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Rixter
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Solar Cells and LEDs

02/16/2021 9:35 PM

Here is something interesting. A solar cell converts light into electric current and a LED converts electric current into light. It turns out that, like motors and generators, LEDs and solar cells are reversible opposites. A LED can produce a voltage if light is shown on it, and it turns out that applying a current through a solar cell will emit light, albeit near-infrared.

Cell phone cameras are sensitive to near-infrared. The first chance I get, I plan on trying to see the emission by connecting a battery to a solar cell using a phone camera. Solar cells are interconnected by fine wiring, and seeing an image would identify broken circuits.
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LG_Dave
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#1

Re: Solar Cells and LEDs

02/17/2021 12:04 AM

I have used a digital camera to watch the LED on a TV remote.

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Rixter
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#2

Re: Solar Cells and LEDs

02/17/2021 4:59 PM

Well, I tried it out with a broken decorative yard light from which I removed the solar cells. I connected a half-dead 9v battery and it was drawing about 400 ma. I wasn't able to see anything with the phone camera. The phone camera can see the TV remote output but is not sensitive enough to see the solar cell output.

I have some night vision glasses that I was able to see the glow from the solar cell when the current was on.

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dkwarner
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#3
In reply to #2

Re: Solar Cells and LEDs

02/18/2021 12:04 AM

Interesting. I have a FLIR-one IR camera attachment for my iPhone, and I certainly have a non-functional yard light. I'll see if I can try that...

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Rixter
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#7
In reply to #3

Re: Solar Cells and LEDs

02/18/2021 9:18 AM

FLIR-one detects and images heat, or far-infrared, 5-20 micron wavelength. The solar cell emits near-infrared, 1-2 micron wavelength, corresponding to the bandgap of silicon, ~0.7 volts. You'll probably see the heat if enough current flows through it to warm it up.
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tonyhemet
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#4

Re: Solar Cells and LEDs

02/18/2021 1:25 AM

This may be off topic. An observation : I installed a 4 foot LED strip light in my shop, when I turned the light on it was very bright, when I turned the light off, the LED strip went dark.

I thought the light was too bright so I laid a piece of cardboard in the full length and width of the plastic diffuser cover, then light would only emit from the sides of the diffuser.

Now the led strip will dimly glow all night. I disconnected the 120v power supply to the light in reasoning that the light switch was leaking current, still the light glows dimly.

My only guess is that the cardboard is holding a charge and energy is being released to power the led strip.

This past summer I noted that when I opened the door and windows of the shop and did not turn the light switch on, the same effect occurred as if the sunlight was " charging " the cardboard .
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SolarEagle
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#5
In reply to #4

Re: Solar Cells and LEDs

02/18/2021 2:12 AM

Maybe the led's are phosphorescent, wait a while and the glowing should stop...

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Rixter
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#8
In reply to #5

Re: Solar Cells and LEDs

02/18/2021 9:33 AM

Maybe the led's are phosphorescent, wait a while and the glowing should stop...

I've seen fluorescent lights and old tv sets have an after glow.
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tonyhemet
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#9
In reply to #5

Re: Solar Cells and LEDs

02/18/2021 9:40 AM

I forgot to mention that the glow lasts all night
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Rixter
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#11
In reply to #9

Re: Solar Cells and LEDs

02/18/2021 1:02 PM

You don't live under HV power lines, do you?

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tonyhemet
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#12
In reply to #11

Re: Solar Cells and LEDs

02/18/2021 1:19 PM

Actually yes, well sort of. telephone poles with hv wires . There is a pole in the front center of my property 1/2 way within the public easement.

The poles are about 125 ft high, two tier, 4 conductors per tier.
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dkwarner
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#13
In reply to #12

Re: Solar Cells and LEDs

02/18/2021 2:05 PM

Hmm... Poles that high probably carry 100 kV or more. How far are they from the shop?

Sounds like Rixter has hit the nail on its head.

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tonyhemet
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#14
In reply to #13

Re: Solar Cells and LEDs

02/18/2021 7:43 PM

As the crow flies, maybe 300 ft (?)

I have a digital tv antenna that feeds into two units with filters, although my scanner uses crystals and there is no background noise so em must/may not be enveloping the lamp.

Sorry I didn't mean to hijack this post, just thought I could put in my two cents for all its worth.
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dkwarner
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#15
In reply to #14

Re: Solar Cells and LEDs

02/18/2021 9:55 PM

The TV and scanner are sensitive to vastly higher frequencies than the EM waves emitted by power lines, so I don't think the lack of interference tells you anything about the possible energy being emitted by the power lines.

