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Old 09-02-2021, 09:59   #46
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Re: Adding Solar Panels - Looking for best practices

Don't forget that a bigger battery bank still goes dead if you can't replenish it.
You need to replace the 100 watts per day no matter how large.
A bigger solar system may recharge the smaller bank quickly enough.
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Old 09-02-2021, 11:46   #47
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Re: Adding Solar Panels - Looking for best practices

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After more reading, decided to take your advice and upgrade battery bank to 320-400 AH. Also going for 100 amp alternator with programmable external regulator. $$$ Thanks for the good advice!
You're welcome. Our boat is Puffin Pearson 10M #6 sailing out of Beverly.
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Old 13-05-2021, 14:23   #48
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Re: Adding Solar Panels - Looking for best practices

We lost 2 solar panels in high wind (semi-flexible, failed to secure them adequately before we left the boat for the afternoon). Remaining 2 panels are 130W 22.3V 5.8A attached to a Victron 100/50 MPPT.

We're currently cruising in Mexico, and not convenient (or cost effective) to ordering/replacing them until we are closer to the US border.

Someone gave me 2 used 100W 20V 5.6A panels. I'd like to use them if I can to boost our capacity back up. I'm looking for recommendations of how to wire them all together. Are they close enough in size/capacity to be combined on the same controller?

I was thinking of putting the 130W panels in series and the 100W in series, and then parallel to the controller. I have 10 ga wire running the 30 ft to the controller.
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Old 13-05-2021, 14:47   #49
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Re: Adding Solar Panels - Looking for best practices

If you put them in series 100W-100W and 130W-130W to the same controller then they will all run at the lower voltage, about 20V, because the knee on the I-V curve of the 100W will drop them out of production very quickly above that value. You'll lose about 13W/panel (10%) from each of your 130W panels. That would be better than nothing, you'd still gain ~174W.

I'd probably try them set up as 100W-130W and 100W-130W in series/parallel. The slightly lower Imp of the 100W means you'll lose 0.2A or about 5W from each of the 130W panels that way, so should result in a slightly better harvest.

You can see there's not a huge difference either way, and both should greatly improve your solar production, so in the end I'd select whichever is easier to implement - the specs are close enough that it will work.

All calculations are paper, real world is a different beast, but paper is all we really have to go on.
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Old 14-05-2021, 07:43   #50
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Re: Adding Solar Panels - Looking for best practices

My two panels are 110 watts each. I was planning to run them in series to a Victron 75/15 controller. Should I up-size the controller?
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Old 14-05-2021, 07:46   #51
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Re: Adding Solar Panels - Looking for best practices

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My two panels are 110 watts each. I was planning to run them in series to a Victron 75/15 controller. Should I up-size the controller?
RSB333
Assuming your open circuit voltage can't reach 75 volts in cold weather, you'll be ok with the 75/15. It will slightly limit your max output under ideal conditions, however, so you may want to step up to the 100/20.
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Old 14-05-2021, 10:59   #52
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Re: Adding Solar Panels - Looking for best practices

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My two panels are 110 watts each. I was planning to run them in series to a Victron 75/15 controller. Should I up-size the controller?
RSB333
If there is any shading - there will be on a sailboat - wire them in parallel.
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Old 14-05-2021, 14:05   #53
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Re: Adding Solar Panels - Looking for best practices

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If there is any shading - there will be on a sailboat - wire them in parallel.
But if the panel voltage isn't high enough, you'll lose power in parallel as the controllers won't wake up as early in the morning. The Victron controllers need battery voltage + 5 volts to wake up (then battery + 1 volt to keep charging).
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Old 14-05-2021, 14:25   #54
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Re: Adding Solar Panels - Looking for best practices

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But if the panel voltage isn't high enough, you'll lose power in parallel as the controllers won't wake up as early in the morning. The Victron controllers need battery voltage + 5 volts to wake up (then battery + 1 volt to keep charging).
That should not be a problem and in practice isn't. Panel voltage should be high enough when the sun is up - it is current that is low early in the morning.

I have installed panels on a powerboat in a boathouse and they were showing close to max voltage with just a bit of daylight entering from the open end. Current non-existent of course.

Here is the reason why there is a 5 volt spread before controller start.





In series if there is any shading - and there will be a lot of the time on a sailboat - there will be virtually no output.
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Old 14-05-2021, 15:01   #55
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Re: Adding Solar Panels - Looking for best practices

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...In series if there is any shading - and there will be a lot of the time on a sailboat - there will be virtually no output.

Is that really true? Does it apply to all panels?

The reason I ask is that we have three new panels above our dinghy davits wired in series and when the occasional wind generator shadow falls on them I don’t see any drop in output.
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Old 14-05-2021, 20:07   #56
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Re: Adding Solar Panels - Looking for best practices

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Is that really true? Does it apply to all panels?

The reason I ask is that we have three new panels above our dinghy davits wired in series and when the occasional wind generator shadow falls on them I don’t see any drop in output.
Here is a good comparison between series and parallel.



My first choice with 2 panels would be a controller for each panel. That way one panel cannot affect the other.

Second choice parallel on a sailboat which will always be subject to shade. The amount of shade will vary - lots if the panels are on the dodger, less if on a stern arch. Series on a stern arch could work better than series elsewhere on the boat.
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Old 14-05-2021, 23:10   #57
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Re: Adding Solar Panels - Looking for best practices

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Here is a good comparison between series and parallel.







My first choice with 2 panels would be a controller for each panel. That way one panel cannot affect the other.



Second choice parallel on a sailboat which will always be subject to shade. The amount of shade will vary - lots if the panels are on the dodger, less if on a stern arch. Series on a stern arch could work better than series elsewhere on the boat.

That video is quite a few years old now, so I still raise the question for modern panels. I guess I’ll run a few experiments with my panels with deliberate shading and see what happens.

The big benefit of series panels is the increase in voltage and decrease in current, especially for boats like ours where the battery bank to be charged is 14m or so of wire run from the panels. We mount our regulators right next to the positive charge bus bar and much prefer 100V in the long run over 14V. YMMV
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