I've been thinking of making a quick and dirty IV-curve tracer for solar panels, and I finally got the time.
It consists of an IRF520 MOSFET to function as a VCR, an INA260 breakout board to take the measurements and an Arduino to generate a PWM and gather the data onto an SD card.
Everything is working as it should, the data is neatly collected and there's no magic smoke. Success!
Or so I thought until I started to look at the data and plotting the actual IV curve...
It looks awfully linear and not at all how I expected, and I can't for the life of me figure out why.
I've been doing some reading on MOSFET and logic level PWM and I've come to the conclusion that the IRF520 is not the best match for the Arduino. But I've measured currents up to around 3A, which seems to be about what I can expect from the IRF520 with Vgs at 5V.
I have also included a reference PV cell to calculate the irradiance in w/m2.
The graph is based on these circumstances:
* Panel data: Voc = 21.5, Isc = 3.92, Vmp = 17.3, Imp = 3.56, Pmp = 60W
* about 800w/m2 irradiance 90 degrees to the panel. Not all over the panel tough, this might explain the low Isc.
* Vgs is a 980Hz PWM, that is stepping duty cycle from 0 to 255 bits 1 bit at a time.
* The light source is a bunch of 250W lights.
So Voc seems to be as stated by the panel datasheet.
Isc is low, but I've confirmed with a multimeter that with the setup I used it actually was about 1.6 A.
So now, let's get to my qeustion: Why is the current decreasing linearly ? I have a hard time telling if it's related to the MOSFET and/or the INA260 or the fact that i don't have the full 1000w/m2 irradiance or something else...
Any thoughts on this would be really helpful!
I guess my knowledge is lacking, and I don't even know I don't know. So I hope to learn something new!
Thank you for reading!
It consists of an IRF520 MOSFET to function as a VCR, an INA260 breakout board to take the measurements and an Arduino to generate a PWM and gather the data onto an SD card.
Everything is working as it should, the data is neatly collected and there's no magic smoke. Success!
Or so I thought until I started to look at the data and plotting the actual IV curve...
It looks awfully linear and not at all how I expected, and I can't for the life of me figure out why.
I've been doing some reading on MOSFET and logic level PWM and I've come to the conclusion that the IRF520 is not the best match for the Arduino. But I've measured currents up to around 3A, which seems to be about what I can expect from the IRF520 with Vgs at 5V.
I have also included a reference PV cell to calculate the irradiance in w/m2.
The graph is based on these circumstances:
* Panel data: Voc = 21.5, Isc = 3.92, Vmp = 17.3, Imp = 3.56, Pmp = 60W
* about 800w/m2 irradiance 90 degrees to the panel. Not all over the panel tough, this might explain the low Isc.
* Vgs is a 980Hz PWM, that is stepping duty cycle from 0 to 255 bits 1 bit at a time.
* The light source is a bunch of 250W lights.
So Voc seems to be as stated by the panel datasheet.
Isc is low, but I've confirmed with a multimeter that with the setup I used it actually was about 1.6 A.
So now, let's get to my qeustion: Why is the current decreasing linearly ? I have a hard time telling if it's related to the MOSFET and/or the INA260 or the fact that i don't have the full 1000w/m2 irradiance or something else...
Any thoughts on this would be really helpful!
I guess my knowledge is lacking, and I don't even know I don't know. So I hope to learn something new!
Thank you for reading!