I-V curve

[rubberlele]

Hi! I cant understand this solar I-V curve thingy. Can someone please explain it? How come when voltage increases, current will go down? and one more thing, if i wanna do an experiment on my solar panel? What should i do? Thanks!

 

[Roff]

Hi! I cant understand this solar I-V curve thingy. Can someone please explain it? How come when voltage increases, current will go down? and one more thing, if i wanna do an experiment on my solar panel? What should i do? Thanks!

I think it is easier to understand if you observe that it has a short-circuit current of about 15ma and an open-circuit voltage of about 17V. What this means is that, as you increase the load current from zero (decrease the load resistance), the voltage will drop fairly slowly until you reach about 14 ma. Decreasing the load resistance past that point will result in very little more current output. Why does it do that? You can't reason with it. It's just the way it works.

 

[rubberlele]

Thanks Ron, i took this figure from a friend, so if i have my own solar panel and i wanna determine its I-V curve, wat can i do? Should i connect different resistors and then measure Voltage across the resistor?

 

[evandude]

yes, ronH is right. You were just thinking about it backwards. it makes more sense to think of it as the voltage going down when the current goes up. probably would have made a little more sense if they'd switched the axes.

 

[evandude]

Thanks Ron, i took this figure from a friend, so if i have my own solar panel and i wanna determine its I-V curve, wat can i do? Should i connect different resistors and then measure Voltage across the resistor?

that would be a simple way to do it. with enough various combinations of resistors you should be able to interpolate the I-V curve pretty well.

 

[rubberlele]

Thanks evan, so what should i do is, connect the panel to a resistor, measure the voltage across it, then change the value of the resistor to a higher one and measure voltage across it, and so on yeah? how can i get the value of current? Is it V/R?

 

[evandude]

yeah, I=V/R. you would probably be best off starting with larger resistors and working your way to smaller values, (going from low current to higher current)

 

[rubberlele]

ohh..okay...actually in my workplace here, we have somesort of electronic load, but since i dunno how to use it, better use the good ol' resistor.

 

[Roff]

EDIT

The curve you erased appears to be power, labeled on the right side vertical axis. Is the current in ma or in amps (If it's amps, this is one mozam solar cell!)?

 

[rubberlele]

okay Ron this is the original one. This curve i got it from a software called PV Pro Design. It will determine the I-V curve for a specified solar panel.

 

[rubberlele]

and this one is from the manufacturer, for the one that i got from the software, its for 2 solar panels in parallel, or so i think

Number of Parallel Module Strings:1 Array Slope: 21.00
Number of Modules in Each Parallel String: 2 Array Azimuth: 0.00

 

[Nigel Goodwin]

Interesting that performance falls off with increasing temperature?, when you have to have the panel in incredibly bright sunlight to work - seems rather counter productive?.

Be interesting to know how bright that specified level actually is?.

 

[rubberlele]

for the whole day today, i collected data for my pump. I found out that during bright sunlight and higher temp, my pump will have more L/min. I think so