Panel upgrade question

[Mlux]

Hope this doesn't belong in the beginner section...
Want to upgrade my motorhome panel with the priority being on better performance in low-light conditions/longer charging hours. Thus I'm leaning towards a higher voltage panel, as well as obviously closer to my controller maximum input wattage. But curious if I'm thinking along the right lines as I'm new to solar systems.

Current 12 volt system: (2) 80ah AGM deep cycle batteries
Renogy Elite 20 amp MTTP controller (max solar voltage input: 100 VDC, max input power: 260 watts at 12v)
80-90ish watt panel, not sure of exact specs as this was all pre-installed when I recently bought the motorhome, but through some testing I'm seeing typical voltages, (up to 20v), and amps, (up to 3), coming from this wattage panel.

Panel options: Offgridtec 200 watt
VMP 40v
VOC 46.6v
IMP 5.05A
ISC 5.45A
or.... Viasolar 250 watt
VMP 20.2V
VOC 24.1V
IMP 12.37A
ISC 13.56A

Both will obviously increase overall performance in regard to charging time, but with a slightly higher priority on lower light conditions (longer charging hours as well as cloudy days) I'm thinking the 40V panel is the way to go with my current understanding of solar systems. How am I doing? Thanks for reading!

 

[littleharbor2]

Panel voltage isn't what you should be concerned with in regards to better charging. You will get near max Voc/Vmp in most lighting conditions. The current is what you need to focus on. If your panels are mounted flat on the roof of your RV you really are struggling to get much current at this time of year. Either of those panels will work for you but you need to get them aimed better, especially in the winter. They will work fine in the summer, even laying flat on the roof. Can you make them tiltable? It may be a PITA to get up on top of your RV to adjust their tilt but it would be worth it in the long run. Are you more stationary of do you tend to move on a regular basis?.
There is also the option to have the panel freestanding and place it away from the RV. This can be quite effective in that you can follow the sun throughout the day. This also allows you to park in the shade, if available, and still have full sun on the panel.

 

[Mlux]

Panel voltage isn't what you should be concerned with in regards to better charging. You will get near max Voc/Vmp in most lighting conditions. The current is what you need to focus on. If your panels are mounted flat on the roof of your RV you really are struggling to get much current at this time of year. Either of those panels will work for you but you need to get them aimed better, especially in the winter. They will work fine in the summer, even laying flat on the roof. Can you make them tiltable? It may be a PITA to get up on top of your RV to adjust their tilt but it would be worth it in the long run. Are you more stationary of do you tend to move on a regular basis?.
There is also the option to have the panel freestanding and place it away from the RV. This can be quite effective in that you can follow the sun throughout the day. This also allows you to park in the shade, if available, and still have full sun on the panel.

Thanks for the reply. Good advice. I tend to be more mobile than stationary, but it could definitely be worth looking into a mount that I can tilt, even rotate, for those times I am stationary for a few days. I have a ladder mounted out back so getting on the roof isn't a big deal really. The house batteries are wired into the alternator so charging is more important those times I'm camped out a few days.

As for between the two panels, it does seem a little like the old expression "six of one, half a dozen of the other." While the 250watt has a higher amp output rating, I thought ultimately it wouldn't matter with a MTTP controller.

 

[littleharbor2]

With a REAL MPPT controller it's watts in, = watts out minus a small efficiency loss.
With a PWM controller it's, amps in = amps out.
Your first panel is 5.05 amps imp. With a 12 volt system you might see, 5.05 amps @ 14 volts, yielding a whopping 70.7 watts.

 

[Mlux]

With a REAL MPPT controller it's watts in, = watts out minus a small efficiency loss.
With a PWM controller it's, amps in = amps out.
Your first panel is 5.05 amps imp. With a 12 volt system you might see, 5.05 amps @ 14 volts, yielding a whopping 70.7 watts.

Lol, well as I said, an improvement either way, better than the max I've ever seen so far in one day, a whopping 43 watts! ?. Thank you for the watts in-watts out simplification, this is very helpful in comparing. Much appreciated!

 

[scrubjaysnest]

We have 5 100 watt panels with Imp = 5.5 amps each . Have only seen this once on a bright sunny day at 40 degrees F. The 2 panels on the roof can be tilted. The 3 have pvc frames and can be placed in the sun and tilted as needed. 10 awg from the roof panels. 8 awg for the 3 portables with the option to extend up to 100 feet from the rv. Batteries are 100 Ah AGM's. 2 awg wire from the baby box to the 45 amp pwm cc. 2 awg from the cc to the batteries.