Do two separate arrays requie two controllers?

It depends on whether or not you want to use an MPPT charge controller or a PWM controller. With the wire run distances you are talking about I'd have suggested MPPT so that you can run the array at a higher voltage. To run it at a higher voltage you want to have 2 parallel strings of 3x100w panels. It doesn't matter if the strings are at different angles to each other as long as each individual string is facing the same direction. The basic rule is series panels should face the same direction and parallel panels can face different directions if needs be. If you have a PWM charge controller you should make 3 strings of 2x100w panels because a PWM can't transform a higher voltage array to a lower battery voltage while increasing current. With PWM the maximum current you get is what the panels give. You will however need very thick conductors. Same story applies with strings and direction. Each of the 3 strings should face the same direction for those in series.

But to answer your first question you don't need 2 charge controllers provided you wire the array cleverly. The charge controller should just be rated at 1.5x the array power. 2 charge controllers would be necessary if you need 2 separated power sources at different voltages.

In larger systems multiple charge controllers are used simply because they don't make charge controllers big enough to handle more than about 80amps.

Morningstar released this last week: Parallel Charging Using Multiple Controllers With Separate PV Arrays.

Morningstar manufactures solar controllers for charging battery banks with nominal voltages of 12 to 48 Vdc and a range of maximum charging currents from 4 to 60 Amps. The TriStar and TriStar MPPT controllers have the highest charging current ratings with 30A, 45A or 60A maximum charging. Larger battery banks often require greater charging than a single controller can provide. Generally, there is no problem with charging battery banks with several charging sources. The TriStar MPPT manual states the following. “Multiple TriStars can be installed in parallel on the same battery bank to achieve higher charging current. Additional parallel controllers can also be added in the future.”
Here are a few considerations for the use of parallel solar controllers:
● Each solar controller must have its own separate solar array and each array is configured and sized in accordance with the solar controller specifications.
● The batteries need to be designed to handle the combined charging currents. Contact the battery manufacturer if there is any question as to recommended max. charging current.
● The charging sources and controllers are set up properly (explained below).

....

Morningstar’s TriStar and TriStar MPPT controllers have been designed to coordinate parallel charging control effectively without the need for intercommunication between products. While it is always possible to have one controller handle most of the charging regulation alone, as in cases when using 3rd party charging sources, the TriStar and TriStar MPPT controllers’ voltage regulation is accurate enough to synchronize and coordinate the charging regulation for parallel operation.

http://www.morningstarcorp.com/wp-content/uploads/2015/03/ParallelTSandTS-MPPT-030112015.pdf

petefink wrote: »

First, thanks to all of you. I have no controller picked out but if I want to try the single MPPT controller and do 2 parallel strings of 3x 100w panels for the higher voltage (36V?), will it matter that one of the panels in the string (the one on the roof) will almost always be at a different angle from the horizon than the other two (the two on the frame) in the string? thank again.

If you have one panel in a series string facing a different angle (even with an MPPT controller) it may become reverse biased when it's receiving less sunlight than the others. Having 2 parallel strings helps lessen the severity, but there will always be a concern. Modules have diodes to guard against damage by reverse bias, but it's still not good to have shaded modules or cells in a series configuration. But do give it a try, it may work out ok. Watch the modules during the course of the day, keep the system under load to make sure the panels are working @ 100%. When you see a module or a cell or two becoming shaded, check their temperature - if they become too hot to touch that's not good at all...

Just to clarify my point on the shading issue - I don't want to cause more alarm than is due. I had my first set of panels located underneath a set of bay windows, where they would become partially shaded at certain times of they day. I noticed that when one cell on a module of 72cells became shaded it would get so hot I couldn't touch it even for a second! This was because the current was flowing "backward" through the shaded cell. The module had 3 mosfets in the junction box acting as diodes that could bypass 24cells at a time if need be, but that still meant that under full load there could be 23cell's worth of power being dissipated in one cell. Now consider a module being 16% efficient at converting sunlight into electricity and you can see the shaded cell getting much hotter than it would if it were just down to plain solar heating. The effect gets worse as the already overheating cell gets illuminated again once the shadow moves away. The effect is much less serious if say 2 or more cells get shaded instead of just one because the ratio of illuminated cells to shaded cells is smaller. Needless to say I moved my array to a place where they can't be partially shaded during the brighter times of day...

After reading through this thread I think I'll drag my old Sunsaver 10 along this summer and see what differences I note with the 120 watt panel mounted to the trailer roof and the the other two panels set up in their normal configuration. Maybe interesting to see what if any differences occur with all three panels through the TS-45 vs treating as two different arrays.