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Solar Panel Sizing w/ oversized MPPT on RV

Crocdundee

New Member
Joined
Apr 21, 2024
Messages
14
Location
California
Just a bit of background. I am a newbie to DIY solar, but have been a few months in the planning of an upgraded Victron system in my RV. I have recently received most of the Victron equipment for my install (MPPT, MPII, Lynx, etc) and hoping to receive the last bit of materials soon to start wiring. Some of my equipment I feel is oversized for my current needs (a friend gave me a great deal on his MPPT), but I am hoping it will help when we plan to add an AC and other electrical in the future. I've read Will's book and Victron wiring unlimited and will be closely following an Explorist.Life 24v wiring diagram. My last equipment purchase is going to be the mono solar panels and I am just a bit overwhelmed by trying to fully understand and find a good value in the sea of solar panels available online.

My system would include...
MPPT 250/100-Tr VE.Can
MultiPlus-II 24/5000/120-95 120V
2 x 230ah 24v Litime LiFePO4 (460ah @ 24v)
  • What should I look for when ordering solar panels for an oversized MPPT/Inverter?
  • Could the oversized MPPT be an issue?
  • Is sticking to panels with a voltage in the high 30s the main recommendation (i.e. >1.8x battery bank voltage) or would going with even higher voltages be better (i.e. 405 watts @ 49.6 VOC)?
My goals are to max out the RV roof area with ~1800-2400 watts of solar (300-400 watt panels in 3S2P), which still comes way under the limits of the 250/100 MPPT. Again, just trying to make sure I am not missing any potential issues when picking out the solar panels.

Clear skies
 
Last edited:
Just a bit of background. I am a newbie to DIY solar, but have been a few months in the planning of an upgraded Victron system in my RV. I have recently received most of the Victron equipment for my install (MPPT, MPII, Lynx, etc) and hoping to receive the last bit of materials soon to start wiring. Some of my equipment I feel is oversized for my current needs (a friend gave me a great deal on his MPPT), but I am hoping it will help when we plan to add an AC and other electrical in the future. I've read Will's book and Victron wiring unlimited and will be closely following an Explorist.Life 24v wiring diagram. My last equipment purchase is going to be the mono solar panels and I am just a bit overwhelmed by trying to fully understand and find a good value in the sea of solar panels available online.

My system would include...
MPPT 250/100-Tr VE.Can
MultiPlus-II 24/5000/120-95 120V
2 x 230ah 24v Litime LiFePO4 (460ah @ 24v)


  • What should I look for when ordering solar panels for an oversized MPPT/Inverter?

No special considerations.
Voc must be +5 above battery voltage
Vmp must be +1 above battery voltage

  • Could the oversized MPPT be an issue?

No.

  • Is sticking to panels with a voltage in the high 30s the main recommendation (i.e. >1.8x battery bank voltage) or would going with even higher voltages be better (i.e. 405 watts @ 49.6 VOC)?

Optimal efficiency is Vmp = 1.5X system voltage, BUT as you go with higher PV voltage, you gain in less losses from wiring, so it's mostly a wash.

RV roof protrusions tend to cast partial shading on panels, which destroys production. Favoring parallel over series may be to your advantage.

My goals are to max out the RV roof area with ~1800-2400 watts of solar (300-400 watt panels in 3S2P),

If you're going with 3S 60 cell panels, you don't need the 250/100. The 150/100 would work fine for that.

which still comes way under the limits of the 250/100 MPPT.

Limited to 2900W on a 24V system.
 
No special considerations.

As always, thanks a ton for your response Eggo, it really is appreciated! I didn't consider wiring them all in parallel or in a 2S3P configuration. Will have to revisit the pros and cons of both options. I had originally planned to order the 150/100, as you're right, that's the one that is recommended through the MPPT calc. It changed a bit when my friend sold me his new spare MPPT 250/100 for $400, so figured it might be worth it down the road. Have a good rest of your weekend.
 
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As always, thanks a ton for your response Eggo, it really is appreciated! I didn't consider wiring them all in parallel or in a 2S3P configuration. Will have to revisit the pros and cons of both options. I had originally planned to order the 150/100, as you're right, that's the one that is recommended through the MPPT calc. It changed a bit when my friend sold me his new spare MPPT 250/100 for $400, so figured it might be worth it down the road. Have a good rest of your weekend.

Nice deal on the 250/100! Mine was purchased long before the price decrease and was nearly $1000.
 

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