diy solar

diy solar

Use the same negative cable for multiple seperate panels and controllers

Not to hijack but this brings up a question I have. So let's say you have two (or three) controllers as mentioned. When it comes to distribution through load or to the battery, how is that handled?

I think the simplest way would be to wire the controllers to busbars, where they connect up with the rest of your system. If you think about how you would normally wire panels in parallel, it would be similar to that, just on the other side of the charge controller. Another way to think about it would be that it would be just like wiring a single charge controller, just replicated 2 or 3 times or however many controllers you put in parallel.
 
I'm not sure this is the case (the cost savings), it would depend on your specific situation (panels, controllers, voltages, etc) but as an example, here are two options of roughly the same output capacity from Victron:

1 x 100V 50A Victron Smartsolar = $325
3 x 75V 15A Victron Smartsolars = $355

The single controller is a bit cheaper with a bit more capacity (in both cases about 10%), but nowhere near '1/3 the price', it may be different with other companies, but Victron's SCC pricing from what I've observed is often somewhat linear with a small premium paid for multiple smaller controllers.
I think the cost savings come due to the fact that I don't need a larger controller and only need 2 wires instead of 6.
My reasoning here is that no more that 2 panels can get sun light at the same time and thus I don't need to have one large controller that could handle 3 panels in full sun light but I can go smaller.
 
I think the cost savings come due to the fact that I don't need a larger controller and only need 2 wires instead of 6.

I think the difference in wiring between parallel panels 1 controller and parallel controller might be less than you think. Parallel panels with a single controller would require roughly 1/3 of the wire, but 3x the thickness, so you will buy less wire at a higher cost per foot, or more wire at a lower cost per foot.
Of course there are other considerations, parallel panels will require fuses and combiners, and a single disconnect, parallel controllers would require 3x disconnects but no fuses or combiners

My reasoning here is that no more that 2 panels can get sun light at the same time and thus I don't need to have one large controller that could handle 3 panels in full sun light but I can go smaller.

This idea is worth exploring. I was under the impression that when homes did this they usually use separate MPPT for the east and west facing sub arrays, but I might be mistaken. If @gnubie says it'll work well enough, it probably will, but I'm torn because I also expect there is a reason that the marine guys frequently use/recommend multiple MPPT controllers.
 
I think the difference in wiring between parallel panels 1 controller and parallel controller might be less than you think. Parallel panels with a single controller would require roughly 1/3 of the wire, but 3x the thickness, so you will buy less wire at a higher cost per foot, or more wire at a lower cost per foot.
Of course there are other considerations, parallel panels will require fuses and combiners, and a single disconnect, parallel controllers would require 3x disconnects but no fuses or combiners
Also the wire could be smaller than 3x since 1 panel is guaranteed to be always shaded (teh sun can't shine on the 2 sides and the top of a boat). So I think I could get away with the same wire as let's say 1.5 x of the single set up

This idea is worth exploring. I was under the impression that when homes did this they usually use separate MPPT for the east and west facing sub arrays, but I might be mistaken. If @gnubie says it'll work well enough, it probably will, but I'm torn because I also expect there is a reason that the marine guys frequently use/recommend multiple MPPT controllers.
Yes that is still a bit of a mystery what the actual loss is. Another reason to have multiple controllers on a boat would be for redundancy.
 
Back
Top