Measuring Solar panel voltage with Arduino

Using Arduino Project Guidance
1

Hi,
I have a solar panel which voltage output I'd like to measure. It is capable of producing 18.50 V at maximum.
I know that the my Aardu can only have 5 volts as an analog input.
I have created a resistor circuit to make the voltage drop below 5 volts. Image is attached.
I measured the voltage with a multimeter just to make sure and it gives voltage below 5 volts. Cool.
By the way, the Arduino is powered via USB.
I'd like to print the read voltage to a serial port so I wrote the following code:

void setup()
{
Serial.begin(9600);
}

void loop()
{
int sensorValue = analogRead(A0);
float voltage = sensorValue * (5.0 / 1023.0);
Serial.println(voltage);
delay(1000);
}

When I wire the ardu and the resistor circuit together, which is connected to the solar panel, the analog pin does not seem to read values for it always prints 0.00.

Can you advise me what am I doing wrong?
Thanks

resistorpack másolata.jpg
resistorpack másolata.jpg1100×1000 96.2 KB

2

In the mean time I just figured out the the wiring should be swapped. Sorry.

3

Yes.
You have drawn the solar panel with the wrong polarity.
solar- goes to ground, and solar+ goes to R1.

What are the values of the resistors. 10k would be ok.
Leo..

4

I wouldn't be very concerned about your solar panel until you have connected your resistors across your arduino 5V and GND and read the voltage from the voltage divider using the analog input. This is basic troubleshooting common sense. Eliminate the unknown and verify you measurement hardware is working before attempting to measure an unknown.

Disconnect your solar panel.
connect your resistors to your 5V
measure the voltage.
If that works then try the solar panel.