Solar questions

Maybe a slight adjustment in your equipment would work better?
3 Newpowa 210 watt 24 volt panels with a controller that will handle at least 35 volts input. That gives you 18.75 amps for 10 gauge cable.

Richard

I recommend eight brackets for panels that big.

The use of Z brackets make the panels hard to remove. Cut 2 pieces of aluminum angle and bolt together as a Z but easy to remove.

Teleman wrote:
I'm mounting three 210 watt Newpowa panels on my 30'Class A motorhome. I'm using Renogy Z brackets to mount them to my fiberglass roof. The panels are pre drilled to accept 8 of these brackets. Do you recommend 4 or 8 brackets per panel? Also I'm using the MPPT controller in my Redarc 40A DC to DC charger which has an input voltage of 9-32V. I need to run the panels in parallel to keep the voltage low enough but that means I need to use 6ga wire to run from the point of parallel conection. Do they make connectors that will fit 6ga wire? Or do I need to splice the cables? Thanks in advance.

I used 6 brackets on my 325 watt panels which are a little bigger. so I think 6 and you will be good.

Steve

4 are plenty for the panels, but for the fiberglass roof I would use at least 6.
I second on cutting your own angle iron aluminum brackets if this is possible for you. I did this and then just use self-tapping screws into the sides of the panels where it is safe to do so through the frame and not hit any critical parts.

Are you using VHB tape to the roof or mounting with hardware through the roof? Fiberglass roof can be a solid roof or can be rolled-out sheets that are more flimsy, so just curious.

You can use wire that is thinner than the electrical optimum gauge of course and it will work just fine. The differences will be only noticed when you need maximum charge and every last solar particle you can catch..

I would just get a higher amp controller so you can run in series and use the thinner wire. Is this an option? Did you keep the receipt for the controller? In the long-run you will be glad you did.

I used 4 brackets per 250W panel but those brackets were home-made, thick and rigid 1/4" aluminum angles, and huge 6" long each, enough space to run 4 screws through each one. Yours are probably small, 2 screws per each and, given FG roof - I would say 6 or 8 brackets. If you use a sticky tape - I would say use all 8, there are no holes to drill.

6 GA wire - not sure. 2*310W in parallel = 20A current. Compared to 8 GA you'll save maybe 1 AH out of ~200 AH daily harvest, big freaking deal.

I recommend 8 ga which will provide higher voltage to the controller and allow for another panel if desired.

Your panels have a Voc (open circuit) of 39V+. Your controller MUST have a higher voltage maximum rating. This includes several several more volts for increased voltage due to lower temperatures which increases the panel voltage.

Voc can and does occur due to cloud edge effect or driving conditions, etc.

Voc math example: I recall your temperature compensation is -80mV/degree C +- 10.
Lets use -100mV as an example. This means for every 10 degree C drop the Voc increases 1.0V. ie For every 10 degree C increase the voltage drops 1.0V.

FYI I decided to wire my panels in serial for several reasons. Reduced wiring loss. With an AC between panels 2 and 3 I have a total of 64' (round trip) of 10 ga wire. This results in 1/3 the amps and 3X the voltage. Clarification - For 3 serial panels vs 3 parallel panels.

Serial panels with bypass diodes also have much better shade tolerance than parallel panels which appealed to me. Almost all panels have bypass diodes and certainly all 24V panels.

CA Traveler wrote:
I recommend 8 ga which will provide higher voltage to the controller and allow for another panel if desired.

If wired in series, yes. Higher voltage, lower amps, can use thinner cable.

This was my reason for wiring 2*250W in series, using (very common, cheap and easy to work with) 10 GA cable. Total input 70V, most 30-40A controllers allow at least that much. The OP will find several times more 10 GA solar cable on the market than 8 GA, especially if he needs it with MC4 connectors. Now, 6 GA sounds like a pain, MC4 for it probably don't exist, will need an ugly junction box on the roof.