Not impressed with solar yield - Would a smaller MPPT or another panel help?

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sportswagoneer asked Aug 15, '22

Not impressed with solar yield - Would a smaller MPPT or another panel help?

I have a Sunbeam Tough Black rated at 114W above the companionway of my sailboat. The image below shows the PV voltage & current, Battery input current and yield in watts for two normal sunny days in Norway. It's hovering around 10% of the nominal yield rather than the 50% I would have expected.

The controller is a Victron MPPT 75/15. I see that the recommendation for optimal effect is to connect 2 panels in series to that controller - but struggle to understand how much of a difference that would do?
Would a 75/10 yield more?
Data for the panel can be found here:
https://www.sunbeamsystem.com/tough-black-solar-panels/
EDIT: Page with actual data:
https://shop.sunbeamsystem.com/product/tough-114w-black-flush-solar-panel/

MPPT Controllers Solar Panel solar sizing

screenshot-2022-08-15-at-13-50-40-neste-sommer-2-v.png (104.1 KiB)

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JohnC answered · Aug 15, 2022 at 02:02 PM

Hi @Sportswagoneer

The nature of the graphs suggests shade to me, and this can happen even from a rigging wire or handrail. The real issue you have though is that the mpp is being tracked to below 15V, rather than the 19V of the specsheet. Erik has touched on this, but the difference in Vpv to Vbat once tracking is 1V. So if it actually managed to raise the Vbat to near 14V, the mppt would shut down.

You'd need another panel in series to avoid this. Or even try a PWM controller rather than the mppt.

Many panels have diodes to help with shade, but it depends on the shade. Usually a strip of shade right across the panel will devastate output regardless.

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patricknl commented · Aug 17, 2022 at 11:54 AM

Looks like it to mee too.

For me 12v system on my RV I went with a 80V+ system to over come partial shade and a too low output.

On a boat it can be harder. 3x30 or 40w at 60-70V VOC would be optimal for your mppt. One panel is “enough” in optimal conditions only in my opinion.. and the reality is far from optimal.

Rule of thumb for me when designing a pv system for friends or myself: I try to ger atleast twice (or triple) the battery voltage if possible.

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sportswagoneer patricknl commented · Aug 17, 2022 at 03:48 PM

Thanks. The relevant alternative for me is two more panels - and connecting them all in series should be OK for the MPPT Controller - but the panels spcify Vsystem Max at 65V, which would be slightly more than the sum of the 3 Voc’s.

Have sent the panel manufacturer an e-mail regarding this - we’ll see if there’s any reply….

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sportswagoneer commented · Aug 15, 2022 at 02:28 PM

Thanks! That makes sense. So the Vmp is more or less a given nominal dimension for each panel? (Strange then that it cant be set in the MPPT settings…?)

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JohnC ♦ sportswagoneer commented · Aug 15, 2022 at 03:04 PM

The Vmp can't be set because it's determined by the mppt. The panel makers do the same under STC conditions and publish those, but real-world insolation conditions may differ considerably. The max power point still gets tracked, and it's usually downwards in V..

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sportswagoneer JohnC ♦ commented · Aug 15, 2022 at 03:25 PM

I see. So the actual Vmp is a function of the actual install case (including shade etc.) and the number of panels in a series - but it’s difference downwards from the nominal Vmp indicates a reduction in overall output?

And if I where to add panels in series - should I then expect the MPPT to track towards 2x15V? Or to close in towards 2x19V? And would both these scenarios increase the yield from the original panel?

(Sorry for interrogating you - I‘ve tried to find good read-ups on this but failed.)

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JohnC ♦ sportswagoneer commented · Aug 17, 2022 at 11:44 AM

@Sportswagoneer
I wouldn't expect any miracles, shade is an insidious and capable enemy. Maybe twice the Vmp (and output) you see now, which may actually extend your day a little at each end. But that won't mean much overall if heavily restricted.

One downside with series strings is that the worst panel may bring down the output of it's neighbour too. This mightn't mean much either.

All you can really do is try it.

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Answer 1 · 2022-08-15T12:08:15Z

klim8skeptic answered · Aug 15, 2022 at 12:08 PM

Data for the panel can be found here:
https://www.sunbeamsystem.com/tough-black-solar-panels/

Marketing nonsense aside, where are the actual technical specifications?

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sportswagoneer commented · Aug 15, 2022 at 01:39 PM

Sorry - their "shop" page has the table of actual specs:
https://shop.sunbeamsystem.com/product/tough-114w-black-flush-solar-panel/

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Answer 2 · 2022-08-15T12:31:58Z

Trevor Bird answered · Aug 15, 2022 at 12:31 PM

Hello @Sportswagoneer … if the panel is above your companionway, doesn’t that mean it is below the boom, hence in the shade? I’m not sure about the maximum height of the sun in Norway but remember the yield is proportional to the Sin of the angle above the horizon. If the angle is 30 degrees it will have half the yield. If it is in shade and partly shaded they wild will fall away dramatically. A different controller will make no difference.

