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Post Info TOPIC: Solar panel configuration on roof.


RV-Dreams Community Member

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Solar panel configuration on roof.


Okay guys and gals. I have decided to go with a roof mount system instead of ground thanks to the responses ( Sushi, Larry) on this site but have another question:

I will have four 100w panels on the roof. I want to run them in series/parallal (sp?) configuration. Three of the panels will fit side-by-side nicely but the fourth has to be placed away from the bank of three due to the roof vent. While watching a youtube video on installing a series/parralel setup the man doing it said to make sure and have the series panels close together. Sooooo the fourth will be about 14" away from the third one. Do you think this will matter much or should I maybe just close off the vent so I can have them all close together? Thanks crew.



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Charles Cunningham


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“While watching a youtube video on installing a series/parralel setup the man doing it said to make sure and have the series panels close together.”

I’ve never read that panels in series need to be close. Do you have the video site?



-- Edited by LarryW21 on Wednesday 11th of July 2018 04:36:06 PM



-- Edited by LarryW21 on Wednesday 11th of July 2018 04:37:26 PM

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Winnebago TT 2101DS & Tahoe LTZ, 300 watts WindyNation solar-parallel w/MPPT, 2 Trojan T-125s. TALL flag pole. Prefer USFS, COE, BLM, USF&WS, NPS, TVA, state/county campgrounds. 14 year Army vet-11B40 then 11A - old MOS 1542 & 1560.



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www.youtube.com/watch happens around 1:30 into the video.

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Charles Cunningham


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Thank you for sending. I’m not schooled in series installations so I don’t know.

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Winnebago TT 2101DS & Tahoe LTZ, 300 watts WindyNation solar-parallel w/MPPT, 2 Trojan T-125s. TALL flag pole. Prefer USFS, COE, BLM, USF&WS, NPS, TVA, state/county campgrounds. 14 year Army vet-11B40 then 11A - old MOS 1542 & 1560.



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I'm kind of shooting from the hip here but here goes for what it's worth (I'm learning too). You are talking about series/parallel installation. This confuses me. As most panels seem to be 12 volts I'm confused about why you would want to wire them in series thereby producing 24, 36 or 48 volts depending on the number of panels you wire in series. It would seem to me that you would want to wire your panels in parallel so you maintain 12 volts but at 4 times the amperage. Remember that in all cases volts x amps = watts. Thus a 100 watt panel at 12 volts results in about 8 amps. If you wire the panels in series you get 48 volts but the same 8 amps. This doesn't seem to make sense as you would then need to convert this 48 volts back to 12 volts to which would generally result in some loss. If you wire the panels in parallel you get the needed 12 volts but at 32 amps. I believe this is why you want the panels close to each other as amperage requires large wires (think of the battery cables on your coach starting battery) and the longer the run the larger the wires need to be. If my calculation are correct if you have a 20 foot run from the panels to the controller you would need 4 AWG for the 20 foot run. Pretty big wire. It seems to me that you may be better off combining your panels at or near the controller and running smaller (12 AWG?) wire to the combination point near the controller. Then again, I've never done this and hopefully someone more practiced in this discipline than I am can shed some light on this subject because you really don't want to get the wrong due to fire danger etc.

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Arcaguy, Thanks for posting, very informative.Below is a link that gives a real good explanation as to why the series/parallel combo is a good alternative. The guy takes four 100w panels and sets them up in various configurations, test and explains the results of each test so you can see for yourself and judge/decide which config. is best for "your" needs. I have done a ton of internet searching and found this site to be the best so far. Enjoy. write back and let me know your thoughts.

www.ybw.com/forums/showthread.php

Also Larry, if you're out there or if anyone else knows ; are members able post pics to this website?

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Charles Cunningham


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I found this wire size chart which should be of interest. It looks like my 4 awg may have been a little big but it's that better safe than sorry thing.

www.bluesea.com/resources/1437

This chart is much easier to understand than the other one I was looking at. But, (isn't there always one of those) be aware that the circuit distance is what is important so double the actual distance to allow for the round trip of the electrons.

