diy solar

diy solar

Panels in series vs Parallel question.

jaxone

New Member
Joined
Mar 19, 2022
Messages
21
Location
Denmark
Hi guys.

So finally I have bought an inverter , EaSun SM IV 5.6KW and in the first phase I had 8 panels in series :
VOC 41.3 , MPP Voltage 34.8V at 10Amps. - 380W each.

Everything worked according to plan and I was satisfied with the final results and the installation itself.

After 2 weeks , I decided to add a few more panels and I have bought 4 more (minimum order was 4).

Connecting 12 in series will trigger the system overload on the PV as the Max. PV Array Open Circuit Voltage is 450V.

I was thinking to go with 2 parallel strings of 6 panels or go with 11 in series (11 in series would mean 454.3V for VOC) ?
When I go with :

2 strings of 6 I would have 20amps but only 208.8V and 2280wat per string thus 4560W total.
1 string of 11 at 10 amps will 382.8V and 4180W

From PV to the inverter I have around 20-25m.

I only use around 2200Watt when I run everything connected to this but in a normal day operation the consumption is around 400 watt but I would always use the surplus
to charge the 225AH 48V flooded battery bank.


So what would you guys recommend ?
 
2 strings of 6 I would have 20amps but only 208.8V and 2280wat per string thus 4560W total.
Best

1 string of 11 at 10 amps will 382.8V and 4180W
Worst. You should NEVER exceed max input volts. You will cook your inverter. The Voc is rated at 25C (77F) and as temp decreases, the voltage increases by .35% per degree.
Temp compensated Voc would be closer to 10 panels. If you provide your coldest possible temp (record lows?), we can do the math.
 
Well, for now I run with 10 in series , waiting for some more PV wiring to come ... was a bit afraid to leave 11 in series.
Temps here ... min I saw was -15 celsius.

For 2 x 6 in series, would the 208V be enough ? ... AC comes in at 220-230V, goes out at same rate. (Europe).
 
Temps here ... min I saw was -15 celsius.
That's a 40 deg C drop
41.3Voc x .0035 x 40 = 5.78V increase

(41.3 + 5.78) x 10 = 470V too high!
(41.3 + 5.78) x 9 = 423V

For 2 x 6 in series, would the 208V be enough ? ... AC comes in at 220-230V, goes out at same rate. (Europe).
Enough for what? What is the input voltage range or MPPT range of your inverter? The solar input (DC) has little to do with the grid input (AC).
 
What is the exact "temperature coefficient Voc" of your panels? It will be value roughly equal to -0.3%/ºC.

10 of your panels in series will have a Voc of 413V. At a temperature of -15ºC and a temperature coefficient of -0.3%/ºC your panels will reach 462.6V. That is higher than the maximum 450V.

So unless your panels have a much better temperature coefficient than normal you should only use up to 9 panels in series.
 
That's a 40 deg C drop
41.3Voc x .0035 x 40 = 5.78V increase

(41.3 + 5.78) x 10 = 470V too high!
(41.3 + 5.78) x 9 = 423V


Enough for what? What is the input voltage range or MPPT range of your inverter? The solar input (DC) has little to do with the grid input (AC).
Well, as I said, I'm a total noob in here :)

The range of the inverter operating voltage is 120Vdc~430Vdc... with only 6 in parallel at MAX output would be 208v and when the sun is hiding a bit I am thinking voltage would drop dramatically and won't be enough to open up the working voltage ?

Thinking if the PV voltage is 208V the inverter has to work a bit harder to come up to 220-230VAC ?

We go towards (I hope so) the summer time now so I won't see temps bellow 0 before next year hopefully and when / if 0 it will be in the night when the sun does not shine anyway. (I am thinking here and NOW , don't wanna go on the roof just now to disconnect 1 panel at 11:30 pm )

The specs of panels : https://files.gwl.eu/inc/_doc/attach/StoItem/8014/Datasheet_EXS-380MHC-B.pdf
Can see some temp specs there but can't work out the numbers :(
 
Last edited:
with only 6 in parallel at MAX output would be 208v and when the sun is hiding a bit I am thinking voltage would drop dramatically and won't be enough to open up the working voltage ?
Yes, having an array voltage higher in the range to charge in lower light conditions is a plus for these reasons. You'll likely get full voltage but lower amps (this is the job of the MPPT and beyond what we need to worry about). A great reason to get a great SCC.
Thinking if the PV voltage is 208V the inverter has to work a bit harder to come up to 220-230VAC ?
Good question. Another great reason to get a great SCC.
Can see some temp specs there but can't work out the numbers
What do you want to work out?
Vmp x Imp = panel watts (working volts x working amps = panel output)
 
What do you want to work out?
Vmp x Imp = panel watts (working volts x working amps = panel output)
I was thinking at the temperature numbers :)

Regarding "Good question. Another great reason to get a great SCC." ... we all start somewhere and we learn along the way. Some mistakes are more expensive than others but still a learning curve.
 
and in the first phase I had 8 panels in series :
You could always go back to this if it was working well.
Get a second smaller (backup and redundant) SCC to work with your 4 new panels.
2S2P would work well with a Victron 100/30 or the likes.

Just a thought.

I was thinking at the temperature numbers :)
Oops sorry, missed the key word in there.

Looks like the temp coefficient is .26%/degC

41.3Voc x .0026 x 40 = 4.3V increase

(41.3 + 4.3) x 10 = 445.6V too close for my comfort level!
(41.3 + 4.3) x 9 = 410V

This does not change what i would do or recommend.
 
when / if 0 it will be in the night when the sun does not shine anyway.
Typically a day's lowest temperature is just at sunrise. A solar panel's Voc can be reached at first light. So it is quite possible for solar panels to be at Voc when it's still at the coldest part of the day.

If you currently have 10 panels in series then you can reach the 450V maximum at -4ºC if your panel's temperature coefficient is at -0.3%/ºC. If the coefficient is as much as -0.35%/ºC then you'll reach 450V at 0ºC.

Look at the specs for your panels and post the actual coefficient.

Edit: I now see you did post the specs. It's -0.26%/ºC. 10 panels in series will reach 456V at -15ºC. Still too much.
 
Thanks MisterSandals and rmaddy , taken in consideration all your advice !
Think I will go with 8 like I had it before for a while and when the budget allows it I will order 4 more and will go with 2 strings of 8.

To dark now to go on the roof and re do the Circuit with 9 panels (I have 10 in series now) but will monitor it closely tomorrow and if needed I'll call wifi to shut it down from the PV circuit breaker tomorrow if needed.
 
On another idea ... what if I put 2 strings in parallel like 8 in series + 4 series ? Thinking not to "waste" the unused power.
Or 8 in series where 4 of them are in parallel (12 total) ?
 
All of the parallel strings need to be the same. You can't take a string of 8 and a string of 4 and then parallel those two strings. With 12 panels your only option, with one charge controller, is 6S2P.
 
All of the parallel strings need to be the same. You can't take a string of 8 and a string of 4 and then parallel those two strings. With 12 panels your only option, with one charge controller, is 6S2P.
Roger that.

Thought I can do some combination. Guess will have to wait till I have some more money and buy some more panels just to be sure I won't have issues in low light conditions like we have over here by runing 6SP2. Thinking a bit backwards , the 8 in series barely make 120V in early morning and late afternoon.

Time will tell and we learn on the way.

Thank you very much for the time guys. I'll post some photos with the setup tomorrow if the weather permits it :)
 
Back
Top