patrickj avatar image
patrickj asked

MPPT 100/20 48V and solar sizing

I'm adding solar to charge my teardrop trailer's 12V 100ah AGM battery starting with one Ecoflow 110W portable solar panel with the potential to add a second panel in the future. I found a good deal on the 100/20 48V which will nicely accommodate the upscale to 220W so bought it.

Now that I'm digging into the installation guide and its recommendations for sizing solar arrays, I'm wondering if a single 110W panel will be sufficient for this controller to operate efficiently. Should I replace it with the 75/15, which is what the MPPT calculator recommends for the lone panel? Or will the 100/20 48V work fine until I choose to add another panel?

smart solar set-up help
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snoobler avatar image snoobler commented ·

I'm not sure what is influencing you, but a 110W panel on a 100/20 MPPT charging a 12V system will work great.

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patrickj avatar image patrickj snoobler commented ·

What I was seeing in the installation manual was this line::

  • The nominal PV voltage should be at least 5V higher than the battery voltage.

The Ecoflow 110W panel's Voc (21.8V) and Vmpp (18.4V) are only marginally above 17V. I thought this might mean the *nominal* voltage could be much lower. However, looking again at the MPPT sizing calculator:

System calculations

PV input voltage
PV max. voltage @ min. temperature 25.2 V
PV min. voltage @ max. temperature 13.5 V

So I think the panel's nominal voltage under normal operating conditions will be generally in the right range. Correct?

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snoobler avatar image snoobler patrickj commented ·

The "nominal" voltage of that panel is 12V. It's a throwback to pre-MPPT days when that was the size of panel you need to properly charge a 12V battery - 36 solar cells.

Voc is the number you consider for the +5V requirement. Once started, the panel only needs to be 1-2V higher than battery.

21.8Voc is for 25°C. Using typical Voc temp coefficient for panels, your panel Voc should stay above 18V until cell temperatures are > 75°C. Cells are commonly +20°C above ambient when in full sun.

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patrickj avatar image patrickj snoobler commented ·
Thanks for the explanations. :)
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1 Answer
Ivar Eisma avatar image
Ivar Eisma answered ·

Agree, that will work just fine. Just make sure you put it on 12v AGM in the settings (I assume it's the Bluetooth version of the 100/20)

The 20A max output is pretty much perfect for your battery size. You probably won't hit that with a single small panel but putting two panels together later will give you a decently fast charge.

Focus on getting your consumption low, there are always items that use more juice than you thought. Often it's cheaper to replace those than getting a huge system.

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patrickj avatar image patrickj commented ·

Thanks Ivar and @snoobler

After more research I was coming to the same conclusion, so it's great to have your assurances I'm on track, and the additional advice as well, Ivar.

Yes, it's the Bluetooth SmartSolar version. ::)

<smile> I hear you on lowering consumption. Aside from LED house lights, a vent fan and charging devices (phone, laptop, camera), the main draw on the system was originally a 45qt 12V thermoelectric cooler (which pulls power constantly to cool contents to 20F below ambient environmental temperature - not often optimal). I just replaced it with a 42qt 12V refrigerator.(which cost twice as much, but cools more efficiently, is better insulated, and only engages as necessary to maintain temperature in a chosen range.).

I went with the 100ah battery in hopes of powering everything for a couple or three days between charges via shore power or driving. Hopefully a single 110W panel will keep the battery comfortably juiced for much longer periods. But if that's not enough, Victron's MPPT sizing calculator says the 100/20 can handle three 110W panels in series on a 12V system-- and oversizing would allow a couple more in parallel.

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snoobler avatar image snoobler patrickj commented ·

The MPPT 100/20 48 will readily accept a 3S3P array of those 110W panels without exceeding PV voltage or PV input current limits. If weather is mild in your area, and it never gets below -12°C, the unit could accept a 4S3P array.... You'd pretty much output 20A all day long with an array of that size!

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patrickj avatar image patrickj snoobler commented ·
Yeah. I was looking at that on the MPPT sizing calculator. I think it's top end is 3 110W panels in parallel and another three in series. Impressive!


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