100W panels, 2S 3P vs. 3S 2P

[NPhil]

I have a "mobile solar power testbed" (a system in development which is also a lab, for my education, comprised of odds and ends stuffed into and attached onto an old minivan) which, this morning has 6 (most days it's 4, but today is cloudy) Newpowa 100S-12H panels on top. I run a 24V Lithium battery system (at about 26.3 when the test was run), using a Epever Tracer AN 40A controller, and have been attaching panels in pairs. So, I had 2S 3P up there today, and about 1.5A at 27.8V coming in (normally, it's nearer 10A, with 4 panels), so I thought this medium heavy cloud cover might be one of those edge cases where I will see the, eh, light on recommendations I have heard for more panels in series for better performance, specifically 3S in preference to 2S, especially on a 24V system. So, I changed 3 pairs of panels to 2 triptychs of panels (artfully, of course), and output dropped to 1A, at about the same voltage. I changed back to 3 pairs, of course, and back to around 1.5A. It's anecdotal, of course, but, I wonder why?

 

[NPhil]

I have a "mobile solar power testbed" (a system in development which is also a lab, for my education, comprised of odds and ends stuffed into and attached onto an old minivan) which, this morning has 6 (most days it's 4, but today is cloudy) Newpowa 100S-12H panels on top. I run a 24V Lithium battery system (at about 26.3 when the test was run), using a Epever Tracer AN 40A controller, and have been attaching panels in pairs. So, I had 2S 3P up there today, and about 1.5A at 27.8V coming in (normally, it's nearer 10A, with 4 panels), so I thought this medium heavy cloud cover might be one of those edge cases where I will see the, eh, light on recommendations I have heard for more panels in series for better performance, specifically 3S in preference to 2S, especially on a 24V system. So, I changed 3 pairs of panels to 2 triptychs of panels (artfully, of course), and output dropped to 1A, at about the same voltage. I changed back to 3 pairs, of course, and back to around 1.5A. It's anecdotal, of course, but, I wonder why?

Oops. I need to delete (it's a duplicate) but can't see how to.

 

[pollenface]

17v of pv per 12v of battery is most efficient for the 4210AN up to 200w if you read the efficiency charts in the back of the manual, but that not practical for everyone.

I would configure them as convenience allows while staying within the input specs, 3s2p sounds good.

Amps going to battery depend on your loads, charging stage, battery SOC etc. If load conditions are identical day in/day out maybe look at your total Wh generated for the day?

 

[NPhil]

Amps going to battery depend on your loads, charging stage, battery SOC etc. If load conditions are identical day in/day out maybe look at your total Wh generated for the day?

I run this thing every day, in 2S (17V for 12 should be equivalent to 34V for 24V, I guess). But, I saw that chart, which recommends 3S, and people keep saying "pile on the series", so, when I had some marginal conditions, I thought I would try switching back and forth, to see if there was a difference. Not a well controlled trial, but also not results which cry out for more testing. I'll stick with 2S, I guess.

 

[Substrate]

Safety note to protect the parallel wiring:

Whenever you parallel more than two panels, then each panel needs its own fuse.

In other words, with 3 or more panels in parallel, if one of the panel wires degrades and shorts against a frame or other structure (or gets nibbled on by critters exposing a short), the others will dump into that short, usually with more than twice what your cabling for the individual panel would support and can smoke the wiring.

Obviously not good for casual hobbiest setups across shingled roofs, etc.

Just so you know...

 

[MisterSandals]

17v of pv per 12v of battery is most efficient for the 4210AN up to 200w if you read the efficiency charts in the back of the manual

This is interesting and multifaceted. Does this efficiency chart take into consideration any gains one might get by having a higher array voltage that starts producing earlier and in lower light conditions? Basically a longer charging period, everyday (varies for every setup).

I suspect that the efficiency graph shows the momentary efficiencies for array voltage vs battery voltage. And I could see how electronically it would be easier, cheaper and more efficient to modify input voltage by a smaller amount while producing charging voltage.

And we have seen SCCs get poo poo’d for having low max input voltage restrictions. And that makes sense for these efficiency and possibly component cost arguments. But to attract a wider customer base, having a wide input voltage range and MPPT range is very useful and desirable (and profitable?).

I thought I would try switching back and forth, to see if there was a difference. Not a well controlled trial, but also not results which cry out for more testing. I'll stick with 2S, I guess.

I am curious to hear your results!

