Solar array advice & MPPT

[Cdn_bacon]

I'm currently researching a project to install flexible solar panels on my boat. I had planned to use (2) 100W flex panels however they would span over a Bimini SS tube frame and from what I've read that is a huge risk for micro-cracking and fire potential. This brings me to version 2 of my project which is to install (4) 50 W panels which I can install between frames on the soft Bimini.

Boat House Batteries: 240Ah house battery (lead-acid), 12V system.

My question: Would I be better off to put the 4 panels in series and use a 150/35 MPPT controller or put 2 in series + 2 in parallel and stick with a 75 / 15 MPPT (which I already own).

I'm struggling to understand which would be better from a battery charging stand point? Neglect any pro/cons to shading as this isn't a factor for the panel placement (either they all will be in the shade or none will). I want to get the most charge potential out of the array.

Panel Info:

Renogy panels. 50W Amp: 20.3V, Voc: 24.3V, Imp: 2.74A, Isc: 2.75A.


On a side topic: How bad would it be to use a larger panel spanning a SS tube if I mounted the panel onto a piece of twin wall polycarbonate to go over the frame hard point? Pic showing a 100W panel mockup on a my bimini.

[Jammer]

Originally Posted by Cdn_bacon

My question: Would I be better off to put the 4 panels in series and use a 150/35 MPPT controller or put 2 in series + 2 in parallel and stick with a 75 / 15 MPPT (which I already own).

With matched, unshaded panels, it won't matter. Wire it whichever way you want.

On a side topic: How bad would it be to use a larger panel spanning a SS tube if I mounted the panel onto a piece of twin wall polycarbonate to go over the frame hard point? Pic showing a 100W panel mockup on a my bimini.

I ended up deciding to put hard panels over my bimini and will be installing them in another month or two. I looked at soft panels and was not satisfied with cost, longevity, and safety, particularly in applications like a bimini where there will inevitably be some movement. It is an appearance and windage tradeoff. Perhaps you will find better answers.

[markcouz]

Go with the 2s2p using your existing MPPT and save the cash - the only minor benefit of the 4s system is slightly reduced power loss from panels to MPPT due to lower current, after that it is all the same.

[Cdn_bacon]

Typo correction:

Renogy panels. 50W Vmp: 20.3V, Voc: 24.3V, Imp: 2.74A, Isc: 2.75A.

[Cdn_bacon]

Originally Posted by Jammer

With matched, unshaded panels, it won't matter. Wire it whichever way you want.





I ended up deciding to put hard panels over my bimini and will be installing them in another month or two. I looked at soft panels and was not satisfied with cost, longevity, and safety, particularly in applications like a bimini where there will inevitably be some movement. It is an appearance and windage tradeoff. Perhaps you will find better answers.

I seriously looked at hard panels but the boat is seasonal and only in the water 4-5 months a year. I did look at hard panels but believe it or not there's no one local to bend tubing to make an add on frame to my existing bimini. I live in the middle of no where lol. Plus with the short season I couldn't justify the added cost.

[Cdn_bacon]

Originally Posted by markcouz

Go with the 2s2p using your existing MPPT and save the cash - the only minor benefit of the 4s system is slightly reduced power loss from panels to MPPT due to lower current, after that it is all the same.

This is what I've been trying to figure out. In terms of overall power provided over the course of a day, would one setup give more Amps than the other?

[Jon Hacking]

I've had 4x120W Kyocera rigid panels since 2001, when they were $4/W.

In 2017 I added 4x120W flexible Hi-Power panels, mounted on top of my rigid bimini, using a brand recommended by a fellow cruiser. They were horrible, never performing very well at all.

You may have your own reasons to go with flexible, but I'd strongly recommend going with fixed panels if you possibly can. Not only will you get far more Watts for your dollar, they'll last longer as well.

Also, they do NOT need external frames. The frames they come with are VERY strong. My new panels are 1x2m monsters (400W & only $200 each in 2019). They're supported by my Targa-bar at the leading edge, but my davits can only support them out at about the 1.15m point, meaning that .85m (33", or almost 3') is unsupported except for their frames. Yet they're very strong, & have already survived Typhoon Rai/Odette in the Philippines.

As for your question about putting them all in series or in 2P2S, I agree with Jammer & Mark: I'd recommend going 2P2S & saving the $$ a new MPPT would cost you. This assumes that there's no shading.

There's a very slight performance gain going 4S, because there's less wiring losses, since the current is only half as much. Remember that wiring losses are proportional to current squared, so lowering the current will lower your losses. But in this case, the losses would be minimal (if you use reasonable wire) so the savings would be minimal, & not worth the extra $$ for the new MPPT. That $$ would be much better spent on bigger panels.

[PSGB]

Take a look at what LightLeaf Solar offers. You get the lightness of a flexible panel on a rigid platform.

https://www.lightleafsolar.com/

[pjShap]

You might be able to find any needed mounting parts from a vendor like https://www.geminiproducts.net/, without needing a local custom fabricator.

[HeywoodJ]

As previously mentioned, 4S will give you higher voltage/lower current from the panels to the controller, meaning slightly (if you want "slightly" quantified you have to get into the weeds of wires sizes, run lengths, etc.) lower power loss in the wiring. However, you will also have a slight decrease in the efficiency of the dc-dc conversion within the controller. In the end this comes out pretty close to a wash (with reasonable values for both scenarios).

Universally, the higher the voltage ratio between input and output the lower the efficiency of the conversion. The easy way to think of this, at 6:1 (90V to 15V), for every electron coming in the converter has to split that power to 6 electrons going out, and each split costs some efficiency. For a 3:1 (45V to 15V) there is half the splitting, and a small gain in efficiency in the conversion.

A very long way of saying that in terms of A into your battery you will have a hard time seeing a difference between 4S and 2S2P, all other conditions being equal.

Here's a pretty typical efficiency curve family for a 24V system:

[Jammer]

Originally Posted by Cdn_bacon

I seriously looked at hard panels but the boat is seasonal and only in the water 4-5 months a year. I did look at hard panels but believe it or not there's no one local to bend tubing to make an add on frame to my existing bimini. I live in the middle of no where lol. Plus with the short season I couldn't justify the added cost.

You can do it without bending anything. I'll post photos of mine when it's done, but there are other examples. Look at the brackets that geminiproducts.net makes and some of their samples.

[Madehn]

You can bend your own tubing it’s not that hard or simply use fittings on SS tubing that can work also. If the panels are long enough you can mount them to existing Bimini tubes using SS U bolts. If you feel like the frames are not stiff enough bolt in some additional flat bar aluminum or SS to stiffen them.

[Scubaseas]

https://www.geminiproducts.net/solar-panel-mounts/

https://www.custommarineproducts.com...ting-kits.html

Go hard panels. They last a lot longer than flexibles.

[hjohnson]

Originally Posted by Cdn_bacon

My question: Would I be better off to put the 4 panels in series and use a 150/35 MPPT controller or put 2 in series + 2 in parallel and stick with a 75 / 15 MPPT (which I already own).

I would do the 2s2p configuration, with the two series pairs on either side of your boom. That way, if one side is shaded by the boom, the other side will generate power cleanly. Even a portion of the panel being shaded will dramatically reduce the power generated from the entire string.

[Sailing Hanse37]

We have 4 semi flexible Renogy 100watt panels on our bimini. They are now 4 years old and still doing their job as new. 1 panel had to be replaced because of delamination. Renogy replaced the panel under warranty.