Uneven string split for better low-light performance?

[SeaGal]

Just had a random thought, sat here with lots of rain and virtually no solar generation

Assuming one had 16 x 400W panels, all facing the same direction with no shading, with VoC of (say) 40V and an inverter with 2 strings and start-up of (say) 120V with max input of 500V. By default I guess most people would spit the panels into 2 strings of 8, so each string had VoC of 320V.

But, I just wondered if one were to split reconfigure the string panel wiring into (say) a string of 10 and a string of 6 panels (giving one string a VoC of 400V and one of 240V) , would that perform better in low light levels - i.e. would the string of 10 panels kick in sooner than a string of 8?

Maybe by typing this, I've realised the answer to my own question, in that yes the string of 10 would kick in sooner, but the string of 6 would kick in later, so the net gain would be zero

(To clarify: I mean configure the system to have 2 strings (one with 10 panels, the other with 6) rather than 2 string of 8 panels each, using dual MPPT inverter (one for each string) in both situations.)

Hmm - thoughts?

 

[crossy]

Our 32 panels, whilst all pointing the same way are split over 5 (five, count them) MPPTs due to shading issues later in the day (house is in the way later in the day).

We're lucky in that there's no shading to the east so everything starts roughly together and then fades out after about 3PM.

Part of the fun of DIY is to be able to actually try different arrangements and compare performance, it doesn't always work out how you expect.

We are effectively ground mount with all the panels on the car-port so reasonably easy access to fiddle about.

Interestingly, the two 350W panels on the el-cheapo PowMr MPPT controller start well before the longer strings on the grid-tie and AiO hybrid.

 

[timselectric]

It depends on what you mean by "split".
Split onto two MPPT's
Or parallel on one MPPT.
I don't see either as beneficial. But the second choice would actually be worse. As it would only output as two strings of 6.

 

[CoolWill]

I would imagine that anything gained by the higher voltage string is offset by what's lost by the lower voltage string that will start later and drop out sooner.

 

[SeaGal]

It depends on what you mean by "split".

Soz, my bad choice of word - have corrected the original post.

I mean configure the system to have 2 strings (one with 10 panels, the other with 6) rather than 2 string of 8 panels each, using dual MPPT inverter (one for each string) in both situations.

 

[littleharbor2]

Solar panels will put out near full Voc under an incandescent light bulb. This is meaningless, being open circuit. The only time you get any meaningful power is when current flows and that wont happen till there is sufficient light intensity.

 

[Zwy]

I have a 3K Growatt on my truck camper. If the unit is parked in the shop or in low light conditions, the unit will boot when VOC is high enough, then begin to place a load on the PV, then shut down and keep repeating the process.

Which makes for 2 observations, one, there might be sufficient PV voltage for a SCC to switch on and boot up but use battery power to boot up. Once a load is placed on PV, the voltage drops low enough the unit will shut down. This is due to the PV not providing enough power.

Just because VOC might be high enough to boot up a SCC, doesn't mean the panels can provide power once a load is placed on the circuit. VOC is open circuit voltage, just like reading battery voltage with no loads connected. Once a load is placed upon the battery, then voltage will drop.

 

[timselectric]

Soz, my bad choice of word - have corrected the original post.

I mean configure the system to have 2 strings (one with 10 panels, the other with 6) rather than 2 string of 8 panels each, using dual MPPT inverter (one for each string) in both situations.

Then there probably wouldn't be much of a difference. You should get the same daily total production.