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diy solar

Panels in parallel or series?

JeremyG

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Apr 2, 2023
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Canada
Hello solar enthusiasts.

I've got 3x 230 watt panels on my front porch.
Ran out of room, so I put 2 more on my ROOF, roof.
There are 3 panels in the shed, because the snow showed up and I couldn't get them installed in time (the wiring is waiting patiently for them)


So, my question is, 5 panels at 230 watts is 1,150.
I'm guessing if I hook them up in series, they would charge the batteries with 1150 watts.

If they're in parallel (bus bars in strategic places), does that still add up to 1150 watts of charging?
 

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In theory yes. 80% of that is more likely. Panel angle, line loss, equipment efficiency, and shading all play a part.
 
You obviously will need a charge controller- that will have a PVmax rating (maximum DC voltage allowed on the PV inputs) which can vary dramatically (from as low as 50-60v, up to 500v or more, depending on the manufacturer/model involved...)
Your panels will have a Voc rating (which again can vary dramatically, from as little as about 20v, to over 80v- again depending on manufacturer and model involved)

Series works best for total daily production, then series/parallel, then all in parallel (you are talking anything up to 30% difference in the daily total generation here, so series really is the way to go)- however you have to ensure that the panels all get the same sun (easier if they are all in the one place lol) a shadowed panel isn't the end of the world (as it will still produce some power) but it will have an effect on your strings production... (the entire string will only produce as much current as the lowest panels output current)

Check the panels for a rating- in this case the important one is the Voc (voltage open circuit) multiple that by the number of panels in the string and see if it is 80% of the PVmax rating on the input of the charge controller...

Ie my panels here are 250w, Voc of 38.8v

1707222146394.png
And the dual inbuilt charge controllers of the inverter are rated at 250vdc, and the 4 external charge controllers are 150vdc
1707222281338.png
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So in my case, I can have 3 in series with the 150v (3 x 38.17v = 114v, 20% less of 150v is 120v) charge controllers and 5 in series with the 250v ones (5x 38.17v = 190.85v, 20% less of 250v is 200v)
You should always leave that 20% 'leeway' as 'usually' the panels will run less than their ratings- BUT in certain conditions (cool panels, with 'light' input of more than 1000w/m^2) they can spike 10-15% above the values listed for STC... and if your charge controller is already at its limits- magic smoke comes out... (you might have to do a 'series/parallel' connection to hit the power limits of the charge controller in some cases...)


The other issue is the current rating of the charge controller- many mistake it for the current limit IN- wrong, it it the maximum current OUT that it refers to...
So my 60A ones on a '12v nominal' battery bank are limited to only 750W of panel input (mine can be 'overpanelled' ie handle more power (but NOT voltage) coming into them, but will 'limit' at that 750w level, cheap ones again might 'let the smoke out')
However on a 24v nominal battery bank, they can handle 1.5kw of panels, and on a 48v system, 3kw of panels- so your battery bank voltage will play a bit part on what current limit you need (if you have more panels than a single controller can handle, it is quite safe to have two or more connected together - on the BATTERY side only- ie all solar inputs are separate and do NOT connect at any point- the only 'shared' connection is at the battery bank...

eg my 150v ones can handle 3 kw on a 48v battery bank, but only 3 of my particular panels in series (750w)- so to get to the full wattage limit of 3000w, I would have to put 12 panels in a '4 parallel strings array of three series panels in each string'
You can also have different arrays facing in different directions eg my 'temporary' array has 3 panels facing north, and another three on a separate charge controller facing west for increased afternoon production (the north facing panels hit their peak at midday, but by 3pm are noticeably dropping off in output- when the west facing ones are just hitting their peak then and keep going until sunset...
(they are limited to only 3 because the 'temporary' battery bank is 16x 400Ah LYP cells, currently connected in a 4S4P arrangement to feed 12v to the caravan- when the house is finished, they will be transferred to it and reconfigured as a '48v' nominal bank (16S)
1707223479131.png
 
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