Solar Panel Voc-MPPT?

BFL13 wrote:
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 20.3ish. That's fine, I just want that Isc. ( I know they have different coefficients from 25C)

But now with MPPT and a 24v panel I am seeing the same sort of thing.
Panel is rated Voc 37v and Isc 8.3a In the sun trying it out I got 34.5 Voc (varies -did see 36 at one point) and Isc of 8.24a

Normally, I would be happy at seeing that Isc, but now I am wondering if that 34.5 Voc instead of 37 rated would show up as lower amps to the battery via the MPPT.

(Vmp is 30v and Imp is 7.7a)

Is it still the case with MPPT that if you are seeing the Isc at the panel, all is well, or with MPPT does Voc matter now, or what?

Thanks.

Solar panels will produce usable voltage/power from their Voc all the way down to battery voltage and then they don't produce usable power anymore.

So higher voltage panels have a wider power margin that an MPPT controller can take advantage of.

If you assume the controller is ideal, then power in equals power out - lets keep this analysis simple.

Example: Power in equals 150W when V = 30V and I = 5A. Power out equals 150W when the battery voltage equals 13.3V which means the current has increased to 11.29A.

The above example is one benefit of the MPPT controller - higher panel voltage and less losses.

The other advantage is the panel voltage will be able to produce power between the 30V value all the way down to the 13.3V battery voltage, so it has a voltage margin of 16.7V which gives the panel a wide power range into the lower light levels.

If a PWM panel only produced 17V for the same irradiance, it would only have about a 3.7V margin and would cut out much sooner as the light intensity diminished - much less power capability.

Good luck with your quest...

:)