# Flexible solar panels

Solar Expert Posts: 104✭✭✭
I just bought a van with a pop top (a manual roof Sportsmobile). I want to add solar to the roof, so I’m looking at flex panels like the Renogy 100W. Weighs about 4#, Voc 22.5, Ioc 5.75.

I don’t need to milk every last miliamp out of this setup but I do need just enough solar to keep up with charging laptops and phones, and running a fan. I have one Group 32 200Ah house battery which is also charged when I’m driving.

Would the Victron MPPT 75/10 work? I prefer VIctron, but I’m not sure if a 22.5 VoC is enough for that controller to be efficient.

More or less, that controller will act like a PWM (cheaper) controller with your panel (your panel is probably around 18 Volts Vmp-std standard test conditions).

1b) The PV voltage must exceed Vbat + 5V for the controller to start. Thereafter the minimum PV voltage is Vbat + 1V
Yes, the system will work, but ideally, you want Vmp to be > 20 volts (allowing Vmp to fall in hot weather/full sun) to meet the minimum Vbat+1V:
• 15 volts charging + 1 volt = Vmp-array >=16 volts.
And Hot panels (full sun, no wind, hot weather), Vmp (and Voc) can fall from Vxx-std (marketing numbers) by 80%:
• 16 volts Varray-minimum / 0.80 hot weather derating = 20 Volts Vmp-std suggested minimum array voltage (Vmp-std)
-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 104✭✭✭
So two of those panels in series would be a much better match.
The "optimum" array would be:
• 14.75 volts * 10 amps = 147.5 Watts into battery (STD conditions)
• 147 Watts STD / 0.77 panel+controller deratings = 184 Watt array "optimum"
You can over panel the array/controller too... The MPPT controller will safely and "normally" "clip" the output current to 10 amps in Cool, Clear conditions, around solar noon (panels pointing at sun). PWM controllers cannot modulate/clip output current reliably.

Always refer to other controller requirements... Such as Array Isc (short circuit current) is Isc-array-input 13 amps maximium--Certainly safe with two of your 100 Watt panels in series.

If you have room for 2x 100 Watt panels--That will be a good solution for you.

Some other random comments... I am not a fan of "flexible solar panels"... I suggest that such panels are only "good" for 2-7 years (at best) before they start to fail/delaminate/etc.

Whatever panels you choose--Make sure they are well mounted so that driving and/or winds at camp don't come loose and get blown off the trailer.

"Glass panels" will last 20+ years normally... But they must be handled with care as they are, more or less, single weight tempered safety glass... Which will shatter very easily if dropped, "torqued" from poor mounting, or are hit with stones/metal tools.

Some folks will pack the panels in storage for the trip, and then place the panels "out in the sun" while camping under shade (keep RV and family cooler). If you do choose to stake the panels out XX feet from the trailer, make sure they are well supported so they don't blow away (or "walk away" with a bit of human help).

Running the panels in series raises Array Vmp working voltage--Very helpful for longer cable runs (smaller AWG wiring needed with high voltage/low array current).

When working with solar charge controllers, always make the Vbatt connections first, and then the array. And disconnect array first followed by battery connections. Solar charge controllers can be damaged if connected to the solar array and not connected to the battery bank--Or the controller will not "boot correctly" (controller needs battery bank voltage to properly boot and configure its output voltage of 12/24/48 volts battery bus).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 104✭✭✭
edited April 2023 #5
Thanks for the detailed explanation. Yeah, I am not a fan of flexible panels (I just got done installing a glass panel on my trailer) but because I have to push up the roof on the van by hand (at least for the first 6” before the springs kick in) weight is a huge issue. So I am hoping to get flexible panels up for the light weight. I like the Victrons because I can monitor them from a simple bluetooth app - and I have no other convenient way of accurately measuring voltage or current.

Oh and using remote panels isn’t an option at all for me; the whole point of this van is that I can take it for a day or 7 in a remote location, and be simple. No setup and take down other than popping the roof up if needed. No fancy awnings, nothing like that. Fridge, stove, toilet, small water tank, and a bed big enough for me and my dog.