranging from 300 to 550 Voc. Often a few minutes after sunrise the inverters or MPPT's hooked up to them start trying to turn on but they quickly turn back off because there isn't enough power to keep thier internals powered up. They go through this cycle 4 or 5 times over a 30 minute period they finally stay on. I've never observed that behaviour in the full moonlight.

 

[AntronX]

Full sun is 440,000 times brighter than full moon. Scale that to 10kW PV array and you get 23 mW under full moon. Enough for small indicator LED.

 

[12VoltInstalls]

Full sun is 440,000 times brighter than full moon. Scale that to 10kW PV array and you get 23 mW under full moon. Enough for small indicator LED.

That proves I was off by a decimal place LOL

 

[Reed Cole]

Full sun is 440,000 times brighter than full moon. Scale that to 10kW PV array and you get 23 mW under full moon. Enough for small indicator LED.

Sounds like a good way to know if the moon is full.

 

[Hogheavenfarm]

interesting replies, I knew the current would be small, didn't know how small though, "enlightening" discussion, "shed some light" on the subject.

 

[12VoltInstalls]

interesting replies, I knew the current would be small, didn't know how small though, "enlightening" discussion, "shed some light" on the subject.

By the dark of the moon she planted…

 

[efficientPV]

Thinking volts is a complete misunderstanding of solar panels. Panels are current generators. The fact that it is 2 volts is the panels can barely produce enough current at night to even overcome the panel leakage. This was similar problem with people accepting ohms law hundreds of years ago. The experiments in producing more current by adding more batteries didn't work. They thought voltage didn't matter. They didn't think about internal resistance of batteries.