One MPPT controller or Two?

It is pretty easy to estimate the average harvest from your solar power system... You can use something like PV Watts and enter in some basic information. Say you have a fixed array mounted flat, and are out of Boston MA:

Month    Solar Radiation (kWh/m 2/day)
1      1.85    
2      2.79    
3      3.79    
4      4.61    
5      5.58    
6      6.03    
7      6.03    
8      5.43    
9      4.25    
10      3.15    
11      1.89    
12      1.58    
Year      3.92

The farther to the north you are, the more having a tilted array can help harvest. The same panels mounted at 42 degrees from horizontal:

Month    Solar Radiation
(kWh/m 2/day)
1      3.36    
2      4.36    
3      4.79    
4      4.92    
5      5.33    
6      5.41    
7      5.60    
8      5.64    
9      5.13    
10      4.65    
11      3.14    
12      2.98    
Year      4.61

Get quite a bit more power in winter, a bit less in summer.... Depends on what time of year and where you camp as to what is the best for you.

Then,, power wise:

600 Watts * 0.52 AC end to end system efficiency * 4.36 hours (Feb 42 degree tilt) = 1,360 Watt*Hours per day for 120 VAC loads
600 Watts * 0.61 DC end to end system efficiency * 4.36 hours (Feb 42 degree tilt) = 1,596 Watt*Hours per day for 12 VDC loads

PWM vs MPPT charge controllers... Most 100 Watt solar panels have Vmp~18 volt output--Perfectly fine to put panels in parallel to a PWM controller to charge the battery bank on an RV.

MPPT charge controllers are more expensive and allow you to use "GT Solar Panels" (grid tie) that are larger (200 watts and larger) and Vmp not 18 volts (typically Vmp~30 volts)... GT panels tend to be cheaper and may or may not be easier to mount to your RV (fewer panels, fewer electrical connections, fewer bolts, etc.). An "expensive" MPPT controller + cheap GT panels may be less expensive than a cheap PWM controller + expensive 100 Watt panels.

If you have different tilt on the panels--You should use one MPPT controller per array--So that sends up the costs with two MPPT controllers. In a smaller/basic RV system, MPPT controllers are a nice to have, but really not going to give you a lot of extra power unless you do a lot of snow camping (very cold weather will increase the array Vmp voltage--Which MPPT controllers can harvest as extra energy--typically 10% or so more in very cold conditions).

You are correct--Solar electric panels do not work well with shading. A good PWM controller should work OK (single controller with panels at different angles).

Many MPPT charge controllers use fans for cooling (particularly the larger units)--Fans running during the day may be an issue for an RV where you are "on top" of the controllers. The new MPPT controllers frequently have more option/computer communications/programmable options and can be very nice. Personally, I am not convinced that I would run two MPPT controller vs just a single charge controller for your situation (cost/mounting space/wiring for two controllers vs harvest efficiency). I would try one charge controller and see how your harvest works out.

And lastly... it is just Watts not Watts per Hour... Watts is already a rate (like gallons per hour). And Watts*Hours is an amount (like gallons pumped). We do not need to use Watts per Hour in solar

-Bill

I believe that this installation has the panels mounted with 3 tilting "to the left" and 3 tilting "to the right"... Sort of a virtual tracking array.

Shaded panels and MPPT--Not really worried about that... Shaded panels (even with just a little shading) produce near zero useful current/voltage/energy.

For me, as I see the issue... It is the Vmp of the panels.... Different orientation, different cell temperatures, different Vmp point for panels. Solar Guppy who used to post a lot here over the years was very clear that each orientation needed its own MPPT controller. Since he had the equipment to accurately measure the output of lots of different controllers/combinations, he is certainly one to listen too.

From another point of view, "hot panels" are the ones directly facing the sun... As one array becomes more "off angle" and the other becomes more on angle to the sun... The off angle array is getting cooler, but producing less current--So, it becomes less "important" in the equation. More or less, that is why I am not sure a second MPPT charge controller is always worth the costs. MPPT controllers also have "tare" losses (consume power just because they are "turned on"--Switching losses)... Having two controllers running has somewhat more losses than one controller sharing both arrays--Another reason I am not sure I would be worried about a couple percentage points of increased production + increased tare losses, vs a single controller and miss-matched Vmp (due to temperature/operating points) as the sun moves across the sky.

-Bill