what's the gain doubling panels

[Robert K]

I am in the process of putting solar on my MH. I have 2-180 watt panels with a 40 amp mppt controller.
Charging 4 225 amp 6volt batteries.

What will I gain by going to 4 180 watt panels.
(A)Faster recovery on batteries
(B)better recovery on cloudy days
(C)Nothing when conditions are optimal
The 4 panels would be series parallel
The 2 panels probably won't matter which way they are wired
Will be running 10 gauge wire to controller as it should only be 20 amps from panels and the controller will only take the 10 wire

thanks Bob

 

[Lou Schneider]

You'll double your power output up to the point where your controller maxxes out (40 amps going to the batteries), i.e. you'll probably double the output on a cloudy day but the controller will allow some additional current but not the maximum the panels can produce on a sunny day. The controller will ignore any additional power beyond what it can handle. You'll also decrease the battery charging time in both cases as you'll have more bulk charging current available.

180 watts divided by 12 volts = 15 amps. So you should be seeing a theoretical maximum output of 30 amps at 12 volts for two panels.

Double that for 4 panels and you can theoretically get up to 60 amps out of the controller. But your controller will limit the output to 40 amps.

 

[Robert K]

this is the spec on panels .
It shows 10 amps but that would be at 18 volts max

 

[Isaac-1]

Making the assumption that you are wiring these batteries up in series parallel for a 12V nominal power bank and they are standard flooded lead acid batteries, using Trojan T105 batteries as an example, your maximum allowable charge rate will be 58.5 amps, you therefore would probably be better off with a larger than 40 amp MPPT controller for those times when you peak amp output may be higher, though given those numbers listed above a 40 amp MPPT controller is going to be close to peak output for those panels in most real world conditions, still one size larger MPPT controller may be a good idea.

p.s. you would gain A and B as things are now, though not as much as if you were to have a slightly higher rated MPPT controller.

 

[Lou Schneider]

A Maximum Power Point Tracking controller (MPPT) will convert that 30% excess voltage into up to 30% more current, so each panel will contribute up to 15 amps current going into your batteries, subject to the controller's 40 amp maximum output. With 4 panels you'll get more current under low light conditions but not the full 60 amps output potentially available under full sun.

If you have a simpler PWM controller that doesn't convert excess voltage into more current, you'll only get a maximum of 10 amps per panel under full sun and about 30% less current than an MPPT controller in low light. Four panels at 10 amps each will max out, but not exceed the controller's 40 amps current limit under ideal conditions. Under low light you'll get about 30% less output than using a MPPT controller.

 

[Ex-Calif]

Static loads are also subtracted from charging rates so you theoretically drain the batteries less from the nominal coach loads.

In theory this can extend boondocking time in cases where you may have had a daily consumption deficit in the past and needed a generator boost.

 

[Gary RV_Wizard]

180 watts divided by 12 volts = 15 amps. So you should be seeing a theoretical maximum output of 30 amps at 12 volts for two panels.

Battery charging voltage will be more like 14v and the panel wattage is probably rated at an even higher voltage than that, maybe the 16-18v of its raw output. I think dividing by 14v instead of 12 would give a more accurate estimate. 180 divided by 14 = 12.8 amps

 

[solarman]

you will have a total of 720 W and at 12 V will require a 60 amp controller to maximize harvest.
those batteries will be happy with that charging current.
standard practice Gary is to use nominal battery voltage to calculate controller Amps.
battery voltage during charge of course depends on SOC.. so could be as low as 11 V