Check My Math Real Quick - Adding 6 335w Panels to my 18 290w Array

[Hedges]

When @Hedges and I present opposing views/recommendations, always go with @Hedges

If two people are perceived as knowledgeable, but one is known to be more knowledgeable, it helps to identify that person.

Both approaches may work. Unless one of us identifies a safety hazard, feel free to try both.
I do make mistakes, and get absent minded/careless. Last time I did that, I happened to live to tell the tale.

Looks to me like existing array is 86% the Vmp of new array. Even if current doesn't increase when pulled to lower voltage (it does), worst case simple estimate is you get 86% power from new array. KISS, just accept those figures and enjoy more power.

Multiple orientations is good, keeps batteries charged longer through the day and reduces likelihood of clipping.

I would like to have seen Andy turn off the MPPT and allow the array to sit at Voc. I suspect he would have measured a small current flow through the lower voltage array.

Less than you might expect. I thought I/V curve of panel would indicate current drawn when backfed, but I tried it with one panel in a dark room (looking for light emission), and around Voc it only drew about 1/2 of Isc or less.

Yes ... but can you translate @Hedges for me ?

Can it be done ... or can't it. (I think I understand that it can be done)

Just go for it, report the results.

 

[Hedges]

Again, you're losing about 300W of performance at a minimum. You're arrays will have two localized power peaks - one where the 330W panels dominate and another where both arrays contribute. I would trust that the Classic can figure it out, but it may not be horribly effective, particularly if conditions are changing rapidly like with passing clouds.

Two separate peaks can confuse some MPPT, they stop at the higher voltage peak which may be lower watts.
Peaks of separate arrays are 15% apart in voltage, so parallel array may just blend into one peak in between.
Either way, the Classic should be smart enough to find it.

I tested a 9s2p array by shading a single panel, making it 9s || 8s, 8/9 = 89% or 11% apart. The output power was close to 17/18ths as much as unshaded array, with a quick check. So I think mixed voltage isn't too bad when not far apart.

 

[MrM1]

I do make mistakes, and get absent minded/careless.

I smoked a BMS last week for this reason.

And then I accidentally set one new 304Ah EVE cell on top of the post of another new 304Ah EVE cell while moving the batteries around (I had set one down beside me, could not see it in my side vision, and set the other one right on top of it's negative post. The result, broke thru the black bottom LFP cover, and dented the bottom of the case. Still going to look at it and watch the cell closely for a leak. Still not sure if it's safe to use or should I replace it. But as of now, for the past 2 days, all 16 cells are holding charge perfectly with a delt of only 0.006)

Sad to say ... but about 18 months ago, I developed double vision that has not gone away, and still cannot be definitively diagnosed. Has created all sorts of Life issues. But was the reason I smoked the BMS and placed the one cell on the other resulting in damage. So yeah, I get the mindless / careless thing. And that is why I ask so many questions. So far, with this solar stuff over the past 5 years, I have been able to amaze my friends, but I don't wanna blow myself up in the process.

I now have to use glasses with a prism in the lens ... or else I see the world like this ...

Just go for it, report the results.

Yeah ... the 335w panels are cheap. I need the power to actually charge the new Big Ax Battery bank. And hey, it's only money ( but those NEO 335s are going out at $87) ?

 

[MrM1]

So I think mixed voltage isn't too bad when not far apart.

And so just to be clear ... 15.5v difference between strings is NOT too far apart?

 

[Hedges]

Not too far apart.
15.5V out of 112V or 97V, around 15%.

Scroll down to figure #9, see how much power curve is reduced if voltage increased about 5% above peak, or reduced about 10% from peak.

https://www.buyers-world.nl/pdfs/tigo-energy/TIGO-impedance-matching-eng-02-20-13.pdf

I expect you'll see less than 15% reduction from what added panels would contribute if they had their own MPPT. So just adding to existing array gives the most Wh/$