(Sorry for writing a novel)

 

[NPhil]

This is interesting and multifaceted. Does this efficiency chart take into consideration any gains one might get by having a higher array voltage that starts producing earlier and in lower light conditions? Basically a longer charging period, everyday (varies for every setup).

I suspect that the efficiency graph shows the momentary efficiencies for array voltage vs battery voltage. And I could see how electronically it would be easier, cheaper and more efficient to modify input voltage by a smaller amount while producing charging voltage.

And we have seen SCCs get poo poo’d for having low max input voltage restrictions. And that makes sense for these efficiency and possibly component cost arguments. But to attract a wider customer base, having a wide input voltage range and MPPT range is very useful and desirable (and profitable?).


I am curious to hear your results!

(Sorry for writing a novel)

My results (beyond my observation that if there is anything added around sunrise and sundown in the 3S configuration, it's not obvious) will follow the end of the present crisis, and the restoration of, eh, normality. Bear in mind that I reside in the San Francisco Bay Area, California.

 

[time2roll]

My Morningstar efficiency chart shows higher efficiency when there is less spread between panel voltage and battery voltage.
How about same test in direct sun?

 

[NPhil]

My Morningstar efficiency chart shows higher efficiency when there is less spread between panel voltage and battery voltage.
How about same test in direct sun?

That is unsurprising, the efficiency of DC-DC conversion is, above some minimum, typically declines somewhat, the higher the difference between input voltage and output voltage. So, if you con't get those Watt-hours lost to reduced efficiency back in output during marginal conditions, you won't gain in total energy production. I can think of these factors, off the top of my head:

1. Difference losses in solar controller.
2. (Possible, I haven't measured it) power gain in marginal conditions.
3. Added weight (in a mobile installation, there are incremental costs) and cost for cable with less serial and more parallel.
4. Greater risk of damage from higher voltages, to components, people, animals and structure.
5. Possible savings and wider selection from requiring a lower Vmax.
6. Conceptually (at least) simpler series multiple panel wiring.

 

[12VoltInstalls]

beyond my observation that if there is anything added around sunrise and sundown in the 3S configuration, it's not obvious

I think latitude and cloud frequency affect this. More sun clearer skies may not benefit? I worked great for me, but you tested in your conditions so that makes it right for you. Except:

I changed back to 3 pairs, of course, and back to around 1.5A

Which IS additional charging but you numbers sound backwards
(I seriesed two 100W panels on a pwm once to get 14-15V of charging. Sure, in good sun I gained nothing but it did make some charge where parallel wasn’t reaching batt voltage. Not that I recommend that but it worked for a month, just never over ~5A)

 

[iamrich]

So, I changed 3 pairs of panels to 2 triptychs of panels (artfully, of course), and output dropped to 1A, at about the same voltage. I changed back to 3 pairs, of course, and back to around 1.5A. It's anecdotal, of course, but, I wonder why?

This doesn't make sense. If you switched from 2S to 3S I would expect a voltage increase. What was the voltage reading for each setup?

 

[12VoltInstalls]

changed 3 pairs of panels to 2 triptychs of panels (artfully, of course), and output dropped to 1A, at about the same voltage.

I missed that detail. He’s right- doesn’t make sense. Should be 1/3 less or more volts barring change of conditions

I changed back to 3 pairs, of course, and back to around 1.5A. It's anecdotal,

That’s not anecdotal
I’m going to edit my prior post because THAT does show an increase in charge due to the voltage change you didn’t see but it sounds backwards. I’ve played with series and parallel panels in full sun for hours and always got expected results.

 

[iamrich]

increase in charge due to the voltage change you didn’t see but it sounds backwards. I’ve played with series and parallel panels in full sun for hours and always got expected results.

Might not be a change at all.

(Just using random values as an example)

2S3P= 30v at 1.5a = 45w
3S2P= 45v at 1.0a = 45w

 

[12VoltInstalls]

Might not be a change at all.

(Just using random values as an example)

2S3P= 30v at 1.5a = 45w
3S2P= 45v at 1.0a = 45w

In watts, ? in the conditions presented

 

[NPhil]

Might not be a change at all.

(Just using random values as an example)

2S3P= 30v at 1.5a = 45w
3S2P= 45v at 1.0a = 45w

That was what I was looking for, plus a little. And I saw that higher voltage, briefly. Then, the controller pulled it down to about the same voltage, except at (of course, since I had 2/3 as many strings), 2/3 the current.