Reading voltage from solar cell

Using Arduino Sensors
1

I would like to read the voltage from a single solar cell using the ReadAnalogVolage sketch.
The Cell puts out a maximum DC voltage of about 2.5 and a current around 100mA in direct
sunlight.

Should I have a resistor on the analog input pin to protect the Arduino Uno board?
I am just measuring the Open Circuit Voltage for now.

Mike

2

The Uno will happily measure voltages between 0 & 5V without any external resistors.

however a solar cell is like a battery - the open circuit voltage tells you very little.
Remember power = voltage * current and if current=0 power = 0.

3

Thanks John

I do understand about having no load. I am in the learning process with Arduino and
writing code. I like to do some simple experiments like reading single and multiple cells,
current reading, Logging, using current and voltage sensor boards. Then moving up to
solar panels.

Mike

4

You may find my pages here interesting - and hopefully useful

5

Even though it is not necessary I would add the resistor as transient protection. It will not noticeably affect the reading. Something no larger than 10K would work great.

1 Like
6

I have read the same suggestion some place as well. I am new to this and trying
to learn best practices early on.

While I wait for my 3V solar cells to arrive I think I will grab a second 10K pot and
wire the circuit up to a second analog pin, add to the sample code, and read two
at once. I think the Arduino experimenters bug has bitten me!

1 Like
7

That bug is mighty powerful! Have fun, that is the most important thing. Thanks for the update.

8

So not a single solar cell. Most solar cells output about 0.45volt to 0.65volt.
2.5volt open circuit could mean a 2volt solar panel (four cells in series).

Open circuit voltage does not change a lot with light level, but cell current does.
Therefore it's best to use cell voltage for a day/night sensor,
and cell current (loaded cell) to measure light levels.
Leo..

9

Yes I keep making that mistake. I call them Cells but your right they are actually mini panels
like the ones you might find on top of solar garden lights. They are made up a collection of
Solar cells to get various voltages and currents.

Mike

10

Sunlight can be measured by putting a low value resistor across that 2volt panel (almost shorting it), and switching the Arduino (assuming Uno) to 1.1volt Aref in setup().
Try something like 10-100 ohm.
Leo..

11

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