300W of panels gauge/distance help?

Hi I am currently trying to get two 150w panels for my RV and decided not to mount them on the top. I have installed a vent on the roof that I can run wire through and am envisioning a system where I have just the panels outside and a spot to connect/disconnect MC4 cables at the vent point up top. The controller and battery will be stored inside (AGM deep cycle 200 amp hours). The distance I am going to need to do this is about 40 feet give or take. The controller I am looking at is a renogy rover 20 amp (max of 10 gauge). Is this system plausible or is the wire length too long for the gauge of the wire? Is another option to keep the battery and controller housed outside or would I encounter a similar problem with loss of power. running wire after the battery pointbest regards.

 

I'll suggest a hatch on the side of the RV vs on the roof!
No, 40 feet is not to far if you connect the panels in series to the mppt controller.

Do keep the distance from controller to battery at a min.

thanks! the reason why I was considering roof output was because I may not always be able to park the hatch that alternative could be used towards the south. Good to know I plan on having the battery very close to the MPPT, would 10 gauge wire do the trick for this connection also. And why would i not want to run the panels parallel in this situation (still learning). Thanks!!

10 Gauge is to small....

Ok but 10 gauge would be appropriate for 30 feet correct, alternatively I would need a controller to incorporate an 8 gauge wire

so I take 150w panel and divide by 18v to get current of 8 amps. That's max and most often will be less.
Voltage drop is based on amps/wire size, if ya parallel 2 x 8A panels ya get 16 amps, still not too much for 10g from panel to controller.
In series it will be 8A @ higher voltage and MPPT handles that.
So you find a voltage drop calculator like genuinedealz.com/voltage-drop-calculator
ya put in 10g, 12v (doesn't matter except for the % calculation), 40' one way, 8A
I get a .657v drop. Now consider 2 in series the Vmp or operating voltage will be 36v or less when warm/hot (panels get hot).
.657/36 x 100 = 1.8% loss as in loss of power, keeping below 3% is a common methodology. With less than ideal sun the current (amps) will be less and the power loss will be less from voltage drop.

Now redo the calculation for controller to batt, the amps will be higher since the controller bucks the input power @ 36v down to 12-15v.
So input is 36v x 8A or 288 watts (some roundoff!!) and the output will be 288/13 = 22 amps.
back to the voltage drop calc, this time looking for 1% or less voltage drop (1% of 13 is .13v).

ya put in 10g, 12v (doesn't matter except for the % calculation), 10' one way, 22A too much voltage drop for peak conditions.
try 5' x 8g and ya get .142 or just over 1% for a 13v charge. This is at peak power which does not happen often.

If the controller has a voltage sense wire then it can be used and the voltage drop from controller to batt is taken care of internally, ie the voltage sense wire knows the voltage drop and increases voltage to compensate.

put a hatch in the floor with enough wire to reach either side!!! pull wire back in when solar not deployed.

Ok I like the idea of running a conduit for the wire straight down through the floor to the underbelly so the wire can reach either way. Panels were originally going to be mounted on roof put i decided against it. So 10 gauge @ say 20 foot from panels to controller, and 10 gauge @ say <5feet from controller from battery would suffice in this model if im not mistaken. Thanks for your thorough input.