300 feet sounds like a pretty good distance, but then its less than three times the estimated height of the towers.

Have you tried replacing the cardboard with other materials, like plastic or sheet metal? Or try wrapping the cardboard in aluminum foil. Let us now what you find...

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Gavilan
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#18
In reply to #11

Re: Solar Cells and LEDs

02/19/2021 3:06 AM

If your suggestion is possible would it be possible to draw parasitic power from the 60 hz field source by using a whole wave resonant scavenger circuit?

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dkwarner
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#21
In reply to #18

Re: Solar Cells and LEDs

02/19/2021 11:26 AM

Certainly. ...or even a half-wave or a quarter-wave.

Unfortunately, λ=V/F=300,000,000m/s / 60/s = 5,000,000 meters, which is 5,000km, or approximately 3,100 miles, so even a quarter wave would be around 780 miles.

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Gavilan
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#22
In reply to #21

Re: Solar Cells and LEDs

02/20/2021 2:57 AM

I thought that was what capacitance and inductance was for.

A series RLC circuit tuned to 60 Hz used as the parasitic power collection circuit, pumping a collection circuit, and charging the storage device.

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dkwarner
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#23
In reply to #22

Re: Solar Cells and LEDs

02/20/2021 12:01 PM

The energy that can be harvested from any varying field is limited by the intensity of the field and the area/volume of the receptor. When the field is relatively weak, the receptor must be relatively large.

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Gavilan
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#24
In reply to #23

Re: Solar Cells and LEDs

02/20/2021 10:53 PM

In a series RLC circuit at resonance, the reactance is zero, and the impedance becomes equal to resistance. A very low resistance translates to a higher current, thus power, at any induced voltage.
If ambient field can light an LED; then it seems reasonable there should be harvestable energy available at that location.
What would the circuit look like in its simplest form?

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dkwarner
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#25
In reply to #24

Re: Solar Cells and LEDs

02/21/2021 12:15 AM

You are absolutely correct.

However, the energy required to make an LED glow at low intensity is really tiny. We have a string of LED lamps in a Ficus plant in our living room. The lamps are plugged in to a wall socket that gets its power from a wall switch.

Obviously, when the switch is turned on, the LEDs glow at normal brightness. When the switch is turned off, one would expect the LEDs to go dark, but they do NOT! They all glow at much lower intensity, but at night time they provide enough light to move around the room with confidence. The current to make them glow is provided by the capacitance between two wires that are not connected to each other, because the switch is on the "low" wire leading to an old two-pin outlet with no ground.

Th left photo is with the switch ON, the right with the switch OFF.

Some years ago, I verified this concept in another thread here in CR4, dealing with a small candelabra using LED lamps in our hallway. I believe that thread was initiated by Andy Germany, who unfortunately is no longer with us...

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Randall
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#20
In reply to #11

Re: Solar Cells and LEDs

02/19/2021 5:19 AM

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RoundedRooster
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#17
In reply to #4

Re: Solar Cells and LEDs

02/19/2021 3:01 AM

Possible a combination of forward current leakage from the remaining energy stored in the output capacitors and a coincidental optical illusion.

Or... it's the cardboard!

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HiTekRedNek
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#6

Re: Solar Cells and LEDs

02/18/2021 6:10 AM

Card board is made from recycled paper.There is probably a high content of phosphorescent scrap in the card board.This will create the after glow you are experiencing.

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Deefburger
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#10

Re: Solar Cells and LEDs

02/18/2021 10:42 AM

I took a cheap usb web camera and removed the lens and popped the red filter out and put the lens back in. You can see the whole spectrum of the camera that way including infrared. However, the infrared image on screen is only black and white as there are no colors mapped to those frequencies for display.

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RoundedRooster
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#16

Re: Solar Cells and LEDs

02/18/2021 10:07 PM

The LED will produce a small amount of current and you'll need to amplify it. This is an old trick for making sensors in the hobby world. Take the metal can off a 2N2222 (and any can type) transistor and you can turn it into an optocoupler. You're far better off just buying components designed for a specific purpose, than trying to convert energy in the opposite direction. Far more efficient to use them as intended, far less not to.

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JWthetech
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#19

Re: Solar Cells and LEDs

02/19/2021 5:02 AM

Folks who live on boats have known this for years. A solar panel without blocking diodes or a relay will discharge a battery during periods when there is insufficient light to generate power. It makes sense the result is in the form of heat e.g. infrared
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Deefburger (1); dkwarner (6); Gavilan (3); HiTekRedNek (1); JWthetech (1); LG_Dave (1); Randall (1); Rixter (4); RoundedRooster (2); SolarEagle (1); tonyhemet (4)

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