# Using Diode As a Solar/Lightbulb Cell

...hi :) a few days back I saw this Instructables..

https://www.instructables.com/id/Using-Diode-As-a-Solar-Cell/

...so I started to experiment how this can be used to charge a cellphone or a battery. I soldered 3 block of 11 diodes in series, each soldered in parallel (as show in the picture)...

...here is it really desorganized (but it works)...

...taped the diodes to a lamp and as you can see a LED lights up (it can shine harder so I want to know how)...

...when I measure Voltage it shows up to 30 V...(!) (don't know why) ...haven't been able to measure Current. ...also I don't understand why the Led haven't burned out and why it is lightning up.

... so my question is: If the LED lights up, does this means that Voltage and Current are flowing?

...and a more general one: Have anyone tried to give diodes this use and how can I improve my approach?

thank you very much! :)

• I've done this with glass 1n4000 series diodes but I couldn't measure any current from a glass 1n914 style. Commented Mar 20, 2019 at 23:44

I am pleasantly surprised by your third image, I would have not expected that result.

To answer your main question, the LED lighting up (even that dim) indicates the presence of voltage and current. However, the dimness also indicates how little current is present.

The electronics explanation of what's going on is that the photons from the light are generating a current in the diode. Each diode that's getting illuminated electrically looks a bit like the schematic below:

simulate this circuit – Schematic created using CircuitLab

Depending on the diode you used, that forward voltage may be around 0.6 - 0.8 V. Without a load, the generated photo current will just flow into the diode. While 30 V sounds suspiciously high for the circuit you have drawn (I would expect maybe 6-8 V instead), you should be able to measure that voltage. This is the open circuit voltage, as there is no load.

If you load down the output, maybe even using a microamp scale on a multimeter, you can see the maximum current your array will provide under those conditions.

The LED lighting tells me that your voltage is probably better than 2.0V, and maybe 1-10µA of current is flowing, which is not a whole lot of power. There are a bunch of things that are hindering how much power you can extract from this setup, here are a few:

• Exposed Area - Each one of those diodes has maybe 1 mm^2 of silicon in it. Probably half of it isn't facing the light, and a good chunk may be covered by opaque materials, such as aluminum.
• Illumination Intensity - Typically, indoor lighting is pretty dim compared to the sun. The current output is mostly proportional to the amount of light that hits each of the diodes. If you took it outside, you would get more power under direct sunlight.
• Angle of incidence - The angle that the light hits the diode should be perpendicular (90 degrees) and this will be difficult to align for each individual diode

These issues are why this diode array will never out-perform a solar cell of the same shape and size - the solar cells have been optimized for turning light into power, and these diodes have been optimized for being electrical diodes.

• thank you W5VO... I have been busy improving and applying what you told me... in theory if I connect diodes in parallel I can get higher currents... if you have time please give a look to the project log... hackaday.io/project/164769/logs again, thank you very much! Commented Apr 5, 2019 at 16:08
• @chunkymouse I think the next step would be to try and measure the short-circuit current of your diode array. Just use your meter, with the leads connected for measuring current, directly across the terminals of your diode. You might also look for higher efficiency LEDs, as that may be an easy way to get better brightness for the same amount of current. I would guess that the open circuit voltage would only need to be twice the forward voltage of the LED, so you may be able to double up that way.
– W5VO
Commented Apr 5, 2019 at 18:23
• ...yeap, I am still unable to measure it... think the current is really really low Commented Apr 5, 2019 at 23:59