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sportswagoneer commented · Aug 15, 2022 at 01:41 PM

There's certainly shade from the boom and a non-optimal angle above the companionway - so I don't expect anything near the nominal yield. But 10-15%??

These panels are suposed to be optimized for partial shade etc....

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Answer 3 · 2022-08-15T13:34:15Z

Erik Sporns answered · Aug 15, 2022 at 01:34 PM

PV Voltage needs to be 5V over battery voltage before the mppt starts properly working. Without finding a datasheet about the cells, it looks like the cell Vmpp is to low. But its just an educated guess.

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sportswagoneer commented · Aug 15, 2022 at 01:47 PM

The datasheet is in their "shop" pages. Sorry I posted the marketing link before:

https://shop.sunbeamsystem.com/product/tough-114w-black-flush-solar-panel/

The Vmp is 19.14 and my lithium batteries will normally hover around 13.3 when not on shore-power charging. So that should be a difference of about 6.

The Victron manual states that the Delta V must be 5+ to start charging but that it can be as low as 1 after starting. Since the panel does start charging and the current does not return to 0 during the day, I have asumed that it passes the 5V threshold (albeit maybe a little late) and does not shut down due to low voltage difference. (But maybe it could be more effective at a higher (serial) voltage from 2 or 3 panels?)

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Answer 4 · 2022-08-15T14:01:15Z

sportswagoneer answered · Aug 15, 2022 at 02:01 PM

If I where to add more panels, then two of these 55W's would be the obvious choice for my deck:
https://shop.sunbeamsystem.com/product/tough-55w-long-black-flush-solar-panel/

I could either add them so that all three would be in serial or add the two 55W's as parallell to each other but in series with the 114W.

I've looked at the MPPT sizing calculator but can't figure out if I can use it for a connection of different kinds of panels in serial/parallell like this...

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sportswagoneer commented · Aug 15, 2022 at 02:34 PM

So am I right in thinking that by adding 2x55W (parallell to each other) in series with the current 114W, the result would be fairly close to this (2x2 55W), matching my current 75/15 MPPT?

I’m a bit confused that the “PV power ratio” is deemed “oversized” but still green? Is this OK?

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sportswagoneer sportswagoneer commented · Aug 15, 2022 at 03:15 PM

This install would look something like this:

Would greatly appreciate comments!

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1fec68f3-0871-418c-ae58-6d764a932071.jpeg (159.7 KiB)

Answer 5 · 2023-06-12T10:30:06Z

smith-morten answered · Jun 12, 2023 at 10:30 AM

@Sportswagoneer Hi!

What solution did you end up with? I also have a similar Sunbeam panel installed in the same location and have almost no output. I use the same Victron 75/15.

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bkt commented · Aug 01, 2023 at 09:49 AM

Hi,

I have the same configuration since june 2022 (2x 55W + 1x 144W tough black Sunbeam, all in paralel but with 1 Sunbeam MPPT 320W).

One 55W panel is inactive this summer (0V / 0A - no explainable cause, no visible damage or visible change) and it is disconnected now, while the other 1x 55+114W give max 300W together (read on the MPPT) per usual day on the north of adriatic sea.

They are on the cabin roof and in june at 12h under full sun without shadow the peak for 1x 55+114W together was 19V / 3,6A (measured on wires) while they usual give cca 15V / 2A (read on the MPPT).

Please let me know your opinion: to change the inactive panel only (refund warranty is expected), MPPT, all together, to add diodes (according to instructions they don't need them), expand with another panel to reach the MPPT max W or simply forget them and make a new independent system on the bimini?

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sportswagoneer bkt commented · Aug 01, 2023 at 04:41 PM

So you're also at around 17% of nominal yield in a normal situation. (15x2=30W as oposed to 169W nominal) with the Sunbeam MPPT.

I eventually got a reply from Sunbeam, who suggested filing a warranty claim - but have had no response to that. Still the same shitty yields.

Sunbeam is adamant on their website that the panels SHOULD be connected in paralell - and wrote in the e-mail to me that connecting non-identical panels in series would void the waranty. Victron on the other hand recommends serial connections to improve eficiency.
It leaves me with the impresion that sunbeam and victron is simply a bad match - but you're geting the same low yield with the sunbeam MPTT.

Sorry - not a helpfull response. I'l leaning towards just finding another panel...

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