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This is good Arca. There are calculators, charts, etc out there that are very difficult to understand but this one is good. Thanks

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Charles Cunningham


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RV Tito posts on YouTube and he did a "show" on series vs. parallel. The study showed no difference in charging on his system either way. See www.youtube.com/watch

 

Within reason, arca, you never get burned using a larger wire. Key is will the larger wire "fit" into the controller. 



-- Edited by LarryW21 on Thursday 12th of July 2018 10:38:20 AM

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Winnebago TT 2101DS & Tahoe LTZ, 300 watts WindyNation solar-parallel w/MPPT, 2 Trojan T-125s. TALL flag pole. Prefer USFS, COE, BLM, USF&WS, NPS, TVA, state/county campgrounds. 14 year Army vet-11B40 then 11A - old MOS 1542 & 1560.



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Tito didn't mention the series/parallel set up and there are instances where this is a good fit. Series/parallel is good where you want to keep the wattage and voltage within range and keeping the same amount of useable power. It can be confusing but check out Renogy's input

www.renogy.com/learn-series-and-parallel/

Tito is also doing the test in optimal conditions with no clouds, trees or poles to shade parts of the panels.

Renogy states "There is really no downside when using the series/parallel set up. But... "To each his own, Larry!

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Charles Cunningham


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LarryW21 wrote:

Within reason, arca, you never get burned using a larger wire. Key is will the larger wire "fit" into the controller. 



-- Edited by LarryW21 on Thursday 12th of July 2018 10:38:20 AM


 Yes, within reason larger is better and a short 1 foot splice to a smaller wire to fit in the controller solves that issue.  One would be hard pressed to measure the IR drop in such as 1 foot or so splice to fit the lugs on the controller.

 



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Bill & Linda
2014 New Horizons Majestic F37RLTSS 96

2016 RAM 5500HD \ 4-Wheel Drive \ Link Air Ride
Classy Chassis RV Hauler Bed Conversion \ Aux Fuel Tank 



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Assuming the wire is sized properly one will find little difference, if any in the real world, between series and parallel operation assuming a proper design.  Again this is true, IF the wire is sized properly for the panels and the length of wire run to the controller, etc. 

However, an advantage of parallel concerns shadows.  If any cell of a panel is shaded and that panel is in series with another panel both panel's outputs will be impacted. Any shadow on a cell acts as a resistor in so many words.  So one view is parallel "protects" power loss on all or some panels due to shadows, including clouds.

We're kind of down in the weeds on this one but if panels could be shadowed at times by an AC unit or a vent then parallel protects from that issue somewhat.  In a worse case where a panel might be damaged, (i.e. tree branch fell on it) in parallel the other panels continue to operate without impact to their output.  Not so in series.

If the feed wire to the controller is proper the higher voltage of serial is minimally beneficial, if at all, vs other potential drawbacks including mechanical wiring challenges.  It's all in the design and the wire size to minimize IR (restiveness) voltage drop.

My view and measurements,

Bill



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Bill & Linda
2014 New Horizons Majestic F37RLTSS 96

2016 RAM 5500HD \ 4-Wheel Drive \ Link Air Ride
Classy Chassis RV Hauler Bed Conversion \ Aux Fuel Tank 



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Agree. If you get a shade spot on a series panel this, like you say can cause "resistance" and effect the whole series configuration. I guess if your gung-ho on series than you can get what is called a "bipass diode" and it will route around the bad spot. If you go all parallel then you get high amperage which can cause some wasted energy (minimal), fires, etc. depending on how many panels you are planning on using and their amp rating. Most probably don't have to be concerned with "overamping." If you need/want tons of power then the series/parallel seems to be your best bet. It looks like solar is not a one-size-fits-all deal and a lot of it is consumer preference, not a right or wrong issue. 100 watts is 100 watts and that's about what you'll get in the end minus some waste regardless of your chosen configuration. But remember I'm a FUNGI (ex military will know that one) so what I say is not been proven in a court of law. Just my opinions.... so far... and I do reserve the right to change my mind. LOL.

Like earlier I was sold on going with ground mount solar panels and couldn't for the life of me figure out why more weren't sold on it. Well, guess what? After a few replies and opinions to the contrary I decided to go with total roof mount. This site is great for the "I don't know what I don't know" types like myself.


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Charles Cunningham
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