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Adrian Sharp avatar image
Adrian Sharp asked

2 x Smartsolar MPPT 100/20 - 24v or 48v system

Hi all. I've been given 2 PV panels. They are different in the fact that one is 235w 36.42 Voc 28.84 Vpm and the other is 240w 36.5 Voc 30.0 Vpm. Both made by EMMVEE but different colour / technology (?). Both appear to be suitable for a 24v system.

So I've taken the plunge and ordered 2 off Smartsolar 100/20 MPPT SCC (allowing for extra PV later) as I am assuming that each PV panel will have different MPPT characteristics (different Vpm's). I plan (initially) on using some large Pb (ex diesel) batteries that have been kept charged up with a "smart" charger.

I've also ordered a Multiplus Inverter Charger 800w unit (again allowing for future expansion), to provide an extra charging route if required.

Questions: should I keep to a 24v system and parallel the outputs of the 2 SCC's and use a 24v Inverter, or go for a 48v system with each SCC feeding a separate 24v battery bank, and then connecting the 2 x 24v banks to give 48v for the Inverter. (Cable sizes would obviously be easier with the 48v system.) ?

Can 2 Bluetooth SCC units be monitored independently ?

Has anybody tried a similar setup? Any pitfalls?

Thankyou for your help.

Multiplus-IIbattery chargingBluetooth
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1 Answer
JohnC avatar image
JohnC answered ·

Hi. There's a few points for consideration here:

* 24 vs 48V. If you've already ordered a Multi, then it's locked in - unless of course you return it. Let's assume 24V, which for a modest system with an 800W Multi, is likely quite suitable.

* Those panels are so close in specs that they don't warrant 2 cc's. And their V specs are quite low, so you'll find rather than paralleling them into 2 cc's you'll get better daily production by series wiring into just one of your 100/20's. 20A into a typical 28.8V absorb setting is 576W, so no capacity issue there. Note the Vbat of 28.8 is too close to your Vmp for practical purposes, and you'll get crucified in poorer pv conditions if you parallel those panels.

* Maybe keep the other and grab a couple more modern (say) 300W panels later for your future expansion. Series them too (unless they're weirdos).

* Please don't 'part-charge-half-banks'. Preloved Pb's may well already suffer balance issues, without you building more into your design. Not good practice - please reconsider.

* Cable sizes won't worry you too much at this level.

Please ask again if you need more. Second opinions welcome too. :) Good luck.


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Adrian Sharp avatar image Adrian Sharp commented ·

Many thanks @JohnC for the helpful advice. I hadn’t considered the better option of the two panels in series, but can see the need for the higher voltage. 24 v Multiplus 800 received, 100/20 Mppt and Venus GX arriving soon. New batteries will follow as finances dictate! Happy new year.

Electrocoolman.

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