Rockpals Portable Panels (100W) in series

[miketc]

Hi,

I did a search but didn't find it. I've been a lurker for some time but I've found this community very helpful so hopefully this wasn't already asked before!

I'm trying to assemble a portable solar power grid and was looking into tying a minimum of 4 (12V) Renology / Rich Solar 200W panels in series in order to power my 48V power system. I know it isn't conventional but has anyone attempted to connect the Rockpals 100W (RP082 or SP003) in series? Does it even work? It seems like there are mixed results in people doing it (in amazon reviews) but nothing definitive and absolutely nothing mentioned about doing up to 4 in series. Rockpals has already said no but they also said the 60W (SP002) could not be paralleled (which isn't true). Would this risk damaging the panels?

I'm going to be using a Growatt 48V SPF 3000TL LVM All-in-one along with a battery bank I'm building with 16 Lishen 280AH LiFePO4 batteries / Daly 48V 16s 200A Bms.

 

[Samsonite801]

It seemed to me reading the Q&A on there that maybe the reason they said you couldn't do series, had more to do with the cabling/connection type, and that the seller said 'in one week' we will have the new 100w panel which will support series connection. Because functionally it shouldn't matter, the panel doesn't care how its wired, it doesn't know there is another panel next to it in series.

The main concern I might have with 4x panels in series, is getting the MPPT voltage up high enough. Looking at the Growatt specs:



...They show operating range at 60vdc ~ 115vdc ...with 145vdc max. So me not knowing the panel's full specs, Voc maybe 18-20v depending on which model panel you wanted. So with 4x of them you have roughly Voc 80vdc. That's on the lower end of the Growat spec. I'd rather see Voc higher on the range so the MPPT circuit doesn't have trouble pulling the voltage down on a decent sweep range... I might rather see 5 or 6 panels in series, trying to get Voc closer to the 115vdc end of the spectrum, so when MPPT pulls it down to extract amps it has plenty of range to work with.

That's just my feeling on it, how much difference that would make in real world, I don't know, but some inverter/MPPT charger companies even publish a spec for 'Rated MPPT voltage Range' and also another spec for 'MPPT Operating Voltage Range':



You could try pinging a Growatt rep and asking if they could recommend an optimal voltage to shoot for on Voc, since Voc is on the highest end of what the string will see (and factor in coldest tempurature as well), or also ask them where to put the panel's Vmpp in the range (if the panel publishes that spec as well). If the range of the inverter/charge controller was wider I wouldn't worry so much, but on a charge controller with a such a narrow input range, I just would like to try and get it a bit more nuts on in case it could really make a difference in performance.

 

[miketc]

Thanks for the response. I looked up the datasheet for the rockpals panel and it looks like DC Voltage is 18V at 3.3A Max. I measured the voltage output and got around 22V. I think I'll just stick to (4) Rich Solar 200W panels. The convenience of these smaller panels might be short lived when it comes to longevity of the panels.