Parallel vs. Series panels

[dcaulton]

setting up 4 100w panels going into a 30 amp renogy rover contoller. the four panels will be close to one another on a roof and are shaded vs sunlit together. I could do 2x2 series/parallel or just go series. I'm currently thinking it doesn't matter because both are the same power and the controller steps down to 12v in either case. I considered parallel briefly so I could start adding more panels (e.g., 2 groups of 3) but then I realized the controller can't handle more cells anyway (eg, 21v x 5 exceeds 30 amps x 12v). So growing would involve adding another controller anyway. Am I thinking about this right? or is there some advantage I'm not considering to a 2x2 setup instead of simply dropping 4 in series?

 

[victorpr]

you going 12v or 24v?

 

[Will Prowse]

If you are not increasing your array size, the panels are angled at the sun in the same way, all panels have same amperage output/ age(sounds like they are identical), and each panel has a bypass diode (super common these days), put them all in series.

Older panels/flex panels lack a bypass diode and you need to ensure that none of the panels in a series string is shaded at all unless the entire array output decreases substantially. Thats why parallel/series or parallel connections make sense for some vehicle mounted systems. but..

In your case, and given the size of the array and the likelihood of a bypass diode and matched panels, putting them all in series will work great.

 

[TCgreg]

I would defiantly try wiring them both ways. My 180 watt panels were marketed to have diodes to help with shading. After trying both series and parallel connections I found that even a small amount of shading killed production of panels in series. I contacted the manufacturer (Grape solar) and they confirmed that the diodes in their panels were wired as blocking diodes and not bypass. According to them they have since changed that. I would be interested in trying the test again with their new panels.

I contacted another popular distributer (Continuous Resources) about their 200watt 12v panels. These are the Hightec brand and this is what they said regarding bypass diodes:


Sorry for the delay, we have spoken to Hightec.

Hightec Solar is the actual manufacturer of the panels (I have personally visited the factory).

Here is what they explained to me. The bypass diodes are actually clipped inside the junction box (basically not being used). Here is why.

When panels are connected in series, the polarity is naturally changed. This causes the diode to start to carry current and that causes fire issues (it has literally happened with other manufacturers in the past). Therefore, Hightec clips the connections to the diode so that this does not occur (becuase they know that many people will connect the panels in series).

Did that answer your question?



Thanks,




Matt Dalley
President/CEO
Continuous Resources, LLC


Bottom line, I would set them up in series and test the effects of shading before making up your permanent installation. In my case with the 180 wattt panels production in series with perfect sun was marginally better but terrible when shading even one cell on one panel. Parallel gave me good results in shade and full sun. The high current I carry in parallel had to be mitigated with much larger cables but aside from cost and weight that isn't a big deal.

 

[b.james]

TCgreg- That's a fob off. The bypass diodes are connected across the strings of panels such that if a string is shaded anywhere along it the diode shorts current across that string so the next 3 strings operate as usual and , get full current through them. ie say a 72 individual collectors on a panel are usually 4 strings of 18 . Bypass diodes then cut out one 18 string . Ill try post a pic if I can find it.

 

[TCgreg]

TCgreg- That's a fob off. The bypass diodes are connected across the strings of panels such that if a string is shaded anywhere along it the diode shorts current across that string so the next 3 strings operate as usual and , get full current through them. ie say a 72 individual collectors on a panel are usually 4 strings of 18 . Bypass diodes then cut out one 18 string . Ill try post a pic if I can find it.

I understand how bypass diodes are suppose to work. Ultimately a panel that could bypass every cell would be phenomenal. I am just sharing my experience. Try panels in both series and parallel to see what real world results you get when introducing shading. In my case the panels I purchased only a couple years ago with "bypass diodes" turned out to instead have blocking diodes and my series results were poor. This was confirmed by the manufacturer.

In the case of these 200 watt hightec panels the manufacturer is clipping the diodes (according to them) so no bypass would occur. My advice is simply to test the panels and not rely solely on claims. Panels that came already equipped with mc4 connectors can very easily be swapped back and forth to test performance. If you never park in shaded conditions it wouldn't make sense to consider parallel.

Here is a video that demonstrates what I found doing my own testing. That is not to say that different panels could perform differently. Maybe Will has collected enough panels to do a series vs. parallel test while introducing shading.

Series vs. parallel

Here is another test

series vs parallel #2

More interesting reading

shading experiment

Obviously these two youtube videos and blogs are not indicative of every system but the results are pretty much what I have found going through the exercise myself. I can see where larger 24v panels with more bypass diodes could perform better. For many of us our RV roof does not afford space for 72 cell panels though. 36 cell 12v nom panels were pushing it on my RV.

In any case the best way to go series vs parallel will vary with a users conditions. Test for yourself and see what works best for you.

 

[b.james]

OK So you have tested them . So have I ,but most people I come across have no idea . So I dont think the gif is working here but here is another pic. Not for you ...but for others reading .

 

[dcaulton]

If you are not increasing your array size, the panels are angled at the sun in the same way, all panels have same amperage output/ age(sounds like they are identical), and each panel has a bypass diode (super common these days), put them all in series.

Older panels/flex panels lack a bypass diode and you need to ensure that none of the panels in a series string is shaded at all unless the entire array output decreases substantially. Thats why parallel/series or parallel connections make sense for some vehicle mounted systems. but..

In your case, and given the size of the array and the likelihood of a bypass diode and matched panels, putting them all in series will work great.

They're identical richsolar Polycrystaline 100w cells as you recommended. I did three in August and they worked amazingly well. As the sun rises there's a 10 minute period when some are shaded, but then they're all in the sun and angled the same. Thanks!

 

[dcaulton]

you going 12v or 24v?

12v. in retrospect 24v would be a good option, but I bought renogy batteries that can't be serialized. 12v works well though.

 

[dcaulton]

At cabin now. Went with serial and they are working great. Even with low angle and cloudy days are producing nicely.