Solar Panel Voc-MPPT?
Wondering if there is any relationship between measured Voc and MPPT performance with a 24v panel. My 12v panel has a Voc rating of 21.9 and Isc of 8.2, but I often see 8.2ish when Voc is only 20....
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Afain, you're wrong. I now realize you know very little on the workings of controllers & PV cells; just enough to be dangerous.
In my previous post, I didn't say the power is fixed! It can vary all over the place. I just picked one operating point; when the mppt controller outputs 100W. Guaranteed, mppt performance will degrade 14.3% when battery voltage increases from 12.0V to 14.0V.
Also, you don't have a clue how pwm works. This system outputs a current that's a few percent less than than the short circuit current of the panel. Isc is NOT affected by temperature! If anything, current increases a little with temperature.
Sal
In my previous post, I didn't say the power is fixed! It can vary all over the place. I just picked one operating point; when the mppt controller outputs 100W. Guaranteed, mppt performance will degrade 14.3% when battery voltage increases from 12.0V to 14.0V.
Also, you don't have a clue how pwm works. This system outputs a current that's a few percent less than than the short circuit current of the panel. Isc is NOT affected by temperature! If anything, current increases a little with temperature.
Sal
ken white wrote:Salvo wrote:
Careful when making a mppt to pwm comparison. Not only is mppt highly temperature dependent, but also battery voltage dependent. PWM can also be effected, but not as extreme.
For example, you got a mppt controller that outputs 100W. If battery voltage is 12.0V, charging current is:
I = P / V = 100V / 12.0V = 8.33A
If battery voltage rises to 14.0V, charging current is 7.14A, a 14.3% reduction.
Sal
The controller controls the rate of the battery's voltage change, and hence charge (input current).
Power delivered by the panel, and required by the batteries, will never be fixed and will be varied by the MPPT controller as needed so a fixed % analysis is moot.
As a side note, the MPPT controller is no more temperature dependent than the PWM controller and while you do get a larger change in voltage due to more series cells when using the higher voltage panels, the change in available power is nearly the same between panel types, so its really a wash...
