question

danjwilko avatar image
danjwilko asked

Dual 100/20 or single 100/50?

Hi all,

Appreciate a similar question has been asked before but I’m unsure which way to go with our setup.

We currently have a 24v system with 600w of panels, the original plan was to have a 24v system and upgrade to a 48v system with a dual set of 100/20 mppt’s, now it looks like we’ll be staying 24v for the foreseeable.

Side note: we have maxed out the 100/20 twice with the winter sun.

I was looking at adding a second 100/20.(adding more panels up to 600w on each). But I didn’t know If going to a single 100/50 would be a better since it can handle 1400w else I’d be limiting the two 100/20’s to max 1200w (580 each technically).

But having the two would offer redundancy however cabling costs come into play being 35/40m away from the array.

Having just the one larger setup would follow the KISS philosophy.

The second question was heat generated by the 100/20mppt (only warm at the moment not hot hot), would that affect the longevity of the unit? I assume the 100/50 would be better on the thermal side due to being larger and made from alloy rather than plastic?


So yeah not sure which way to go in all honesty.

Appreciate any and all input, trying to decide is a pain lol.

Regards

Daniel.

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JohnC avatar image
JohnC answered ·

Hi @Danjwilko

Unless you're adding more panels, I wouldn't do anything. That you've 'maxed out' a couple of times won't do any harm to the mppt, and adding another will gain very little, if anything, in overall output. This sort of clipping can also happen at times of 'cloud edge effect', and that's usually for fleeting periods anyway.

Not sure why you wouldn't be looking at just a 100/30 either? I wouldn't worry about heat dissipation, these things will derate to protect themselves if they need to, and unless you experience this regularly, nothing to worry about.

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danjwilko avatar image danjwilko commented ·
Thank you for your input it is appreciated.


We are looking at adding panels hence the dilemma.

I would have gone for the 100/30 in hindsight if we wasn’t wanting to go 48v route which the 100/20 fitted the bill.

However since we’re now sticking with the 24v system I would either add another 100/20 each with 600w of panels or go for the larger single 100/50 and either sell the 100/20 or use it in a smaller project.

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JohnC avatar image JohnC ♦ danjwilko commented ·
@Danjwilko

What you decide on with the added panels will determine where to head. Also how they're strung depending on their environment (selective shade, etc.).

Also with those long wires. If the added panels have different specs, then you may need an additional mppt and an additional wire pair anyway.

But don't buy the panels first. Do your plan first and work from there. You may even find an advantage moving up from the 100/ mppts with longer panel strings (higher V and lower Amps). There's tradeoffs every direction you look, so you need to determine the balance that's best for you.

I reckon simple is best, like one mppt if you can. These mppts are reliable as hell, and redundancy doesn't count for much with me.

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kevgermany avatar image kevgermany ♦♦ JohnC ♦ commented ·
@Danjwilko

Also watch the current limits on the connections. MC4 max is 30A.

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