Adding more panels, but facing different direction

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Adding more panels, but facing different direction

Post by Pabloesguapo » Sun Jul 19, 2020 9:12 am

I know there's another thread here addressing the same question, but it got so long, and it seemed like it went down some serious rabbit holes, I got confused. I'd like to take another stab at understanding this.

Here's the old thread.

Here's my situation. I'm completely off-grid and always will be. I have 27 Kyocera panels facing south going into two combiners, one of six circuits, one of three, they go into a midnight classic 150 charge controller, and a classic light charge controller, In "follow me" mode. They control the charge into 16 Rolls s530 batteries, two strings of 8, for a 48 volt system, 800Ah @20hr. I am running 2 Outback FX 3648 inverter Chargers.

I obviously need much more charging capacity. I would like to fill up that second combiner it's a 6 bay, but I'm only using three. I don't have any more south-facing roof to put any more panels on. I have tons of east and west facing roof. Now, I read in that previous thread that it might not be a good idea to fill up the rest of that charge controller with panels facing a different direction. Is it dangerous, or is it just not optimal? If it's just not optimal, I can deal with the less than best bang-for-the-buck scenario, I just need to get more electricity into my system to keep my batteries charged. If it's dangerous, I don't want to blow anything up.

I also would like to know which direction I would set those panels if I could, east or west? Someone mentioned in the thread that there will be performance differences based on heat as well. How much difference are we talking about here? Is it better to try to get more energy into the batteries early in the day, or make my day last longer?

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Re: Adding more panels, but facing different direction

Post by raysun » Mon Jul 20, 2020 10:36 am

Adding panels facing a different direction is not optimal, and if the array is properly wired, not dangerous.

The choice of East or West facing would depend a great deal on local conditions like cloud cover, daytime temperatures, etc. The battery will usually benefit from the charge cycle being substantially completed in lower ambient air temperatures, so that may argue for mornings rather than afternoons in many climates.

The biggest issue with panels pointed in different directions is the challenge is presents to MPPT charge controllers finding an optimum power point from the array. It may be easiest to employ the existing unused capacity in the combiner, but may prove to be a false economy. Should performance suffer, separating the new sub-array to it's own controller would certainly optimize performance.

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Re: Adding more panels, but facing different direction

Post by Mike Curran » Mon Jul 20, 2020 11:03 am

One way to get around this problem is to install module level power electronics (MLPE's) on each module, such as the Tigo optimizers I have on my garage roof array. They basically determine the MPPT per individual module instead of one device (e.g., your Midnites) for the whole string.

You might be able to get away with just putting them on the new arrays and leaving the south-facing ones without them, but im not sure about that. Will cost a few extra bucks but they do work for situations like yours.


- Mike

Edit: As Raysun suggests, another charge controller would work just as well and may even cost less than a bunch of optimizers. I'm using them because of shading issues on some modules, not because they're in different positions as you're planning.

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Re: Adding more panels, but facing different direction

Post by pss » Mon Jul 20, 2020 11:25 am

Several years ago I read an article that measured PV output at different latitudes both north and south and the effects of angle of the panel on output. I haven't been successful at relocating that article recently, but the upshot was if you think you can get do better facing East or West or can't get the best angles, the overall best PV output ANNUALLY was to simply mount the panels nearly flat on the roof, like a 4-6 degree angle south at most. This gives output from the East, West and in between when you cannot track the sun or adjust for perfect south as in your situation. You might give this solution a try with the caveat that adjusting tilt and direction later for your weather will let you optimize the panel mounting after a couple of years.

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Re: Adding more panels, but facing different direction

Post by SandyP » Mon Jul 20, 2020 7:48 pm

raysun wrote:
Mon Jul 20, 2020 10:36 am
The choice of East or West facing would depend a great deal on local conditions like cloud cover, daytime temperatures, etc.../..
I would also add that the choice may be determined as to what times you are using power. If mostly in the morning then East facing vs afternoon use and West facing. Better to have the power from the panels/cc than drawing down your battery bank and then recharging.

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Re: Adding more panels, but facing different direction

Post by 706jim » Mon Jul 20, 2020 8:44 pm

I have 1 kw facing southeast and 1 kw facing southwest. This is partly due to shading concerns. The system works well with an Outback FM80 charge controller. Doesn't seem to be any problem with the controller figuring out a good charge algorithm.

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