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Solar plan!


Callum4878

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Hi all, 

I know this has probably been done to death, but I have hatched a cunning plan to install my own solar array, and just wondered if any of you could see any obvious pitfalls in my plan.

I’ve decided upon 500w from 5off 100w flexible panels, mainly for aesthetic and available space reasons, and my preference would be to wire them in series to a 60A MPPT charge controller. I know some installations have a parallel setup, or even a combination of series/parallel, and it’s mainly this I’m puzzling over.

I already have 5off Renogy panels, and I’m considering their controller, anyone recommend a better choice?
Keith

 

 

 

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Flexible   panels have a short life span and poor output on a roof  because they get too hot. Compare the warranty for a flexible panel with that for a rigid one. However, you already have the panels so it is a bit late now.

 

Series panels need a high voltage controller- multiply the open circuit voltage by the number of panels in series and add at least 10%, to allow for cold bright mornings raising the Voc above the spec.  Check the controller is rated for this voltage.

 

Parallel have advantages in that you can shade one panel and still get the output from the rest.  Series panels need to have bypass diodes for this scenario AIUI or you will lose all output.

N

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Hi N, thanks for the reply. I was aware of the shortcomings of flat mounts, but don’t like the framed tilty ones, so I’ll have to live with the shortfalls. My five panels will be mounted all in the same area of my boat , so from what you say series would be acceptable. Controller I’m about ready to order is 150v max and 60A output, and my calculations say 110v 5A in and 12v 42A out, so it allows me a little for expansion if required..

Thanks again

Keith

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1 hour ago, Callum4878 said:

Hi N, thanks for the reply. I was aware of the shortcomings of flat mounts, but don’t like the framed tilty ones, so I’ll have to live with the shortfalls. My five panels will be mounted all in the same area of my boat , so from what you say series would be acceptable. Controller I’m about ready to order is 150v max and 60A output, and my calculations say 110v 5A in and 12v 42A out, so it allows me a little for expansion if required..

Thanks again

Keith

 

If you'd have said 4 or 6 panels then I'd have said wire each pair in series and then in parallel to an MPPT charge controller such as those from Victron, which have a good reputation and are considered amongst the best out there (we have one on our other boat and will have one on our narrowboat). The advantage of series/parallel is the higher voltage at dawn and dusk means the MPPT will get enough voltage to start charging the batteries a little earlier in the day (and will continue charging a little later in the day). The other advantage of increasing system voltage is a smaller cable size is needed and all else being equal there's a smaller percentage voltage drop from panels to MPPT and as these controllers use some clever trickery to turn increased volts into increased amps every bit of voltage drop saved counts.

 

The downside of wiring panels in series is if a tree branch or whatever partially shades one panel then it will reduce the output from the two-panel series array far more in practice than you'd think. [edited to add: and if you wire all of your panels in series the effect of partial shading will be greatly increased so personally I wouldn't do it. It's OK on a house roof but not on a narrowboat roof).

 

Wiring all panels in parallel increases the shade tolerance of the solar array but removes the benefit of extra voltage earlier and later in the day. But on balance we think each pair of panels wired in series and then parallel is a pretty good 'best of all worlds' compromise.

 

The other thing is, with flexible panels, along with reduced life and lower performance due to increased heat build up, you will also find that you will get less output per panel than rigid panels that are lying flat (and dramatically less output than angled rigid panels).  This is because a flexible panel curved to a narrowboat roof will always have at least part of it facing away from the sun. We have rigid panels on our other boat and will have rigid panels on our narrowboat. But I'll concede that flexible panels look better. Each to their own.

 

Edited by Jackofalltrades
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3 hours ago, Jackofalltrades said:

 

 

The downside of wiring panels in series is if a tree branch or whatever partially shades one panel then it will reduce the output from the two-panel series array far more in practice than you'd think. [edited to add: and if you wire all of your panels in series the effect of partial shading will be greatly increased so personally I wouldn't do it. 

 

Wiring all panels in parallel increases the shade tolerance of the solar array but removes the benefit of extra voltage earlier and later in the day. But on balance we think each pair of panels wired in series and then parallel is a pretty good 'best of all worlds' compromise

 

The common fallacy that MPPT controllers convert volts to charge the batteries, they convert watts. In early morning and late evening series connection does increase the voltage available but as the current available is in the milliamp region so the watts are very small and possibly not enough to actually power the controller. The power loss by partial shading of a panel can be measured in amps so tens or even hundreds of watts. Panels in series will be limited to the amps the most shaded will pass possibly 10% of full sun and easily 50% just having a rope across one, panels in series are limited in voltage to the reduced volts of the most shaded panel probably 90% of full sun. Watts being volts x amps, series has major limitations for partial shade from trees, ropes, plant pots etc.  

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Understand what you’re saying about odd numbers in parallel, my 5 100w panels in series gives me an optimum 5a at 100v pressure, 4 connected series/parallel 10a @ 40v, but connecting the 5th in parallel would do nothing, and in series 5A @ 60v.

Think I’ll either just connect 4 panels to start, and try to squeeze another 2 in later, or try my all in series plan to start, with a view to adding a 6th and rewiring later. Controller i’m getting will handle any of the above configurations, and rewiring is quite simple.

Thanks for the responses.

Keith

 

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Also slightly depends what you mean by 'flexible' panels.

 

Are we talking about the type you can roll up, or the type bonded to a stainless steel plate, which with care can be mildly curved to follow the contour of the roof.

 

As said, I understand you can get issues with heat built up, especially if you cannot maintain a small air gap for cooling.

 

However obviously as you way, there are also both pros and cons to bulky 'domestic' panels littering the place!

 

 

Daniel

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Hi Daniel, they are easily flexible enough to follow the roof contour, and I was thinking of mounting them on thick beads of Sikaflex to give them a slight air gap, but still open to suggestions for this.

Hate the look of the framed ones, so I’d no choice really.

Went for Renogy panels, which is up there with the top reviews, and I’ve bought a 60A mppt controller of theirs, which I’m very impressed with, wasn’t cheap mind.

Just waiting for a couple of cables to my batteries and two fuses, then it’s install time. All this sun I’m missing out on ?

 

Keith

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On the subject of flexible panels, I have an array of flexible CIGS panels for practical purposes (access across the roof as a single-hander is paramount), and the heat disadvantage isn't as great as is often made out - I feel it's probably offset by the long hours of sun that have heated the roof to begin with. I don't struggle to meet my energy requirements with 400W from spring to autumn.

 

You can also install them on top of some closed-cell foam to insulate them. I meant to, but thanks to the pandemic the foam proved hard to get (it's still at my parents house a year on).

 

A mixture of series and parallel makes most sense - consider the layout such that you're less likely to shade across the paralleled arrays - ie parallel the front and back half, or the port and starboard sides.

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Panels are easily flexible enough for my roof contour, good to know you find 400W adequate, I’ve gone for 500 initially, but expect to go up another 100 if the series only connection doesn’t work out.

Had seen a vlog about the corrugated panels, and may try that if I can do it neatly enough.

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