300 watt on Renogy Rover 20a MPPT CC?

[DETstru]

I currently have the Renogy 20A MPPT CC and (2) 100W 12V Renogy panels on my van. I have room for a third 100W 12V panel and believe my current Rover 20A CC is capable of handling it. The panels are wired in series. The battery is a single 12V 100AH LiFePO4 battery.

My main question is regarding going over max watts (last line of this post). Thanks to all who read

Panel specs:

• 100 W, 12V
• Short-Circuit Current (Isc): 5.21A
• Open-Circuit Voltage (Voc): 24.3V

CC specs:

• Max. PV Input Power: 12V/260W, 24V/520W
• Max. Solar Input Voltage: 100V
• Max input current = ???? not sure

If I'm doing my math right:

• Input current to the CC should still only be 5.21A max, which is the same as it is now.
• Input voltage will be 72.9V max, well under the 100V limit
• Input wattage could be as high as 300W, which is over the 260W limit, but I don't think my current 200W have ever produced more than 150W. Which implies that the potential 300W will never produce more than 225W, which is under the 260W limit. If it did go over the 260W limit, would that damage the CC or simply not capture all the production?

 

[MrThisIsME]

The CC will simply clip the power over 260w. Your 300 watt panels are well within 20% of overage which should be fine. Regardless, it is doubtful, being on a flat surface, you will see 260w often. In other words, you are over paneling correctly.

 

[MichaelK]

Actually, I could see you upgrading all the way to 400W without problems. I normally derate panels to 85% output for real-world production, but with a van, and panels laying flat, the derating is normally higher, say 65-75%. Another factor is the actually charging voltage, which is more likely to be ~13V to start, raising gradually to ~14. As the voltage raises, the amperage typically goes down. So, here is the math for four panels....

[(100W X 4 panels)/13V charging] X 65% = 20A.

So, it's doable. If you happen to park the van on a steep slope, and the panels get a better angle to the sun for some time, the extra amperage will just get clipped off.

What you can do to reconfirm this before doing the wiring is to switch the controller's display to amperage, and read what the max amps going into the battery is right now. I'll bet you it's no more then 10A. Just multiply whatever real-world number you see by the extra panels and you'll have an accurate estimate of what to expect.

 

[DETstru]

Thanks MrThisIsMe and MichaelK for the replies!

I will definitely be adding the third panel now, much appreciated. I don't have room for a fourth unfortunately (I don't think I'd need it anyway). I will take a look at the output amps before making any changes.

I'm also thinking that all my current wiring and fuses are still fine as-is?
Since the current from the panels to the CC is staying the same (because they are in series). And the current from the CC to the battery won't be changing by too much.

• 10 ft, 10 AWG wires from panels to CC w/ 10A fuse
• Very short 10 AWG wires from CC to battery w/ 20A fuse

Based on some online calculators, I think I still have plenty of margin on both.

Thanks!

 

[fratermus]

If it did go over the 260W limit, would that damage the CC or simply not capture all the production?

As others have noted, MPPT controllers "clip" power at their max output. The clipping point will depend on bank voltage at the time:

• 12.1v x 20A = 242w
• 13.4v x 20A = 268w
• 14.0v x 20a = 280w

It is possible to throw so much panel at it that it can't protect itself, but the proposed setup is nowhere near that. I'd absolutely put 300w on a 20A mppt.

 

[MichaelK]

Oh, BTW, looking at the Voc of 24.1, four in series would bump up to 96V+, which would pass 100V even before the weather drops to freezing, so four would not be good for THAT controller.

 

[DETstru]

Oh, BTW, looking at the Voc of 24.1, four in series would bump up to 96V+, which would pass 100V even before the weather drops to freezing, so four would not be good for THAT controller.

Right, voltage would be too high for 4. Three will be plenty for me though! And without having to change fuses or wiring it'll be an easy add.

 

[Magicjack]

Question can 3-100 watt panels in series connect to rv using existing zamp same plug?

 

[MichaelK]

Question can 3-100 watt panels in series connect to rv using existing zamp same plug?

What is a "zamp"? The 5.21A value is the Isc, which the controller is not going to see. It is going to take in the Imp under load, which is more likely to be around 5.0A or a bit less.

So, for the three panels wired in series, the most you will ever see is ~5A running at ~60V. With the panels laying flat, derate them to 60%, so that means ~3.0A amps in the real-world. So, you don't really even need 10 gauge for 3A. That is where MPPT really shines, where most of your power is coming from higher voltage rather than higher amperage. So, once the power is exiting the controller, you are likely to see 13-14A charging amps at the battery.

 

[fratermus]

What is a "zamp"?

Zamp provides "solar ready" <cough walled garden cough> gear for RV manufacturers. My understanding is the basic setup is:

zamp panels w/built-in controller -> SAE port in side of RV, wired backwards (compared to other panels with similar terminators) -> wire to battery bank

If anyone knows otherwise please advise.

can 3-100 watt panels in series connect to rv using existing zamp same plug?

If the setup is already 2x in series through the zamp port then 3x in series would be no different, {current-wise}. @MichaelK says, the current will remain the same with panels in series.