More MPPT Confusion and Question

[BFL13]

Still trying to understand my MPPT set-up and what would be the effect of changing things a bit.

My 230w (30.0 Vmp x 7.7 Imp) poly panel has a Vmp of 30.0v with a measurement tolerance of +/- 3%
So actual Vmp could be anywhere from 29.1 to 30.9

My wiring zoo from panel to controller, measured in action this summer showed panel at EG 29.3 and at controller input 29.0

Voltage drop was therefore 0.3 at about ??7.7a Imp?? (Rated Isc is 8.3a and was getting that panel disconnected)

(I have the controller output wattage then at 203w (12.7Vbat x 16a) but that is after controller efficiency loss and whatever else)

So the question is, where it is trying to stay at Vmp at the "knee" of the IV curve, how bad is that 0.3 voltage drop? What would my controller output be if I cut that voltage drop in half say?

I am thinking (backwards? getting mixed up here) that the controller will "see" the panel voltage as 0.3v lower than it is. But on the IV curve that lower voltage would make the amps higher but if it is lower then amps are way down the knee drop off

Rating max is 230w (30 x 7.7) I measure 29.3v at the panel which is where the controller has set the voltage thinking that is the MPP?

But the controller input voltage is 29, not 29.3 so does that mean the controller's idea of MPP is 0.3 low or 0.3 high?

The IV curve where Vmp is at the knee which has a huge drop off in amps so a small change in voltage must have a big effect, but which way?

I am trying to calculate how much I can improve my wattage as seen at the controller output by reducing that 0.3v loss to the input by x amount and see if it is "worth it." But I am all mixed up 😞

[12thgenusa]

No sense trying to improve 1% loss.

Remember MPP isn't static. The number you are referencing is only at standard conditions.

A good MPPT controller will always be trying to set panel voltage to return maximum power to the controller regardless of what's happening in between.

[ken_white]

Its all about those pesky watts...

You can reduce power losses in the cabling to a lower level, but this will cost both time and money.

Personally, I live with the few watts of losses I have in my cables and just let my MPPT and panels do their thing.

[BFL13]

I did try that as one of my quickie tests last summer, but it didn't seem to make any difference to the amps at the battery within the margin of error so I can't say for sure. I won't be able to test again until next April so for now I was hoping to be able to calculate what ought to happen.

I am thinking I might as well put the Eco-Worthy inside where it is easier to get at, even if it costs me part of an amp. (Temp comp not an issue) Hoping to compensate for that somewhat at the panel end if I can ever figure out this MPPT /IV curve/Voltage drop with an answer in amps

[JiminDenver]

So run the panel closer to the controller and see if there is an improvement.

[BFL13]

Voltage calculator says my panel to controller connection is equivalent to #7 gauge copper (pair at 35ft one way at 29v and 8 amps) and I have approx. 1% loss with that 0.3v drop

It is actually a hodge-podge of jumper cables and wiring and connections that could be tidied up better ( panel is portable out away from trailer)

I take such a hit on the panel power from sun heating it (10% power loss) that I am not sure how much good it would do (in amps to the battery) in the big picture even if cut my voltage drop to 1/2 %

I just don't know enough about MPPT to figure what that drop I have now does to the controller output where it thinks the Vmp it picks is one thing and it is actually 0.3v different from that.

[red31]

wouldn't .15v x 7.7 be about 1 watt?

ain't mppt suppose to sweep back and forth to find Pmp?

[AlbertaNewbie]

what do you have for wire gauge on each side of the controller.

[BFL13]

I am prepared to live with it but I am interested in seeing what can be done all the way from panel to battery to do better than last summer, if anything.

I can't help the panel heating that costs me about 10% of its power, so any improvement I can make has to be from panel to controller and controller to battery, and I can't change the controller itself.

If reducing voltage drop on the wiring and connections will be insignificant at the battery then it is what it is.

I was thinking of moving the controller to inside the rig where I can see the display and play with the buttons, but this would increase voltage drop from controller to battery. I can calculate what that would cost me in amps to the battery.

If I can predict the amps to the battery effect of reducing the loss from panel to controller as in the OP question, then I could figure what the total cost in amps if any would be and decide if that is "worth" bringing the controller inside.

[MrWizard]

I think your trying too hard
Learn to live with it , with what it is..any gain will be insignificant