Series-Parallel Grouping

[Zen]

In trying to finalize the plan for my array, I'm wondering what the limitation on "in-series groups" are. If I wire two "in-series groups" in parallel, do the voltages have to match? (i.e., same number of similar panels)

e.g., If I have (5) 12V panels and want to make 2 groups wired in series, then parallel connected, I end up with math like:

1st series group of 3 panels (24Voc/10A) = 72V/10A
2nd series group of 2 panels (24Voc/10A) = 48V/10A
Parallel connection = ? V / 20A
Explosion? 60V?

 

[Craig]

I don't think you will get an explosion but I think you wont get full efficiency. Not sure of the physics but I think you will only get the lower voltage. Safest thing to do would be just use 4 panels or have 2 different charge controllers which is what I do for similar problem. Some sort of diodes may help.

 

[Zen]

Thanks Craig. The array size requirements are very tight and obviously want to get as much there as possible.

I could wire 5 in series for a total of ~125Voc/10A, but don't I need to add some buffer (25%)? MPPT is capped out at 145 VDC.

Maybe diodes for shading, but I have yet to learn much about those.

For some reason all of the sizes that are available in my ranges end up in odd panel numbers!

 

[Craig]

I would like to say the 125 would be ok but I think we need some more expert commentary on that.

 

[Zen]

Craig, your systems look really great and orderly. I love the streamlined, clean and safe approach you use. Thanks for your feedback. Yes, expert commentary is what we are here for!

After a little more research, I find that the max open voltage is the max possible and no extra buffer is needed, as in fuse sizing. This is good news for me and allows more possibilities for the array. Should I incorporate a breaker at the PV to controller connection? It'd be nice to stop the flow from the panels at will.

When/if I need to add breakers/disconnects for parts of my system, I'd like to look at using those DIN rail units if applicable. So nice and tidy!

 

[Donald Siegel]

I ran four panels in series that hit 120v max with my MPPSolar all I one listing 145v max and thought I had enough room under that cap. For that inverter it shut down the charge controller every time. I tried 3 in series cutting the voltage 25% and it runs fine. The 145v max is likely 120v max and not getting above 80-85v max is going to produce more reliable power, at least if your using an MPPSolar all in one.

 

[Zen]

Thanks for the advice fellas. I didn't really think of the inverter/controller having its own issues, only the panels under the worst (coldest) conditions spiking voltage.

I've been trying to apply the chinesium rule (oughta be a law) throughout my system design for wire sizing, cutoffs and capacities, etc. At this stage I hope the array will work out great with 800W/100Voc/10A. I suppose with 4 panels I could series/parallel for 50Voc/20A as well.

This leads me to the next related question; when I (eventually) double the system by adding 2 more batteries, exactly twice the panels, and parallel another 24v MPPSolar unit...will I be able to handle twice the voltage capacity? Will I need to run 2 arrays through separate controllers?

 

[Craig]

I would add a second controller just for redundancy. But I buy cheap ones so two isn't gonna break the bank. Just make sure your controller can handle whatever energy you put into it. I think my cheapies can only handle 1400 watts each.

 

[Donald Siegel]

I have four 250 watt 37.5v, 8.68 amps panels now in run 3 in series (one disconnected). I’m considering putting four of them in parallel to get improved performance. I’ll do the math on the new wire gauge requirement first. So I’m trying to figure out if my MPPSOLAR can handle max 35 amps yet I know I will likely get much less on their best day. The label says max solar charging current is 80 amps, but is solar charging current the same thing a max solar panel current? I read the manual max panel volts are listed but this is the only max amp number I can see.

 

[Craig]

What's your battery system if you have a 12v battery then you can only handle 960 watts a 24 v system will handle 1920 watts whats gonna happen is the MPP will process whatever you give it and only output a max of 80 watts at whatever voltage your batteries are.

 

[Donald Siegel]

Thanks for the advice. The batteries are now a bank of 8 lifepo4 100 amp. I’m adding a second bank of two Renology sealed gel 200 amp 12 v batteries that will go in series. I’ll use a 3 position marine battery switch, and reset the charging profile when I charge each. The system is used an AC backup as it gets to 120F here and I have a one room 900 watt backup AC where the inverter is. The second bank to extend run time. I also considered two in series two in parallel , but was interested in all parallel for consistent power even when one panel gets shaded.

 

[Zen]

Not sure what you're getting at, there. I re-read this thread from the beginning. I feel you need experience with the system you're building, and you'll 'get it', through reading manuals, reviewing best practices online, and probably come up with your own answers at that point.

If you're adding more solar, and the existing controller is maxed-out (given the head-room issue mentioned previously), you can tie them to a second controller to charge the same bank of batteries.

Lots of info here. We were discussing max voltage into the MPPT with a buffer of 25%.

We all agree that running much less than the stated max was ideal. It's kinda far off time-wise, but I wanted to know how doubling the system would affect this particular aspect of voltage input.

If I start with 100Voc array and then double that array in parallel (keeping the same voltage) and also parallel connect a second 24V PIP Inverter/SCC...

Would I have "290" VDC Max input for the 100Voc from the arrays? Of course this is just "on paper" using the 145VDC maximum X 2.

Great suggestions here and it seems there are enough options to handle the solar input effectively. Yes! Manuals, research and reading. I promise I'm not lazy; but the avenues of getting the right info can be overwhelming. Also, the MPP manual is good and came with it. Early on there was trouble getting the manual from China, but Will posted it on his website:

http://mppsolar.com/manual/PIP-LV%20110_120VAC/PIP-LV%203KVA%20manual-20160823.pdf