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davisdaler avatar image
davisdaler asked

MPPT Solar Charger Sizing

Hi Guys, New to group, working on designing small system for van. Specs:

1. (1) 400 watt mono panel, VOC : 37.07V, VMP: 31.01V, ISC: 13.79A, IMP: 12.9 A

2. 3 - 12V 100ah Lithium life04 batteries in paralell, (300ah), may add a 4th later if needs not met

3. Also using, Orion XS 12/12-50A Dc-DC Charger to charge from Alternator, also Multiplus-II Inverter / Charger 12/3000/120/50,

I plugged in the information on the Victron Energy MPPT Calculator, but I wasn't sure what to enter for a single 400 watt panel info : in Series & Strings boxes I used 1 and 1 respectivly. I used 3M cable length, and 10.0 for crossection.

The calculation spit out numerous results for MPPT Units with declining efficiencies. Top of the list was 1. Smart Solar MPPT 100/30 @ 91% efficiency (undersized). Next was Smart Solar MPPT 100/50 @ 57% efficiency ( undersized).

My 2 part question :

1. Is the MPPT 100/30 a good choice for the above configuration?

2. If I wanted to add 200w more in panels and another 100ah battery down the road should I use a different unit so I'll be covered? like MPPT 100/50? Or should I just go with the MPPT 100/30 for now to maximize efficiency with the present system ....and then just plan on changing the MPPT later for best efficiency for the upgrade? I think the 4000W panel and 300-400ah battery bank will work out but I might add more loads in the future knowing me. Thank you in advance for any advice.

MPPT Controllers
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Justin Cook avatar image
Justin Cook answered ·

The MPPT Calculator is the best way to play with different PV configurations, yep! And you're correct, a single panel is 1p1s.

https://mppt.victronenergy.com/

A single 400w panel charging a 12vNom battery bank could only possibly (under ideal conditions, which of course don't exist) generate about 29A of charge current, so the 100/30 would be appropriate.

And if you're adding more panels of different specs down the road, you'll want a separate controller for them, yes - it is not recommended to install panels of differing specs on a single controller.

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davisdaler avatar image davisdaler commented ·

Thanks,....and Yes ...with the one 400watt panel , its not ideal, however using the vehicles alternator to charge will help. It's only when parked for several days in cloudy weather is when I will suffer low battery bank power. When I plug the numbers into a " solar panel to battery bank CHARGE TIME CALCULATOR, using 75% depth of discharge, I get 8.3 hours at full sun. We know that doesn't exist in one day. We'll see how it goes.

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