[SOLVED] Voltage drop in solar panel when it is connected to load

I am using a 10W solar panel for a sun tracker project. I need to monitor the power at regular intervals.

But the voltage across the panel drops when I connect the load. The drop is in the range of 15V to 4V/5V.
The load that i am connecting is 2 10W resistors of 75ohms in parallel i.e 37.5 ohm in effect.

This value was chosen to match the characteristic resistance of the panel. **broken link removed**
I used the closest value I could find, actual value is 30 ohms approx.

The ratings of my panel are : 10W, 36 cells, Voc = 21.5V, Isc = 0.6A, Vp = 17.5V, Ip=0.58A

Is there a way i can minimize this drop?

Even though Panel IP is .58A many times it might be less, especially as the irradiance changes there will be lot of fluctuations.
you may have to test with higher resistance value.

Ya there are a lot of fluctuations. Current value goes to a max of .57 which is fine but the problem is voltage, it goes to a max of 2.59V.

What bothers me is that power values that I get, it goes to a max of 1.45W. I expected the panel to give a higher output. Its it okay for a 10 W panel to give such low outputs.

The load that I have connected, is it fine or can i change it to minimize the drop..??
PS: I am using a 200W light bulb as a source of light.

Here is a list of values that I recorded, incase that helps.

Voltage sensor: 2.58 Current sensor: 0.38 Power: 0.98
Voltage sensor: 2.58 Current sensor: 0.38 Power: 0.98
Voltage sensor: 2.59 Current sensor: 0.42 Power: 1.07
Voltage sensor: 2.58 Current sensor: 0.41 Power: 1.05
Voltage sensor: 2.58 Current sensor: 0.38 Power: 0.98
Voltage sensor: 2.59 Current sensor: 0.39 Power: 1.01
Voltage sensor: 2.58 Current sensor: 0.43 Power: 1.11
Voltage sensor: 2.59 Current sensor: 0.43 Power: 1.11
Voltage sensor: 2.59 Current sensor: 0.44 Power: 1.14
Voltage sensor: 2.58 Current sensor: 0.43 Power: 1.12
Voltage sensor: 2.59 Current sensor: 0.43 Power: 1.13
Voltage sensor: 2.58 Current sensor: 0.45 Power: 1.16
Voltage sensor: 2.59 Current sensor: 0.47 Power: 1.21
Voltage sensor: 2.60 Current sensor: 0.55 Power: 1.42
Voltage sensor: 2.59 Current sensor: 0.51 Power: 1.31
Voltage sensor: 2.60 Current sensor: 0.52 Power: 1.34
Voltage sensor: 2.60 Current sensor: 0.56 Power: 1.45
Voltage sensor: 2.60 Current sensor: 0.51 Power: 1.32
Voltage sensor: 2.59 Current sensor: 0.46 Power: 1.20
Voltage sensor: 2.59 Current sensor: 0.45 Power: 1.16
Voltage sensor: 2.59 Current sensor: 0.46 Power: 1.19
Voltage sensor: 2.59 Current sensor: 0.43 Power: 1.12
Voltage sensor: 2.59 Current sensor: 0.46 Power: 1.19
Voltage sensor: 2.59 Current sensor: 0.46 Power: 1.20
Voltage sensor: 2.58 Current sensor: 0.42 Power: 1.08
Voltage sensor: 2.58 Current sensor: 0.40 Power: 1.03
Voltage sensor: 2.59 Current sensor: 0.44 Power: 1.15
Voltage sensor: 2.58 Current sensor: 0.43 Power: 1.10
Voltage sensor: 2.59 Current sensor: 0.40 Power: 1.02
Voltage sensor: 2.58 Current sensor: 0.40 Power: 1.02
Voltage sensor: 2.59 Current sensor: 0.43 Power: 1.11
Voltage sensor: 2.59 Current sensor: 0.45 Power: 1.16
Voltage sensor: 2.59 Current sensor: 0.42 Power: 1.08
Voltage sensor: 2.57 Current sensor: 0.41 Power: 1.04
Voltage sensor: 2.58 Current sensor: 0.43 Power: 1.11
Voltage sensor: 2.58 Current sensor: 0.41 Power: 1.06
Voltage sensor: 2.58 Current sensor: 0.40 Power: 1.03
Voltage sensor: 2.58 Current sensor: 0.38 Power: 0.98
Voltage sensor: 2.58 Current sensor: 0.28 Power: 0.72
Voltage sensor: 2.56 Current sensor: 0.16 Power: 0.41

You ought to measure open circuit voltage and short circuit
current at the panel, all externalities aside, and verify that
you have what you think you have at the source.

Maybe your resistances are of 7.5 ohms or the panel is not receiving full sunlight. Otherwise you may need to replace the panel.

PS: I am using a 200W light bulb as a source of light.

Click to expand...

Think again!

I don't expect that the solar panel has a specification "10 W output with 200 W lamp". 10 W can be achieved with direct sunlight.

Found the problem, I was using a potential divider circuit to reduce the panel voltage for the ADC of micro-controller. It was the voltage of the potential divider that I had been looking at all the while. Upon scaling it with the same factor that the circuit had reduced it the voltage seems fine now. It comes somewhere around 10V.

So, stupid of me.

Thanks for help everybody.